Hindered Settling

The case for scales, rates, and numbers in geology

2011-10-16T08:13:00.000-05:00

A long time ago I used to study geology in a nice city called Cluj, in the middle of that interesting part of Romania known as Transylvania. This was a place and time where and when I learned about quartz, feldspar, species of coral and foraminifera in great detail, heard about sequence stratigraphy and turbidites for the first time, and went on some great geological field trips. Not to mention the half-liter bottles of beer that would be significant components of any decent geological trip or spontaneous philosophical discussion in the evening. The less pleasant part was that many of the classes I took involved brute-force memorization of fossils, minerals, chronostratigraphic names, and formations. Although the geological vocabulary that I picked up was pretty broad and proved useful as a good set of words, terms, and definitions to play with, I forgot many of the details by now. If you asked me what was the difference between granite and granodiorite, I would have to check. I don't remember at all what fossils are characteristic of the Late Jurassic. And, despite doing some fieldwork myself over there, I cannot remember the stratigraphic nomenclature in Transylvanian Basin; I would have to look it up (probably in this paper).

After college, it took me about one year to realize with convincing clarity that there was a lot left to learn. I went on to grad school on the other side of the planet, at a well-known university. Many of the classes I took over there were - unsurprisingly - quite different; a lot more focus on laws, processes and the connections between geological things than the 'things' themselves. It was also there that I started to see the links between geology and physics and math. I picked up quite a bit of math and physics during high school, but then quickly relegated them to the status of "stuff that is rarely used in geology". At grad school, it dawned on me that numbers and mathematical laws are not only useful in geology, but are in fact necessary for doing good earth science. Maybe I am stating the obvious, but here it goes anyway: geology deals with enormous variations in scale, both in space and time; and it is not enough to say that the river was deep (how deep?), the tectonic deformation was fast (how fast?), the sea-level highstand lasted long (how long?), or the sediment gravity flows were high-energy flows (I am not even sure what that means). One of the most important things I learned was an appreciation for physical and quantitative insight in geology, that is, having at least an idea, a feel for what are the scales and rates involved in the formation of the rocks you are looking at. I cannot say it better than Chris Paola, one of the important and influential advocates of moving sedimentary geology closer to physics and math:

"For the 'modal' sedimentary-geology student, it is not sophisticated computational skills or training in advanced calculus that is lacking, but rather the routine application of basic quantitative reasoning. This means things like estimating scales and rates for key processes, knowing the magnitudes of basic physical properties, and being able to estimate the relative importance of various processes in a particular setting. Understanding scales, rates and relative magnitudes is to quantitative science what recognizing quartz and feldspar is to field geology. Neither requires years of sophisticated training, but both require repetition until they become habitual."

Developing these skills is a lot easier if one is not afraid of tinkering with simple computer programs. Want to really understand what Stokes' law is about? There is no better way than typing the equation into an Excel spreadsheet or a Matlab m-file and see how the plot of settling velocity against grain size looks like. What about settling in a fluid with different viscosity? Change the variable, and compare the result with the previous curve. High-level programming languages like Matlab or Python* are a lot easier to learn than languages closer to 'computerese' and farther from English, and they are great tools for these kinds of exercises and experiments. As somebody interested in stratigraphic architecture, I have become especially fond of creating surfaces that vaguely resemble real-world landscapes and then see how the evolution of these surfaces through time - deposition over here, erosion over there - creates stratigraphy. Complex three dimensional geometry is a lot easier to grasp if you can visualize and dissect it on the computer screen.

Of course, numbers, diagrams and images that come from computer programs are only useful if they demonstrably say something about the real world. Data collection in the field and the laboratory are equally important. But nowadays we often have more data than we wished for, and quantitative skills come handy for visualizing and analyzing large datasets - and comparing them to models.

Not everyone is excited about the growing number of earth scientists who tend to see equations 'in the rocks'. The logo of the Sedimentology Research Group at the University of Minnesota features the Exner equation carved into a pebble, allegedly as a response to the exclamation "I haven't seen yet an equation written on the rocks!" There is some concern that many geology graduates nowadays do not get to see, to map and to sample enough real rocks and sediments in the field. Although I think this unease is not entirely unsubstantiated, I wouldn't want to sound as pessimistic as Emiliano Mutti - one of the founding fathers of deepwater sedimentology - does in the last phrase of a review article:

"This approach raises a problem, and not a small one: in connection with data collection in the field, how many field geologists are being produced in these times of increasingly computerized geology; and how good are they?"

As far as I know, geological field work is still an important part of the curriculum in many departments of geology - as it clearly should be. The number one reason I have become a geologist was that I loved mountains, hiking, and being outdoors in general, way before I started formally studying geology. And I still take every opportunity to go to the field. But I cannot see the growth of "computerized geology" - and of quantitative geology in general - as a bad thing. Does dry quantification take away the beauty and poetry of geology? I don't think so. Unweaving the rainbow, unfolding a mountain, and reconstructing a turbidity current only add to our appreciation of the scale and grandeur of geology.

* I will let you know later whether this is true about Python...

** I have started writing this post for Accretionary Wedge #38, mostly because I found the call for posts quite inspiring, but haven't finished it in time. Read all the good stuff at Highly Allochthonous.

Salt and sediment: A brief history of ideas

2011-07-16T20:36:00.011-05:00

Salty weirdness
Salt is a weird kind of rock. At first sight, it behaves like most other rocks: if you pick up a piece, it is hard, it is heavy, and it breaks if hit with a hammer. But put it under stress for thousands of years, and salt will behave like a fluid: relatively small forces can cause it to flow toward less stressful surroundings. This often means it will try to find its way to the surface.

When deposited, sand and mud have lots of pore space filled with water and have relatively low density. However, as they get buried by more sediment, much pore space is lost, both through compaction and cementation. Sediments turn into sedimentary rocks, become harder, and their density increases. In contrast, salt doesn't have much pore space to begin with; its density will stay the same, regardless of depth of burial. As both salt and sediment are buried to greater depths, an unstable condition develops: lighter salt lying under denser material. In addition, the location of the salt layer in the sediment column is not entirely random: it is in the nature of sedimentary basins to initially place salt at the bottom of the sediment pile. Extensive salt layers usually form early in a basin's lifetime, when seawaters invade for the first time shallow depressions on a continent that is about to split into two along a rift zone. The Dead Sea is an obvious example that comes to mind.

Layering salt and sediment in this unstable order is a recipe for a spectacular geological show. As salt is trying to find its way to the surface, it forms drop-shaped blobs called diapirs; but also ridges, walls, and salt sheets. Several sheets can connect laterally into a huge salt canopy, a new salt layer that is entirely out-of-place or allochtonous. Salt can also act as a lubricating layer at the base of a thick sequence of sedimentary rocks. But I am rushing ahead a little bit; salt tectonics is such a new - but rapidly growing - science that salt canopies, despite their widespread presence in the subsurface Gulf of Mexico, were not recognized and described until the 1980s.

Tectonics vs. buoyancy, Europe vs. America
Before the beginning of the twentieth century, even with the role that salt played in human history, little was known about how salt domes formed. This was an age of rampant speculation; surface data was scarce because salt does not last very long after exposed as it quickly gets dissolved and washed away by precipitation. Many geologists thought that formation of salt domes didn't require any significant salt deformation or displacement. But things have changed dramatically in 1901, with the discovery of the Spindletop oil field on top of a salt dome in southeastern Texas. The recognition that oil is often found on top of and around salt domes created a much stronger interest in understanding how exactly salt formations are put in place.

European geologists thought that the main driving force was compression, the force that causes folding and thrusting and builds mountains. In Romania, where the Eastern Carpathians take a sharp turn toward the southwest, salt was found in the cores of oil-bearing anticlines. The contacts with the surrounding rocks were clearly discordant. These are the structures that prompted Ludovic Mrazec, professor of geology at University of Bucharest, to coin the term "diapir" in 1907.

Mrazec's explanation of how salt diapirs form. From Barton (1925).

Salt in Germany and Poland also seemed to occur invariably in a compressional setting, in the cores of folds, next to folds that had no salt associated. It seemed obvious that salt was 'pushed up' by tectonic forces, and it appeared unlikely that the rise of salt itself was causing the folding.

But the discovery of a multitude of salt diapirs in the Gulf of Mexico made it clear that they can occur far away from any mountains and compressive tectonic forces. The much simpler setting and relative lack of deformation in the Gulf proved informative. "The Roumanian salt-dome geologist possibly may have more to learn from the American salt domes than the American salt-dome geologist has to learn from the Roumanian domes. The occurrence of the American domes in a region of tectonic quiescence suggests that tectonic thrust cannot have the importance postulated by Mrazec" - wrote Donald Barton in 1925.

This was also the time when the density difference between salt and sediment came into discussion. Gravity measurements in the Gulf of Mexico showed anomalies above salt domes that were due to the lower density of salt. It was increasingly recognized that density inversion must play an important role in diapirism, especially where compressive tectonic forces were absent. In addition, by the 1930s geologists have reached a consensus that salt diapirs must somehow punch through the overlying sediment. They seemed to ignore the fact that, as Wade (1931) put it, you cannot drive a putty nail through a wooden board. As mentioned before, salt does behave like a fluid over geological time scales. But how can it penetrate thick layers of hardened sedimentary rock?

A brilliant idea: downbuilding
The solution to this problem came in 1933, from the same Donald Barton who was discussing the differences between European and American salt domes in 1925. He suggested that diapirs can form without much piercement of the sediment above. Instead, once a small dome is initiated, it simply can stay in place, always at or close to the surface, while sediment is deposited around it and the source salt layer subsides: "it is the sediments which move, and not the salt core. The energy requirement (...) is very much less than if there were actual upward movement of the salt."

The evolution of salt diapirs through 'downbuilding'. Salt domes are always close to the surface and diapirism goes hand-in-hand with sedimentation. From Barton (1933).

This was a key insight: it got rid of the "room problem", the need for moving huge volumes of hard rock out of the way of the rising salt. It also highlighted that salt movement can happen at the same time with sedimentation, a fact that became abundantly obvious later as high-quality seismic data became available. But the concept of 'downbuilding' was ignored for the next fifty years.

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Animation showing how downbuilding works. Blue represents salt, yellow is sediment. To mimic mass balance for salt (-- what is lost from the source layer must go into the salt dome), the blue area is kept constant through the animation. Right-click image for animation controls.

The beauty of instabilities
The main reason for conveniently forgetting Barton's idea was that density inversion between two fluids could be nicely studied in the lab and described with elegant equations. In one of the papers that kicked off this fascination with Rayleigh-Taylor instabilities, Nettleton (1934) used corn syrup and less dense crude oil to visualize diapir-like blobs of fluid in a transparent cylinder and to show that gravity alone, without any help from contractional forces, was enough to generate structures similar to salt domes.

Less dense crude oil (black) forming diapir-like blobs as rising through higher-density corn syrup (yellow). Redrawn from Nettleton (1934).

One problem with this approach was that oil and syrup can be photographed during deformation, but the transient structures could not be carefully dissected and analyzed later. Materials of higher viscosity were needed for that; however, increasing the viscosity resulted in a density difference too small to get the fluids moving in the first place. The trick was to place the whole experiment in a centrifuge and use the centrifugal force to imitate a larger-than-normal gravitational force. This approach formed the basis of a productive line of research on gravity tectonics in the laboratory of the Norwegian-Swedish geologist Hans Ramberg. The results are probably more relevant to what is happening deeper in the Earth, at higher temperatures and pressures, where most rocks become more similar in behavior to salt.

Modern salt tectonics
By the late 1980s it has become quite obvious that kilometer-thick piles of sedimentary rock cannot be treated as fluids and salt-sediment interaction is more similar to placing and deforming slabs of brittle material on top of a viscous fluid. Seismic from salt-bearing sedimentary basins suggested that the history of salt movement and sedimentation were highly interconnected and Barton's downbuilding concept was strongly relevant.

Three-dimensional seismic data also showed the variety and complexity of allochtonous salt bodies in salt-rich sedimentary basins. Sandbox experiments with more realistic material properties and ongoing sedimentation during deformation were performed and the results beautifully visualized. The behavior of turbidity currents flowing over complex salt-related submarine topography was investigated. Hundreds of scientific papers were written on salt tectonics, both by industry geoscientists and researchers in the academia.

N-S cross section in the Gulf of Mexico. Large volumes of the Jurassic Louann salt have been displaced and squeezed into a salt canopy surrounded by much younger sediments. From Pilcher et al., 2011

And there is quite a bit left to explore and understand.

References and further reading
Barton, D. C. (1926) The American Salt-Dome Problems in the Light of the Roumanian and German Salt Domes, AAPG Bulletin, v. 9, p. 1227–1268.

Barton, D. C. (1933) Mechanics of Formation of Salt Domes with Special Reference to Gulf Coast Salt Domes of Texas and Louisiana, AAPG Bulletin, v. 17, 1025–1083.

Hudec, M., & Jackson, M. (2007) Terra infirma: Understanding salt tectonics. Earth Science Reviews, 82(1-2), 1–28.

Jackson, M. (1996) Retrospective salt tectonics, in M.P.A. Jackson, D.G. Roberts, and S. Snelson, eds., Salt tectonics: a global perspective: AAPG Memoir 65, p. 1–28. [great summary of the history of salt tectonics]

Mrazec, L. (1907) Despre cute cu sȋmbure de străpungere [On folds with piercing cores]: Bul. Soc. Stiint., Romania, v. 16, p. 6–8.

Nettleton, L. L. (1934) Fluid Mechanics of Salt Domes, AAPG Bulletin, v. 18, p. 1–30.

Pilcher, R. S., Kilsdonk, B., & Trude, J. (2011) Primary basins and their boundaries in the deep-water northern Gulf of Mexico: Origin, trap types, and petroleum system implications. AAPG Bulletin, v. 95(2), p. 219–240.

Wade, A. (1931) Intrusive salt bodies in coastal Asir, south western Arabia: Institute of Petroleum Technologists Journal, v. 17, p. 321–330, 357–361.

Where on Google Earth? WoGE #296

2011-07-08T09:00:00.000-05:00

Hindered Settling hasn't hosted a Where-on-Google-Earth in a long time, but WoGE #295 (hosted at Andiwhere's) had such a range of colors and geological features that I couldn't refrain from looking for it and, once found it, had to post the solution. So, after a short break in the game (busy week!) here is WoGE #296 -- the rules of the game are nicely described over here. I invoke the Schott rule. Posting time is July 8, 2011, 14:00 UTC.

click on image for larger view

Stretching the truth: vertical exaggeration of seismic data

2011-04-17T21:22:00.001-05:00

If someone showed a photograph of the famous Cuernos massif (Torres del Paine National Park, Chile) like the one below, it would be - probably, hopefully - obvious to everybody that something is wrong with the picture. Our eyes and brains have seen enough mountain scenery that we intuitively know how steep is 'steep' in alpine landscapes. The peaks in this photograph just look too extreme, too high if one takes into account their lateral extent.

The Cuernos in Torres del Paine National Park, Chile, vertically exaggerated by a factor of two.

For comparison, here is the original shot:

The Cuernos, beautiful, without exaggeration.

Yet this kind of vertical stretching of images is the rule rather than the exception when displaying seismic sections, both on computer screens and in scientific papers. There are two main reasons for this: first, subsurface geometries are often more obvious when vertically stretched and slopes are larger than in real life. Second, more often than not, we have no precise knowledge of the actual vertical scale. Raw seismic reflection data is recorded in time: we are measuring how long it takes before a seismic wave propagates down to a discontinuity and comes back to the surface. This time measure is called 'two-way traveltime'; in order to convert it to depth, knowledge of the velocity of sound through the rocks is needed:

depth = seismic_velocity * two-way_traveltime / 2

The problem is that the velocity of the wave varies as it goes deeper (usually increases with depth as rocks become 'harder'); and, unless we are looking at perfect layercake stratigraphy (not that common!), it also changes laterally. So, if we want to look at the actual geological structures, without distortions due to varying velocities, we need to do a depth conversion and we need a 'velocity model' that roughly describes the spatial distribution of velocities. Precise velocity measurements often come from wells where depth is well known; less precise estimates can be backed out from the seismic recordings themselves, but the solution is often non-unique and multiple iterations are necessary to build a good velocity- and depth model. As a result, seismic reflection data is often interpreted with two-way traveltime on the vertical axis, without depth conversion; and not knowing the true vertical scale makes it easier to use vertical exaggeration with vengeance.

A recent paper, published in Marine and Petroleum Geology, shows that vertical exaggeration of seismic data is indeed very common. Simon Stewart of Heriot-Watt University has looked through 1437 papers published between 2006-2010 and found that 75% of the papers show seismic displays with vertical exaggeration of a factor larger than 2. Only 12% are shown with roughly equal horizontal and vertical scales.

Histogram of vertical exaggerations in 1437 papers. From Stewart (2011).

One of the effects of vertical exaggeration is the strong steepening of dips. A 10 degree slope at a vertical exaggeration of 10 becomes an almost vertical drop of 60 degrees; it is hard not to think of these exaggerated slopes as steep slopes, even though they are not that abrupt in reality. Depositional geometries often have very small dips and significant vertical exaggeration is needed to illustrate the overall shapes.

The paper suggests that published seismic sections should be labeled with an estimate of the vertical exaggeration, in addition to the usual horizontal and vertical scales [I am guilty myself of not doing this as it should be done]. Even better, one can go further and create several versions of the figure with different vertical exaggerations. The cross section of a submarine lobe deposit below is a fine example of such a display. Showing only the version that was exaggerated vertically 25 times would suggest that this is a deposit at the base of a steep slope; the 1:1 figure at the top brings us back to reality and clearly shows that this morphology and stratigraphy are both extremely flat.

Dip section of a submarine lobe deposit, offshore Corsica. From Deptuck et al. (2008).

To see more about scales and vertical exaggeration in geology, check out this recent post at Highly Allochthonous; and the nice illustrations that Matt has put together over at Agile*.

References

Deptuck, M., Piper, D., Savoye, B., & Gervais, A. (2008). Dimensions and architecture of late Pleistocene submarine lobes off the northern margin of East Corsica Sedimentology, 55 (4), 869-898 DOI: 10.1111/j.1365-3091.2007.00926.x

Stewart, S. (2011). Vertical exaggeration of reflection seismic data in geoscience publications 2006–2010 Marine and Petroleum Geology, 28 (5), 959-965 DOI: 10.1016/j.marpetgeo.2010.10.003

Snorkeling and geology in Kealakekua Bay, Big Island, Hawaii

2011-01-15T22:41:00.003-06:00

For a long time, I didn't think it was worth spending more than an hour on a beach, even the most beautiful ones, unless there were some nice cliffs nearby showing some interesting geology. My views in this regard have changed dramatically about three years ago, when I spent a week on The Big Island of Hawaii, and the hotel where we were staying offered free rental of snorkeling gear. I put on the mask and the fins, trying to remember how this was supposed to work (I did a bit of snorkeling in Baja California many years before that), and put my face into the not-too-interesting-looking waters in the front of the hotel.

Kealakekua Bay in Google Earth, with some explanations added

I was in for a surprise. The water was far from crystal clear, but I could still see fantastic coral creations lined up along the bay and lots of fish of so many colors and patterns that it felt unreal. Until then I thought that this kind of scenery was hard to see unless you were a filmmaker working for Discovery Channel or a marine biologist specializing in tropical biodiversity. The next day I spotted a couple of green turtles frolicking in the water, clearly not bothered by the nearby snorkelers, and I already knew that I needed to look into the possibility of buying a simple underwater camera.

Lots of coral, mostly belonging to the genera Lobites (lobe coral) and Pocillopora (cauliflower coral)

Three years later I went back to the Big Island with more excitement about tropical beaches, plus bigger plans and a bit more knowledge about snorkeling. After going through a few well-known snorkeling sites on the west coast, like Kahalu'u Beach in Kona and Two Step near Pu'uhonua o Honaunau park, we got on a nice boat (run by a company called Fair Wind - strongly recommended!) and did some snorkeling in Kealakekua Bay.

Visibility in Kealakekua Bay is usually very good

Old wrinkles of pahoehoe lava getting encrusted by algae and corals and chewed up by sea urchins

Kealakekua Bay is difficult to reach; there is no road and no parking lot nearby. You either have to hike in, paddle through the bay in a kayak, or take a boat. I have heard before that this was the best snorkeling spot in Hawai'i, but I think that is an understatement. Unlike all the other spots we tried during the last few years in Hawaii (and that includes several beaches on Kauai and Hanauma Bay on Oahu, the presidential snorkeling site), the water at Kealakekua Bay was calm and very clear, with fantastic visibility.

Heads of cauliflower coral, with yellow tangs for scale

I will not attempt to describe this whole new world; instead I will let the photographs speak for themselves (as always, more photos at Smugmug). Even better, if you go to the Big Island, make sure that you visit this place with some snorkeling gear.

Yellow tangs (Zebrasoma flavescens) often congregate in large schools and it is difficult to stop taking pictures of them

When I was at Kealakekua Bay, I didn't know much about the local geology. The big cliff bordering the bay toward the northwest, called Pali Kapu o Keoua (see image above), shows a number of layered lava flows that belong to the western flank of Mauna Loa; and I suspected that this must have been a large fault scarp, but that was the end of my geological insight. A couple of hours worth of research after I got home revealed that Pali Kapu o Keoua was a fault indeed: it is called the Kealakekua Fault and it has been mapped, along with the associated submarine geomorphological features, in the 1970s and 1980s by U.S. Geological Survey geoscientists. It turns out that one of the shipboard scientists and key contributors to these studies was Bill Normark (see also a post about Bill at Clastic Detritus). While in California in the late 1990s, I was lucky to get to know Bill and have some truly inspiring discussions with him about turbidites, geology, and wine, so this was a doubly valuable little discovery to me.

So what is the origin of the Kealakekua Fault? The Hawaiian Islands are far away from any tectonic plate boundaries, so there is not a lot of opportunity here for inverse or strike-slip faults to develop. However, the Hawaiian volcanoes are humongous mountains and their underwater slopes are extremely steep by submarine slope standards: gradients of 15-10˚ are common. [This is in contrast by the way with the relatively gentle slopes of 3-8˚ the subaerial flanks of the volcanoes, a difference that - it just occurred to me - has to do something with the different thermal conductivities of water and air. Water is ~24 times more efficient at cooling lavas, or anything for that matter, than air, so once a volcano sticks its head out of the water, basaltic lava flows are pretty efficient at carrying volcanic material far away from the crater, thus building gently sloping shield volcanoes. The same flows are promptly solidified and stopped by the cool ocean waters as soon as they reach the coast.] Slopes that are this steep are also unstable; the underwater parts of these volcanoes tend to fail from time to time and large volumes of rock rapidly move to deeper waters as giant submarine landslides. Seafloor mapping around the islands revealed that the underwater topography is far from smooth; instead, in many places it consists of huge slide and slump blocks.

Topographic map of the Big Island. Note the location of Kealakekua Fault and the rugged seafloor to the southwest of it, marking the area affected by slides and slumps. This is a map based on higher-resolution bathymetric data collected during a collaborative effort led by JAMSTEC (Japan Marine Science and Technology Center). Source: U.S. Geological Survey Geologic Investigations Series I-2809

Kealakekua Fault is probably part of the head scarp of one such giant landslide, called the Alika landslide. This explains the steep slopes in the bay itself: after a narrow wave-cut platform, a spectacular wall covered with coral - the continuation of the cliff that you can see onshore - dives into the deep blue of the ocean as you float away from the shore. In contrast with submarine landslides that involve well stratified sediments failing along bedding surfaces and forming relatively thin but extensive slide deposits, the Hawaiian failures affect thick stacks of poorly layered volcanic rock and, as a result, both their volumes and morphologic relief are larger (see the paper by Lipman et al, 1988). The entire volume of the Alika slide is estimated to be 1500-2000 cubic kilometers. That is about a hundred times larger than all the sediment carried by the world's rivers to the ocean in one year! The slides have moved at highway speeds and generated tsunamis. There is evidence on Lanai island for a wave that carried marine debris to 325 meters above sea level; this tsunami was likely put in motion by the Alika landslide*.

You don't want to be snorkeling in Kealakekua Bay when something like that happens. And it will happen again, it is a matter of (geological) time. Giant underwater landslides are part of the normal life of these mid-ocean, hotspot-related volcanoes.

Reference
Lipman, P., Normark, W., Moore, J., Wilson, J., Gutmacher, C., 1988, The giant submarine Alika debris slide, Mauna Loa, Hawaii. Journal of Geophysical Research, vol. 93, p. 4279-4299.

*tsunamis generated by landslides is a whole new exciting subject that we have no time now to dive or snorkel into.

Morphology of a forced regression

2010-11-25T00:27:00.003-06:00

'Forced regression' is an important concept in sequence stratigraphy - it occurs when relative sea level falls and the shoreline shifts in a seaward direction, regardless of how much sediment is delivered to the sea. This is in contrast with 'normal' regressions, which take place when relative sea level doesn't change or it is rising, but rivers bring lots of sediment to the coast and are able to push the shoreline seaward. These concepts are commonly illustrated with simple cartoons (like the ones on the SEPM sequence stratigraphy website), showing how beach deposits stack in a dip direction, and how their tops are eroded by rivers as sea level continues to fall.

Unless you live in a horizontally challenged flatland (vertical-land? 2D seismic-land?), real regressions happen in three dimensions, and their morphology is much more complicated, more interesting, and more beautiful than what one can dream up with a few lines in a single cross section. The example below is an airborne lidar image from Finland. The original data has a horizontal resolution of 2 meters and a vertical resolution of 30 centimeters.

Airborne lidar image of uplifted coastal plain in Finland
Image courtesy of Jouko Vanne, Geological Survey of Finland

The two dominant morphologies and deposit types clearly visible in the image are (1) ancient coastlines, formed as sand brought to the sea by rivers was reworked by waves into beach ridges; and (2) an incised river valley that cuts through these shoreline deposits. Note how the river seems to be incising and migrating laterally at the same time, generating a scalloped valley edge. The reason for this forced regression during a time of global sea-level rise is the isostatic rebound of the Scandinavian Peninsula after the retreat of the ice sheet.

Looking at this crystal-clear morphology, it is tempting to think that this area must look very interesting in Google Earth as well. It turns out that it doesn't; this is actually a pretty heavily vegetated land, not too spectacular on conventional satellite imagery (see figure below). The laser rays of the lidar are able to see through the non-geomorphological 'noise' and show stunning geomorphological detail.

Comparison of satellite image from Google Earth with detail of lidar topography

To explore a higher resolution version of this image, and for additional lidar visualizations of similar beauty, check out Jouko Vanne's Flickr site. The National Land Survey of Finland has started collecting this kind of data in 2008 and they are planning to cover the whole country with high-resolution DEMs within a few years.

A great way to spend taxpayer money, as far as I am concerned.

Einstein, tea leaves, meandering rivers, and beer

2010-11-20T20:10:00.003-06:00

If you make your tea the old-fashioned way, ending up with a few tea leaves at the bottom of the teacup, and you start stirring the tea, you would expect the leaves to move outward, due to the push of the centrifugal force. Instead the leaves follow a spiral trajectory toward the center the cup. The physical processes that result in this 'tea leaf paradox' are essentially the same as the ones responsible for building point bars in meandering rivers. It turns out that the first scientist to make this connection and analogy was none other than Albert Einstein.

In a paper published in 1926 (English translation here), Einstein first explains how the velocity of the ~~fluid~~ tea flow is smaller at the bottom of the cup than higher up, due to friction at the wall. [The velocity has to decrease to zero at the wall, a constraint called 'no-slip condition' in fluid mechanics.] To Einstein it is obvious that "the result of this will be a circular movement of the liquid" in the vertical plane, with the liquid moving toward the center at the bottom of the cup and outward at the surface (see the figure below). For us, it is probably useful to think things out in a bit more detail.

Einstein's illustration of secondary flow in a teacup

A smaller velocity at the bottom means a reduced centrifugal force as well. But overall, the tea is being pushed toward the sidewalls of the cup, and this results in the water surface being higher at the sidewalls than at the center. The pressure gradient that is created this way is constant throughout the whole ~~water~~ tea column, and overall it balances the centrifugal force (unless you stir so hard that the tea spills over the lips). This means that the centrifugal force wins at the top, creating a velocity component that points outward, but loses at the bottom, creating a so-called secondary flow that is pointing inward. The overall movement of the liquid has a helical pattern; in fact, those components of the velocity that act in a direction perpendicular to the main rotational direction are usually an order of magnitude smaller than the primary flow.

Einstein goes on to suggest that the "same sort of thing happens with a curving stream". He also points out that, even if the river is straight, the strength of the Coriolis force resulting from the rotation of the Earth will be different at the bottom and at the surface, and this induces a helical flow pattern similar to that observed in meandering rivers. [This force and its effects on sedimentation and erosion are much smaller than the 'normal' helical flow in rivers.] In addition, the largest velocities will develop toward the outer bank of the river, where "erosion is necessarily stronger" than on the inner bank.

Secondary flow in a river, the result of reduced centrifugal forces at the bottom

I find the tea-leaf analogy an excellent way to explain the development of river meanders and point bars; just like tea leaves gather in the middle of the cup, sand grains are most likely to be left behind on the inner bank of a river bend. Yet Einstein's paper is usually not mentioned in papers discussing river meandering -- an interesting omission since a reference to Einstein always lends more weight and importance to one's paper (or blog post).

A recent and very interesting exception is a paper published in Sedimentology. It is titled "Fluvial and submarine morphodynamics of laminar and near-laminar flows: a synthesis" and points out how laminar flows can generate a wide range of depositional forms and structures, like channels, ripples, dunes, antidunes, alternate bars, multiple-row bars, meandering and braiding, forms that are often considered unequivocal signs of turbulent flow. [This issue of Sedimentology is open access, so do click on the link and check out the paper!]. As they start discussing meandering rivers and point bars, Lajeunesse et al. suggest that Einstein's teacup is extremely different dynamically from the Mississippi River, yet it can teach us about how point bars form:

A flow in a teacup with a Reynolds number of the order of 10² cannot possibly satisfy Reynolds similarity with the flow in the bend of, for example, the Mississippi River, for which the Reynolds number is of the order of 10⁷. Can teacups then be used to infer river morphodynamics?

The answer is affirmative. When dynamical similarity is rigorously satisfied, the physics of the two flows are identical. However, even when dynamical similarity is not satisfied, it is possible for a pair of flows to be simply two different manifestations of the same phenomenon, both of which are described by a shared physical framework. Any given analogy must not be overplayed because the lack of complete dynamic similarity implies that different features of a phenomenon may be manifested with different relative strengths. This shared framework nevertheless allows laminar-flow morphodynamics to shed useful light on turbulent-flow analogues.

Apart from helping understand river meandering, the tea leaf paradox has inspired a gadget that separates red blood cells from blood plasma; and helps getting rid of trub (sediment remaining after fermentation) from beer.

That explains the 'beer' part of the title. And it is time to have one.

References

Einstein, A. (1926). Die Ursache der Meanderbildung der Flusslaufe und des sogenannten Baerschen Gesetzes Die Naturwissenschaften, 14 (11), 223-224 DOI: 10.1007/BF01510300

Lajeunesse, E., Malverti, L., Lancien, P., Armstrong, L., Metivier, F., Coleman, S., Smith, C., Davies, T., Cantelli, A., & Parker, G. (2010). Fluvial and submarine morphodynamics of laminar and near-laminar flows: a synthesis Sedimentology, 57 (1), 1-26 DOI: 10.1111/j.1365-3091.2009.01109.x

Wave ripples on an eroding beach

2010-09-12T00:43:00.005-05:00

I shot these photos in 2003, at Sea Rim State Park in east Texas, close to the border with Louisiana, a relatively remote and beautiful state park along the Gulf coast that suffered a lot of damage during both Hurricane Rita in 2005 and Hurricane Ike in 2008. On that chilly November day the light was great and the variety of shapes and patterns created by wave ripples and exposed during low tide was amazing.

Wave ripples are more symmetric than current ripples. Needless to say, wave ripples originate thanks to the back-and-forth movement of sand by waves, whereas current ripples form under unidirectional flows (like rivers and turbidity currents). Wave ripples are also more regular than current ripples, extend for much longer distances laterally, and often terminate - or continue - in 'Y'-shaped junctions. For the same wavelength, they are also taller; the L/H ratio of most wave ripples is between 4 and 10, in contrast with current ripples that have an L/H value of ~20.

Perfectly symmetrical ripples form under bidirectional currents that are perfectly symmetrical themselves; but this tends to be the exception rather than the rule, as shoaling waves create a net shore-directed movement of the water. The resulting ripples are asymmetric, with the steeper side facing the coast, but still more symmetric and more regular than pure unidirectional ripples. Weak tidal currents can cause the asymmetry as well. The photo below shows wave ripples with a significant asymmetry that makes them difficult (if not impossible) to distinguish from current ripples.

This set is also asymmetric, but to a lesser degree:

Sea Rim State Park is at a location along the Gulf coast where the beach is eroding and the coastline is retreating; it is a typical example of a transgressive coast. The erosion is the results from both sea-level rise and from lack of longshore sediment transport strong enough to nourish the beach with sand. The evidence for the transgression is quite obvious: banks of well-consolidated muds that were originally deposited in the lagoon behind the coastal barrier are being eroded by the advancing waves:

The complexity of sinuous channel deposits in three dimensions

2010-08-15T15:29:00.005-05:00

The beauty of the shapes and patterns created by meandering rivers has long attracted the attention of many geomorphologists, civil engineers, and sedimentologists. Unless they are fairly steep or have highly stable and unerodible banks, rivers do not like to follow a straight course and tend to develop a sinuous plan-view pattern. The description and mathematical modeling of these curves is a fascinating subject, but that is not what I want to talk about here and now. It is hard enough to understand the plan-view evolution of rivers, especially if one is interested in the long-term results - when cutoffs become important -, but things get really complicated when it comes to the three-dimensional structure of the deposits that meandering rivers leave behind. The same can be said about sinuous channels on the seafloor, created and maintained by dirty mixtures of water and sediment (called turbidity currents). An ever-increasing number of seafloor and seismic images show that highly sinuous submarine channels are almost as common as their subaerial counterparts, but much remains to be learned about the geometries of their deposits that accumulate through geological time.

Using simple modeling of how channel surfaces migrate through time, two recent papers attempt to illustrate the three-dimensional structure of sinuous fluvial and submarine channel deposits. In the Journal of Sedimentary Research, Willis and Tang (2010) show how slightly different patterns of fluvial meander migration result in different deposit geometries and different distribution of grain size, porosity and permeability. [These properties are important because they determine how fluids flow - or don't flow - through the pores of the sediment.] River meanders can either grow in a direction perpendicular to the overall downslope orientation, or they can keep the same width and migrate downstream through translation. In the latter case - which is often characteristic of rivers incising into older sediments -, deposits forming on the downstream, concave bank of point bars will be preferentially preserved. These deposits tend to be finer grained than the typical convex-bank point bar sediments. In addition to building a range of models and analyzing their geometries, Willis and Tang also ran simulations of how would oil be displaced by water in them. One of their findings is that sinuous rivers that keep adding sediment in the same area over time (in other words, rivers that aggrade) tend to form better connected sand bodies than rivers which keep snaking around roughly in the same horizontal plane, without aggradation.

Map of deposits forming as river meanders grow (from Willis and Tang, 2010).

Cross sections through the deposits of two meander bends (locations shown in figure above). Colors represent permeability, red being highly permeable and blue impermeable sediment. From Willis and Tang, 2010.

Check out the paper itself for more images like these, plus discussions of concave-bank deposition, cutoff formation, and filling of abandoned channels.

The second paper (Sylvester, Pirmez, and Cantelli, 2010; and yes, one of the authors is also the author of this blog post, so don't expect any constructive criticism here) focuses on submarine channels and their overbank deposits, but the starting point and the modeling techniques are similar: take a bunch of sinuous channel centerlines and generate surfaces around them that reflect the topography of the system at every time step. However, we know much less about submarine channels than fluvial ones, because it is much more difficult to collect data at and from the bottom of the ocean than it is from the river in your backyard. The result is that some of the simplifications in our model are controversial; to many sedimentary geologists, submarine channels and their deposits are fundamentally different from rivers and point bars, and there is not much use in even comparing the two. Part of the problem is that not all submarine channels are made equal, and, when looking at an outcrop, it is not easy - or outright impossible - to tell what kind of geomorphology produced the stratigraphy. In fact, the number of exposures that represent highly sinuous submarine channels, as observed on the seafloor and numerous seismic images, is probably fairly limited. One thing is quite clear, however: many submarine channels show plan-view migration patterns that are very similar to those of rivers, and this large-scale structure imposes some significant constraints on the geometry of the deposits as well.

That being said, nobody denies that there are plenty of significant differences between real and submarine 'rivers' [note quotation marks]. A very important one is the amount of overbank - or levee - deposition: turbidity currents often overflow their channel banks as thick muddy clouds and form much thicker deposits than the overbank sediment layers typical of rivers. When these high rates of levee deposition combine with the strong three-dimensionality of channel migration, complex geometries result that are quite tricky to understand just by looking at a single cross section.

Cross section and chronostratigraphic diagram through a submarine channel system with inner and outer levees (from Sylvester et al., 2010).

One of the consequences of the channel migration is the formation of erosional surfaces that develop through a relatively long time and do not correspond to a geomorphologic surface at all (see the red erosional zones in the Wheeler diagram above). This difference between stratigraphic and geomorphologic surfaces is essential, yet often downplayed or even ignored in stratigraphy. In terms of geomorphology, the combination of channel movement in both horizontal and vertical directions and the extensive levee deposition results in a wide valley with scalloped margins and numerous terraces inside:

Three-dimensional view of an incising channel-levee system (from Sylvester et al., 2010).

This second paper is part of a nice collection focusing on submarine sedimentary systems that is going to be published as a special issue of Marine and Petroleum Geology, a collection that originated from a great conference held in 2009 in Torres del Paine National Park, Southern Chile.

PS. As I am typing this, I see that Brian over at Clastic Detritus is also thinking about submarine channels and subaerial rivers... Those channels formed by saline density currents on the slope of the Black Sea are fascinating.

Willis, B., & Tang, H. (2010). Three-Dimensional Connectivity of Point-Bar Deposits Journal of Sedimentary Research, 80 (5), 440-454 DOI: 10.2110/jsr.2010.046

Sylvester, Z., Pirmez, C., & Cantelli, A. (2010). A model of submarine channel-levee evolution based on channel trajectories: Implications for stratigraphic architecture Marine and Petroleum Geology DOI: 10.1016/j.marpetgeo.2010.05.012

A hike in the Bucegi Mountains, Romania

2010-07-10T19:45:00.004-05:00

Recently I had a chance to revisit a fantastic hiking trail in the Bucegi Mountains, located in the Romanian Carpathians (or Transylvanian Alps, for those who prefer a more exotic name). The Bucegi are among the most spectacular hiking and climbing places in Eastern Europe, with some of the tallest cliffs in the region. Back in the good old days when I used to live closer to some significant topographic relief (as opposed to a living on a %^$#@ flat passive margin), this hike was one of our favorites. The main attraction is a steep climb along a valley floor that usually has some snow even during the summer months. In the steepest sections there is no proper trail and usually there is nobody else around; this is the perfect place if you want some outstanding scenery without the crowds.

The predominant rock type in these mountains is the Bucegi Conglomerate, a Cretaceous formation with lots of limestone clasts. The limestone pebbles, cobbles and boulders were eroded from Jurassic carbonates that outcrop in the western parts of the Bucegi. This is one of the thickest conglomerate accumulations I have seen and I know of; its thickness reaches 2000 meters in places. It was probably deposited as fan deltas along a rocky coast, with rivers that were directly depositing coarse-grained sediment onto a submarine slope. There is evidence for deposition by sediment gravity flows: many conglomerate layers show no obvious stratification (which one would expect in a river deposit) and normal grading is common. Toward the top, there is one spectacular layer, likely deposited by a single flow, with limestone blocks tens of meters across. [These blocks are often called olistoliths.]

Typical Bucegi Conglomerate (photo taken in 1995)

Originally these rocks were described as 'molasse' (one of those terms that probably were invented only to hide our ignorance about the relationships between mountain building and sedimentation), likely reflecting deposition in shallow marine environments. In the late seventies, when the idea that thick piles of coarse sediment could be of deep-marine origin was still big news in geology, the Bucegi Conglomerate actually made it onto the pages of Nature.

View Bucegi Hike in a larger map

In any case, our hike in June was long and strenuous (see the map above), but the weather was outstanding and we had the whole mountain to ourselves: apart from the meteorologists at the Omu Peak, we haven't seen a human being while hiking.

Here are a few more photographs (see the rest at Smugmug):

There is still plenty of snow in the 'Valea Alba' ('white valley') in June

The artist previously known as erosion

That's all conglomerate

When you clearly need a log-scale for grain size (note the two limestone 'grains' and the normal grading above the lower one)

This picture gives an idea how big the limestone blocks in the previous photo are: note the two guys in the front for scale

Deep-sea landscapes from the ice age

2010-05-27T06:44:00.017-05:00

The upcoming edition of Accretionary Wedge is going to focus on geo-images. I was always fascinated by the beauty of landscapes and landforms, natural patterns and textures, as many of the posts on this blog can testify; that is one of the reasons why I became a geologist.

However, this time I want to show a different kind of geo-image. These are not usual photographs; they are pictures of landscapes that existed thousands or millions of years ago. The 'photographer' uses acoustic waves instead of light. Once the data is recorded, a whole lot of processing and editing is required to get a reasonable result. Most often it is not trivial to make sure that the final image indeed comes close to capturing one geological moment in time, and part of it is not hundreds of thousands or millions of years older than the rest. It is a bit like stacking vertically pictures that come from time-lapse photography, but parts of the older images are erased later and get replaced with pixels that belong to more recent shots.

I am talking about maps that come from three-dimensional seismic surveys, especially their shallower sections located near the seafloor. Using this kind of data, it is possible to reconstruct ancient landscapes through careful mapping. The result is never going to be perfect, or even comparable to present-day satellite imagery, on one hand due to the limited lateral and vertical resolution, and on the other hand due to the removal of significant parts of the stratigraphic record through erosion.

Still, it is amazing that it is possible to reconstruct for example how the Gulf of Mexico looked like during a glacial period. The images below come form the continental slope of the Gulf, and are buried a few hundred feet below the seafloor. This morphology most likely formed during a glacial period when rivers were crossing the exposed shelf and delivering sediment directly onto the upper slope.

source: Virtual Seismic Atlas

Two submarine channels are visible, both of them directly linked to a delta that was deposited at the shelf edge. Colors correspond to thickness: red is thick, blue is thin. The next image shows the surface underlying the channels; in this case, the topographic surface is draped with seismic amplitude:

source: Virtual Seismic Atlas

There are more images from this ancient landscape available at the Virtual Seismic Atlas, a great resource for geo-imagery in general (see this post at Clastic Detritus for more detail). It is best to view these 'photographs' at larger resolution (which is pretty big in this case!) -- you can do that if you go to the VSA website.

Garmin Forerunner 110 GPS watch - a review

2010-05-15T13:12:00.016-05:00

A couple of years ago I decided to take running a bit more seriously and to try to keep track of when, how much, and how fast I run. As a dedicated Apple-afficionado and beginner runner, the obvious choice was the Nike+ sensor (which you place in the sole of your shoe), coupled with an iPod Nano. I have been using this setup for about two years now, and I was fairly happy with it. It was easy to start using it, it definitely helped me run more and faster than before, and GPS units were just too big or too nerdy (even for me) to carry around on a Saturday morning run in the park.

However, it has always bugged me that the precision and accuracy of the Nike+ system was far from perfect, and I knew that GPS watches could do much better, not to mention that you can also put your run on a map. I caved in to the temptation a few days ago and ordered a Garmin Forerunner 110 GPS watch; here are some initial observations.

The Forerunner 110 is designed to be relatively small and simple, with limited functionality. In other words, it is targeting people like me: mostly outdoor runners (it is not very good for biking and useless for indoor running) who don't need all kinds of functionalities that most other Garmin GPS watches have. It gives you basic information like pace, time, distance, and heart rate (if you are using it with a heart rate monitor), and that's about it. The relatively small size and reasonably good (=minimalistic) look means that you can wear this gadget on your wrist pretty much every day, without looking like a total nerd.

In terms of usability, the Forerunner 110 does pretty well. It doesn't rely on the touch interface that is built into the latest and greatest Garmin sports watches; instead, it has four large buttons that are easy to push when you want to -- or not to push inadvertently when you don't want to. This can be important in the middle of a sweaty run when you are not really in the mood for the subtleties of dealing with a sensitive touch interface. For example, I often have problems with the touch-wheel of the iPod nano. Recording a run basically comes down to (1) waiting until the watch gets a GPS fix; and (2) pushing the 'start/stop' button. In my limited experience, getting a GPS fix works pretty well and relatively fast, although it did take about 5 minutes the first couple of times. That is too much for a runner. Yesterday and today however it was much better, it locked on to the satellites in less than a minute.

So far so good. The one major issue I ran into was that, after a first recorded run, when I wanted to upload the data to the Garmin Connect website, I couldn't get the watch to talk to my MacBook. It took lots of trial-and-error and one-and-a-half hours on the phone with the Garmin help desk to figure out that the charging clip that's supposed to attach to the four exposed contacts on the back of the watch was not exactly where it should have been, despite the fact that the watch was charging (or it looked like it was charging anyway). This might be just a reflection of my limited intellectual capabilities, but I doubt that I am the only one who will run into this problem.

When it comes to uploading your workout data to a website for visualization and analysis, the Garmin ecosystem definitely leaves the Nike+ setup in the dust. The obvious advantage is the visualization of your runs in Google Maps. This is a major plus for a map-lover; but in addition to that, the Garmin Connect website makes it very easy to export the data and visualize it with Google Earth or any other software that can handle geospatial data. No export options exist for the runs you have recorded with the Nike+ sensor. In addition, the quality and usability of the Garmin graphs showing pace/speed through time is way better than the flashy but largely useless attempt that Nike has put together. Compare these two graphs (representing the same run):

Nike+ website

Garmin Connect

The Nike+ graph is pretty close to useless, whereas the one from Garmin Connect looks like a plot based on real data and it shows real trends (e.g., that I was running significantly slower during the last half of the run). And this is not a reflection of poor data quality coming from the iPod software; it turns out that the resolution of that data is much better than what Nike shows you. In general, Garmin treats the workout data in a much more scientific yet simple manner, also giving you the options of taking the data elsewhere, whereas the Nike website is colorful and animated, but has limited and closed information that has been dumbed down too much for my taste.

To wrap it up, despite a few - hopefully short-lived - annoyances, I am fairly happy with this new gadget. I will try to find out later how well it can be used for geotagging photographs while hiking or doing field work, something I still don't have a simple solution for.

Update (6/20/2010): I have been using this watch for more than a month now. It works pretty well for running, although I did have a problem today: it froze at one point, and I couldn't record any new data. It was very hot and humid, and I guess the contacts on the back side of the watch couldn't handle the amount of salty sweat I was producing. Now it works again. Also, it is a good idea to turn on the GPS reception a few minutes before you start the run because sometimes it still takes 2-3 minutes to get the coordinates.

In terms of using it for hiking and geotagging photographs: I did a hike using both this watch and an older Garmin unit, and noticed that the accuracy of theForerunner 110 is better than that of the Garmin eTrex Vista Cx. The watch worked much better in the forest and in a deep, narrow valley, where the GPS signal must have been weak. The problem is that the battery of the Forerunner 110 doesn't last long enough for a full-day hike; after about 5 hours of constant GPS recording, I couldn't use it any more.

Update (2/4/2011): It looks like this watch (certainly the one that I am using) has a major flaw: when connected to a computer, the USB connection is easily broken because of the questionable design of the contacts on the back of the watch and the clip. The watch freezes and the only way I could get it back to life was to do a hard reset. This means that any data you have on the watch is lost. I have lost running data due to this issue several times; the last time it was especially annoying since it successfully got rid of the GPS record of my first marathon. Thanks, Garmin!

Evapor-art from the Permian Castile Formation, west Texas

2010-05-08T13:46:00.012-05:00

The Late Permian Castile Formation is a ~500 m thick accumulation of evaporites in west Texas and south-eastern New Mexico. Its most striking feature is the vast number of alternating thin layers of lighter- and darker-colored deposits, layers that seem to be continuous across most of the Delaware Basin. The white laminae are mostly gypsum and anhydrite; the darker layers consist of calcite and organic matter.

Most experts agree that these laminations reflect seasonal changes; that is, a pair of white and dark layers corresponds to one year. The thicker gypsum layer was deposited during the dry season; the thinner calcite layer with the organic material formed during the humid season when algae were more abundant and only carbonates could precipitate from the lower-salinity water [for more details, see this paper].

The image above gives an idea how laterally persistent these laminations can be; the two photographs come from cores that are 24 km (~15 miles) apart (source: Kirkland, D.W., 2003, An explanation for the varves of the Castile evaporites (Upper Permian), Texas and New Mexico, USA, Sedimentology 50, p. 899-920).

These evaporites are often affected by small-scale faulting and folding; the resulting patterns are quite variable and aesthetically pleasing (well, at least according to me). I shot these photos on a recent geological trip to Guadalupe Mountains National Park, in a roadcut near highway 180; more pictures here.

Texas wildflowers

2010-03-28T21:40:00.010-05:00

The weather has been awesome around here lately (yes, in Houston!, the weather!, awesome!), and otherwise uninteresting roadside places are starting to be flooded with colors. Here are a few shots; more over at Smugmug.

This one is actually from 2008:

One of the issues with photographing flowers is that parts of the pictures are often out of focus, as it is obvious in this shot:

And a way to deal with that is to take a number of pictures that are focused at different distances and then merge them in Photoshop (as described in this video). This image was put together from four different photographs, and is a somewhat better version of the previous scene (the fact that the wind was pretty strong didn't help):

Three photos from California Academy of Sciences, San Francisco

2009-12-27T18:43:00.007-06:00

This is a fantastic place! Clearly worth a visit if you have a few hours to spend in San Francisco.

More photographs here.

Madagascar giant day gecko

Coral reef from the Philippines

Jellyfish

Lunar Crater volcanic field, Nevada

2009-12-23T16:37:00.014-06:00

I was on my way to San Francisco / AGU last week when I saw these volcanoes and shot these pictures through the airplane window. It turns out that this is the Lunar Crater volcanic field in Nevada, named after the largest crater that is more than 1000 meters across and about 130 m deep. There are 95 vents that are 4.2 million to 15,000 years old. Lunar Crater is the largest feature in the image below; it is a maar; most of the other vents formed cinder cones.

Here is a map showing the Houston - San Francisco flight track and the location of the volcanic field:

View Lunar Crater volcanic field in a larger map

Three photos from Kauai

2009-11-27T22:51:00.007-06:00

The rest are here.

Colors in Alakai swamp

Green turtle at Tunnels Beach

Na Pali Coast

Hillslope diffusion

2009-11-26T07:46:00.030-06:00

Modeling erosion and deposition of sediment using the diffusion equation is among the important subjects that are usually omitted from sedimentary geology textbooks. Part of the reason for this is that ‘conventional’ sedimentary geology tended to only pay lip service to earth surface processes and was more interested in describing the stratigraphic record than figuring how it relates to geomorphology. Nowadays, a good discussion of stratigraphy and sedimentology cannot ignore anymore what geomorphologists have learned about landscape evolution. (One textbook that clearly recognizes this is this one.)

But let's get back to the subject of this post. Hillslope evolution can be modeled with the diffusion equation, one of the most common differential equations in science, applied for example to describe how differences in temperature are eliminated through heat conduction. In the case of heat, the heat flux is proportional to the rate of spatial temperature change; on hillslopes, the sediment flux is proportional to the spatial rate of change in elevation. This last quantity of course is the slope itself. In other words,

q = -k*dh/dx,
or

q = -k*slope,
where q is the volumetric sediment flux per unit length, k is a constant called diffusivity, h is the elevation, and x is the horizontal coordinate.

We also know that sediment does not disappear into thin air: considering a small area of the hillslope, the amount of sediment entering and leaving this area will determine how large the change in elevation will be:

dh/dt = -dq/dx,
in other words, deposition or erosion at any location is determined by the change in sediment flux.

Combining this equation with the previous one, we arrive to the diffusion equation:

dh/dt = k*d²h/dx².
Note that the quantity on the right side is the second derivative (or curvature) of the slope profile. Large negative curvatures result in rapid erosion; places with large positive curvature have high rates of deposition. Through time, the bumps and troughs of the hillslope are smoothed out through erosion and deposition.

The simplest possible case is the diffusion of a fault scarp. The movie below illustrates how a 1 m high fault scarp gets smoothed out through time; the evolution of slope and curvature are also shown. The dashed line indicates the original topography, at time 0. [The plots were generated using Ramon Arrowsmith's Matlab code; right-click the flash animation for playback controls].

More complicated slope profiles can be modeled as well; here is an example with two fault scarps:

Note how both erosion and deposition get much slower as the gradients become more uniform.

The simplicity of the diffusion equation makes it an attractive tool in modeling landscape evolution. In addition to hillslopes and fault scarps, it has been successfully applied in modeling - for example - river terraces, deltaic clinoforms, cinder cones, fluvial systems, and foreland basin stratigraphy. However, it is important to know when and where the assumptions behind it become invalid. For example, steep slopes often have a non-linear relationship between sediment flux and slope as mass movements dramatically increase sediment flux above a critical slope value. Also, the models shown here would fail to reproduce the topography of a system where not all sediment is deposited at the toe of the steeper slope, but a significant part is carried away by a river. And that brings us closer to advection; a subject that I might take notes about at another time.

Further reading: 1) The book "Quantitative Modeling of Earth Surface Processes" by Jon Pelletier has a chapter with lots of details about the diffusion equation. 2) Analog and numerical modeling of hillslope diffusion - a nice lab exercise.

Upcoming conference on seismic geomorphology

2009-10-24T18:14:00.007-05:00

Ever since geoscientists and engineers started using seismic waves to figure out what lies under our feet, seismic reflection technology kept improving and today most oil-rich sedimentary basins have a wide coverage of high-quality three-dimensional datasets. In addition to finding structures and locations in the subsurface that are likely to be filled with hydrocarbons, these huge data volumes can also be used to reconstruct landscapes that are long gone from the Earth's surface. After all, stratigraphy is what is left behind from an ever-changing topography, and it is a mistake to think that stratigraphy can be understood without knowing a few things about geomorphology and landscape evolution.

Seismic data confirms that the past, indeed, is not that different from the present: if you peek (that is, listen) into these volumes of rock, you see ancient meandering rivers and submarine channels, deltas, barrier islands, mouth bars, and estuaries. However, in addition to and beyond the excitement of seeing another beautiful example of a sinuous channel or other depositional and erosional features, a lot remains to be learned from the true and large-scale three-dimensionality of these datasets. For a geologist, there is no other data type that offers such a degree of three-dimensionality. Even the largest outcrops offer only random two-dimensional sections through a system; the temptation is strong to convince ourselves that we can extrapolate to get an idea about the third dimension, but more often than not we are probably wrong, at least in the details of our extrapolation. This is actually worse than the case of "The Blind Men and the Elephant"; it is more like the blind men and a random cut through the elephant (but I will stop this chain of analogies right there).

Long story short, I (re)started to blog about this subject because there is going to be an SEPM research conference in Houston, a conference that focuses on using three-dimensional seismic data to better understand how sediment moves or gets deposited on continental slopes. It should be an interesting collection of talks and papers.

The image above is from the conference website and announcement; it happens to come from a paper that I am going to present, on a shelf-edge delta and its related slope channels in the Gulf of Mexico (the higher-resolution version is coming soon...). Colors represent thickness (red is thick, blue means thin). There are two leveed channels taking sediment from the shelf-edge delta into the deep ocean.

Two gigapans from Cliffs of Moher, Ireland

2009-07-19T17:29:00.006-05:00

I shot these gigapans recently, while we were visiting some deep-water rocks in County Clare, Ireland (see more detail on these rocks and a few photos from the trip). One afternoon we took some time off from the turbidites to do a bit of geo-tourism at the Cliffs of Moher, a series of spectacular escarpments along an 8 km long stretch of the western coast of Ireland. They are 702 feet (214 meters) high at the highest point and expose Late Carboniferous (Namurian) sandstones and shales that were mostly deposited as deltaic and fluvial sediments of the Tullig and Kilkee cyclothems.

This place is one of the most visited tourist attractions in Ireland, and for a good reason: the combination of the cliffs, the landscape, and abundant wildlife is, indeed, spectacular.

This is a view to the south (launch full screen viewer):

And this is a view to the north (from O'Brian's Tower; launch full-screen viewer):

Unfortunately, these stamp-sized windows do not do justice to the panoramas; it is a good idea to click on the "Launch full-screen viewer" links.

More reasons to conclude that coastal 'chevrons' are not related to mega-tsunamis

2009-05-09T11:18:00.035-05:00

If there was any doubt left that coastal sand accumulations called 'chevrons' are *not* related to gigantic tsunamis (see previous thoughts on the subject here and here; Ole also has a recent blog post, and see a news release here), the May issue of Geology provides additional arguments to show that this is the case. Joanne Bourgeois of University of Washington and Robert Weiss of Texas A&M University, both experts in the sedimentology of tsunami deposits, present two lines of arguments. First they show that the orientation of the Madagascar chevrons is significantly different from what is predicted through modeling the tsunami. While the tsunami wave tends to hit the coast with an overall perpendicular orientation, due to wave refraction, the 'chevrons' are oriented at various angles to the coast, angles that are more consistent with predominant wind directions. Second, they look at the sediment transport conditions and suggest that even coarse sand must have been in suspension in flows deep enough to create the chevrons. However, dune-like bedforms cannot develop without sediment being transported as bedload; therefore, the bedforms must have a different origin than mega-tsunamis. The obvious alternative is parabolic dunes; these well-known bedforms show up when vegetation partially covers the dune's tails and slows down sediment transport. The authors don't hesitate to draw the conclusion that

The extraordinary claim of "chevron” genesis by mega-tsunamis cannot withstand simple but rigorous testing.

I am far from being a tsunami expert, but I find this subject fascinating. The issue of suspended load vs. bedload and stratified or laminated vs. graded bedding is equally important for deposition from tsunami waves and turbidity currents. It is worth spending a bit of time and blogspace to explore the kind of analysis of sediment transport conditions that this paper presents.

Although I see no reasons to disagree with the paper's conclusions (as it could be predicted from my previous posts on the subject), at first reading I didn't fully understand the line of reasoning about suspended load vs. bedload. So here goes my attempt to understand it.

The argument goes as follows. The Rouse number is the ratio between the settling velocity of a certain grain size and the shear velocity of the flow, multiplied by von Karman's constant (which is ~0.4): Ro = ws/k*u_shear. For a grain of a given size, if the Rouse number is larger than 2.5, the grain's settling velocity is much larger than the upward-directed component of the turbulence, and the grain tends to stay close to the bottom, in the bedload. [This is equivalent to saying that the settling velocity has to be larger or equal to the shear velocity, a condition also known as the suspension criterion]. If the Rouse number is less than 0.8, the flow is turbulent enough to keep the grain fully suspended. In between these values, there is a zone of transitional behavior. For the flows that might have deposited the chevrons, the Rouse number is always less than 2.5, regardless of how the other parameters like the Froude number, grain diameter, and roughness length are varied. Although the authors state that the flows must have been deeper than 8 m (because most chevrons are higher than 4 m, and the flow must be at least twice as high as the bedform), there seems to be no other constraint on tsunami behavior [note that I did not have access - yet - to the supplementary web material].

So the question is: doesn't this reasoning apply to other types of flows as well? For example, the Mississippi River is certainly deeper than 8 m in many places -- does this mean that it is able to suspend very coarse (2 mm diameter) sand? In other words, what is the difference between flow in a tsunami run-up and the Mississippi River? The answers might be obvious to many, but they are certainly not obvious to me.

One thing we can do is to create a different kind of plot: instead of plotting the Rouse number against flow depth, let's plot velocity vs. depth. I have a better feeling for what are reasonable velocities for different kind of flows than I do for Rouse numbers. The Rouse number would form the third dimension of the plot; one can visualize that as a contour map of Rouse numbers as a function of flow depth and velocity:

The Rouse numbers shown in this plot are valid for a grain diameter of 2 mm and roughness length of 1 m (using the same equations for settling velocity and shear velocity as in Bourgeois & Weiss 2009). Anything coarser than this cannot be called sand any more. So if this grain size doesn't stay in the bedload, there is no chance for finer sediment either. It is obvious from the plot that, for flows deeper than 8-10 m, very coarse sand will be part of the bedload unless flow velocity is larger than ~5 m/s. The Mississippi River at New Orleans has velocities on the scale 1.5 m/s, so 1-2 mm sand should definitely stay close to the bottom, and in fact it does.

We know however that tsunamis are not exactly tranquil flows like the big old Mississippi at New Orleans. The larger ones are fast and furious and Google Earth might need massive updates after they rearrange entire coastal landscapes. [Don't get me wrong, I am not trying to diminish the power and destructive force of the Mississippi.] In other words, the Froude number of a tsunami run-up is larger than the Froude number of the Mississippi River. The Mississippi is relatively slow and deep; the tsunami is fast and relatively shallow. The Froude number is the ratio between velocity and the square root of gravity multiplied by flow depth:

Fr = u/√(g*d)
This number for the Mississippi is much less than one (these flows are called subcritical flows). On the other hand, tsunamis are waves of very large wavelengths, and they behave even in the open ocean as shallow water waves (wavelength 20 times larger than water depth). For these kinds of waves, the velocity is solely a function of water depth:

u = √(g*d)
If we assume that the tsunami run-up has a comparable velocity to that of the tsunami wave in the nearshore zone, we find that the Froude number of the run-up must be around 1. This is obviously a very back-of-the-envelope argument, but the point is that these flows must have in general relatively large Froude numbers. If we plot the lines for Fr = 1 and Fr =1.5 on the depth-velocity diagram (see above), we can see how different likely tsunami behavior is from that of large rivers. It also becomes evident that even coarse sand would not be part of the bedload in these flows, especially not in flows deep enough to build the 'chevrons'. Which means that sandy tsunami deposits are likely to be largely unstructured or poorly structured sand sheets rather than several m thick accumulations of cross-bedded sand.

And that ends my Saturday exercise in Fluid Mechanics 101.

Reference
Bourgeois, J., & Weiss, R. (2009). "Chevrons" are not mega-tsunami deposits--A sedimentologic assessment Geology, 37 (5), 403-406 DOI: 10.1130/G25246A.1

Links to this post:
Scientia Pro Publica #4

Normal grading

2009-03-28T13:42:00.014-05:00

In sedimentology, the word 'grading' has nothing to do with exams and assignments. Instead, it refers to a regularly decreasing or increasing grain size within one sedimentary layer. Because it is much more common than the other alternative, upward decreasing grain size is called 'normal grading'. Grains that consistently increase in size toward the top of the bed are responsible for 'inverse grading'. Upward fining and coarsening are related terms that are often used to describe grain-size trends in not one, but multiple beds.

Normal grading in a turbidite from the Talara Basin, Peru

The simplest way to generate normal grading is to put some poorly sorted sand and water in a container, shake it up, and then let it settle. The larger grains will settle faster than the smaller ones (as Stokes' law tells us) and most of the large grains will end up at the bottom of the deposit. [Note that some fine grains will be at the bottom as well - the ones that were already close to the bottom at the beginning of sedimentation.] This kind of static suspension settling is not how most sediment is deposited on a river bed or a beach; even if a grain is part of the suspended load, it usually goes through a phase of bedload transport, that is, a phase of jumping and rolling and bouncing on the bed, before it comes to rest. The resulting deposit usually has lots of thin layers, laminations, and there are no obvious and gradual upward changes in grain size.

What is needed is a sediment-rich flow that suddenly slows down or spreads out and looses its power to carry most of its sediment load. Grains are getting to the bottom so fast that there is not much time for the flow to keep them rolling and bouncing around; instead they quickly get buried by the other grains that are ready to take a geological break. While this is still quite different from static suspension settling (because the flow did not come to a full stop), it can be thought of as a modified version of static settling: all is needed is a horizontal velocity component, in addition to the vertical one. Of course, the segregation of the coarser grains to the bottom of the flow may have started much earlier. Typically, they never made it to the top in the first place.

Conglomerate bed in the Cretaceous Cerro Toro Formation, Torres del Paine National Park, Southern Chile. There is some inverse grading at the base of this bed, before the size of the clasts starts decreasing

Such large, sediment-laden flows are not very common, certainly not on a human timescale. When they do occur, they tend to show up in the news, especially if human artifacts, or humans themselves, become part of the normally graded deposits. Deposits of snow avalanches, volcanic ash-laden pyroclastic flows, subaerial debris flows, tsunamis, submarine turbidity currents can all show normal grading. The images shown here all come from deposits of large submarine gravity flows. Some of them (like the one below) have a muddy matrix, but the grading is still obvious (the two large clasts at the top of the bed have lower densities).

Normally graded conglomerate layer with a muddy matrix, Cerro Toro Formation, Chile

In recent years, some questions have been raised about the common presence of normal grading, especially in turbidites. The fact is that normal grading is often seen in rocks of all ages, and, in a simple view, it is a reflection of larger grains getting quickly to the bottom.

Normal grading is normal, after all.

Description does not suffice for an explanation

2009-03-08T12:30:00.008-05:00

On February 3, 1967, J. R. L. Allen gave the fifth "Geologists' Association Special Lecture", entitled "Some Recent Advances in the Physics of Sedimentation". This is from the introduction:

"Two stages can generally be recognised in the historical growth of a reasonably advanced scientific discipline. There is an early, descriptive stage in which with little guide from theory, an attempt is made to collect, define and analyse phenomena. In the later, explanatory stage we see that efforts are concentrated on the production of generalisations and on the explanation of the reduced phenomena in terms of general laws. Of course, there is never a single point in time at which there is change over the entire scope of a discipline from the descriptive to the explanatory stage. The change is, rather, uneven, taking place earlier in some branches than in others, and more gradually in one branch than in another.

Sedimentology stands today in a period of transition. Its subject matter is sedimentary deposits, and its goal the origin and meaning of these in the context of planetary studies in general. But it is apparent, except to adherents of geological phenomenalism, that sedimentary deposits cannot be explained in terms of themselves. Already we are in possession of major generalisations about these deposits, and our chief task for some years should be to explore and ratify them in terms of general laws in order that our understanding of the sedimentary record can be made sharper. In those parts of the field where major generalisations have already been established, the provision of further descriptive data is of little value, except in so far as light is shed on the problems of particular deposits. These are validly a part of the subject, leading to a refinement of certain planetary laws. But the other and no less important laws in terms of which we should seek to frame our understanding are those of general chemistry, physics and biology. In order to achieve this framework in the case of detrital sediments, it will be necessary to set aside for a while the problems of particular deposits. This will, of course, be unacceptable to those who claim that geology, or sedimentology, is only to do with rocks as conceived in a historico-geographical manner. But they will be proved wrong, provided we keep our major goals in mind, for it is a mistake to suppose that a description will suffice for an explanation. Most of our explanations will probably turn out to be no better than qualitative, so complex are most sedimentary systems, but we should nevertheless attempt them and try to frame them as exactly as possible."

Forty years after publication of the paper, this seems as timely as ever.

Reference:
Allen, J. R. L., 1969. Some Recent Advances in the Physics of Sedimentation. Proceedings of the Geologists' Association 80:1-42.

Three photos from Chilean Patagonia

2009-03-05T15:21:00.020-06:00

I was lucky to attend a few days ago a field conference in southern Chile, looking at deep-water rocks in an area that includes Torres del Paine National Park. It was good to be back in this place of unbloggable beauty. The conference was well organized (of course! - Brian was one of the conveners) and we were extremely lucky with the weather: no rain at all on the outcrops, beautiful sunshine most of the time. Although I have been to Chilean Patagonia three times before on various geological field trips and even did some field work there, I realized during this conference that it doesn't matter how many times you have seen some rocks, there is always a chance to rethink what you thought you have already settled in your mind (see blog title). It was also good to see that these field conferences are increasingly not just about the local geology: many if not most presentations and spontaneous discussions compare the local outcrop data with sedimentary systems from other basins, and try to think about how the always-too-small outcrops would look like in seismic sections and volumes.

Brian did not have time to take a lot of photos, so here are three shots (more here). As if anybody needed more shots of the Paine Grande and the Cuernos.

Conference participants examine the turbidites of the Punta Barrosa Formation

The Paine massif (Paine Grande and Cuernos), with Rio Serrano in the foreground

Strong winds on Paine Grande

Update - here is a Gigapan:

Launch full screen viewer

[it is strongly recommended that you do launch the full screen viewer if you want to do justice to the Gigapan]

The science of espresso, with a dash of geology

2009-01-10T08:20:00.011-06:00

Almost every morning, I start the day with an experiment on flow in porous media. First, I generate some fine-grained sediment with a well-defined average grain size and proper sorting; then I use that sediment to fill a little basin of sort and try to mimic compaction. Finally, I use a machine to put water under pressure and force it to flow through this miniature sedimentary basin. Then I sit down to drink the fluid which is not simple water anymore, due to its interaction with the grains; and its taste and consistency tell me whether I got the grain size and the porosity right.

That's a geologist's view of making espresso. Unless you have a fully automated and ultra-expensive espresso machine, creating a high-quality caffeine concoction is not trivial, because the water must have the right temperature and has to spend the right amount of time in contact with the coffee grains that have the right size. The right temperature is 85–95 °C (185–203 °F), and, at least with our simple machine, the trick is to start the brewing at the right time. Better espresso machines do not use steam to generate pressure because that makes the water too hot; instead, they have a motor-driven pump that generates the ~9 bars of pressure. The correct grain size is easily achieved with a burr grinder (as opposed to a simple blender); a good espresso grind is a fine grind, because the water spends relatively little time in contact with the grains.

The duration of this contact is the most difficult bit to get right. To get a good shot with lots of crema, it cannot be less or more than 20 to 30 seconds. Not just grain size, but grain sorting as well play a role. If the coffee grinder produces a poorly sorted 'sediment' (and that's what a blender does), the coffee will not be porous and permeable enough. Another factor is how well the sediment is compacted; that is, how much pressure do you apply to the coffee during tamping. This affects permeability again. Finally, it matters how much coffee you put in the coffee holder; the thicker the layer that the water has to go through, the longer the trip becomes for the same amount of water.

After using the machine hundreds of times, I still manage from time to time to produce something undrinkable. The art and science of espresso making started to make more sense once I started to think of it in terms of Darcy's Law.

Henry Darcy was a French engineer who initially had made a name for himself by designing an enclosed and gravity-driven water-supply system for the town of Dijon. Later he had time and opportunity to do experiments of his own interest. In 1855 he measured the discharge of water under variable hydraulic heads through sand columns of different heights, and found that the discharge was directly proportional with the hydraulic head and inversely related to the height of the sand column:

Q = AK(H1-H2)/L,
where A is the cross sectional area of the sand column, L is the height of the sand column, K is the hydraulic conductivity (which is constant for the same granular material and same fluid), and H1-H2 is the hydraulic head. This is Darcy's drawing of his experimental setup:

The hydraulic conductivity depends on both the properties of the fluids and of the granular material; these properties are the viscosity and density of the fluid, and the permeability of the sediment:

K = kρg/μ,
where K = hydraulic conductivity, k = permeability, ρ = fluid density, and μ is the dynamic viscosity.

In coffee speak, the hydraulic head is given by the pressure generated by the machine, and is fixed; one cannot change the density and viscosity of water either. The most important variable is coffee permeability, which is influenced by size, sorting, and packing (compaction) of the coffee grains. Also, it helps if you get the value of L right, that is, you shouldn't try to save coffee.

Darcy's Law was established with some simple experiments, and it has since then been generalized and derived from the Navier-Stokes equations, but it has a huge range of applicability, from ground-water hydrology to soil physics and petroleum engineering.

Add to that list everyday espresso making.

ps. Fantastic resource on Darcy's work and his law here.

Earth, water, wind, and fire: 'Lava viewing' in Hawaii

2009-01-02T20:57:00.012-06:00

Our Christmas gift to ourselves was a little trip to the Big Island of Hawaii, something we were thinking (dreaming) about for a long time. There are many great posts about the Hawaiian volcanoes on the geoblogosphere (see for example the ones here and here); I will try to add a few notes and pictures without being too repetitive (and will try to seem less ignorant in volcanic and hard-rock matters than I actually am).

Probably the most memorable experience we had was the lava viewing at Kalapana. This is where 'officially' you can get relatively close to the place where the lava from Pu`u `Ō`ō enters the ocean. The USGS has a nice website with updates on what's going on. I was so anxious to see this place that we had to go there on our first day in Hawaii, that is, on December 22. You have to drive all the way to the end of road 130; there are some big 'No trespassing' signs at one point, but everybody seems to ignore them, and there is an official parking lot at the end of the road, way beyond the 'no trespassing' signs. It is best to get there 30-60 minutes before sunset, and to stay until it's completely dark, to see the potential show both in daylight and in nighttime darkness. Unfortunately, on December 22 we didn't see much, apart from a beautiful sunset and a few small puffs of steam:

Sunset at the Kalapana viewing site on December 22, 2008

That was a bit of a disappointment, but I knew I had to give it another try. After talking to a ranger from Volcanoes National Park, we drove back to Kalapana five days later. This time, the show was definitely on. More than that, it was spectacular. A huge column of steam formed where the active lava tube spills the lava into the sea, and repeated explosions painted red the lower part of the column. From time to time, several tornado-like funnels formed and connected the steam cloud to the ocean.

Steam cloud with mini-tornadoes on December 27, 2008; lava-viewing boat on the left for scale

As the sun goes down, the explosions become more colorful and more obvious

S-shaped funnel between the steamy sky and ~~cool~~ hot ocean

This was such a uniquely beautiful scene. I wish we went there more than two times, because the whole spectacle changes as a function of the activity of lava flow, weather conditions, the direction and nature of lighting.

I have also learned that it is not easy to take good photographs of fast-moving and rapidly changing distant things in the dark. Here is the proof:

Zoom, baby, zoom*

2008-12-11T22:50:00.006-06:00

For a few months now, I have been spending (wasting?) some time with a gadget called Gigapan, a robot that can take hundreds of shots of the same scene with a simple point-and-shoot camera. The pictures are taken in a well-defined rectangular grid pattern so that there is the right amount of overlap between all neighbors. Later the photos can be stitched into a gigantic photograph on a computer and shared with the world through the Gigapan.org website and, even better, through Google Earth. [If you are a tiny bit familiar with geoblogs, you must have seen some of the gigapans that Ron Schott has put together; he is one of the earliest and most enthusiastic adopters of the technology and has assembled an impressive set of panoramas on the gigapan site.]

I have to confess that I had to actually buy this thing and start playing with it to realize how different gigapixel panoramas are from the usual few-megapixel digital photographs. The idea is simple: a ten megapixel camera takes photos that contain ten million pixels; if you put together a 10x10 grid of such photographs into one image, you end up with a gigapixel panorama. Because some overlap is needed between the photographs, more than 100 pictures are necessary to exceed the gigapixel limit. But the point is that the more pixels there are in a photograph, the more information it contains and the more sense it makes to zoom in and see the details - details that are usually non-existent in a conventional digital picture. The other side of the coin is that it is only worth taking gigapans of scenes with plenty of small-scale and variable detail (although I am getting to the point that I see a potential gigapan everywhere).

I do not think that gigapixel images will replace conventional (that is, megapixel) photography. There is only a limited number of things that the human eye can see at one time; and often the value of a good photograph comes not from the pixels it captures, but from the ones it consciously ignores. Beauty and the message an image can hold are scale-dependent; and zooming in to see the irrelevant detail could be a distraction.

That being said, I am all for taking home as many pixels as possible from outcrops and landscapes in general. The gigapan system is simple and works surprisingly well, and it *is* exciting to explore big outcrop panels from the scale of entire depositional systems to the laminae of single ripples or even grains.

No photos or panoramas posted/embedded this time; but here is a link to my giga-experiments.

* title is courtesy of Kilgore661

Images from South Africa: Patterns

2008-11-30T09:59:00.008-06:00

A few more photos from the same trip that I already posted photographic highlights from. To be more factual and fair, the title should be "Images from the Western Cape", because I have only seen a few places in South Africa, and all of those places are in the Western Cape province. Anyway, here are three photos of... well, not much, just some visually interesting patterns.

Halophytic (salt-loving) vegetation in the supratidal zone of the Langebaan Lagoon, West Coast National Park

Old tree trunk at Groot Constantia winery, Cape Town, the first winery in South Africa, created in 1685

A look at the pebble (beach near Cape of Good Hope)

Liesegang bands in sandstone

2008-11-21T01:01:00.009-06:00

Liesegang bands are poorly understood chemical structures often seen in rocks, especially sandstones. They were discovered more than a hundred years ago by the German chemist Raphael E. Liesegang, when he accidentally dropped a drop of silver nitrate solution on a layer of gel containing potassium dichromate, and concentric rings of silver dichromate started to form.

In sedimentary rocks, Liesegang bands appear well after the sediment has become a rock (that is, it got compacted and cemented). Stratification and lamination within the sansdtone are typically cross-cut by the Liesegang bands; fractures usually have a more obvious effect on the distribution and orientation of these.

The rocks shown here are turbidites of the Permian Skoorstenberg Formation, in the Karoo desert of South Africa. This Liesegang banding developed in the neighborhood of a small thrust and consists of brown bands of iron oxide that entirely 'ignore' the original lamination of the sandstone (not visible in the photos), but clearly like to precipitate along some of the fractures in the rock.

Images from South Africa: Landscapes

2008-11-02T16:02:00.008-06:00

Follow-up from previous post: three landscape photographs, hot off the memory card, uploaded from a hotel room in Cape Town.

Karoo landscape

Table Mountain landscape

Cape Town landscape
In case you want to see more, the rest of the pics are here.

Images from South Africa: Flowers

2008-11-02T01:08:00.010-05:00

I have spent some time in South Africa, mostly looking at turbidites of the Tanqua Karoo. One of course cannot refrain from looking at other things as well, apart from turbidites, so here is a taste of how the Karoo looks like after an unusually wet winter. Apparently there haven't been this many flowers in the last 40 years or so. The rest of the photos are here.

Hurricane sedimentology

2008-09-19T08:25:00.016-05:00

Hurricane Ike knocked me off the Internets for a while, but things are slowly getting back to normal. I haven't been so close to - that is, in the middle of - a hurricane before; I have to say it was quite an adrenaline rush to hear and, to a lesser degree, watch the wind going by our windows with gusts of (probably) more than 100 miles per hour. In Houston, the damage was largely restricted to fallen trees and a few broken windows; fortunately not too exciting (see a few post-Ike photos over here). However, things are very different as you get close to the coast. Along the East Texas coast, the storm surge (unusually large for a category 2 hurricane) has shifted the coastline a few tens of meters landward, deposited lots of washover fans toward the lagoonal sides of the barrier beaches, and destroyed a large number of homes in the meantime.

It is worth playing the before-and-after game with the aerial imagery shot by the NOAA's Remote Sensing Division and made available in Google Earth. Here are a few screenshots from the Bolivar Peninsula.

Before:

After:

The light-colored lobes in the upper part of the 'after' image are the washover fans that in places reach the lagoon. Even more interestingly, there are some beautiful little fans built by the water flowing back toward the sea; for each fan, you can see the erosional 'drainage' area and little tributary gullies merging into a single large channel seaward, that turns from erosional to depositional as it widens. This is more clear in the zoomed-in pictures below.

Before:

After:

Note how some of the streets and roads that were perpendicular to the coast have become sites of preferential water flow and therefore locations for these channels.

Of course, all this cool sedimentology (I cannot wait to be able to get out there and have a closer look) also means that many-many homes have just become part of the stratigraphic record. These beaches and islands are the product of the interaction between storms like Ike, when large amounts of sand is eroded from the beach and transported offshore, and fairweather conditions, when sand has some chance to be deposited on the beach (if there is a large enough source of sand somewhere - usually not the case along most of the present-day Gulf coast).

The message should be already boring, but apparently it is not: these beaches and the barrier islands they create are geologically extremely active creatures, and in general it is not a good idea to build homes on them, certainly not right next to the beach. Hurricanes will be around for a while (and some experts say they are getting larger and stronger); and they are very good at creating large storm surges that are highly destructive on shallow shelves with low gradients, such as the continental shelf in the northern Gulf of Mexico.

Water escape structures in a Cretaceous delta, Wyoming

2008-08-21T22:52:00.022-05:00

I spent a few days in Wyoming, at a conference and field trip focusing on clinoforms, organized by SEPM (Society for Sedimentary Geology). Clinoforms are sedimentary layers with a depositional dip of a few degrees that form packages of relatively large thickness (let's say more than a few meters; could be hundreds of meters in some cases. The point is that the foresets of ripples, sand dunes and other bedforms could be called clinoforms but they should not be). [Warning! - my definition]. After a couple of days of morning talks (many very good ones) and afternoon posters, we spent two additional days visiting some outcrops in southern Wyoming.

These photos come from exposures of the Maastrichtian Fox Hills Sandstone of the Eastern Washakie Basin, a sandstone of deltaic and fluvial origin that links through shaly clinoforms to turbidite sands and shales of the Lewis Shale, deposited in water depths of more than 400 meters (see reference below).

The photo above shows one set of smaller-scale clinoforms truncated by a cross-bedded sandstone unit above, probably of fluvial origin. This is a prograding shoreline. It was a matter of debate whether the erosional surface at the base the fluvial sands is a sequence boundary or not, and could be a blogworthy subject in itself, but I will refrain from discussing it here and now. What I think - at least visually - are more exciting are the water escape structures in the photograph below.

There are two sandy layers visible in the picture; the lower one is somewhat darker colored and more massive-looking than the upper one, which is more laminated and has an overall lighter color. The height of the rock surface covered in the photo is about 1.5 m.

A likely explanation for the structures is as follows (sorry for the arm-waving -- it would be nice to put some numbers here - sedimentation rates etc., but life is too short for that right now). Soon after the first (darker) layer was deposited, another flood of the river brought more sediment to this location, and started depositing sand, mostly along a flat bed that resulted in parallel lamination. The underlying sediment was still very porous and unconsolidated, and some of its pore water was trying to get to the surface as the weight of the overlying deposit increased. Thin layers of finer-grained and therefore less permeable sediment got in the way however; and the escaping pore water had to travel laterally until it found the most vulnerable spots to go again upward. There are two of these vertical water escape conduits in the photo. As all the water coming from the lower layer had to go through a limited number of these spots, the velocity of the pore fluid must have increased significantly, until it actually was able to fully suspend the sand it encountered. In other words, some of the sand along these vertical escape zones got fluidized and carried away. The white structureless patches of sand are sedimentary intrusions. The light color suggest that these sands are much 'cleaner' than the rest of the rocks; the finer grains (responsible for the darker color) were washed away.

One interesting detail is that the trough cross-bedded sand between the two intrusions thickens into the depression, suggesting that the water was trying to get out in real time, that is, at the same time as the upper layer was being deposited.

Below I linked in an amateurish-looking gigapan; and here is another post on water-escape structures.

Launch full screen viewer

Reference:
Carvajal, C.R. & Steel, R.J. (2006), Thick turbidite successions from supply-dominated shelves during sea-level highstand. Geology, 34, p. 665-668.

Fossilized snake with exploded head

2008-07-12T11:39:00.007-05:00

There is a temporary exhibit called "Geopalooza! A Hard Rock Anthology" at the Houston Museum of Natural Science. If you are in Houston this summer (until August 24), this is something absolutely worth checking out: you can see some outstanding geodes, crystals, meteorites, and fossil specimens. I have been to many natural history museums, but I rarely get as high as I did at the HMNS the other day ['getting high' is the right terminology here: you get to (or have to) listen to Led Zeppelin and Bob Dylan while looking at the rocks]. Even if you are not too much into rocks, minerals, fossils, and natural science in general, these pieces are so beautiful that they can simply be viewed as works of art.

Here is for example a fossil snake from the Eocene Green River Formation in Wyoming. This formation has not only one of the most significant fossil sites in the US, but it also contains the largest oil shale deposit in the country: there are 1.5 trillion barrels of shale oil within the former lake sediments. Preservation of both fossils and of organic matter requires special conditions on the lake bottom: a partial or total lack of oxygen not only prevents oxidation of organic material, but also makes life difficult for critters that otherwise would totally churn the sediment and leave no undisturbed animal remains behind.

One of the museum curators was around when I was checking out this snake and she explained that the reason why the head bones are in such a disarray - compared to the beautifully arranged backbone and ribs - is that, as the snake's body started to decompose, the easiest way out for the accumulating gases was through the head.

I think this snake must belong to the species Boavus idelmani, and is probably one of the best preserved fossil snakes in North America.

The rest of the photos from Geopalooza are here.

Three photos from Vargyas Valley, Transylvania

2008-07-05T19:06:00.008-05:00

A few weeks ago I have spent some time back home in Transylvania (it is actually a place previously known as home), and took a day to visit a special place, the 'canyon' of the Vargyas River; we used to do a lot of caving and hiking here when I was in high school. A small patch of Mesozoic limestones was somehow forgotten in the middle of a lot of softer pyroclastic deposits, and a nice little canyon developed, with lots of caves and typical karst morphology. Make no mistake, this is not a 'grand' canyon, it is not even among the largest canyons in Romania or Transylvania.

But often it is lesser known and more hidden places that have a special atmosphere, a special combination of colors, shapes, shades and minor details that you can never forget.

The Vargyas River

One of the caves

Chlorophyll rules at this time of the year

More pictures here. And here is a map:

View Larger Map

The internal structure of the Peyto Lake delta

2008-07-05T17:18:00.015-05:00

I have pledged a while ago not to blog about Peyto Lake anymore, but I have recently discovered some beautiful GPR profiles that I have to share to make the story more complete.

Derald G. Smith of the University of Calgary and Harry M. Jol of the University of Wisconsin - Eau Claire have looked at the internal structure of the Peyto Lake delta using a technology called ground-penetrating radar (GPR). The principles used in GPR data acquisition are similar to those of reflection seismology, but electromagnetic waves are used instead of acoustic energy, and reflections occur at boundaries with different dielectric constants rather than boundaries with different acoustic impedances. Compared to reflection seismic surveying (or digging a deep hole), the nice thing about GPR is that it is non-destructive: it can be used in situations where you want as little disturbance as possible. For example, it would be a bad idea to do seismic surveying of a leaking reservoir, but it is OK to look for the leaks using GPR. GPR is also used by archaeologists.

But let's return to Peyto Lake. Although it has long been postulated that coarse-grained deltas with steep slopes (called Gilbert deltas, after the American geologist G.K. Gilbert) have a simple internal structure consisting of a topset, foreset, and bottomset, - and there are numerous ouctrop examples that show small coarse-grained deltas with such a structure -, it is not easy to prove that modern-day active deltas behave the same way. You can easily walk around on the top of the Peyto Lake delta and examine the surface morphology and characteristics in as much detail as you want; but without cool technology like GPR you can only wonder what does it look like inside. [Digging a large trench in the middle of one of the most beautiful national parks is not an option.] So Smith and Jol set out to check whether the topset-foreset-bottomset geometry is valid for this delta or it has a more complicated internal structure.

With only one day of data collection in the field (kind of unusual in the earth sciences!), they have clearly shown that the river feeding Peyto Lake is indeed building a textbook example of a simple Gilbert-type delta. The near-horizontal topset layers consist of gravels deposited by the braided river that is active today on the top; the underlying foresets are also likely to be coarse-grained and they dip at about 25 degrees toward the lake. This angle is close to the underwater angle of repose.

It is somewhat puzzling why the authors do not talk at all about the fate of finer-grained sediments (sand, silt, mud) that enter the lake; it is clear that turbidity currents directly originating from the river mouths are important agents of sediment transport in the lake (see more about this here). [They were probably focusing on presenting the results of the GPR survey.] The GPR signal is strongly attenuated in sediment finer than sand, and this might be the reason why reflections get poorly defined in the area where the bottomset is supposed to develop. In fact, I am not convinced I can differentiate the 'bottomset facies' the authors talk about.

So here is a representative GPR dip section showing the topset and the foreset:

It is also worthwhile looking at a section perpendicular to this; note how different the topset and foreset look like in this direction. Reflections are much more discontinuous in this image, suggesting that the spatial scale of sediment transport is more limited in a direction perpendicular to the river flow on the top of the delta (this is kind of obvious) and perpendicular to downslope processes within the lake (this is not so obvious).

Reference
SMITH, D., JOL, H. (1997). Radar structure of a Gilbert-type delta, Peyto Lake, Banff National Park, Canada. Sedimentary Geology, 113(3-4), 195-209. DOI: 10.1016/S0037-0738(97)00061-4

Where on (Google) Earth? #138

2008-07-04T18:59:00.008-05:00

It must be obvious by now that I am a lazy blogger - it looks like I settled down to a comfortable and boring average of one post per month.

But. I got back my WoGE-mojo yesterday, and bumped into Peter's WOGE screenshot while gliding over the karstified limestones of the Dinarides in Montenegro.

So here is WoGE number 138. No rules. Have fun.

Crop circles of the deep sea

2008-06-07T07:44:00.020-05:00

If 'cereologists' (people who seriously think that crop circles are made by aliens) knew about deep-water trace fossils, I am sure at least some of them would argue that these structures must also be the work of extraterrestrial intelligence. Many of the traces are so intricately constructed that they raise the question: how is it possible for a not-too-brainy animal to create such patterns.

This group of trace fossils is called 'graphoglyptids' (don't ask me why) and they are usually found on the soles of turbidite sandstones, layers of sand deposited in the deep sea (that is, in water depths of more or much more than a few hundred meters). Their shapes can be relatively simple meanders, can include multiple levels of meandering, meanders with bifurcations, spirals, radial patterns. The most interesting and most famous member of the group is Paleodictyon, an easy-to-recognize trace fossil with almost perfect honeycomb-like hexagonal patterns.

Many years ago I was lucky to do some work on trace fossils of the Carpathian flysch with two of the best trace fossil experts; since then I haven't worked with trace fossils but now I wish we did more documentation of the trace-fossil-rich outcrops in the Romanian Carpathians. The Paleodictyon pictures below show turbidite sandstone soles from the Buzău Valley; I haven't been there for a while but I hear that many of the outcrops are covered now.

The first weird thing about graphoglyptids is that they developed high diversity in an environment with limited amounts of low-quality food (lack of sunlight, hence no primary production; and stuff that sinks down from the photic zone usually has already been food for some other animal). The second weird thing is that they are not simple grazing traces like the tightly meandering patterns of sea urchins; the most widely accepted idea is that they are farming traces. In other words, these guys (whatever they might be, nobody really knows) create well aerated open burrow systems a few millimeters below the sea floor, with multiple openings to the sediment surface, so that chemosynthetic bacteria move in to get the necessary oxygen to oxidize methane and hydrogen sulphide, their favorite food.

Again, despite the abundance of these traces in turbidite successions, it is not clear what is the animal that likes to build delicate hexagonal burrows in the deep sea. It is clear however that the exact same structures have been found near the Mid-Atlantic Ridge. In 1976, Peter Rona of Rutgers University and his colleagues were looking at photos of the Atlantic seafloor and discovered some interesting geometric patterns of black dots. When Adolf Seilacher of the University of Tübingen, probably the most famous trace fossil expert, saw the pictures, he got very excited: he became convinced that it was a modern Paleodictyon. Unfortunately, no other data than the photographs with the black dots was available; no animals recovered from the sediment, and no hexagonal patterns seen below the surface. It took more than 26 years before Rona and Seilacher had the opportunity to do a new dive with the submersible Alvin and to show that the black dots on the seafloor indeed represent small shafts that belong to a hexagonal pattern a few millimeters below, a pattern identical to Paleodictyon (more details in an article by Peter Rona in Natural History Magazine; picture below is from the same article and is © of The Stephen Low Company).

This story is fascinating as it is, but it is best to see it in amazing colors and resolution, in the IMAX movie "Volcanoes of the Deep Sea", a documentary about the black smokers of the Atlantic and the discovery of modern Paleodictyon.

The mystery of the tracemaker of Paleodictyon - and all other graphoglyptids - remains unsolved: despite the outstanding success of taking IMAX-quality pictures at the bottom and the middle of the Atlantic Ocean, no animal was ever found in the sediment samples, and we know much more about how actual crop circles are generated than we do about the behavior of Paleodictyon.

Further reading

A beautifully illustrated new book by Adolf Seilacher:
Seilacher, A. (2007) Trace Fossil Analysis. Springer, 226 p.

Paper on trace fossils in the Carpathian flysch:
Buatois, L.A., Mangano, M.G. and Sylvester, Z. (2001) A diverse deep-marine ichnofauna from the Eocene Tarcau Sandstone of the Eastern Carpathians, Romania. Ichnos, 8, 23–62.

Links to this post: Book of Barely Imagined Beings

Some questions about the 'megatsunami chevrons': addendum

2008-05-10T08:59:00.010-05:00

A couple of months ago I have written about some coastal 'chevron dunes' that have been interpreted as the onshore deposits of humongous tsunamis. The subject has been on the tip of my fingers for quite some time and I thought I managed to google up most of the related papers, news articles, and blog posts, but it turns out that I missed one highly relevant discussion: in the January 2008 issue of GSA Today, there is a short paper by Nicholas Pinter and Scott E. Ishman of Southern Illinois University, entitled "Impacts, mega-tsunami, and other extraordinary claims". [Note to self: looking things up in Google and Google Scholar is not always enough, not even for blogging.]

Pinter and Ishman criticize both the idea that several impact-related megatsunamis occurred during the last 10,000 years and the hypothesis that a 12,900 year old impact caused "Younger Dryas climate event, extinction of Pleistocene mega-fauna, demise of the Clovis culture, the dawn of agriculture, and other events". The first idea is promoted by Dallas Abbott (at Lamont Doherty Earth Observatory) and her co-workers, but there is no real peer-reviewed publication yet; the second has been put forward by Richard Firestone (of the Lawrence Berkeley National Laboratory) et al. in Proceedings of the National Academy of Sciences and a book. The evidence for the 12.9-ka impact includes magnetic grains, microspherules, iridium, glass-like carbon, carbonaceous deposits draped over mammoth bones, fullerenes enriched in 3He, and micron-scale “nanodiamonds”. Pinter and Ishman suggest that

the data are not consistent with the 4–5-km-diameter impactor that has been proposed, but rather with the constant and certainly noncatastrophic rain of sand-sized micrometeorites into Earth's atmosphere.

But I am going to focus here on the 'chevron dune' part of the story. Pinter and Ishman have essentially the same main issue that I have blogged about: landforms that are morphologically identical to the so-called chevron dunes are well-known in the literature and they are called parabolic dunes. There is no need to introduce a new term:

We suggest that these Holocene features are clearly eolian, and that the term “chevron” should be purged from the impact-related literature.

The eolian origin of the alleged megatsunami deposits is difficult to deny taking into account that wind direction measurements at two sites perfectly match the orientation of the sand dunes (figure from Pinter and Ishman):

Dallas Abbott and her co-workers address Pinter and Ishman's criticisms in a short reply. This is what they have to say about the chevron dunes:

Pinter and Ishman also claim that chevron dunes in Madagascar and on Long Island are aeolian in origin. We visited both locations and found many features that seem incompatible with an aeolian origin. First, parts of the chevrons in both locations contain fist-sized rocks. These rocks are too large to be transported by the wind. Second, the orientations of the chevrons do not match the current prevailing wind direction. In both areas, some of the thicker sand deposits are being reworked into classic windblown dunes. The direction of movement of these dunes differs 8° to 22° from the long-axis of the chevrons. Third, the degree of roundness of the grains in the chevrons is not characteristic of wind transport over long distances. In both locations, sand grains on the distal ends of the chevrons are not well sorted or well rounded. Sand moved by the wind obtains an aeolian size and sorting distribution after only 10–12 km of saltation transport (Sharp, 1966); however, at Ampalaza in Madagascar, the chevron is >40 km long and rises to 63 m above sea level. At its distal end, the chevron is 7.2 km in a direct line from the coast and contains unbroken, unabraded marine microfossils and conchoidally fractured sand grains. It is impossible to transport unabraded marine microfossils to this location via wind-generated saltation. The site is too far above sea level for storm waves, and there is no local agricultural activity. The chevron was deposited by a tsunami.

Well, these seem valid counterarguments at first sight -- but it would be nice and it would be time to see actual data: images, measurements, grain size distributions. Which parts of the chevrons are reworked into eolian dunes? What is the difference in the morphology of tsunami dunes and eolian dunes? How does this relate to flow dynamics? What are those "rocks" that occur within the dunes? Where do they occur exactly? And so on. The fact that the authors end their reply with an unqualified strong statement like "The chevron was deposited by a tsunami" suggests that they are unwilling to admit that not every piece of evidence favors their interpretation and that some legitimate questions can be raised. They do this after first admitting that parts of the dunes were indeed reworked into classic wind-blown dunes.

So, at least as far as the 'chevron dunes' are concerned, I have to concur with Pinter and Ishman's harsh conclusion:

Both the 12.9-ka impact and the Holocene mega-tsunami appear to be spectacular explanations on long fishing expeditions for shreds of support. Both stories have played out primarily in the popular press, highlighting how successful impact events can be in attracting attention. The desire for such attention is understandable in an environment where science and scientific funding are increasingly competitive. The National Science Foundation now emphasizes “transformative” research, and few events are as transformative as an impact. In an era when evolution, geologic deep time, and global warming are under assault, this type of “science by press release” and spectacular stories to explain unspectacular evidence consume the finite commodity of scientific credibility.

References

Pinter, N., Ishman, S.E. (2008). Impacts, mega-tsunami, and other extraordinary claims. GSA Today, 18(1), 37. DOI: 10.1130/GSAT01801GW.1

Abbott, D.H., Bryant, E.F., Gusiakov, V., Masse, W., Breger, D. (2008). Impacts, mega-tsunami, and other extraordinary claims: COMMENT. GSA Today, 18(6), e12.

Firestone, R.B., West, A., Kennett, J.P., Becker, L., Bunch, T.E., Revay, Z.S., Schultz, P.H., Belgya, T., Kennett, D.J., Erlandson, J.M., Dickenson, O.J., Goodyear, A.C., Harris, R.S., Howard, G.A., Kloosterman, J.B., Lechler, P., Mayewski, P.A., Montgomery, J., Poreda, R., Darrah, T., Hee, S.S., Smith, A.R., Stich, A., Topping, W., Wittke, J.H., Wolbach, W.S. (2007). Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling. Proceedings of the National Academy of Sciences, 104(41), 16016-16021. DOI: 10.1073/pnas.0706977104

Climbing Ripples I.

2008-04-05T17:13:00.047-05:00

Ripples, dunes, cross bedding and cross lamination have always been some of the sexiest subjects in sedimentary geology. They are certainly responsible (in part) for my choice of a certain walk of life that consists of studying dirt. You might say that everything has been already said about ripples and dunes, and you clearly get that feeling if you read some of J.R.L. Allen's work on the subject (and that can be a lot of reading, by the way) or look at the fantastic multimedia material that David Rubin at the USGS put together. [Of course, there are numerous other authors who have written great papers on the subject, but it is not my purpose here to write a history of bedform sedimentology. Although that would be an interesting subject, if somebody had the time for it.]

However, little of this material gets into the standard sedimentology and stratigraphy textbooks. Maybe rightly so: after all, textbooks are not supposed to include all the details about any particular subject. And maybe there are higher-density issues out there, like whether we should call something a turbidite or a debrite. [Sorry, I could not refrain from typing that].

Take for example climbing ripples. They form when several trains of ripples are superimposed on each other and they seem to 'climb', by generating stratigraphic surfaces that are tilted in an upcurrent direction. [Note however that these surfaces are *not* topographic - or time - surfaces; more on that later]. Numerous textbooks and many papers mention climbing ripple cross lamination, but often the explanation is something like "they indicate high rates of deposition", or "the steepness of the climb and stoss-side preservation are a function of the ratio between suspended-load and bedload". The question is, what do we *exactly* mean by 'high rates of deposition'? If we cannot put numbers on it, it is not that informative. Also, by 'suspended load', do we mean suspended load concentration? Or deposition from suspended load and bedload, respectively? Those statements are not necessarily wrong, but they do not do justice to the models that have been published many years ago, models that actually have some numbers and equations behind the "conclusion" section.

The key paper that I am talking about is "A quantitative model of climbing ripples and their cross-laminated deposit", by J.R.L. Allen, published in 1970 in the journal Sedimentology.

The most important relationship that Allen has derived links the angle of climb ζ (see the sketch below) to the rate of deposition M (measured in units of mass over unit time and area), the rate of bedload sediment transport j, and the ripple height H:

tanζ = MH / 2j

This is simply based on decomposing the sediment flux to and through the bed into vertical and horizontal components (plus a relationship between the horizontal sediment transport rate in ripples and the horizontal migration rate of the bedforms). Note that the quantity j refers to the sediment mass that moves through a cross section perpendicular to the general current direction, and does this by being part of the ripples themselves. In other words, there is no direct equivalence between M and suspended load deposition, and j and bedload deposition. Although it is possible that in general suspended load contributes more to M than deposition from bedload, it says nowhere that grains transported within the bedload cannot be deposited on the stoss side of the ripples and thus contribute to the vertical growth of the bed.

Obviously, if the angle of climb is smaller than the dip of the stoss side, there will be no stoss side preservation and the resulting cross lamination will look like in the sketch below (which, by the way, was quite an effort to generate in Matlab; you can easily do this and much-much more with David Rubin's Matlab code, but I wanted to understand things a little better by coding something simple myself):

This is often called 'A-type' (or subcritical) climbing ripple cross lamination, but everybody knows what you are talking about if you "simply" call it climbing ripple cross lamination with no stoss-side preservation.

In contrast, aggradation is much more prominent if the angle of climb is larger than the slope of the stoss side, and in this case deposition takes place on the stoss sides as well, resulting in 'S-type' (or supercritical) lamination:

Of course, it says nowhere that the rate of deposition M or the bedload transport rate j must stay constant through time. If the ratio of these quantities changes, the angle of climb will change as well. This sketch shows an example where the rate of deposition M increases through time:

One of the main points of the paper is that there is a fundamental difference between the rate of deposition M and the bedload sediment transport rate j. A rate of deposition larger than zero means that the sediment transport rate within the flow must decrease from an upcurrent position to a downcurrent position; a simple mass balance tells us that this change in the sediment transport rate has to equal the rate of deposition. In other words, the rate of deposition M is a derivative of the sediment transport rate, and as such, does not belong in the same drawer of physical quantities as the bedload transport rate.

Along the same line of thought, Allen emphasizes that climbing ripple lamination says something about flow uniformity and steadiness. A uniform and steady flow can only form a single train of ripples; either non-uniformity or unsteadiness is needed to have climbing-ripple deposition.

That's it for now; to be continued. It's time to do my taxes.

Further reading: Brian has a Friday Field Photo and a Geopuzzle on climbing ripples. Here are some pictures and a movie of climbing ripples generated by a turbidity current in a flume.

(Petroleum) geology in the movies: There Will Be Blood

2008-03-23T08:29:00.017-05:00

[This is a contribution to Accretionary Wedge #7.]

One of the most memorable movies I have ever seen happens to be about a geologist who strikes it rich with oil in Southern California of the early 1900s. It is also probably the only movie with quite a bit of geology in that has won two Oscars (but I am not really a movie junkie so corrections are welcome).

Of course, I am talking about There Will Be Blood, director Paul Thomas Anderson's epic story about greed, religion, vengeance, murder, and other delightful human endeavors, written, shot, and acted so well that it is an instant classic, a piece of work comparable to the greatest Greek tragedies. Daniel Day-Lewis took home a second Oscar for his work, and there is a good reason for that: his performance is so powerful that in my mind the only other film character of comparable strength and weight and effect is John Proctor in "The Crucible", ...which also happens to be played by Daniel Day-Lewis.

Despite (and because of) its greatness, this movie is not for the faint-hearted. It is very unlike the average Hollywood production, and, if you want to leave the theater with that sweet reassurance of knowing exactly what is good and what is bad, well, then skip this one. Despite the almost unequivocal depiction by critics of the Daniel Day-Lewis character as a monster - and, I admit, Daniel Plainview is not exactly a charming person -, let's recognize that many of his thoughts and emotions are not foreign to most individuals that belong to the 'Homo sapiens' species. To me, the most scary and most monstrous character of the movie is Eli Sunday, the equally greedy but extremely irrational and hypocritical church leader and faith healer, played very convincingly by Paul Dano.

In any case, it is worth suffering through the two-and-a-half hours, if for nothing else but the realistic depiction of the oil industry at the beginning of the twentieth century. The movie does very well in terms of 'geological correctness'; certainly much better than most disaster movies with Bruce Willis in the driving seat saving the World from the evil forces of Nature. The only minor issue I can think of is whether it is possible to find oil in a silver mine (Daniel Plainview is a silver prospector before he turns into an oil man). It's been a long time since I read anything about ore deposits, but silver likes to accumulate in somewhat ~~hotter~~ different places than oil (unless it is in placer deposits).

Still, the best geological 'delicacy' in the movie comes at the very end. I would have never thought that you can make petroleum geology (or reservoir engineering) the centerpiece of a shocking movie scene, replete with human tragedy and profound proclamations about delicate philosophical issues.

Further reading: an excellent little piece about the geological aspects of the movie here.

And finally, here is a passage that gives an idea of how some people think about geologists (source):

"The fact is, Plainview is barely human to begin with, so watching him grow coarser and uglier and more full of himself seems a theme more suited to a geologist than a storyteller."

Ouch.

Some questions about the 'megatsunami-chevrons'

2008-03-09T15:53:00.019-05:00

The allegedly tsunami-related chevron-shaped nearshore deposits are back in the center of attention, at least among geo-bloggers. And rightly so: the idea that lots of coastal sand sheets all over the world were generated by relatively recent, impact-related mega-tsunamis of unimaginable scale is a fascinating hypothesis and, if proven true, it would revolutionize not only our understanding of frequency of meteorite impacts, but also change the predominant views about coastal geomorphology.

However, I have to confess that I find the geomorphologic and sedimentologic side of the argument fairly weakly constructed and documented, at least in the papers I was able to google up. Here are a few questions that could be asked to clarify some issues.

Many of the aerial photographs of the so-called chevrons could be used as textbook examples of parabolic dunes. Parabolic dunes are U-shaped wind-blown dunes usually fed by coastal sand deposits. Their nose points in a downwind direction, that is, the opposite way from barchan dunes. While wind strengths, direction, and sediment source are the main players in the generation of barchan dunes, vegetation plays a key role in the development of parabolic dunes. The 'arms' of a parabolic dune are left behind because they have a lower migration rate than the main body and the nose. The lower migration rate is due to plant growth in areas of lower sedimentation and/or erosion. There is a strong correlation between vegetation cover and dune migration rate or activity. This image comes from a recent paper by Duran et al.,

and it shows active (on the left) and inactive (on the right) parabolic dunes. Here is a sketch (source):

So the question is: if 'chevrons' are indeed different from classic eolian parabolic dunes, what is this difference, both geomorphologically and sedimentologically? Are they internally stratified? Do they show large-scale cross-bedding? What are the typical grain size distributions? Are they different from typical wind-blown sand? (One of the arguments is that large boulder fields occur in several places; however, my impression is that the boulders described here do not occur within, below, above, or right next to any chevron deposits. This short report claims that large pieces of rock are all over the place in the Madagascar chevrons, but no actual data is presented). The Madagascar chevrons featured in the New York Times show the signatures of typical parabolic dunes: U-shape, vegetated back sides and sandy crest plus nose. Why would an old tsunami deposit be vegetated only in certain places? The simple fact that these dunes are not entirely covered by vegetation suggests that their sandy parts do consist of wind-blown sand. Of course, tsunami deposits can be reworked by the wind, but why would the tsunami-related morphology be so well in tune with the eolian signature?

Second, if the chevrons are indeed produced by tsunamis, the tsunamis must have been humongous. Dune heights are related to flow depth, and a rule of thumb is that flow depth has to be around 6 times the dune height. So a 50 m high dune would require a 300 m high wave. Is that really possible? How big an impact do you need to generate such humongous waves? Also, what about the backwash? Why are most of the chevron dunes pointing systematically in one direction, and do not seem to be altered by any seaward oriented flow?

Third, are any features of the chevrons consistent with what we know about well-documented recent and ancient tsunami deposits? Tsunami-related sandy layers tend to be comparable to turbidites: largely unstratified, normally graded units suggesting rapid deposition from flows of decreasing velocity; they do not show large-scale cross bedding that requires relatively steady flow over longer time scales. In contrast, the chevron morphologies suggest that they are internally well-stratified, as the result of stoss-side avalanches. Here is a sand layer from the 1998 Papua New Guinea tsunami (source):

Obviously, it may turn out that there are tsunami-related coastal dunes and wind-blown parabolic dunes, with very similar morphologies, but fundamentally different origins. At the moment, the geomorphologic and sedimentologic evidence for this extraordinary hypothesis seems quite preliminary. And, needless to say, extraordinary claims require extraordinary evidence.

ps. 1: Lots of information on tsunami deposits here.
And a paper arguing for wind-blown origin of some deposits from the Bahamas, previously interpreted as tsunami-related: Kindler, P. & Strasser, A. (2000) Palaeoclimatic significance of co-occurring wind- and water-induced sedimentary structures in the last-interglacial coastal deposits from Bermuda and the Bahamas. Sedimentary Geology 131, 1-7.

ps. 2: More good stuff on megatsunamis and their deposits at Highly Allochthonous.

Teaching of evolution in Romania: an endangered species

2008-03-01T10:46:00.011-06:00

Romania is one of those countries that, after the fall of supposedly atheistic communist governments, are still struggling with the place of religion in public life and in education. The new Romanian constitution goes beyond guaranteeing freedom of religion and explicitly endorses state support for religious organizations ("Religious cults shall be autonomous from the State and shall enjoy support from it, including the facilitation of religious assistance in the army, in hospitals, prisons, homes and orphanages." - article 29). Yes, that is right: religious cults are autonomous but they enjoy state support. In other words, they do what they want with taxpayer money. Historically established religious denominations get government recognition; this is a major issue, because in practice only those religions enjoy 'religious freedom' who are recognized by the government. In other words, "Recognized religions have the right to establish schools, teach religion in public schools, receive government funds to build churches, pay clergy salaries with state funds and subsidize clergy's housing expenses, broadcast religious programming on radio and television, apply for broadcasting licenses for denominational frequencies, and enjoy tax-exempt status." (source). Note that the majority of Romanians see absolutely no problems with the government giving money to religious organizations, including funding for teaching religion in public schools. Religious institutions enjoy almost unlimited trust from the public (as opposed to the senate, the parliament, or universities), and if you dare to criticize a priest or a religious organization, you will quickly find yourself under a flood of attacks from people of all walks of life.

In parallel with the state-supported resurgence of religious life, the boundaries between secular and religious education are getting blurred. At the end of 2006, the secretary of state for research and education at that time, Mihail Hardau, signed a ruling that eliminated virtually all references to evolution from the science standards for public schools. In the meantime, 73% of the Romanian high-school students already think that the universe and humans were created by God. Scientific literacy is so low in the country that very few people see this as a negative development; even some biology teachers say that Darwinism does not necessarily contradict creationism and it is out of date anyway. Most journalists and politicians who express an opinion on the subject only prove that they did not even take the time to look up the words "Darwinism" and "evolution" in a dictionary.

This is sad news for me. I learned basic biology in communist Romania, in the eighties, and at that time there was no place for God and creationism in biology classes.[Of course, that was about the only good thing about communism -- so I am delighted it is a thing of the past, do not get me wrong]. Although my understanding of evolution largely comes from popular science books rather than those old biology lectures, at least you could not finish high school without hearing about Darwin and evolution. Now it is different: it has become difficult to get through the public education system without being indoctrinated (on taxpayer money) with the dogma of your favorite religion, and you might only hear about Darwin in the context of outdated atheistic thinkers who are not relevant any more.

If you want to help, here is the email address of the Romanian Ministry of Education: informare.publica@medu.edu.ro; more info here. Also, if you have a blog or website, feel free to spread the word. More people in Romania and outside Romania need to realize that the integrity of science education in one of the largest countries in Europe is at stake here.

A new way to enjoy photographs

2008-02-27T21:47:00.007-06:00

Anybody who takes more than ten photos per year (and everybody has at least a point-and-shoot camera these days) needs a good online photo sharing service. I have been a diehard fan of Smugmug for several years now. I love the elegant, somewhat Apple-like interface, the slick animations, the ability to easily organize and tag photos, the fact that pictures can be displayed at seven different sizes, that it is easy and fast to order high-quality prints, not to mention the significant integration with Google Maps and Google Earth. While I have realized that Flickr seems better equipped for more 'Web 2.0' interactivity (maybe largely due to the sheer number of users and photographs), and that there are far more photographs of turbidites on Flickr than Smugmug , I find the Flickr user interface confusing and its design inferior to that of Smugmug, with a lack of style that does not do justice to the zillions of great photos that are out there on the servers.

Having said that, I have recently started to use and appreciate Flickr a lot more. The reason: the updated Apple TV can stream photos directly from Flickr. Television sets with high-definition screens might be a bit ahead of the time due to the limited number of easily (and cheaply) available HD TV programming and movies, but they are perfect for displaying even relatively low-resolution photographs in brilliant colors and surprising clarity. After all, the best HDTVs have a pixel count of 1080 x 1920, and you get more than two megapixels with most digital cameras. Sitting down with a glass of wine and discovering good photographs on a big screen while listening to music is my favorite new pastime and I think it is a lot more enjoyable than browsing photos on much smaller computer screens that usually have a lot of clutter in addition to the photograph.

Now, if Apple was smart and kind enough to put Smugmug on Apple TV as well...

Dish structures

2008-02-23T08:49:00.013-06:00

Dish structures are sedimentary structures found in thick sand (or sandstone) that have concave-up, bowl-like shapes. They form when water is trying to escape from rapidly deposited sand but encounters horizontal barriers of somewhat lower permeability (usually zones with smaller grain size and/or dispersed mud). These force the water to flow laterally until it finds a place where it can go upward again. In the meantime, the subtle permeability differences get enhanced as muddy particles are washed away from the cleaner parts of the sand and concentrated in zones of lower permeability. The sides of these lower perm zones bend upward as the water finds its way up. Eventually pillar structures, vertical zones of cleaner sands can form on the sides of the dishes.

Initially dish structures were thought to be related to the (still somewhat fuzzy) mechanics of sediment transport and deposition in high-concentration gravity flows. However, clear examples that showed primary sedimentary structures (like cross lamination) being cross cut by dish structures proved that the latter are secondary structures, formed soon after deposition.

Probably because rapid deposition of sand is a requirement for the formation of dishes, these sedimentary structures are largely restricted to deep-water sands. Here are some examples that I think are blogworthy:

This one is from the northern California coast. Note the pillar structures between the dishes. [Apologies for the lack of scale - I think this bed is about 4 feet thick].

This is a zoom-in of dish structures in the Cerro Toro Formation of Southern Chile. Lighter-colored areas probably contain less mud than the darker zones.

No scale on this one either (there was no way I could climb up there), but trust me, these are probably among the largest dish structures in the known universe. They were photographed in northern Peru, near the town of Talara.

And to prove that they are really big, here is a photo that gives an idea of their scale:

Geologic misconceptions: 2D vs. 3D

2008-01-22T23:07:00.002-06:00

[This is a contribution to Accretionary Wedge #5]

One of the problems that a geologist is often faced with is the difficulty of reconstructing a complex three-dimensional geometry and history from limited information that is often one-dimensional (e.g., well data, cores) or two-dimensional (outcrops, 2D seismic sections). Humans in general, and geologists in particular tend to look for evidence where the light is better, and we are tempted to think that the beautiful core we have described, the one good outcrop face we have, the one textbook-quality seismic line on our wall is a good representation of the geology and stratigraphy of a much broader area, and that one can build a coherent story without knowing much about the third dimension.

That, of course, may well be true of ‘layercake’ stratigraphy: after all, a single thickness value can be used to fully characterize the geometry of a layer that has the same thickness over a large area. But, as Brian points out, ‘layercake stratigraphy’ should be considered an oxymoron: every sedimentary layer shows some thickness variations if traced for a long enough distance, even if some layers change their thickness more slowly than others. Stratigraphy is only layercake-like for human observers; subtle but persistent variations in thickness and relief can become striking geometries with some vertical exaggeration. Again, if this variation only occurred in one direction, a two-dimensional section along the same direction would summarize very well the whole story.

However, complex three-dimensionality is the rule rather than the exception in geology. Take for example a meandering river: its geometry is complex enough as it is, a single snapshot of a snaky morphology in time. But try imagining what happens as point bars and levees are deposited and cutbanks are cut; the channel changes its position over time and, over thousands and hundreds of thousands of years, it leaves behind an extremely complicated stack of deposits that would probably be difficult to fully understand even if you somehow could see and describe everything at the greatest detail in 3D. Obviously, a nice outcrop or a number of cores through such a deposit can provide a wealth of information, but we would be fooling ourselves if we thought that a single fining-upward sequence with some cross-bedding (that is, the classic point-bar facies model) was enough to understand a fluvial system.

But strong three-dimensionality is not restricted to fluvial deposits; look at any present-day depositional system in Google Earth and you will find that alluvial fans, deltas, barrier islands and tidal inlets, wind-blown dune fields are all intricate patterns, usually with lines running in more than one direction. Yet many of the classic facies and stratigraphic models are either one- or two-dimensional. Maybe, probably, these are necessary and useful simplifications and conceptual models, but they can only be useful if one is also aware how far they are from capturing the full 3D complexity of nature.

That being said, I have to add that 3D is not always better than 2D. Nowadays, some of the best three-dimensional geological datasets are 3D seismic surveys, and, with the increasing availability of such gold-mines of stratigraphic beauty (there are other uses as well, but let’s focus on one thing for now :) ) it is easy to fall victim to the temptations of colorful three-dimensional displays. Despite claims like ‘3D interpretation and visualization are the future’, the truth is that a good set of old-fashioned maps and cross sections are more valuable in the long term than some glossy presentation slides with no exact spatial location.

Unless, of course, you can visualize and share your data relying on an easy-to-use and truly three-dimensional viewer. Like Google Earth. Even William Smith would be excited about that.

Detail from "Geological view and section through Dorsetshire and Somersetshire to Taunton, on the road through Yeovil toWimborn[e] Minster, &c.", by William Smith, 1819. Source: Oxford Digital Library

Geo-highlights from Hindered Settling 2007

2008-01-13T13:20:00.001-06:00

It is kind of late to do this 2007 retrospective, but what the heck. As pointed out by Ron, 2007 has been the year when a real geology blogger community started to develop. The evolution of Hindered Settling from an eclectic mix of notes about science, geology, skepticisim, atheism, technology, etc., written in Hungarian and in English (or Hunglish?), to a much more geoscience-oriented, English-only site is in part the result of this trend.

So here are a few posts from 2007 that I think should be on this list:

Photos from Brazos Bend State Park - if you live in Houston, Brazos Bend State Park is one of the best places to get away from the city and see some wildlife & nature. No mountains, of course, but at least you can look at oxbow lakes and learn about photography. For some reason, the photos I have taken there over the years have become fairly popular.

On the Great Unconformity, James Hutton, and Geologic Time

Photos and impressions from a stunning glacial lake and delta in the Canadian Rockies, with some sedimentology mixed in

On flame structures

Sedimentology on Mars - wet or dry gravity flows?

Thoughts about the Black Sea flood and its potential link to the spread of agriculture in Europe

Absurd catastrophism

2008-01-12T05:43:00.002-06:00

If there was an icon for 'blogging on non-peer-reviewed non-research', in the style of 'blogging on peer-reviewed research', this post would qualify for it. Although it is advertised as publishing "cutting-edge, peer-reviewed, creationist research papers", Answers Research Journal (published by Answers in Genesis) is definitely not cutting-edge, not peer-reviewed, and is clearly not research. The evidence: the first few materials that are available online. There is a paper on "catastrophic granite formation"; here is a passage that gives you a flavor:

"Thus the formation of granite intrusions in the middle to upper crust involves four discrete processes — partial melting, melt segregation, magma ascent, and magma emplacement. According to conventional geologists (Petford et al. 2000), the rate-limiting step in this series of processes in granite magmatism is the timescale of partial melting (Harris, Vance, and Ayres 2000; Petford, Clemens, and Vigneresse 1997), but “the follow-on stages of segregation, ascent, and emplacement can be geologically extremely rapid - perhaps even catastrophic.” However, as suggested by Woodmorappe (2001), the required timescale for partial melting is not incompatible with the 6,000–7,000 year biblical framework for earth history because a very large reservoir of granitic melts could have been generated in the lower crust in the 1,650 years between Creation and the Flood, particularly due to residual heat from an episode of accelerated nuclear decay during the ﬁrst three days of the Creation Week (Humphreys 2000; Vardiman, Snelling, and Chafﬁn 2005). This very large reservoir of granitic melts would then have been mobilized and progressively intruded into the upper crust during the global, year-long Flood when the rates of these granite magmatism processes would have been greatly accelerated with so many other geologic processes due to another episode of accelerated nuclear decay (Humphreys, 2000; Vardiman, Snelling, and Chafﬁn 2005) and catastrophic plate tectonics (Austin et al.1994), the likely driving mechanism of the Flood event."

Here is what I honestly do not understand. Let's accept for a moment the idea that granites can form relatively fast, and pretend that radioactive dating has some major issues, as these people claim (it doesn't, of course), so that all the granites on Earth fit the 6000-year timeframe. But what about the stuff that the granites were generated from? That must be older, right? And if the whole crust is less than a few thousand years old, what about the mantle? And, if one can speculate about "accelerated nuclear decay during the ﬁrst three days of the Creation Week" or "catastrophic plate tectonics", why not just say that granites were created on the second day, after the mantle was ready to start convection by the end of the first day? Or, even better and simpler (Occam's razor!), why not just come up with something like:

And God said, Let there be granite: and there was granite. And God saw the granite, that it was good: and God divided the crust from the mantle.

I am looking forward to the time when somebody realizes that the Universe was created yesterday, and it is only an illusion that we have been around for a bit longer than that. Imagine all the wonderful research opportunities that such a revolutionary working hypothesis would generate. I can already see papers and headlines like:

Updated relativity theory shows that time is shorter than you think

Plate tectonic hit-and-run: after hitting North America yesterday with several microcontinents, the Pacific Plate continued to subduct as if nothing happened

Fossil record from 4:15 pm yesterday shows that lightning-fast giant snails were abundant on Earth for more than 7 minutes

Accelerated ice flow during the last few minutes of Creation Hour is likely responsible for death of Ötzi the iceman

Scuba diver killed by massive rain of pelagic forams

Catastrophic hair growth in early humans

Additional research ideas are welcome; 'Answers Research Journal' is calling for papers now.

UPDATE: In my rush to publish the above results, I forgot to mention some previous work on similar subjects: Afarensis ~~- an expert in~~ points to the Precambrian archaeolog~~y -~~ist, who suggested long ago that the Cambrian explosion was caused by a bacteria trying to form a synthesis with a mitochondria and that peanut butter is a leftover from this explosion. I would only add that there is new evidence suggesting that the Precambrian started at 1 am yesterday, after Creation Hour ended, and it probably lasted for several hours, until the bacteria committed adultery.

Three photos from the Canadian Rockies in winter

2008-01-05T08:33:00.002-06:00

More here.

Upper Falls, Johnston Canyon

Lake Louise

Elk near Bow Valley Parkway

Catastrophic flooding of the Black Sea and the expansion of agriculture in Europe

2007-11-24T15:44:00.003-06:00

Both Ole and Chris have blogged about a new paper, published in Quaternary Science Reviews, that discusses the link between the catastrophic inundation of the Black Sea and the expansion of agriculture in Europe during the Neolithic. I am not going to repeat what they already summarized well; I only want to expand a bit on what I see as the weak points of the Black Sea flood story. [Disclaimer: I am not an expert in the geology and stratigraphy of the Black Sea, and even less of an expert in archaeological matters].

While the recently published Turney & Brown paper presents some nice data and argues convincingly that the start of Neolithic expansion in Europe roughly coincides with the ~8300 yr BP age estimate for the catastrophic flooding of the Black Sea, this correlation does not necessarily suggest a cause-and-effect relationship. The question is still open: yes, the flooding might have caused the migration, but it is also possible that the two events are independently related to the same climatic changes. Very few of the radiocarbon dates, representing the earliest Neolithic sites in Europe, come from the territory of present-day Romania, yet one would expect that the low-lying areas along the lower Danube River would be the first places to be colonized by the population forced out from the inundated shelves of the Black Sea that are the widest east of the Danube Delta. Why are early Neolithic settlements so scarce in this area, which is good for agriculture? In their 1998 book, Ryan and Pitman suggest that Vinca farmers showed up abruptly along the Danube valley, soon after the flooding occurred. The earliest Vinca settlements however are dated at 7500 yr BP, so there is a gap of a few hundred years between the flood and these first settlements. That seems too long; in addition, even if the initial displacement of people living near the Black Sea resulted in the expansion of agriculture into Southeastern Europe, it is questionable how much effect this flooding had on the spread of Neolithic people into Northwestern Europe. It is unlikely that the main motivation to cross the English Channel for people living in today's Northern France was that their ancestors were scared off the shores of the Black Sea many hundreds of years before.

The image below is a screenshot from Google Earth, showing the data published by Turney and Brown. The Neolithic locations are color-coded according to their age, red being the oldest, and dark blue being the youngest. The KMZ file (made with GPS Visualizer and some help from Matlab) is available here.

Regarding the link between the Black Sea flood and Noah's story -- I think it is an interesting idea, but not much more. There were and there will be numerous large floods that affect human lives and human history, and the one featured in the Bible is so generic that it will be difficult to unequivocally link it to any specific event. In addition, the catastrophic flooding of the Black Sea might have been catastrophic only in a geological sense; calculations suggest that it took 34 years to erase the 155 m difference in water level between the Black Sea and the Mediterranean. The slow and relentless rise of the sea must have been disquieting and annoying to people living close to the shore, but, unless they built their huts in the middle of the Bosporus, it probably was not as traumatic for most of them as Hurricane Katrina was for lots of Gulf Coast residents.

The recent (I mean geologically recent) history of the Black Sea region is certainly fascinating and the controversy surrounding the exact sequence and nature of the events can only result in more top-notch oceanographic and archeologic research. And that is always exciting.

Where on (Google) Earth #72

2007-11-23T11:49:00.002-06:00

After the big bend of the Irrawaddy River around an anticline in northern Burma (at T. rex eats fish), here is another Google Earth challenge, following in the tradition of a previous WoGE posted on Hindered Settling.

Schott rule in effect. Post time: 12:05 pm CST, 11/23/2007.

Meme of Four

2007-11-21T22:11:00.000-06:00

Well, Hindered Settling got a bit too settled lately, so it's time to shake it up. Brian's tagging is a good excuse to do that, even though some of this may be too much detail. Here it goes, anyway.

4 jobs you’ve had:
1. teaching assistant (yes, it was a full time job in Romania)
2. does graduate work count as a job?
3. does serving in the Romanian Army count as a job? (probably no)
4. petroleum geologist

4 movies you could watch over & over:
1. Sideways
2. The Lives of Others
3. Annie Hall
4. Black Cat, White Cat

4 places you’ve lived:
1. Sfantu Gheorghe, Romania
2. Cluj, Romania (both #1 and 2 are in Transylvania as well)
3. Portola Valley, California (quite a change)
4. Houston, Texas (quite a change, again)

4 TV shows you love to watch:
1. Seinfeld
2. Extras
3. The Daily Show
4. Kitchen Nightmares (I admit it, too)

4 places you’ve been on holiday vacation:
1. Tuscany
2. Canadian Rockies
3. Paris
4. Yellowstone

4 authors you love to read:
1. Richard Dawkins
2. Steven Pinker
3. Bill Bryson
4. Jared Diamond

4 websites you visit daily:
1. Scienceblogs
2. New York Times
3. Macworld
4. RichardDawkins.net

4 of your favorite foods:
1. Avocado (I hated it a few months ago)
2. Pasta
3. Stuffed cabbage (Transylvanian style)
4. Cheese, mainly Italian

4 places you’d rather be:
1. skiing anywhere
2. in the Vargyas Valley (in Transylvania)
3. San Francisco
4. tasting wine, anywhere

4 lucky people to tag:
no tagging, but - of course - feel free to get and spread the meme

Where on (Google) Earth #69

2007-11-01T21:45:00.000-05:00

As soon as I saw the stunning geology in John's WoGE challenge, I started looking for the solution in the fold belts of Iran that have essentially zero vegetation. My search was successful, so here comes WoGE #69. Have fun.

North is up. Schott rule in effect. Post time: 10 pm CST, 11/01/2007.

Where on (Google) Earth #65

2007-10-22T07:05:00.001-05:00

After John's Argentinian anticline and rivers, here is a new WoGE challenge. Slightly smaller field of view this time, but some textbook geology in it. North is up.

Schott rule in effect (post time 7:15 am CST, 10/22/07). I will be out of town this week, but comments are not moderated, so you don't need me.

Where on Google Earth #62

2007-10-17T20:14:00.001-05:00

With some help from Wikipedia, I found that the image posted by Joe was from a volcanic field in western Sudan. So here comes WoGE #62.

Compared to the Peruvian meanders, this should be easy. Extra points for knowing the story that this place is a good example of -- there is a specific journal article I am thinking about.

Schott rule in effect (post time 8:22 pm CST, 10-17-07).

Update: Brian has the answer; here is a bit more detail about this image. It's the southernmost distributary of the Danube Delta in Romania, called the Sfantu Gheorghe channel. The geometry of the deposits is determined by (1) the river discharge, (2) the wave energy of the Black Sea, and (3) the southward oriented longshore transport. The asymmetry of the lobe is a function of the ratio between the net longshore transport rate at the mouth and river discharge. The longshore currents erode the beach/barrier bars on the northern side of the channel mouth. More details in this paper. This image also comes from Bhattacharya and Giosan (2003):

Black represents sand, gray is predominantly muddy deposits, and the white arrow at the river mouth shows the direction of longshore drift.

The importance of numbers in sedimentary geology

2007-10-11T20:33:00.001-05:00

A few years ago, Chris Paola published a paper in Sedimentology on "Quantitative models of sedimentary basin filling". I was skimming through it today, and found these thoughts about the role and status of quantitative reasoning in sedimentary geology:

...what is needed is researchers who are skilled in the field but at the same time understand what quantitative modelling is about: why and how people make approximations, why approaches to modelling can and must differ, and, above all, what the mathematics in the models mean physically. Just as there is no substitute for experience in learning to work in the field, there is no substitute for experience in developing physical insight. And there is no shortcut: we need researchers who are good at at both traditional, descriptive geology and quantitative geology. For the 'modal' sedimentary-geology student, it is not sophisticated computational skills or training in advanced calculus that is lacking, but rather the routine application of basic quantitative reasoning. This means things like estimating scales and rates for key processes, knowing the magnitudes of basic physical properties, and being able to estimate the relative importance of various processes in a particular setting. Understanding scales, rates and relative magnitudes is to quantitative science what recognizing quartz and feldspar is to field geology. Neither requires years of sophisticated training, but both require repetition until they become habitual.

And:

Some 30 years after the initial 'physics scare' associated with bedforms and sedimentary structures, a set of basic principles from fluid and sediment mechanics now appears routinely in introductory sedimentology textbooks. Popular items include settling velocity and Stoke's Law, the Reynolds and Froude numbers, and the basic force balance for steady, uniform channel flow. This material is typically presented somewhere near the beginning of the book and then is largely ignored. (...) There remains a striking contrast between the role of fluid and sediment physics in sedimentary geology and that of thermodynamics in igneous and metamorphic geology. In 'ig-met' texts the underlying thermodynamic principles are introduced and then applied repeatedly. Whereas in hard-rock petrology, thermodynamics permeates the discipline, in sedimentary geology, sediment mechanics still seems a little like taking vitamins: it is surely good for you, but most people cannot say exactly why. There are several reasons for this. In current practice, process-based interpretation is often applied in a piecemeal, descriptive way, to no apparent end beyond providing the interpreter with one more adjective. In addition, the quantitative material that is traditionally taught more often not the most important. For instance, a real appreciation of the implications of the sediment-continuity equation as the governing relation for physical sedimentation is far more useful than the details of sediment-transport formulae or even the definition of the Reynolds number.

Although I still have a lot to learn myself, I couldn't agree more.

ps. Check out what Lord Kelvin had to say about the importance of numbers in science.

Blogvilági multikulturalitásom vége...

2007-10-05T12:42:00.001-05:00

...elérkezett, legalábbis ami az olvasóimat illeti. Olvasóim nagy része ugyanis (ezt úgy mondom, mintha olyan sok olvasóm lenne) vagy csak az angol bejegyzéseket olvassa el, vagy csak a magyarul írottakat. A tisztelt kivételnek ezután két blogot kell majd követnie: esetleges anyanyelvű gondolataimat ugyanis ezután nem itt fogom képernyőre vetni, hanem a Wordpress-nél. Az új-régi blog címe "Hegyek, fák, kövek", és az új cím http://zsylvester.wordpress.com.

My blogospheric Multiple Personality Disorder is over

2007-10-05T12:29:00.001-05:00

... well, at least for my readers. From now on, 'Hindered Settling' will only feature blog posts in English (or Hunglish, a hungarianized version of it), but those of you (all five of you :) ) who from time to time had to think "ok, one of those posts in some weird Eastern European language again" will not have to do so any more (apart from the last one above). My Hungarian ego has decided to move to Wordpress. If you are interested in weird Eastern European languages, you can check it out here.

Blast from the past: images from Peru

2007-10-04T23:19:00.002-05:00

After several years of thinking and saying that I should do something about my old color slides that are only gathering dust in a corner, I finally did it: I sent a few hundred old pictures to Scancafe to have them scanned. It takes quite a bit of time to get the scans back, but it's worth it. The quality is better than I expected, and even if I had somehow access to the right kind of scanner (the average scanner just won't do it), I would have spent many hours doing this.

So I got the DVD today from Scancafe, and I keep looking at these pictures from Peru, taken during five weeks of field work in the Talara Basin, I think seven years ago, followed by a week of vacation in Cusco and Machu Picchu. They are either very good, or I had too much of a good time.

In either case, I've got to go back.

Where on (Google) Earth #57

2007-10-02T23:55:00.001-05:00

I figured out that the Google Earth image posted by Kim was cut by a famous fault, so I have a chance to post the next installment of Where on (Google) Earth. I don't think this is easy - it is certainly not a famous geologic locality, and I know it would be tough for me. But I have been interested in erosional meanders for some time, so here you go. North is up.

Update -- hint: it is in a forearc basin.

A konspiráció-elméletek fölöttébb szükségtelen voltáról

2007-10-01T20:56:00.004-05:00

Nem olyan rég Hamvas Béla inkoherenciáját próbáltam ecsetelni e bloghasábokon, de nem kellett sok időnek eltelnie, amíg a bejegyzés utáni diskúció teljesen kisiklott, és azon kaptam (ismét) magam, hogy a szeptember 11-hez kapcsolódó konspiráció-elméletek híveivel vitatkozom.

Bevallom, mostanig nem nagyon érdekelt ez a téma, mert annyira egyérteműnek tűnt a dolog. És most is pont olyan egyértelműnek tűnik; ami viszont meglep, az az, hogy milyen ereje van a konspiráció-elméleteknek. Ha úgy véljük, hogy az emberek csak nagyon kis töredéke hiszi azt, hogy szeptember 11-ét valójában nem muzulmán terroristák tervezték el és vitték véghez, hanem az amerikai kormány, nagyot tévedünk. Egy 2006 agusztusi felmérés szerint, az amerikaiak 36%-a véli úgy, hogy a támadásokat vagy az amerikai kormány beleegyezésével és támogatásával hajtották végre, vagy maga a kormány a tettes.

Bár a média nem nagyon foglalkozik a témával, az internet tele van a konspirációt bizonygató szövegekkel és dokumentumfilmecskékkel. A közös ezekben az, hogy megpróbálják ízekre szedni a "hivatalos" történetet: belekötnek abba, hogy az WTC épületek miért omlottak úgy össze, mintha hivatásosan berobbantották volna őket; hogy a Pentagonnál miért nem találtak több repülőgép töredéket, mint amennyit találtak; hogy a terroristák közül miért derült ki utólag többről, hogy nem is haltak meg, hanem életben vannak, stb.

A bajok ott kezdődnek, hogy ezeket a kifogásokat nem bizonyítottan szakértő szakemberek hozzák, hanem lelkes konspiracionista amatőrök. És úgy is vannak a kifogások tálalva: az interneten, YouTube videókon, dátumok nélkül, számok nélkül, kontextusból kiragadva, eltúlozva. Minek szaklapokban közölni például a mérnöki kifogásokat -- hiszen sokkal egyszerűbb csak felhajítnai valamit az internetre, ott nincs peer-review. Minek megpróbálni matematikai modellezéssel bebizonyítani, hogy hogyan omolhattak össze az épületek (vagy hogyan nem), mikor egyszerűbb egy kártyavárat lefilmezni, ahogy összeomlik. Áltudomány ez a javából, és a konspiráció-áltudósok reakciója is pontosan olyan, mint a kreacionistáké vagy az örökmozgó-építőké: azért tudnak csak saját kiadványaikban és az interneten érvényesülni, mert a "mainstream" ellenük konspirál. Csak ebben az esetben még jobban el vannak nyomva a leendő Galileók, ugyanis ezúttal nemcsak a tudósok vannak ellenük, hanem az egész FBI, CIA, amerikai kormány, BBC, CNN, a zsidó kezekben levő média, és így tovább.

Az egyik fő téma a Pentagonnál lezuhant Boeing 757-es állítólagos hiánya a helyszínről. Az összeesküvés-hívők szerint, semmilyen bizonyíték nincs, hogy egy nagy személyszállító repülő csapódott volna bele az épületbe. Nem lehetett például semmiféle törmeléket találni a helyszínen, ami egyértelműen a repülőből származott volna. Valóban? És akkor ezek a fényképek hol készültek? Az a gyanúm, hogy ha történetesen megtaláltak volna egy nagy darabot a Boeingből, az American Airlines logójával rajta, a konspiracionisták arra azt mondták volna, hogy a kormány tette oda. De, ha valakinek nem elég a fényképek sora, akkor vegyük például azt, hogy (1) a Pentagonnál megtalálták a repülő fekete dobozát; (2) azonosították a repülőben levő személyek részét a maradványokból, a DNS-ük alapján. És nem is beszélve, hogy ha a Boeing 757-es valóban nem a Pentagonnál zuhant le, akkor mi lett vele? Lezuhant valahol máshol? Elvitték az UFÓk? Egy másik kifogás szerint a Boeing sokkal nagyobb lyukat kellett volna hagyjon az épületben, mint amekkorát hagyott. A valóság az, hogy a 38 méteres szárnytávolságú gép egy kb. 23 méteres lyukat hagyott a Pentagon első épületén. Józan ésszel nem várható el, hogy a gép mindkét szárnya szép lapos lyukat vágjon a vastag betonfalú épületbe (mint ahogy az történt New Yorkban, ahol a falak jó része üvegből volt), mint a rajzfilmekben a főhős keze-lába az aszfaltba, amikor földet ér a szakadékba való zuhanás után. Dehát a 9-11-es konspirációs sztorikban körülbelül annyi a fizika, mint a Tom és Jerry-ben.

Összeesküvés-elméletek valószínűleg mindig is léteztek, amióta az emberiség az eszét tudja. Végül is nem sokban különböznek a pletykától, amelyiknek egyes pszichológusok szerint nagy szerepe lehetett az emberréválásban. Ráadásul nagy, tragikus, sokkoló eseményeket könnyebb elfogadni, hogyha valami hasonlóan nagy tervezés és konspiráció van mögöttük. Azt a gondolatot, hogy egy maréknyi, viszonylag hétköznapinak tűnő ember elkövethet olyasmit, mint ami 2001 szeptemberében történt, sokkal nehezebb lenyelni.

Félreértés ne essék: egyáltalán nem hiszem azt, hogy amit a média mond és ír, az szent igaz. A szkepticizmus nagyon egészséges egy dolog -- de nem mindegy, hogy hogyan használjuk. Bertrand Russell meghatározásával nehéz nem egyetérteni:

A szkepticizmus, amit én pártolok, csupán a következőkből áll: (1) mikor a szakértők egyetértenek, az ellenvélemény nem tekinthető bizonyítottnak; (2) mikor nem értenek egyet, egy nem-szakértő semmilyen véleményt nem tekinthet biztosnak; és (3) mikor mindannyian egyetértenek, hogy nincs elég adat egy határozott vélemény alátámasztásához, akkor a közember jobb, ha nem próbál ítélkezni.

Ezek a kijelentések elég szelídnek tűnnek, de, ha általánosan elfogadnák őket, teljesen forradalmasítanák az emberi életet.

[Az eredeti angol persze jobban hangzik:

The scepticism that I advocate amounts only to this: (1) that when the experts are agreed, the opposite opinion cannot be held to be certain; (2) that when they are not agreed, no opinion can be regarded as certain by a non-expert; and (3) that when they all hold that no sufficient grounds for a positive opinion exist, the ordinary man would do well to suspend his judgment.

These propositions may seem mild, yet, if accepted, they would absolutely revolutionize human life.]

A 9/11-es összeesküvéselmélet esetén tiszta a képlet, hogy a szakértők mit mondanak. A többi: ál-szkeptikus amatőrök véleménye.

Changing one's mind is not a sign of weakness

2007-09-30T23:14:00.001-05:00

Seed Magazine's second annual science writing contest is over now, and the essays of the first and second prize winners are available online. Here is something worth noting in the piece by Thomas W. Martin:

The goal of science is to find those ideas that can withstand the long and hard barrage of evidence-based argument. That lesson must be experienced anew by the members of each generation, irrespective of their careers. Mastery of scientific concepts and theories is a necessary starting point, but it serves only as a prerequisite to joining the never-ending dialogue. Students must learn first-hand how to both imaginatively create new hypotheses and to dispassionately critique them. Many commentators have rightly implored us to make certain that young people encounter the "thrill" of discovery. While this is undeniably desirable, it is arguably even more crucial that they experience the agony (if only on a modest scale) of having a pet hypothesis demolished by facts.

Several current presidential candidates have insisted that they oppose the scientific account of earth's natural history as a matter of principle. In the present cultural climate, altering one's beliefs in response to anything (facts included) is considered a sign of weakness. Students must be convinced that changing one's mind in light of the evidence is not weakness: Changing one's mind is the essence of intellectual growth.

iPod-kritika a la Cluj

2007-09-24T22:26:00.001-05:00

Először is, elnézést a kötekedésért. De. A kolozsvári Szabadság cikkezik az új iPod(ok)-ról, és az egy mondatra eső hibák száma kiemelkedő.

A cím: "Újra tarol az iPodE". Helyesen: iPod.

Első sor: "A Sony Walkmen találmánya volt az, ami alapvetően forradalmasította az utcai zene hallgatást." Helyesen: Sony Walkman.

"A leghíresebb mp3 lejátszót az Apple készítette el. Az ipod elnevezést azóta generikusan mp3 lejátszókra is használják, akkora sikernek örvendett a Mac zenedoboza." Az iPod elnevezést kimondottan csak az Apple által gyártott lejátszókra használják, legalábbis angol nyelvterületen.

"A siker receptje két tényező volt: a jól sikerült design és a kiváló minőségű hang visszaadási képesség." A hangminőség valóban nem rossz az iPod-on, de nem is jobb, mint sok más lejátszón, és gyengébb, mintha CD-t hallgatnál. A siker receptje nem a hangminőségben keresendő.

"Az alma logos lejátszó kezelhetősége azonban messze elmarad a flash lejátszók mögött: mert ezekhez még az Apple által erőltetett iTunes program szükséges." Igen, az iTunes szükséges az iPod-hoz, de ez nem jelenti azt, hogy az iPod kezelhetősége elmarad a flash lejátszókéhoz képest. Az egyik lényeg az iPodnál az, hogy simán és intuitíven működik az iTunes-zal. Az Apple-nél mindig is fontos volt a szoftver-hardver integráció.

"...a probléma csak az, hogy az Apple szoftvereire jellemzően az iTunes is nehézkes, sőt agresszív szoft." Bárcsak minden szoftver annyira lenne nehézkes és agresszív, mint az iTunes.

"A második shuffle modell is a külalakjával hódította meg a piacot (pedig a 100 eurós lejátszónak még kijelzője sincs)." Amerikában az iPod Shuffle-t 60 dollárért árulják. Nincs kijelzője, de egyszerűen és nagyszerűen működik. És akkora, mint egy ütés tapló.

"Az iPhone megint csak olyan ketyere, amivel az Apple a mások által kifejlesztett megoldásokat fölözi le." Az Apple évek óta dolgozik az iPhone érintésérzékeny képernyőjén és annak szoftverén. Senki eddig nem tudta ezt ilyen szinten megcsinálni.

"A funkciók közt szerepel a netkompatibilitás, mp3 illetve videolejátszás, telefon, GPS, érintős képernyő – mindez egy maximálisan 20 gigabyteos merevlemezzel kombinálva." Az iPhone-on nincs (még) GPS (sajnos). És a merevlemez csak 8 GB-os (sajnos).

Lehetne egyebekkel is kötekedni, de minek.

Diszkléjmer: alulírott megrögzött Apple-barát és boldog iTulajdonos.

New images from Mars: the idea of very recent watery flows is evaporating

2007-09-22T09:20:00.001-05:00

A few months ago I commented on the fact that, despite numerous scientific and media reports, the existence of recent watery flows on Mars is far from being obvious or proven. While there are many rock formations exposed at the planet's surface that clearly suggest flowing water some time in the ancient past - for example, the delta near Holden Crater -, many of the young gullies and debris fans have no unequivocal signatures of recent watery flows.

The high-resolution images with the relatively recent gullies were released in 2000, and a paper was published in Science about how these features suggest the presence of liquid water on the Martian surface. Last year, this idea seemed to get new support, in the form of some images taken in 2005 were showing sedimentary activity on crater walls, when compared to images shot a few years earlier.

(image from Malin Space Science Systems)
The problem is, as I said, that nothing in these images suggest unequivocally the presence of water. Geologist Allan Treiman published a paper in 2003 stating this, but at that time his views were representing the minority viewpoint. Needless to say, the news reports got rid of the last remaining uncertainties and doubts in the story, and presented it as if it was 100% sure that liquid water exists today on Mars.

Now there is new evidence that the recent watery flows are not so watery after all. Rather, they are probably dust avalanches, dry flows similar to the ones that occur on windblown dunes here on Earth. Such flows can only form on steep slopes, that are close to the angle of repose. The problem, of course, is complicated - as many problems in science are - and there is no simple answer. For example, in the image shown above, you can see a fan that has been reincised after its deposition by its own feeding channel, so that the latest active deposition occurs further downdip. Such erosional valleys are probably associated with turbulent flow, suggesting that these fans were probably deposited by watery flows. More recent images (see below) also show details of erosional channels that are suggestive of watery flows. Unless the dust avalanches were highly turbulent density flows, similar to some snow avalanches, and they were even able to cut channels. Again, I think there is no easy and obvious answer.

photo from NASA's Planetary Photojournal
In any case, there are two new papers in Science on this subject, check them out if you have online access (I don't :( ).

Flame structures

2007-09-17T20:17:00.001-05:00

Flame structures are sedimentary structures that usually consist of upward-pointing flame-shaped finer-grained sediment tongues that protrude into coarser sediment (like sand). Almost invariably, the 'flames' are inclined in a downslope direction (in a paleogeographic sense, of course) -- like in these two images from the Precambrian Windermere Group in the Canadian Caribou Mountains.

Flame structures are often interpreted as load structures: the overall higher-density sand sinks into the lower-density underlying shale. That would put flame structures into the category of Rayleigh-Taylor instabilities, which result from density inversion. In geology, one of the most important types of Rayleigh-Taylor instability is related to salt: if buried deep enough, the density of the compacting overlying sediment exceeds the density of salt, and the latter starts flowing upward, giving rise to salt diapirs. Salt diapirs often have mushroom shapes, typical of Rayleigh-Taylor instabilities.

The shapes of the flame structures above actually remind me more of the Kelvin-Helmholtz instability, which is related to shear (that is, different velocities) across a fluid interface, and can occur even if the densities are not inverted. K-H instabilities in the atmosphere can result in elegant clouds. K-H billows are common at the tops of turbidity currents, due to the shear between the static water column above and the moving sediment-laden current below. There is no reason why the instability could not occur at the base of the current as well, if the underlying sediment is still fluid enough, and the current itself is not too erosive.

Here is the classic picture of K-H billows at the top of a density current, from Van Dyke's Album of Fluid Motion.

Clastic Detritus has more on flame structures.

Peyto Lake / Caldron Lake trail

2007-09-10T23:17:00.001-05:00

[This is my last post about Peyto Lake, I promise.]

Here is a KMZ (= Google Earth) file for the trail that leads from the Peyto Lake viewing platform to Caldron Lake. It corresponds to the red line in the screenshot below. It is obvious that we never got to Caldron Lake...

You can also see some of the photos in Google Earth, if you download and open this file.

Why is photographic metadata not treated properly?

2007-09-10T21:11:00.002-05:00

I am looking forward to the day when there will be a good industry standard for adding metadata to digital photographs. Right now, it is a real mess, especially if you want to add new information to the photos that have already been downloaded to the computer.

More to the point: as I mentioned before, I have a small GPS receiver that I like to use whenever I am doing geological field work or I am just hiking (is there a difference? :) ). In addition, I cannot do any of these things (hiking or fieldwork) without having a camera with me and taking pictures all the time. And, when I get home, I try to add the approximate geographic location to at least a number of photographs. This can be done using a variety of software packages that write the geographic coordinates into the EXIF part of the image file, the part that contains all kinds of information about the picture, such as date taken, camera manufacturer, camera model, exposure time, etc.

To combine the geographic information from the GPS with the photos, I am using GPSPhotoLinker, which is by far the best application among those that I have tried (and I have tried many). The nice thing about it is that you don't have to process the photos one by one; the program has a batch mode that does everything in one go, using the time stamps in the photographs and the time data from the GPS unit. [There are other programs that claim to be able to do this, but GPSPhotoLinker actually works.]

In my case, the problems start when I try to edit the pictures with iPhoto. I am a big fan of iPhoto, I think it is a fantastic photo management program, but apparently it is unable to properly deal with the modified EXIF data. If I embed the geocoordinates before taking the pics into iPhoto, they show up correctly in iPhoto, but then they (at least some of them) get corrupted when I export the images from iPhoto (usually to put them on Smugmug). So the only option is to geotag the photos after they have been edited in and exported from iPhoto. Fair enough, I can live with that. The problem is that with the new version of iPhoto (iPhoto '08), GPSPhotoLinker cannot write the coordinates to the exported images.

Scheisse mare, as my friend Radu would say ("mare" means big in Romanian, if you want to know). The only workaround I have found is to open the exported images in Adobe Photoshop, and save them again as JPEG files; after this operation - that probably rearranges the EXIF data - GPSPhotoLinker works fine.

Part of the issues are probably rooted in the fact that the EXIF part of the image can be located anywhere in the file. There is a good reason why the longest section of the the Wikipedia article on EXIF is entitled "Problems".

I hope that things will improve soon. In the meantime, if you have a good workflow or workaround for doing automated geotagging on a Mac, please let me know.

Two pictures from Jasper National Park

2007-09-10T01:10:00.001-05:00

More here.

Three pictures from Banff National Park

2007-09-10T01:04:00.001-05:00

The rest are here.

Miért nem érdemes Hamvas Bélát komolyan venni

2007-09-05T23:33:00.001-05:00

Hamvas Béláról nehéz rossz véleményt hallani vagy találni az interneten. Szőcs Géza Shakespeare-rel és Buddhával emlegeti egy mondatban. A tradíció.org szerint a legnagyobb magyar író. A hamvasbéla.org a huszadik század egyik legnagyobb metafizikai gondolkodójaként mutatja be.

Ha azonban belolvasunk írásaiba, nem sok bizonyítékot találunk a fentiekre. Vegyük például "A bor filozófiáját":

A legtöbben ugyanis azt hitték, hogy az ateisták vallástalanok. Erről persze szó sem lehet. Vallástalan ember nincs. Az ateisták nem vallástalanok, hanem szánandóan fogyatékos értelmük és korcs kedélyükhöz képest komikus vallásban hisznek. Éspedig nemcsak hisznek. Az ateisták mindnyájan bigott emberek. Úgy mondom, hogy mindnyájan, mert még egyetlen ateistával se találkoztam, aki ne lett volna bigottabb még annál a rossz szagú vénasszonynál is, aki vasárnap krajcáros füzeteket árul a templom előtt Szent Homorony csodatevő vizeletéről. Az ateista vallás szentje persze nem Szent Homorony hanem Einstein, és a csodatevő hatalom nem a vizelet, hanem az ultraszeptil. Az ateista bigottéria neve materializmus. Ennek a vallásnak három dogmája van: lélek nincs, az ember állat, a halál megsemmisülés. A három pedig egyetlenegyre megy ki, s ez az, hogy az ateisták rettenetesen félnek Istentől. Böhme azt mondja róluk, hogy Isten haragjában élnek. Nem ismernek mást, csak a haragvó Istent: ezért bujkálnak és hazudoznak. Azt hiszik, ha azt mondják: nincs Isten, nem fognak többé félni. Ehelyett persze még jobban félnek.

Az ateista persze elbizakodott ember, nem is akar más lenni; alázatra, szeretetre nem hajlik, más szóval olyan erőtlen, hogy nem is tud rá hajlani. Inkább kitart félelmében, amit letagad, reszket és bujkál és hazudozik, és egyre fennhéjázóbb lesz. Ebből a vigasztalan kotyvalékból, amelyben tagadás, félelem, hazudozás, bujkálás, fennhéjázás, bigottéria együtt fő, alakult ki a materializmus, mint vallásszurrogátum.

Mindezekből most már világosan látni, hogy az ateistákat erőszakosan meggyőzni nemcsak hogy nem lehet, de nem is szabad. Tévelygők, akik tele vannak aggodalommal, önáltatással, és nagyon óvatosan kell velük bánni.

Ha valaki manapság ennyire durva hangú kirohanást írna a keresztények vagy általában az istenhívők ellen, azaz fogyatékos értelműeknek, korcs kedélyűeknek, hazudozóknak, gyáváknak, fennhéjázóknak, tévelygőknek nevezné testületileg őket, nagy lenne a felháborodás. És jogosan. De ha Hamvas Béla teszi ezt az ateistákkal, akkor az egyszerre számít szépirodalomnak, filozófiának és metafizikának.

De olvassuk tovább a "Bor filozófiáját", mert érdemes (?): olyan gyöngyszemekre találunk, melyekhez képest sok mai áltudományos erőlködés egészen racionálisnak és világosnak tűnhet. Itt van például ez a rész:

Ha valaki a hagyomány alapján a legközelebbi értelmi megfeleléseket ki akarja építeni, ezt a következőképpen teheti:

VÉR
Nap - vasárnap - a - vörös - arany - 1

SÖR
Hold - hétfő - c - fehér - ezüst - 2

VÍZ
Merkúr - szerda - f - sárga - higany - 7

TEA (KÁVÉ)
Mars - kedd - g – ibolya - vas - 4

TEJ
Vénusz - péntek - e - zöld - réz - 5

OLAJ
Jupiter - csütörtök - d - kék - ón - 6

BOR
Szaturnusz - szombat - h - fekete - ólom - 3

Ebben a táblázatban a folyadékoknak értelmi megfelelések szerint való hétszeres kapcsolata szerepel, éspedig a bolygókkal, a hét napjaival, a hét hanggal, a szivárvány hét színével, a hét fémmel és a hét számmal. Amint látszik, a bor napja a szombat, bolygója a Szaturnusz, színe a fekete, férne az ólom, hangja a h és száma a három.

Amit nem egészen értek, az a következő: mivel jobb és értelmesebb az ilyen numerológiával vegyített asztrológia és hamis gasztronómia, mint az imént bigottnak nevezett "rossz szagú vénasszony", "aki vasárnap krajcáros füzeteket árul a templom előtt Szent Homorony csodatevő vizeletéről"?

Hamvas Béla szerint az ateista "vallásnak" három dogmája van. A mai pszichológia, biológia és fizika szerint azonban minden jel arra mutat, hogy ezek tények, nem dogmák:

Lélek nincs, az ember állat, a halál megsemmisülés.

Így van.

Two more images of Peyto Lake

2007-09-01T11:10:00.000-05:00

The first is an annotated screenshot from Google Earth. Unfortunately there is no high resolution imagery at this location (the hi-res tile covering Lake Louise does not reach Peyto Lake).

The second is a panorama (shot with a telephoto lens) showing one more time the delta plain at the lakehead. Click on the images for larger versions.

A day in a delta's life

2007-08-31T22:09:00.000-05:00

I did some hiking recently in the Canadian Rockies. There is some stunning mountain scenery over there, with glaciers, lakes of out-of-this-world colors, icecap-covered humongous peaks, abundant wildlife, and so on. But some of the most exciting finds for a sedimentologist/geologist like myself must be the beautifully developed deltas that enter the glacial lakes. 'Enter' is actually an euphemism here, because the rivers are slowly, but surely filling with sediment these magnificent bodies of water, and it is only a matter of a few hundred or thousand years before most of the average size lakes become relatively uninteresting flatlands.

The delta at the updip end of the well-known (and somewhat overrated) Lake Louise is one of these lacustrine deltas. However, the one that really caught my attention is feeding into Peyto Lake. We got to the Peyto Lake overview area relatively early in the morning, when there was no wind, and the lake's turquoise surface was perfectly smooth. Stunning view from high above, but most of my excitement evaporated (<-- euphemism) when a busload of noisy (<-- euphemism) tourists arrived and the viewing area suddenly felt like a Houston shopping mall on a weekend (<-- exaggeration). So we started our descent toward the lake, on the trail that ultimately, if you are brave enough and rough enough (we were neither of these, but that is a different story), leads to Caldron Lake, above Peyto Glacier.

The classic view of Peyto Lake (click for larger image)
After only a couple of hundreds of meters, the population density dropped to zero, and my excitement not only went back to its previous levels, but exponentially grew as the lakehead delta started to take shape beyond the trees below us. You could see very well the active distributary channels sending slightly muddy or silty plumes into the lake. Because it was relatively cold, the glacier up in the valley was not melting too fast, and the discharge was small, so the plumes themselves seemed nice, but were barely noticeable.

This has changed during the day: as temperatures rose, the river that enters the lake became larger and larger, and by the time we got back to the lakehead delta in the afternoon, the plumes became much larger and much more evident.

The discharge of the river coming from the Peyto Glacier increases during the day and sends larger plumes into the lake in the afternoon
What is even more interesting is the fact that these plumes terminate relatively abruptly and it is very likely that they form density underflows in the lake. In other words, the sediment-rich water descends toward the lake bottom and flows down the slope as an underwater extension of the river, until it reaches the deepest parts of the lake. That is where it slows down and lets all of the sediment settle out, probably forming a graded layer, similar to the graded turbidites well known from marine sediments and rocks.

Such underflows often form in lakes when the sediment concentration in the river entering the lake is relatively high. In addition to the sediment concentration, the density excess can be enhanced by lower temperatures of the river. However, if the river is entering a sea or the ocean, it is much more difficult to form such underflows (that are often called hyperpycnal flows -- just to make it a bit more confusing :) ), because seawater has a lot of salt in it and therefore is denser than the river's water. In this case, the sediment concentration of the river must be much higher to overcome the density of the seawater.

River, minibasin, delta, lake
As you walk up from the lakeshore toward the apex of the delta (which, by the way, has a classic triangular textbook delta shape), the size of the clasts on the delta's surface slowly increases (statistically speaking). Further up, the valley gets narrow and then widens up again, giving place to a small minibasin. This minibasin probably was a lake some time ago, a lake that was completely filled.

The river is a Serious River
Where the delta meets the lake, you can easily get close to the distributary channels and their termination points. The coarser sediment tends to be deposited here from the flow, because the flow expands as it enters the lake and its velocity drops. Lower velocity means (1) lower shear stress at the bottom, and therefore fewer grains carried along the bottom, and (2) lower turbulence in the water column, which translates to less sediment carried in suspension. The enhanced deposition right in front of the channel mouth gives rise to a so-called distributary mouth bar, that tends to split the flow into two branches. With time, the mouth bar becomes an island, and the channel splits into two lower-order and simultaneously active distributary channels.

One of the distributary channels, with a nice mouth bar that splits the flow into two
It turns out, of course, that I am not the first to note how superb this little sedimentary system is -- there are a number of studies that looked at the density underflows of Peyto Lake. This article tells us that Peyto Lake has a 7 m high sill in the middle, which splits the lake into two subbasins. Underflows (or turbidity currents) fill with sediment-rich water the updip subbasin to the spillpoint, and then the underflow spills over into the other subbasin. As far as I know, this is the only documented example of a truly ponded turbidity current. It has also been calculated that 61% of the sediment deposited in the lake comes from the underflows (most of the rest of the deposition is due to delta progradation).

Detailed view of the sediment-rich distributary mouths and their plumes
The sad news is that, with sedimentation rates similar to those observed today, Peyto Lake will be completely filled within less than 600 years. You should go and witness this jawdropping place before that happens.

* * *

PS: As Brian points out, the Peyto delta is remarkably similar to some of the experimental deltas generated at St. Anthony Falls Laboratory. See for example the image above -- it is *not* a lake in the Canadian Rockies!

Két kép a kanadai Caribou Hegységből

2007-08-30T07:38:00.000-05:00

A standard tükör-tó a tábor mellett, alkonyatkor

Gleccserátkelés

A többi itt.

Al Gore, Babeş, Bolyai

2007-08-03T22:01:00.000-05:00

Olvasom, hogy a Babeş-Bolyai Egyetem Al Gore-nak is díszdoktori címet akar adni a 2007-2008-as tanévben. Méltányolandó, Al Gore ugyanis azon kevés politikusok közé tartozik, akik valamennyire komolyan veszik a tudományt, és egész jól közvetítik is azt. A képmutatás gyanújának elkerülése végett azonban Alma Mater-em vezetősége azért is tehetne valamit, hogy saját tanárai és kutatói legalább egy szikrányi szakmai háttérrel és tisztességgel képviseljék az Egyetemet.

Történt ugyanis, hogy egy néhány hónappal ezelőtt kolozsvári klimatológusok körbeülték a kerekasztalt, és megbeszélték, hogy a globális felemelegedést tulajdonképpen nem az emberi tevékenység okozza, és hogy "az utóbbi 30 évben történt meteorológiai változások nem olyan súlyosak mint amilyennek az ökologisták meg a politikusok egy része azt próbálja feltüntetni". Magyarán, az IPCC félrebeszél, Al Gore félrebeszél, a klimatológusok döntő töbsége félrebeszél, de mi, kolozsvári szakértők, mi tudjuk pontosan, hogy miről is van szó.

Persze, mindenkinek joga van, hogy elmondja a véleményét, no problem. De. Ahhoz, hogy valaki fittyet hányhasson az egész tudományos status quo-ra, anélkül, hogy felkeltse a sarlatánság gyanúját, ahhoz először bizonyítania kellene, hogy képes nemzetközi szintű tudományos kutatást folytatni és annak eredményeit közölni, elfogadtatni másokkal. Miután ezt megtette, utána kezdhet a forradalmibb kinyilatkoztatásoknak. A kolozsvári klimatológusok enyhén szólva fordított sorrendben csinálják a dolgokat.

De azért Al Gore-nak díszdoktori címet adnának. Tudom, nem ők, hanem az egyetem vezetősége. De akkor is: a helyes sorrend az lenne, hogy először valamilyen minőségi követelményeket támasztani a saját alkalmazottakkal és publikációkkal szemben, és azután tüntetni azzal, hogy milyen nagy környezettudósok meg harcosok vagyunk.

Valakinek le kellene fordítania ezt, a Babeş-Bolyai Egyetem Környezettudományi Fakultásának hivatalos és állítólag tudományos lapjában megjelent cikket, és elküldenie azt Al Gore-nak:

"Kedves Al, ilyen szintű a környezettudomány azon az egyetemen, amelyik díszdoktori címet akar adni neked, azaz téged akar reklámcélokra felhasznáni. Szégyen reád, hogyha elfogadod."

Miért hagyják el a páviánok a szülőföldjüket?

2007-07-30T22:30:00.000-05:00

A főemlősök többsége - a magányos orángutánokkal ellentétben - szociális lényekként töltik életük nagy részét. Ez érvényes a csimpánzokra, a gorillákra és a páviánokra egyaránt: gyerekkorukat a szűk családnál jóval nagyobb csoportban töltik, nagybácsikkal és unokatestvérekkel, a nagybácsik unokatestvéreivel, az unokatestvérek nagynénjeivel, és így tovább. A páviánok esetében egy kis falura való törzzsé növi magát a társaság, amelyikben néha a 250-et is elérheti a rokonok és szomszédok száma. Sok pávián és szociális főemlős életében azonban eljön az az idő, amikor a nagyon családias és otthonos környezetet és társaságot ott kell hagyni, és a folyó túlsó oldalán, vagy a fennsík másik sarkában tanyázó bandába kell beilleszkedni meg szerencsét próbálni. Hogy az ifjú pávián arra gondolva úszik-e át a folyón, hogy a túlsó oldalon jobb az élet, finomabbak a gyökerek, vagy formásabbak a nőstények, azt nem tudhatjuk. Az viszont biztos, hogy a főemlősök világában mindennapi traumának számít ez: egy kamasz fogja magát, és otthagyja anyját-apját, gyerekkori havereit, és reszketve, de mindenre elszántan nekivág az ismeretlennek.

Ha ez a szöveg a Homo sapiens nevű főemlősről hangzana el, hajlamosak lennénk valamilyen szociológiai magyarázatot találni a jelenségre. A Homo sapiens-nél kevésbé egocentrikus majmok esetében azonban nyílvánvaló, hogy a fiatal és nyughatatlan egyedek távozása mögött egyszerű genetikai és evolúciós logika van. Ha ugyanis a kis páviánok mindannyian következetesen ragaszkodnának az édes anyaföldhöz és a falubeliekhez, akkor a páviánközösség előbb-utóbb azt tapasztalná, hogy egyre több csemetének van több vagy kevesebb ujja meg füle, mint amennyi illik és ildomos hogy legyen. Genetikai szempontból ugyanis túl nagy különbségek lehetetlenné teszik a normális utód-termelést, de az sem jó, ha túl nagy a hasonlóság a hím-pávián és szíve választottja között. Ha semmiféle cserebere nem létezne a különböző főemlős csoportok között, akkor nagyon hamar annyira lecsökkene a genetikai változatosság egy-egy csoporton belül, hogy az semmi jóra nem vezetne. A megoldás egyszerű: a fiatal egyedek egy részét - általában vagy a hímek, vagy a nőstények többségét - egy adott ponton elfogja a mehetnék, és el is megy. A csimpánzoknál és a gorilláknál a nőstények a vállalkozóbb kedvűek, a páviánoknál azonban - talán azért, hogy legyen, amin a primatológusok vitatkozzanak - a hímek vágnak neki az ismeretlen világnak.

Kiderül tehát, hogy a főemlősök többi képviselőivel nemcsak az átlag-állaton-felüli intelligencia meg a többi ujjal szembeszegezhető hüvelykujj köt össze bennünket, hanem az a időzített indulat is, amelyik, sokszor szembeszállva azzal, amit a józan ész és a kényelem diktál, elkapja a fiatalabb nemzedék nyughatatlanabb részét, és arra ösztökéli, hogy hagyjanak csapot-papot, tradíciót és otthont, hagyják a jól ismert patak ívóvizét és a csíki sört, és kipróbáljanak valami mást. A szapienszek esetén, persze, millió kulturális, szociális és gazdasági oldala is van a dolognak, de érdemes és érdekes néha arra gondolni, hogy valahol mélyen a páviánokkal közös gének és neurotranszmitterek lehetnek felelősek az ilyen hajlamainkért.

ps. Ezt a szöveget részben Robert Sapolsky "The Young and the Reckless" című írása ihlette, amelyik a "The trouble with testosterone" kötetben jelent meg (75-90 oldal).

A média jövője jelene

2007-07-27T21:15:00.000-05:00

Apróság, de muszáj megemlíteni: azt írja a július hetedikei Szabadság, a "Tudományos-fantasztikus: a média jövője" című cikkben, hogy

A technika-guruk jóslatai szerint nemsokára a mobiltelefon lesz az a műszer, amelyről egyszerre lehet majd videót nézni, zenét hallgatni, internetezni, chattelni – vagy éppen saját tartalmat készíteni és azt feltölteni a világhálóra.

Nemsokára? Ugyan-ugyan. Ez nem a média jövője, és nem tudományos-fantasztikus elmélkedés, hanem valóság.

A cikkben emlegetett mobiltelefonra egy lehetséges példa az iPhone. Ráadásul már az iPhone előtt is voltak "okos" telefonok, amelyek mindenre képesek, amik a cikkíró szerint csak a technika-guruk jóslataiban léteznek. Az más kérdés, hogy engem igazán csak az iPhone óta kezdett a mobiltelefon-téma igazából érdekelni. Ha idővel még GPS-t is tesznek rá, a Google Maps mellé, akkor valóban ez lesz az egyik legizgalmasabb és élvezetesebb szerkentyű.

A Tarkői Homokkő a Sedimentology borítóján

2007-07-19T21:05:00.001-05:00

Az agusztusi Sedimentology borítóján látható fotó a Bodza völgyében készült, még akkoriban, amikor alulírott arrafele méricskélte a homokköveket. Mint sok zöldfülű doktorandusz, nem igazán tudtam akkor, hogy mire is lesz majd jó a sok rétegtani szelvény, de utólag találtam a válaszra kérdést, és most fordított sorrendben a kérdés és a válasz is benne vannak ugyanabban a Sedimentology számban.

Ha valakit esetleg érdekel -- a cikk lényege az, hogy a bodza-völgyi rétegvastagságokat legjobban a lognormális eloszlással lehet jellemezni, annak ellenére, hogy egyesek szerint a hatványfüggvény-eloszlás (vagy fraktáleloszlás) a domináns a turbiditeknél. A fraktáleloszlás valóban izgalmas, de csak akkor, ha van rá jó bizonyíték -- de sok esetben a bizonyíték hiányzik, és egy egyszerű log-log grafikon alapján egyesek hajlamosak fraktálnak nyílvánítani mindent.

A Tarkői Homokkő - és az olaszországi Marnoso-Arenacea Formáció - esetén világosan kimutatható, hogy a lognormális eloszlás jellemzi a vastagon és a vékonyan rétegzett turbiditeket egyaránt. És nem csak a statisztikai elemzés mutatja ezt, hanem valahogy filozofálgató szinten is szimpatikusabb nekem ez a "megoldás", mint akár a fraktáleloszlás, akár az exponenciális eloszlás, még akkor is, ha ez utóbbiak izgalmas spekulálgatásokra adnak okot, skála-független fizikáról, Poisson folyamatokról, meg önszerveződő kritikalitásról (angol "self-organized criticality").

Na, ez kezd nagyon posztmodernül hangzani, úgyhogy jobb, ha abbahagyom.

Van-e olyan jó a romániai egyetemi oktatás, mint a nyugat-európai? II

2007-07-13T17:48:00.000-05:00

Visszatérve még röviden erre a témára: úgy látszik, a romániai egyetemi oktatók 70%-a pontosan az ellenkezőjét hiszi annak, amit egy frissen közzétett jelentés állít. A jelentést egy elnöki bizottság állította össze, a volt tanügyminiszterrel, Mircea Micleával az élen. Jórészt olyanok vannak a bizottságban, akik jól ismerik a nyugati és a hazai helyzetet egyaránt; többen az Ad Astra tagjai. Szerintem nem árt komolyan venni, amit mondanak.

És ezt mondják többek között:

În învățământul superior şi în cercetare, câteva insule de excelență sunt scufundate într-o mare de mediocritate. Niciuna dintre universitățile noastre nu se află în topul celor 500 de universități din lume conform clasamentului Shanghai şi chiar cele mai performante dintre ele ar trebui să-şi sporească producția ştiințifică de 7-8 ori ca să aspire la un astfel de statut. Dacă raportăm numărul de articole ştiințifice la populație, atunci performanța ştiințifică a României este de 11 ori mai mică decât media țărilor OECD, de 5 ori mai mică decât a Ungariei şi de 2 ori mai mică decât a Bulgariei. Indicele compozit de inovare al României a fost în 2006 de 2 ori mai mic decât al Bulgariei, de 3 ori mai mic decât al Ungariei şi de 5 ori mai mic decât media UE şi are cea mai importantă tendință de scădere dintre toate țările luate în considerare.

A jelentés itt tölthető le.

Van-e olyan jó a romániai egyetemi oktatás, mint a nyugat-európai?

2007-07-11T22:56:00.000-05:00

A válasz, persze, egyértelmű és egyszerű: a romániai egyetemi oktatás és tudományos kutatás, általában véve, messze lemarad a nyugat-európai szinttől. Sok szempontból még a kelet-európai szinttől is, lásd Liviu Giosan és Tudor Oprea írását az Ad Astra-ban.

Ez nem nagy újdonság. Az azonban érdekes, hogy a romániai egyetemi oktatók 70%-a szerint, semmi minőségi különbség nincs a romániai felsőoktatási intézmények és a nyugat-európaiak között. Ezt a Soros Alapítvány egy új felméréséből tudhatjuk meg.

Gondolom, jobbanmondva fogadni mernék, hogy ez ugyanaz a 70%, amelyik (1) életében nem töltött egyszerre egy néhány napnál többet egy nyugati felsőoktatási intézményben; (2) nem igazán tudja, hogy mi az az ISI és mi az az "impact factor". Vagy ha igen, akkor nem akar hallani róla.

Mennyire kell eltájolódottnak és beképzeltnek lennie valakinek ahhoz, hogy azt higgye, a Bukaresti Egyetem pont olyan jó, mint mondjuk a Cambridge University? És hogy a Iaşi-i Egyetem kiadványainak olyan súlyuk van, mint mondjuk, kapásból, a Oxford University Press-nek?

Nagyon.

Tipikus profil: a vallásosság

2007-07-09T21:11:00.000-05:00

Azt írja a Transindex, az MTI és a Reuters híreiből inspirálódva, hogy a múlt heti londoni és glasgow-i merényletkísérletek elkövetői

mindnyájan orvosok, vagy pedig kapcsolatban állnak a gyógyító hivatással. Évek óta dolgoztak nagy-britanniai kórházakban, ahol emberek gyógyítása, életek megmentése a központi feladat. Vajon miként lehetséges, hogy ilyen hivatást választó emberek igent mondjanak mások elpusztítására? - erre a kérdésre egyelőre a Scotland Yard sem tudja a választ.

Továbbá a

nemzetközi tapasztalatok azt mutatják, hogy a militáns iszlamizmus követői széles társadalmi palettáról toborzódnak: dologtalan léhűtők és kisstílű bűnözők éppúgy akadnak közöttük, mint tehetős emberek és egyetemi végzettségű értelmiségiek.

És

egyszerűen hamis az a sztereotípia, miszerint az iszlamista körök tagjai mind hátrányos helyzetű, tanulatlan, az átlagos jövedelemnél kevesebbet kereső és hasonló emberek. A tények az ellenkezőjére vallanak: a merényletek elkövetői között nagy számban találunk magasan képzetteket, akik egzakt tudományban szereztek képesítést: vegyészek, fizikusok, orvosok, mérnökök.

A következtetés:

A profil azt mutatja, hogy nincs tipikus profil.

A válasz ezekre a kérdésekre pedig szerintem (és nemcsak szerintem) nagyon egyszerű: ezeket az embereket nem a társadalmi helyzetük, iskolázottságuk, IQ-juk, szülőhelyük, vagy munkahelyük köti össze, hanem az, hogy mindannyian vallásosak, mégpedig nagyon vallásosak. Hogy ennek napnál világosabb fontosságát és jelentőségét miért nem ismeri fel vagy hallgatja el a Scotland Yard, a szakértők, és a média egyaránt, azt én nem értem. Hacsak nem a vallás és vallásos emberek iránti általános (ál)tisztelet és kesztyűs kézzel való bánás miatt: a vallásról ugyanis csak jót vagy semmit illik mondani. És ahol jót semmiképp sem lehetne kiizzadni, mint például az ilyen cikkekben, ott nem mondanak semmit: úgy tesznek, mintha nem is létezne, és az égvilágon semmi köze sem lenne az egész témához. Hadd idézzem Sam Harris-t a "The End of Faith" című könyvéből:

Hogy láthassuk, a baj magával a muzulmán vallással van, és nem egyszerűen a "terrorizmussal", elég, ha azt kérdezzük magunktól: miért teszik a muzulmán terroristák azt, amit tesznek. Mi viheti az egyértelműen személyes sérelemtől vagy pszichológiai zavaroktól mentes bin Ladent - aki se nem szegény, se nem tanulatlan - arra, hogy barlangban lakjon, és számtalan férfi, nő, és gyermek meggyilkolását tervezgesse, olyanokét, akikkel soha nem találkozott? A válasz erre a kérdésre nyilvánvaló - már csak azért is, mert maga bin Laden ismételgette azt orrvérzésig. A válasz az, hogy az olyan emberek, mint bin Laden, valóban hiszik, amit hisznek. Hiszik, hogy a Korán minden egyes betűje szentigaz. Miért adta életét tizenkilenc tanult, jó anyagi háttérrel rendelkező férfi ezrek meggyilkolásáért? Mert hitték, hogy jutalmul egyenesen a mennybe mennek. Ritkán fordul elő, hogy az emberi viselkedés ennyire egyértelműen és teljesen megmagyarázható lenne. Miért nem akarjuk elfogadni ezt a magyarázatot?

Azért, mert van valami, amit az amerikaiak többsége Osama bin Ladennel, a tizenkilenc gépeltérítővel, és a muzulmán világ nagy részével együtt elfogad. Mi, amerikaiak is komolyan vesszük azt a felfogást, mely szerint bizonyos fantasztikus kijelentésekben minden bizonyíték nélkül hinni kell. Az ilyen hősies hiszékenységi aktusok nemcsak elfogadhatóak, hanem szükségesek is. [...] A vallásos hitnek, azaz a bizonyíték-nélküli-hit eszméjének tett engedményeinknek köszönhetően képtelenek vagyunk megnevezni és kezelni a világ konfliktusainak az egyik leggyakoribb okát.

Paprika Balkanicus

2007-06-28T20:28:00.000-05:00

Néhány héttel ezelőtt Londonban kellett néhány órát töltenem, s mit tehet jobbat ilyenkor az ember (bár meg kell adni, hogy az első osztályú repülőtéri váróteremben lelhető Sauvignon Blanc fajták ingyenes kóstolgatása is elég vonzó tevékenységnek tűnik), szóval, mit tehet jobbat, mint egy kis sétát a belvárosban. A magamfajta extrém science-centrikus személynek persze az első dolog , ami eszébe jut (a Sauvignon Blanc után), az a Newton és Darwin sírja a Westminster Abbey-ben. Utoljára 15 évvel ezelőtt jártam arrafele, és akkoriban még csak sarjadzott bennem a felismerés, hogy milyen izgalmas dolgokra jöttek rá mindketten, úgyhogy jobban érdekeltek a megszokott londoni turista-attrakciók és a fényképezőgépek. [A Sauvignon Blanc is kevésbé izgatott akkoriban.]

A Westminster Abbey azonban zárva van vasárnap; a hozzá tartozó, vasárnap is nyitva tartó boltban pedig csak egyházi dolgokat forgalmaznak, melyek kevésbé érdekelnek, mint a tavalyi krikett- és curling-világbajnokság eredményei. Sehol semmi nyoma Darwinnak vagy Newtonnak. Sauvignon Blancról nem is beszélve.

Mérgemben a Covent Garden felé fordultam, ahol nagy meglepetésemre valami ismerősen szóló zene fogadott. Az a fajta zene, amitől minden keleteurópai felizgul, hogy Dénes Pistát idézzem. Az a fajta, amiről nem igazán tudod eldönteni, hogy román-e, magyar-e, valami szláv erőlködés, vagy leginkább a klezmerre emlékeztet. Magyarán egész jól hangzott, és szemmel láthatólag nemcsak a keleteurópaiak élvezték, hanem a britek és mindenféle turisták is. Paprika Balkanicus-nak hívták a csoportot, egy szerb, egy román, és egy szlovén tag muzsikál benne. És egész jól, meg kell mondanom.

Fura egy élmény volt, Texasból jövet, Afrikába menet, egy kis Kelet-Európa, a Covent Gardenben.

Utána még jobban tudtam értékelni a Sauvignon Blanc-ot a repülőtéren.

Két kép Londonból

2007-06-27T21:17:00.001-05:00

Tizenöt év után újra Londonban, ezúttal csak két repülő közötti néhány órára. Így se rossz.

A többi itt.

Két kép a Houston-i Természettudományi Múzeumból

2007-06-24T21:14:00.000-05:00

Pontosabban a "Cockrell Butterfly Center"-ből, amelyik egy pillangókkal teli esőerdő egy nagy üvegkupola alatt.

Majdnem minden rövid története

2007-06-23T08:22:00.000-05:00

Ez a címe Bill Bryson könyvének, melyet nem olyan rég fordítottak magyarra. Az eredeti angol cím: "A short history of nearly everything", alulírott ezt olvasta, és ezennel jelenti, hogy jó vót. Bryson az egyik legolvasmányosabb és szellemesebb író, akit valaha is olvastam. Ráadásul nem nyomja a szöveget fölöslegesen, és a "Short history" egyike a legjobb tudománynépszerűsítő könyveknek. Még Richard Dawkins is tanulhatna Bryson-tól, legalábbis ami a humorérzéket illeti.

Persze Bill Bryson elsősorban nem tudománynépszerűsítő szövegeiről, hanem útirajzairól híres; a londoni repülőtér könyvesstandjai tele vannak a könyveivel. És nem véletlenül. A múltkor Dél-Afrikába repültem Londonon keresztül, és megvettem a "The Lost Continent" című kötetét. Már az első oldalon elfogott a röhögés, és később több passzusnál folytak a könnyeim a nevetéstől. Ha autentikus képet akarsz kapni a mai Amerikáról, ez az egyik könyv, amit érdemes elolvasni. Itt van például a K-Mart (egy üzletlánc, amelyik 2003-ban csődbe jutott) tökéletes leírása:

Afterwards, to round off a perfect evening, I clambered over to a nearby K-Mart and had a look around. K-Marts are a chain of discount stores and they are really depressing places. You could take Mother Theresa to K-Mart and she would get depressed. It's not that there's anything wrong with the K-Marts themselves, it's the customers. K-Marts are always full of the sort of people who would give their children names that rhyme: Lonnie, Donnie, Ronnie, Connie, Bonnie. [...] Every woman there has at least four children and they all look as if they had been fathered by a different man. The woman always weighs 250 pounds. She is always walloping a child and bawling, 'If you don't behave, Ronnie, I'm not gonna bring you back here no more!' As if Ronnie could give a toss about never going to a K-Mart again. It's the place you would go if you wanted to buy a stereo system for under 35$ and didn't care if it sounded like the band was playing in a mailbox under water in a distant lake. If you go shopping at K-Mart you know that you've touched bottom. My dad liked K-Marts.

Az angolul nem tudó olvasók kedvéért, itt egy gyors magyarítás is:

Később, hogy méltóképpen fejezzem be a tökéletes estét, átballagtam egy közeli K-Martba, és nézelődtem egy keveset. A K-Mart egy nagy üzlethálózat, és minden K-Mart üzlet nagyon egy elszomorító hely. Ha Teréz anyát elvinnéd egy K-Mart-ba, őt is elfogná a depresszió. Nem mintha valami baj lenne magával az üzlettel; a baj a vásárlókkal van. Egy K-Mart mindig tele van olyan emberekkel, akik a gyerekeiknek rímelő neveket adnak: Lonnie, Donnie, Ronnie, Connie, Bonnie. [...] Minden nőnek legalább négy gyereke van, és azok mind úgy néznek ki, mintha valaki más lenne az apjuk. A nő mindig 130 kilós. És mindig valamelyik gyerekét csapkodja éppen, és azt kiabálja, hogy 'Ha nem viseled magad, Ronnie, többet soha nem hozlak a K-Martba!'. Mintha Ronnienak nagyon fájna, ha többet soha nem tér vissza a K-Mart-ba. Ez az a hely, ahova akkor mész, hogyha akarsz venni egy CD-lejátszót 35 dollárnál olcsóbban, és nem zavar, hogy a zene úgy szól belőle, mintha a zenekar egy vízalatti postaládában játszana, egy távoli tóban. Ha a K-Mart-ba mész, tudod, hogy nagyon mélyre süllyedtél. Apám szerette a K-Mart-ot.

If you talk about power laws, read this paper:

2007-06-22T21:39:00.000-05:00

A. Clauset, C. R. Shalizi and M. E. J. Newman, "Power-law distributions in empirical data", arxiv:0706.1062. Let me just repeat three key points that Shalizi summarizes on his blog:

Lots of distributions give you straight-ish lines on a log-log plot. True, a Gaussian or a Poisson won't, but lots of other things will. Don't even begin to talk to me about log-log plots which you claim are "piecewise linear".

And:

Abusing linear regression makes the baby Gauss cry. Fitting a line to your log-log plot by least squares is a bad idea. It generally doesn't even give you a probability distribution, and even if your data do follow a power-law distribution, it gives you a bad estimate of the parameters. You cannot use the error estimates your regression software gives you, because those formulas incorporate assumptions which directly contradict the idea that you are seeing samples from a power law. And no, you cannot claim that because the line "explains" a lot of the variance that you must have a power law, because you can get a very high R^2 from other distributions (that test has no "power"). And this is without getting into the errors caused by trying to fit a line to binned histograms.

It's true that fitting lines on log-log graphs is what Pareto did back in the day when he started this whole power-law business, but "the day" was the 1890s. There's a time and a place for being old school; this isn't it.

In addition,

Use a goodness-of-fit test to check goodness of fit. In particular, if you're looking at the goodness of fit of a distribution, use a statistic meant for distributions, not one for regression curves. This means forgetting about R^2, the fraction of variance accounted for by the curve, and using the Kolmogorov-Smirnov statistic, the maximum discrepancy between the empirical distribution and the theoretical one. If you've got the right theoretical distribution, KS statistic will converge to zero as you get more data (that's the Glivenko-Cantelli theorem). The one hitch in this case is that you can't use the usual tables/formulas for significance levels, because you're estimating the parameters of the power law from the data. This is why God, in Her wisdom and mercy, gave us the bootstrap.

If the chance of getting data which fits the estimated distribution as badly as your data fits your power law is, oh, one in a thousand or less, you had better have some other, very compelling reason to think that you're looking at a power law.

The good news is that, despite having been submitted for publication too soon to cite Clauset et al., this paper is largely following the advice above and is trying to convey the message to sedimentary geologists (hopefully others will look at it as well) that straightish-looking lines on log-log plots with a large R squared are not enough evidence for power-law behavior.

Related previous posts:
The fractal nature of Einstein's and Darwin's letter writing
My talk on bed thicknesses and power laws
On cumulative probability curves
Power laws and log-log plots II.
Power laws and log-log plots I.