Földismei nyelvenczkedések

Kovag. Zöldle. Tülle. Kigyla. Berzle. Jegeczes. Mandolaképű. Törgyületes. Görgyületes. Vaséleg. Tülleszirt. Szemegle. Csengle. Szivagkőzetek. Puhányok és burányok. Talajos lánczburány. Reszelények. Közönséges iglény. Vonalozott gyöngér. Kétkarélyú bölle. Knigti ötizke. Ránczos köldöny. Csehországi csodány. Blumenbachi rejlöny. Ősikék. Talányos hálony. Burtini bagócsa. Sugáros köldöny. Bordacsos zugoncz. Fegyverzett fejbökény. Legyező dörgész. Hosszúröpű tompócz. Kerekdedes iszapka. Díszes lobogány. Reczés serlegőcz. Desznójersi emlőcse. Soros körvöny. Marsi szörbencs. Élesbordájú fúrhabany. Forgonczféle homár. Valdi gyöngyike. Ferde falány. Tövises gerencs. Lapos fodorcza. Bükös bölök. Általános kögöcske. Köröczös csészike. Hatszögű bököcz.

S a nagy hajdanócz.

[Szemelvények Mihálka Antal 1862-es geológia tankönyvéből; T3 Kiadó, 2006, Boér Hunor előszavával].

Sedimentology on Mars: wet or dry gravity flows?

Once again, the 'water on Mars' subject made it to the headlines: researchers claim that recent gully activity that took place in the last few years (as documented by photographs taken in 1999 and 2005) suggests that watery sediment flows (debris flows) are shaping the planet's surface as we speak.

The problem is, of course, that it is difficult to keep water liquid in an environment where the temperature is usually way below 0 degrees Celsius and the atmospheric water vapor pressure is also very low. And, as far as I am concerned, the morphology of the gullies and of the associated deposits does not rule out deposition from dry granular flows at all. Of course, several papers have been written on the subject; here is, for example, an opinion from Allan Treiman (2003):

The salient features of the Martian gullies [Malin and Edgett, 2000, 2001] are consistent with their origin as dry flows of eolian sediment: gully deposits are fine granular material (erodable by wind); eolian sediment are available where gullies form; the distribution of gullies are consistent with deposition of sediment from wind; and the orientations of gullies are similarly consistent with wind patterns. Further, it is clear that granular materials can flow as if they were Bingham liquids, and granular flows can produce landforms with all of the geomorphic features of Martian gullies. No known data concerning the gullies (chronological, geomorphic, or geologic) falsify this hypothesis, so it is worth further investigation.

I just find it interesting that, by the time the story reaches the media, all the uncertainties disappear, and the story is unequivocal: watery flows must occur on Mars today, period.

John McPhee on geological language

Started reading John McPhee's tetralogue on geology, Annals of the Former World. Here is a memorable sampling of the thick sediments of geological language (p. 33):

As years went by, such verbal deposits would thicken. Someone developed enough effrontery to call a piece of our earth an epieugeosyncline. There were those who said interfluve when they meant between two streams, and a perfectly good word like mesopotamian would do. A cactolith, according to the American Geological Institute's Glossary of Geology and Related Sciences, was a "quasi-horizontal chonolith composed of anastomosing ductoliths, whose distal ends curl like a harpolith, thin like a sphenolith, or bulge discordantly like an akmolith or ethmolith." The same class of people who called one rock serpentine called another jacupirangite. Clinoptilolite, eclogite, migmatite, tincalconite, szaibelyite, pumpellyite. Meyerhofferite. The same class of people who called one rock paracelsian called another despujolsite. Metakirchheimerite, phlogopite, ktzenbuckelite, mboziite, noselite, neighborite, samsonite, pigeonite, muskoxite, pabstite, aenigmatite. Joesmithite.

He could have included turbidite, tsunamite, tempestite, unifite, homogenite, debrite, hyperpycnite, and contourite as well. As if this wasn't enough, there are sedimentary geologists who suggest introducing new 'ites' (PDF link) like gravite and densite.

Bullshite.

Bedforms in Matlab - everything you wanted to know about ripple marks and cross beds

David Rubin's bedform-generating code has been implemented in Matlab (in fact, it has been out there for a while). It is a great learning, teaching, and research tool that can be downloaded as part of an USGS open file report. Strongly recommended to anyone having some interest in sedimentary structures, bedforms, and cool Matlab graphics.

That reminds me of something else: it would be nice to have a Matlab version running on Intel Macs. I hope Mathworks will keep its promises and have something ready by early 2007. Having to reboot the iMac in Windows XP is an acceptable solution, but I could live without it [although even Windows XP looks OK on this kind of hardware :) ].

Georeferencing photos on a Mac

Not long ago I managed to georeference some of my photos using GPS measurements. Before I forget how I did this, here are some notes on the process. The key piece of software is GPSPhotoLinker, written by Jeffrey Early. After downloading and installing this nice little program, the next step is to get the GPS tracks from the GPS unit. For some reason, GPSPhotoLinker did not do this for me; so I downloaded GPSBabel, connected my Garmin Vista Cx to the iMac, and saved the tracks in GPX format. [GPSBabel is the same utility that is used inside GPSPhotoLinker]. I tried to open the GPX file in GPSPhotoLinker, but it did not work. The problem was that some of the tracks on the GPS unit were actually saved -- and saving tracks on a Garmin GPS unit (and maybe on other units as well, I don't know) results in losing the time stamp from each datapoint. GPSPhotoLinker apparently is not able to just ignore this part of the GPX file; the only solution was that I manually deleted all the saved tracks from the GPX file. After that, everything went pretty smoothly. GPSPhotoLinker finds the GPS points that are the closest in time to the time stamp of the photograph and writes the latitude and longitude into the EXIF header of the jpeg file. You can choose between 'snapping' photo locations to the nearest GPS datapoint or to interpolate between two points to find the best estimate for the place where the photo was taken. It is important, of course, to record a fairly large number of GPS points when you are taking the pictures.

Once I had the photos tagged with the geographic coordinates, I had two options to display them in the context of a map: either relying on Smugmug, the photo-hosting web service that I use, or on a cool iPhoto plugin called iPhotoToGoogleEarth. With Smugmug, both Google Maps and Google Earth can be used to look at the photos; the drawback is that the displayed pictures are small and you have to go go back to the Smugmug page to see the photos in a reasonable size. The iPhoto plugin generates a kmz file that can be opened with Google Earth and includes all the photos in a reasonable size, that, of course, can be adjusted by the user). The advantage is that you do not have to leave Google Earth in order to look at the photos.

Here is my first try at doing the gereferencing, as shown by Smugmug in Google Maps. It is not a bad idea after all to have a GPS unit handy when you are traveling and taking photos.

PS. In addition to the saved tracks, the other thing that GPSPhotoLinker does not like in the GPX file is the part of the header that refers to the geographic bounds of the file, e.g., "bounds minlat="-51.725563835" minlon ="-98.491744157" maxlat="43.777740654" maxlon="131.500083692"". You have to delete that in order for GPSPhotoLinker to read the file.

PS 2. There is always more to learn. I thought that the ideal workflow for georeferencing photos would be to (1) do the tagging in GPSPhotoLinker, (2) import the photos to iPhoto, (3) export the ones I want to post on the web, and (4) put them on Smugmug. It turns out this does not work well; all the photos I took in California (and were correctly labeled by GPSPhotolinker) ended up in Kamchatka. The point is that the georeferencing must be done (or redone) after the photos are exported from iPhoto.

Digital Earth

Last weekend I discovered (1) that Google Earth was even more amazing than I had previously thought [and now they have a Mac version as well!]; and (2) there is a lot more out there in terms of digital geography if you look a bit harder.

Here is for example this USGS site from which you can download (with some patience) not only the usual satellite imagery but digital elevation models (DEMs) as well, for pretty much the whole globe [thanks to my friend Radu Girabcea for pointing me to it]. Once you've got a DEM, you can use 3dem, a nice little piece of freeware to display the elevation models in 2D and 3D and to drape georeferenced images over the topography. DEMs are available (for free -- at least at this point) with a ~10 m resolution for most of the US and a ~30 m resolution for other areas (I was especially excited to savor the detailed topography of the Carpathians -- the more familiar you are with a place, the more illuminating it can be if you examine the morphology).

Another thing worth taking a look at is NASA's version of Google Earth, that is, World Wind. With one click, you can switch from Landsat images to USGS topographic maps [although I often have problems with the server connection]. Can it get a lot better than this?

Global warming does not cause earthquakes

According to Wired magazine's "Biggest Discoveries of 2005", the most important discovery of 2005 is that

Thanks to the Asian tsunami and Hurricane Katrina, global warming can no longer be ignored.

I agree that global warming can no longer be ignored, but you don't need to know too much about earth science to realize that the Asian tsunami has absolutely nothing to do with it.

The fractal nature of Einstein's and Darwin's letter writing

Power laws are gathering quite some attention again, thanks to a few new papers (e.g., this one and this one) by Albert-László Barabási and his coworkers, published in Nature. Cosma Shalizi and others disagree: once again, just because some dataset on a log-log plot looks like you could easily fit a straight line to it, it is not safe to conclude that it is a power-law distribution.

One of the papers looks at the letter-writing habits of Darwin and Einstein, and concludes that the response times have a power-law distribution with an exponent of 3/2. The other "reports that the probability distribution of time intervals between consecutive emails sent by a single user and time delays fro eamil replies follow a power law". Shalizi and Stouffer et al. claim that these are in fact lognormal distributions.

I am wondering if you could ever get a paper published in Nature that looks at some dataset, shows that it has normal or lognormal distribution, draws some overarching and universal conclusions from that, and... and that's it.

Or, to translate it to the much more mundane language of geologists, that only applies to dirt, not to Einstein's letters: there is no interesting story in showing that bed thicknesses or sedimentary body sizes have a lognormal distribution, but if it's a power law, suddenly you can talk about the "scale-independent physics of turbidite deposition" and the importance of non-equilibrium thermodynamics in the geometries of deltas and everything else under the sun.

That's why power laws are great.

Hurricanes and barrier islands

Here is the reason why one should think twice about buying or building a house on a barrier island that is in hurricane country. This USGS website also shows convincingly that Hurricane Rita should not be misunderestimated :) just because it barely touched the Houston-Galveston area. It did plenty of damage where the right-front qaudrant made landfall - things would have been very different around here if Rita made landfall at Galveston or a bit to the West of Galveston.

And these images of a barrier island that migrates landward as hurricanes go over it make you wonder how much of the geologic record of barrier islands (and beaches in general) actually consist of fairweather deposits. Everything seems to be moving and redepositing during these storms.

On cumulative probability curves

Let's go back to some good old science subjects and take some notes about sediments, something I am supposed to be an expert in.

One of my favorite pastimes lately is collecting examples from the geological literature in which the statistical analysis went incredibly wrong. Take for example the papers dealing with grain-size distributions that advertise cumulative probability plots as the best technique to identify subpopulations in a mixed distribution. Here is what G.S. Visher says in his 1969 paper on "Grain size distributions and depositional processes" (Journal of Sedimentary Petrology, v. 39, p. 1074-1106):

"The most important aspect in analysis of textural patterns is the recognition of straight line curve segments. In figure 3 four such segments occur on the log-probability curve, each defined by at least four control points. The interpretation of this distribution is that it represents four separate log-normal populations. Each population is truncated and joined with the next population to form a single distribution. This means that grain size distributions do not follow a single log-normal law, but are composed of several log-normal populations each with a different mean and a standard deviation. These separate populations are readily identifiable on the log-probability plot, but they are difficult to precisely define on the other two curves." (p. 1079)

I am wondering if this tendency to see straight line segments in cumulative probability plots and to give them some special significance is a syndrome restricted only to geologists - whose abilities for pattern recognition are excellent in general - or one could find such examples from other fields as well. The fact that a certain distribution looks like a straight line on a cumulative plot does not mean that mixtures of the same type of distribution will plot as straight line segments. The excellent sedimentologist Robert Folk has pointed this out in a 1977 discussion of a paper coauthored by Visher (in which they try to prove that the Navajo Sandstone is not an eolian deposit - yeah, right):

"A general defect of the Visher method is exemplified by Kane Creek #2, which is shown as consisting of four straight line segments, implying that it is a mixture of four populations. It can be proved by anyone using probability paper and ordinary arithmetic that such kinky curves can be made by a simple mixing of two (not four) populations that are widely separated; the 'flat' portions represent the gaps in the distribution. Furthermore, mixing of populations on probability paper results in smoothly curving inflexions, not angularly joined straight-line segments."

Despite this, multiple straight-line-fitting to cumulative probability plots is fashionable again, although this time it is done on log-log plots of exceedence probability of either bed thickness or fault size data. But this is going to be part of a paper that I am working on right now (in the evenings and weekends...) -- so more about this later.

Earth-science bloggers

Here is a list of 'earth-science bloggers', put together by the author of greengabro.net, who also asks the question: "Are geologists genetically inclined to dislike the nontechnical nature of the blogosphere? Or are we being discriminated against by our colleagues in physics and biology?"

My talk on bed thicknesses and power laws

At the end of April I am going to give a talk on power-law and lognormal distributions and how they apply to turbidite bed thickness data. Here is the abstract. And here are some previous thoughts and links on the subject of log-log plots, power-laws and bed-thickness distributions.

Creationist karstology

I never knew there was a branch of science called 'creationist karstology'. But now I know: probably the best known (and potentially the only) practitioner of it is Emil Silvestru, who was head scientist at the Speleological Institute in Cluj, Romania, before he immigrated to Canada and became a member - and apparently employee - of Answers in Genesis, a creationist organization. 'Creation Magazine' claims he is a 'world authority on caves' - OK, he probably did indeed spend some time in caves and knows something about them. But how seriously can you take someone who honestly thinks that this is reasonable and this is good science:

After becoming a Christian he quickly realized that the ‘millions of years’ interpretation, so common in geology, was not compatible with Genesis. ‘Once I became a Christian,’ Emil says, ‘I knew I had to “tune up” my scientific knowledge with the Scriptures.’

‘Although philosophically and ethically I accepted a literal Genesis from my conversion, at first I was unable to match it with my “technical” side.’

E-mail discussions with qualified creationist geologists, creationist books, Creation magazine and especially the TJ helped him realise what he calls two ‘essential things’:

1. Given exceptional conditions (e.g. the Genesis Flood) geological processes that take an extremely long time today can be unimaginably accelerated.
2. The Genesis Flood was global, not regional.

   ‘These factors were immensely important in my conversion and my Christian life. I am now convinced of six-day, literal, recent, Genesis creation. That doesn't mean that there are not still some unanswered problems, but researching such issues is what being a scientist is all about.’"

According to Dr. Silvestru, radioactive dating is wrong; he is "now convinced of six-day, literal, recent, Genesis creation" and that "currently prominent creationist modeling of the post-Flood Ice Age is an important tool in understanding the karst in a young-earth framework".

No comment.

To wrap it up, a little piece of blatant misinformation. Asked if he

experienced any ridicule or persecution because of his strong stand on Genesis creation

, I guess back in Romania, Dr. Silvestru says:

"Not really, for two main reasons. First, after so many years of almost compulsory atheism/evolutionism, most people welcome biblical creationism as a breath of fresh air. Second, God has granted me a professional status that practically bars any attempt to ridicule my creationist convictions."

It is true that religion has gained quite some ground since the fall of communism in Eastern Europe; but I don't think that you can make a blanket statement like "most people welcome biblical creationsim as a breath of fresh air". In fact, most of the people I know, even those who are much more sympathetic toward religion then I am, would definitely not consider bibilical creationism a breath of fresh air.

Regarding his "professional status that practically bars any attempt to ridicule" his creationist convictions - well, here is one.

It is also true that they are ridiculous enough by themselves.

Thermodynamics makes sedimentology obsolete (just kidding)

I have re-read some of the Exxon papers on the shapes and evolution of sedimentary bodies (e.g., Energy Dissipation and the Fundamental Shape of Siliciclastic Sedimentary Bodies). This is one of the main conclusions:

"We believe that the sedimentary rock record is built of scale-invariant hierarchies of sedimentary bodies. These bodies are similar in shape and property distribution. Furthermore, sedimentary bodies evolve along a well-defined pathway governed by principles of nonequilibrium thermodynamics and energy dissipation. This pathway is scale-invariant and independent of depositional environment."

In other words, forget about hydrodynamics and process sedimentology, forget about all the work done by Allen, Middleton, Kuenen, and so on, because all you need is nonequilibrium thermodynamics to explain and model sediment bodies of all kinds and shapes, from the smallest to the largest and from an alluvial fan to the abyssal plain. Well, that just does not sound right. To me, there IS a difference between a wave ripple and a sand wave; between the fill of an oxbow lake and the fill of a submarine canyon; and I do not see how on earth debris flows or fine-grained turbidites can be described and modeled as jet deposits. Yes, deltas look like trees or leaves from above - so what? That does not mean I don't have to dig deeper to understand what is exactly going on in deltas and in leaves; nonequilibrium thermodynamics just won't do it.

Power laws and log-log plots II.

Back again to power laws. After some more googling, I found an even more important piece of blogging by Cosma Shalizi: Speaking Truth to Power About Weblogs, or, How Not to Draw a Straight Line. The title says it all: just don't play with power law distributions by fitting straight lines to log-log plots, because chances are that you will get a reasonably looking line and R squared will be relatively large, but that still does not mean that there is a power law distribution. Shalizi is complaining about papers in statistical physics and complexity theory that do such things -- well, he should see what is going on in sedimentary geology, where somebody invented the 'segmented power-law distributions' and now everybody who is measuring bed thicknesses is fitting not one, but two or even more straight lines to log-log plots of cumulative distributions. It's utter nonsense, even more so than with a single straight line, but it looks very sophisticated and regular, and people keep doing these plots and all kinds of fancy interpretations based on them (earthquakes, self-organizing criticality, confinement, erosion, etc.). If it plots as a straight line - fine, it's a power law, we explained everything. If it does not plot as a straight line -- well, just fit two straight lines and talk about two populations, and how the original power-law distribution has been modified by erosion, confinement, etc. - and we explained everything again. I know I am also guilty of some of this in my thesis, but at least I have never done the segmented power law plots.

Power laws and log-log plots I.

Did a bit of reading today on power law distributions, just to refresh my memories from three years ago when I was writing my thesis. And found some interesting papers and notes on the web, e.g., this one. I think we are still far from being able to use bed thickness distributions in a useful, predictive way, even though this has become a popular subject among turbidite experts. One of the problems is that it is easy to play with the distributions (e.g., take an initial power-law distribution and modify it by amalgamation), but things are probably a lot more complicated and cannot be explained just with amlagamation and basin topography. The other problem is that power-law distributions and their exponents cannot be assessed by fitting a straight line to an exceedence probability plot, as it is explained here. This method is bound to give erroneous estimates when dealing with a single distribution, but it is close to meaningless when people want to break out two different populations by fitting not one, but two lines to the exceedence probability plot.

Well, I guess that is enough about power laws for today.