Where on Google Earth? #215

With a helpful Twitter hint from Ron Schott, I won my second “Where on (Google) Earth?” challenge, the 214th edition of this popular geoblogospheric competition. As a result, I get to host the next one, Where on Google Earth? #215.

The aim of the game is to figure out where on Earth this satellite imagery comes from, and then post the coordinates (lat/long, UTM, whatever) and give a brief explanation of the geologic significance of the region. (I’ve got a full post ready to go that goes into more detail on the region; so you need only sketch out the flimsiest of details.)

Post your answer in the comments section once you’ve figured it out. The winner earns the right to host Where on Google Earth #216. If you don’t have a blog of your own, then I’ll be happy to host it here on your behalf. I invoke the Schott Rule, which says that you have to wait one hour for each past Wo(G)E that you’ve won before answering. Posting time is 9:00am on Saturday, October 16.

Here it is:

Please note that north is off to the upper right. You can enlarge the screenshot to full-size by clicking through twice. Good luck!

Friday fold: multilayer buckle folding demo

Check out this video I found online whilst uploading last week’s Friday fold:

This video was produced and published on YouTube by Markus Beckers, Michael Ketterman, Dennis Laux and Janos Urai.

It’s a nice demonstration of how multiple layers of material of different properties and different thicknesses can yield up different flavors of folds. In the movie, there are two materials present: white silicone and gray foam. The silicone layers are stronger (“more competent”) than the foam. But the two silicone layers are different thicknesses. It turns out that this ends up being a decisive factor in determining the way they fold.

We can explain this behavior using the Ramberg-Biot equation:

L = 2 π t (η / 6ηo)

where L is the wavelength of the fold (in other words, the distance from one antiform fold hinge to the next antiform fold hinge); t is the thickness of the folded layer; η is the viscosity (resistance to flow) of the silicone layer (or, in general, the more competent of the two layers); and ηo is the viscosity of the foam layers.

In other words, the (η / 6ηo) part of the equation reflects the viscosity contrast between the affected layers. In the video, this viscosity contrast is a constant, since we’re looking at two layers of the same stuff surrounded by the same matrix of other stuff. The only difference is the thickness of the two silicone layers.

So as far as our video up top is concerned, pay attention to the t value and the L value: the thicker the layer is, the larger the wavelength of the resulting fold. The thin layer has a lower t value, and so it ends up with a shorter wavelength: i.e., there are more folds packed into the same amount of vertical space as its stouter neighbor. The thick layer’s higher t value means it wıll have a proportıonately higher L value. It will have a longer wavelength, and fewer undulations will fit into the available vertical space.

Happy Friday, everyone! I’m heading back to DC tomorrow (from Turkey), so more regular posting wıll resume next week.

Words’ worth IV

Back on the first incarnation of this blog, I occasionally posted about words that bugged me. A few more have piled up since then, so here we go with the latest consideration of “words’ worth”…

First off, let’s consider the use of “outcrops” as a verb. This came up recently on this blog when commenter Tom Skaug pointed out that I was incorrectly using that term. He’s right of course, and has the dictionary citations to prove it. Technically, we should say that a particular rock unit “crops out” on a hillside. Mea culpa. I appreciate the correction. That being said, I know a lot of geologists who speak as sloppily as I write. Using “outcrop” as a verb is reasonably common slang in my circles.

Next, let’s consider some plural words. When reviewing an article recently, I saw the words “maximums” and “minimums” written out by a science writer. I suggested to the editor that these should be “minima and maxima” instead. The editor countered that real people (i.e., non-scientists) don’t speak that way, and that the accepted parlance among the general public is just to tack an “s” on the end of a word to make it plural. However, in Latin, the language that gives us these words, the plural would end with the addition of an “a.” When you look it up in a dictionary, both plural forms are listed. To add insult to injury, my computer’s automatic spell-checker function is putting the red zigzag under my correct Latin versions, and NOT underlining the “-s” versions. I’m beset on all sides!  Still, to me, “minimums” sounds clunky and clumsy, while “minima” is elegant and sleek, like a well-designed scientific instrument.

Okay, here’s another one. Occasionally, graffiti appear on the walls of the bathrooms here at the community college where I teach. When I spot a new scrawl, I write an e-mail to the cleaning staff alerting them to the vandalism. But what do I do when there’s just one little new jotting? Graffiti are plural; the correct singular of this Italian word is “graffito.” But that sounds vaguely ridiculous, right? “Dear Cleaning Staff, There is a new graffito in the men’s bathroom on the east side of the Shuler Building’s second floor.” I feel silly, and maybe a little pompous, if I use the correct singular form of this word. Anybody else have a word like that, where they know how to use it correctly, but they use it incorrectly on purpose for the ease of communication? (…Or possibly to avoid offending someone?)

Along similar lines, data are plural, while datum is singular. Most scientists are comfortable discussing a single datum, and are careful to only use “data” when there’s more than one chunk of information being discussed. But the general public doesn’t parse this distinction as finely. You’ll see “data” used to refer to what really is a lone datum.

Natural gas – I was thinking about this one while driving into work the other day, and the radio newspeople were talking about that big explosion a few weeks ago in San Bruno, California. It got me thinking about the term “natural gas.” What a dumb, non-descriptive term. I mean, do we ever refer to “natural liquid” or “natural solid?” Natural gas is annoyingly non-specific. I get it: it’s a cocktail of different gases, mostly methane, with a dash of ethane and maybe a few other volatile compounds too. If it were pure methane, we would call it “methane,” but it’s often not pure. It’s a mixture. So we can’t call it just “methane,” because that wouldn’t be accurate. The mixture occurs naturally, so we call it natural gas. We trade specificity for meaningless but accurate inclusiveness. Blech. The role of “natural gas” as a fossil fuel is ascendant; we’re going to be talking about it for some time to come. I think we need a better name for the stuff. Suggestions?

Deducing my first anticline

When I was done with my sophomore year at William & Mary, I embarked on a time-honored tradition among W&M geology majors: the Geology 310 Colorado Plateau field course. Jess alluded to this same course in her Magma Cum Laude contribution to this month’s Accretionary Wedge geology blog “carnival,” too.

My version of Geology 310 was led by the legendary Gerald Johnson (a.k.a. “Dr J”), a dynamic and enthusiastic educator who seemed particularly at home in the field. One day, he had us out in Utah (I think) somewhere, and pulled over to the side of the road so we could examine some tilted sandstone layers. We took a strike and dip reading, and plotted it on a map.

310A

Then we descended into a narrow valley, where Dr. J did some “geology at 60 miles per hour,” pointing out shale outcrops in a few places in the valley. Then we drove up the opposite side. We pulled over again. Same sandstone strata: we again took a strike and a dip on the beds. The data was then recorded on our maps with a strike and dip symbol, a broad, squat “T” shape, where the upper bar of the “T” is parallel to the strike of the bedding, and the vertical prong of the “T” is pointing in the dip direction.

310B

“Well,” Dr. J asked us, “What’s going on here?”

We were all silent, trying to puzzle it out. What’s the deal? What is he fishing for? Seconds ticked by, and no one had the right answer. We started to sweat… “Um, the sandstone beds are dipping to the west on the ridge west of the valley,” someone ventured, “and they are dipping to the east on the ridge east of the valley?”

“Yes, but what does that mean?” he replied. Silence…

Eventually, he relented, and spelled it out for us. Imagine this situation from the sides, he suggested, gesticulating the layers dipping off in opposite directions. “These are the same layers, so they were once laterally continuous…” He mimed a cross-sectional perspective:

310C

How could we connect these disparately oriented strata together?

310D

Bam! It hit me: I got the idea of an anticline at that point — the idea that a structure like an anticline could be so large that I couldn’t actually see it from my earthbound human-sized perspective, and I could only infer it from detailed measurements of the rock structures. It was a revelation to me: this valley and its surrounding ridges were part of a massive fold. The anticline must have breached in the middle, with the shale eroding away faster than the sandstone, producing a valley flanked by two ridges.

I’m grateful to Dr. J for putting us through all stages of this exercise: collecting the incremental pieces of data, being forced to think about it in an attempt to come up with an interpretation, and then finally giving us the proper interpretation, once it had become obvious we weren’t going to get it on our own. This last bit is particularly important to me as an educator: sometimes it’s okay to spell it out for students, particularly if it’s their first time walking down a particular path. By revealing the “answer,” Dr. J guided my thinking from data to big picture structure to geomorphological interpretation in a way that I can only describe as “opening up a new pathway” in my mind. Once he showed the way to think about this sort of thing, it was suddenly very easy for me to visualize this sort of complicated four-dimensional story. Once the pathway was there, it was almost effortless to let my thoughts flow along that pathway. Weird how one’s perspective can change in a moment, and how that influences everything that comes after.

For me, this exercise and ensuing discussion constituted an important moment in developing my ability to think like a geologist. I don’t think my brain will ever be the same.

Friday fold: Siccar Point, Scotland

As with last week, I’m going to show you someone else’s fold today. This one should have strong resonance with most geologists, because it’s a fold in the tilted (and contorted) older strata exposed below the famous unconformity at Siccar Point, Scotland:

fold_siccar

I found this image on the British Geological Survey’s online repository of images, which are available for public use with attribution. I found out about the BGS photo repository via a post on StructuralGeology.org.

The photo was taken by T.S. Bain in 1979. Rock hammer (lower left) for scale.

The specific rock type here is shale, and their age is Silurian. Note the thinning of the limbs of the fold, and the relatively thick hinge area.

Happy Friday – may your workday rapidly thin (like the limbs of this “similar” fold), and your weekend be as thick as this fold hinge!

EARTH: the biography, by the BBC

Last week, I watched the BBC/National Geographic series “EARTH: The Biography,” hosted by Iain Stewart.

Stewart is a charismatic host, with a thick Scottish accent that cannot disguise his enthusiasm for geology. The five episodes focus on: volcanoes, ice, oceans, atmosphere, and “rare planet.” Overall, I thought the series did an good job covering some of the greatest stories in geology with an emphasis on presenting the latest ideas. Snowball Earth gets screen time, for instance, and the ocean-anoxia hypothesis for the end-Permian extinction, too. They also cover ocean acidification, a topic I feel deserves wider press.

The series is well-produced. Stewart zips all around the globe, and the editors seamlessly incorporate imagery from other BBC series (like Planet Earth) as supporting content where appropriate.

Here are some of the tidbits I gleaned from the show:

Two billion tonnes of the Andes are carried down the Amazon every year (in the form of sediment weathered and eroded off the Andes). Along similar lines, 40 million tonnes of dust from the Sahara Desert are dumped on the Amazon Basin every year. I wonder if the Sahara dust is included in their sediment volume estimates, or whether it is deducted since it’s not of Andean origin. Great statistics regardless.

They tell the story of Joesph Kittenger in the atmosphere episode. He did a skydiving jump from 90 miles up! After free-falling through almost the entire Earth’s atmosphere, this crazy dude lights up a cigarette! Those were the days.

Four million tonnes of the Sun’s mass are converted into energy every second. Whoa.

Humans now move more rock and soil than all natural processes combined. Ergo: Anthropocene.

The Mediterranean Sea loses three times as much water to evaporation than it gains from rivers and rain. Without the Straits of Gibraltar to let in Atlantic water, it will dry up (and it has dried up, multiple times in the past). In illustrating this, Stewart goes into a salt mine beneath Sicily and shows some BEAUTIFUL contorted salt laminae. Worth watching the whole series just for those gorgeous patterns. (here’s one shot)

The footage of Fayetteville Green Lake in New York is excellent — this is a deep lake with pronounced internal stratification of water and not much mixing — the deep parts of the lake have become anoxic and euxinic (enriched in H2S). They illustrate this by diving into it and the water turns PINK. It is presented, of course, as an analogy for one of the leading models for the end-Permian extinction: global ocean euxinia. It is astonishing to see pink water, and enticing to think about, but the show commits a major “fail” when they don’t tell what this substance is, or where it comes from. They describe the water as having “something deadly” in it, and then say it’s a “highly toxic poison,” or “a gas as deadly as cyanide,” but never do they (a) call it hydrogen sulfide, and (b) explain that it comes from certain kinds of bacteria that thrive in low-oxygen waters. Another complaint: they don’t say when the Permian-Triassic extinction occurred, just the same old saw about it being the “greatest” extinction in Earth history, and that it occurred “before the dinosaurs.” The word “Permian” is never used.

I have some other criticisms, too…

The phrase “a blink of an eye, geologically” is used too often. Twice in the first episode alone!

They show an image of a comet moving like a badminton birdie, with the tail pointing back where the comet came from. This isn’t accurate — comet tails point away from the sun (dragged downstream by the solar wind).

At one point, when discussing the history of life on Earth, Stewart suggests that “life needs catastrophes.” I would argue that life has diversified due to catastrophes, but that catastrophes are not necessary for life to continue. In a non-catastrophic situation, life just perpetuates itself and may exhibit increasing specialization or genetic drift within the parameters available in its environment. But “needing” a catastrophe every now and again? Only if diversification of life is the goal — I take issue with this verb.

In another episode, Stewart is describing convection in the mantle, and says that “magma” is moving upwards. This is false: it is hot rock (a solid), less dense than neighboring relatively-cold rock. The “magma” idea for the Earth’s mantle is a popular misconception which Stewart is opting to elide rather than confront.

At another point, in praising the Moon, Stewart suggests that the planet Earth’s climate would have switching between freezing cold and boiling hot if it were not for the Moon’s influence. No explanation is given for this extraordinary claim. He may indeed have a chain of evidence and inference in mind when he says this, but without a robust explanation, this statement comes off as “because scientists say so”: an authoritative statement with no supporting detail which shows how science comes to a particular conclusion. Worse, he then cranks it up with the future fear factor — they go into great detail about how we have determined that the Moon is drifting further away from Earth over time, and then suggests ominously that Earth will then lose its climatic stability. So now we’ve got alarmism too, but again, no explanation of the supposed causative relationship is given.

Overall, it’s an enjoyable series, and I was pleased to have it to watch when I had the flu last week. Check it out, and let me know what you think.

Champlain thrust fault

champlain_01

Over the summer, I went up to Vermont to visit my friends the Clearys. Joe Cleary is a college friend and a talented luthier. He and his wife Tree and their children Jasper and Juniper have settled in Burlington, a lively town with a lot of cool stuff going on. Joe took time out one morning to show us a superb example of a thrust fault on the shore of Lake Champlain. It is on private property, but Joe got permission for us to hike there first. Our group that day consisted of Joe, Lily, and me, plus by a stroke of good luck, my pal Pete Berquist was in Burlington at the same time, with his friend Amy. The five us were Team Burlington for the day.

There are two rock units involved in the faulting at this location. Consider the first:

champlain_17

This is the Dunham Dolostone. It’s early Cambrian in age. It’s resistant to erosion, and stands up in cliffs above Lake Champlain. The distance from my ten little piggies down to the water is probably fifty feet. Below the Dunham Dolostone, you can find the Iberville shale. It is actually younger than the overlying dolostone. (We know this from unfaulted stratigraphy elsewhere in the region.) The Iberville shales are Middle Ordovician in age. They are relatively weak (‘incompetent’) rocks, and have been sheared out by the faulting. Here, Team Burlington demonstrates the sense of shear, by leaning over in the direction that foliation has rotated towards:

champlain_02

Looking in one direction along the base of the fault to show the differential weathering of the two units:

champlain_04

Flip it around 180°, and you see the same thing in the other direction:

champlain_06

Pete, Joe, and I crawled underneath the ominously overhanging dolostone to check out the detailed structure of the fault. Here’s Pete tickling the sheared out shales, looking for little sigmas…

champlain_05

The shales had nice veins of calcite running through them, and the high contrast of light and dark reveals some lovely folds, like this one:

champlain_03

Pete goes into professor mode, gesticulating and using the verb “shmoo” to describe the reaction of the shale to a gazillion tons of dolostone sliding over top of it:

champlain_07

Another nice fold (little tiny blue Swiss Army knife, 5.7 cm in length, for scale):

champlain_09

And another nice fold:

champlain_10

This fold is transitioning into a shear band:

champlain_16

Here’s my favorite part of the outcrop, a big fold with little parasitic folds all over it, showing opposite senses of shear on the opposite limbs of the big fold:

champlain_12

S-folds on the upper limb, Z-folds on the lower limb. Sweet, eh?

Here, a sort of S-C fabric has developed, with foliation tipped over the the left, and then near-horizontal shear bands running along through it:

champlain_11

Here’s something weird. Perhaps a reader can explain it. Here’s a shot of some of the veins, with the same 5.7 cm knife for scale:

champlain_13

Now we’ve zoomed in, and you can see some detail in the vein:

champlain_18

What are those lines? Is that more “S-C” fabric? I mean, it can’t be cross-bedding in a vein… but I’m having trouble visualizing what process of shearing the vein could yield such a delicate, even distribution of dark material amid the vein fill. What the heck is going on here?

Okay, now that you’ve twisted your brain up thinking about that, you can relax with a structure whose meaning is obvious. Some artistic and romantic previous visitor (not a member of Team Burlington) had arranged pebbles weathered from the two rock units into a bimodal icon of love:

champlain_08

Displacement along the Champlain Thrust is estimated at 30–50 miles (48–80 km). These dolostones started off near the New Hampshire border, then crossed Vermont, almost but not quite making it into the Empire State! The Champlain Thrust is the westernmost thrust fault that has been associated with the Taconian Orogeny, a late Ordovician episode of mountain building associated with the docking of an island arc with ancestral North America. Looking up at the fault trace:

champlain_15

A final glance at the thrust outcrop, looking north and showing the fault’s gently-inclined easterly dip:

champlain_14

Joe, thanks for taking the time to bring us out there!

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