26 April 2017

Pseudocraters at Lake Mývatn, Iceland

Check out this scene and tell me what you see:

The scene is near the southern end of Lake Mývatn, astride the Mid-Atlantic Rift in northern Iceland.

If you thought that looks a lot like a cinder cone, you’re thinking a lot like me! However, these aren’t really cinder cones in the sense of being volcanic vents. Instead, these features result from steam explosions that occurred after a basaltic lava flow advanced over soggy lake sediments. Squished and heated, the water flashed to vapor around 2300 years ago and blew holes through the overlying basalt, dragging chunks of basalt and lake sediments along with it. Like this:

It must have been an exciting thing to witness!

Here are few more views of the region:

And of course I made a GigaPan image (handheld). Here it is in both Flash-based and HTML5-based displays:

Link 0.20 Gpx Handheld GigaPan by Callan Bentley

A word of caution: this part of the lake is beset by enormous swarms of hideous large “midges.” We explored it looking like this:

Be forewarned: If you decide to visit the pseudocraters of Lake Mývatn, bring your head-net!

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25 April 2017

Hidden Figures, by Margot Lee Shetterly

I haven’t yet seen the blockbuster movie Hidden Figures, but I’ve heard great things about it. This post is about the book it’s based on, also called Hidden Figures, by Margot Lee Shetterly. It chronicles the work of numerous African-American women at NASA and its predecessor organization, NACA, through the middle of the last century. The book is a robust documentation of these women’s childhoods, educations, motivations, and lives. It chronicles their mastery of calculation and engineering, and their dedication to important work on behalf of the United States of America. It is also a story of the changing face of Hampton, Virginia, through time. Shetterly is a Hampton native, and she taps into both paper primary sources (artifacts such as employment records and newsletters, photographs, etc.) and her own personal interviews to learn what life and work were like for black women doing intense mathematical work at high security clearance in the development of supersonic aircraft and rockets that would leave the Earth. It is not a story that is wears persecution on its sleeve; rather it is a celebration of what these women accomplished, despite the discriminatory practices of the society they dwelt in. From the wind tunnel to the lunchroom, Hidden Figures is an affirmation and an important record of a group of professionals who did a meticulous job making sure that heroes like Chuck Yaeger and John Glenn were able to achieve what they did and return home in one piece. For too long, these mathematicians, “computers,” and aeronautical engineers haven’t gotten the attention they deserve. Their contributions were critical, and this books pays them the tribute they are due.

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24 April 2017

The bizarre world wherein we march for science

I marched on Saturday.

In spite of the congested conditions in both the local atmosphere and my sinuses, I felt compelled to add my voice and presence to the March for Science, an event that was probably the first of its kind since the Enlightenment, aiming to push back against anti-science attitudes from the current occupant of the White House and his contemporaries on Capitol Hill. I tried to keep my message nonpartisan and positive. This is what I came up with:

My former student Maddy Rushing (interviewed on NPR here) also attended, and her sign was a lot funnier than mine:

We gathered with other friends and colleagues to stand up for rational thought, empirical evidence, and professional expertise. We advocated for supporting science through federal funding, and basing policy decisions on peer-reviewed study of tangible evidence. In our view, the Trump administration is dismissing critical scientific insights to the detriment of the United States and the planet Earth.

It was a delight to see so many like-minded participants, despite the nasty weather. I’ve read estimates that about 40,000 people attended the DC March, and that seemed about right to me. There were a LOT of people there.

I’ve never done anything like this before – but I’ve never been so motivated to defend something so near, dear, and vital before. There are many noble causes, but this was the first time I felt as if things were so far from normal that I needed to protest. I feel like the assertions we were giving voice to at the March for Science were things that should not have to be stated, much less defended or marched for. It should go without saying that we’re better off without infectious diseases, enabled by high-speed accurate digital communication, with foresight of coming threats. The world is a demonstrably better place because of scientific advances. I’m only alive because of science (seat belts, antibiotics, surgery). The rain that fell on the marchers was clean, thanks to the scientific study of atmospheric pollution (and legislative reaction to it). We knew the rain was coming, thanks to the scientific study of the weather, meteorology. To prepare for the rain, we donned Gore-tex jackets (a technology only possible thanks to science). The Jumbotrons on which we watched Michael Mann, Bill Nye, and Cara Santa Maria talk — and Jon Batiste play jazz (what a good choice!) — were another form of technology built using scientific principles.

…Even Carl Sagan joined us!

As rainy days go, it could hardly have been better. Here’s our posse, also including Robin Rohrback, James Blondell, and my colleague Ken Rasmussen:

Photo by Victoria Martin

I felt glad to have been able to contribute, and I was delighted to run into so many neighbors, colleagues, friends, and science celebrities there.

Donald Trump, did you hear us? Lamar Smith, did you hear us? In case you missed our show of support for evidence-based policy, I’ll be dropping you each a note in the mail later this week! 😉

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21 April 2017

Friday (coal)d

Often I feature a fold photo here on Friday, but today I give you a folded coal, so therefore a “coald” – this is from the Pennsylvanian Conemaugh Formation on the Alleghany Plateau in West Virginia, near Bismarck.

Photo by Sebastian Andres Kaempfe Droguett.

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17 April 2017

Liesegang rings in a natural sandstone “tile”

I found this nice specimen in the field last Friday:

It’s a slab of sandstone, defined by two mutually-perpendicular bedding-perpendicular joint sets. This square “tile” that evidently saw repeated episodes of soaking by groundwater, as evidenced by the Liesegang banding (iron oxide deposits that accumulate at the “soaking front” resulting in distinctive concentric ring patterns, increasingly circular toward the interior. The center-most one looks a bit like an Easter egg – apropos for today!

Here are two presentations of a GIGAmacro I made of the slab:


Link 0.65 Gpx GIGAmacro by Callan Bentley

If these repeated soakings bolster the sandstone with their additions of iron oxides, one result is that a network of similarly effected tiles may weather out in a “box” like pattern, a phenomenon known as boxwork. Like this:

(Thank you, Photoshop!) …Imagine the reinforced cracks, stiff with rust, holding up to the onslaught of weathering while the light centers get etched out into a series of little cubicles. That would be boxwork.

Fluids can soak into solid rock, especially something porous and permeable such as a sandstone, but this slab clearly shows that it’s easiest for those fluids to flow along fractures in the rock; the same fractures that make up the modern edges to the “tile.”

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15 April 2017

Basement xenoliths in Catoctin Formation, Compton Pass

My son and I hiked Compton Peak in Shenandoah National Park this morning, and saw these two lovely examples of xenoliths.

The example above is small, but it shows clearly the difference between the coarse, felsic basement rock (Mesoproterozoic granitoid, comprising the xenolith) and the surrounding fine-grained dark green metabasalt of the Catoctin Formation (Neoproterozoic). Here’s another, bigger example:

These two Blue Ridge examples both illustrate the principle of relative dating by inclusions – you cannot break off a piece of granitic basement to mix it into basaltic lava unless the granite already exists.

Hope you’re having as similarly insightful weekend!

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12 April 2017

Weathering along perpendicular joint sets, Arran

Check this out:

That’s a beautiful example of weathering in a dolerite dike on Arran. The igneous rock was broken along two more or less perpendicular joint sets, and then fluid flow along those fractures helped “rot” the adjacent rock through oxidation and hydrolysis. The resulting brownish weathering rind  grows at the expense of the unweathered black rock. Because there is more surface area at the corners of the rock blocks (where two joints intersect), there is more weathering there, and thus the blocks of rock become increasingly spheroidal over time.

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11 April 2017

The Sixth Extinction: A Sigma Force Novel, by James Rollins

I did a double-take in the library last week. I was scanning the shelves of audio books, looking for something interesting, when I saw one called The Sixth Extinction. Ahh, such a good book – Elizabeth Kolbert did such a great job with – WAIT – This one has “James Rollins” listed as the author. It wasn’t Kolbert’s book. It was a different The Sixth Extinction. The full title is The Sixth Extinction: A Sigma Force Novel. It’s an adventure novel, the tenth in a series I had not been aware of. Out of a sense of curiosity, I checked it out. It’s basically a thriller -a pulp adventure novel without much to redeem it in terms of intellectual stimulation. However, I think it’s worth mentioning here, briefly, because it does weave in numerous scientific threads that are worth exploring. One idea that features in the novel is the idea of XNA, an information-containing nucleic acid with a backbone built of a substance other than the sugars deoxyribose or ribose. The novel opens at Mono Lake, California, site of the most famous “arsenic life” controversy from a few years back. The novel unfortunately relies on the trope of the “mad scientist,” in this case a conservationist with geneticist chops, who basically wants to replace the Earth’s biosphere with something more robust – an ecosystem of genetically engineered creatures whose genes are written in XNA. Surprisingly, there’s a hidden ecosystem based on XNA hidden in caves beneath Antarctica. Anyhow, the rest of it is pretty much to be expected: good guys, bad guys, a fetish for guns and military culture, romance sub-plots, gruesome deaths for bad guys but not good guys, etc. Unremarkable in that regard – very much cut from the same cloth as Clive Cussler’s Dirk Pitt novels. This Sixth Extinction is popcorn; a beach read. You’re much better off if you read Elizabeth Kolbert’s The Sixth Extinction instead.

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7 April 2017

Friday fold: paper demo

My colleague Nick Schmerr (University of Maryland, College Park) posted this photo today, and he was kind enough to let me share it as a Friday fold:

It’s a “type 2” fold interference pattern demonstration for his Structural Geology course — made of paper!

Very cool – I love it when faculty bring physical models into their teaching – the three-dimensional shape of this sheet of paper says more than even the best drawn 2D representation of a complicated fold.

Thanks for sharing, Nick!

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6 April 2017

Stac Fada

Here’s a funny rock you might meet in Scotland’s North West Highlands:

This is the Stac Fada member of the Clachtoll Formation, in the Stoer Group. It’s a very poorly sorted sedimentary deposit which some workers have interpreted as a volcanic mudflow deposit (a lahar), and others think is a meteorite impact deposit.

Eroded cobbles of it can be found all along the Minch coast of the Stoer Peninsula. They look like this:

Note the angular greenish blobs? Those are devitrified glass. But was it volcanic glass (obsidian) or meteorite impact glass (suevite)?

The light-colored bits are chunks of the Lewisian gneiss basement, as seen a little better in these examples:

Let’s go to the source to investigate! It’s up-section from the MISS which are the oldest fossils in Britain, and just a scootch up along the bay.

Here’s a map of the namesake peninsula where this distinctive rock can be found: Stac Fada, north of Clachtoll on the Stoer Peninsula of the North West Highlands.

When you get there, you’ll see both weathered and fresh exposures of the green-glass-bearing sandstone and conglomerate:

…And you’ll find big pieces of the Lewisian basement present, too:

You’ll also note these astounding folded “rafts” of sandstone:

(Note the black-raincoat-covered GigaPan at the right of the image above, and the yellow pencil near the middle of the next two images for a sense of scale.)

Getting something that big (literally the size of a Zodiac raft) in a unit that’s otherwise glass-chunk-rich conglomerate is a puzzler. That a chunk this coherent could survive complete disaggregation by the violence of a meteorite impact boggles the mind.

Here’s a smaller one – look for the layering and the change in texture – both the folded sandstone and the coarser matrix are both hidden beneath black and yellow lichens on the outcrop surface:

Evidence to support the meteorite impactite interpretation comes from mineralogy and geophysics. First to consider is the mineral reidite, which is found in the unit. It’s described by Reddy, et al. (2015) as “unambiguous evidence of shock pressures in excess of ∼30 GPa.” Then there’s the crater (probably): not too far to the east we find the Lairg Gravity Low, which is the sort of geophysical signature we might expect for a crater. Here’s a look at the Bouguer Residual Gravity field for northern Scotland from Rollin (2009), republished in Simms (2015). The dark blue areas are gravity lows deeper than -15 mGal. Pretty striking, right? However, we can’t see the crater directly, because it’s hidden beneath a shield of Moine schist which was later thrust over the top of the hole, as seen here (yellow colors) from the BGS’s Geology of Britain viewer:

That’s frustrating. If I were king of world geological funding, I might be tempted to pierce the Moinie and insert a drill core into that Lairg Gravity Low, as the USGS has done with the Chesapeake Bay Impact Structure in several places, part of one of the cores of which was petrographically evaluated by students in my department.

Anyhow, I’ll bet you’re itching to explore the poor sorting, the glassy shards, and the sandstone rafts on your own. So now let’s go to the GigaPans & GIGAmacros for a closer look… Same routine for posting them as I’ve been doing lately: Both non-Flash and Flash-based embed options for you. Click through to the source if neither one shows up on your browser! 🙂


Link 1.03 Gpx GigaPan by Callan Bentley

Link 0.51 Gpx GigaPan by Callan Bentley

Specimen (front and back):

Link 0.50 Gpx GIGAmacro by Callan Bentley

Link 0.65 Gpx GIGAmacro by Callan Bentley

Also, I’d be remiss if I didn’t point out this lovely suite of GigaPans of thin sections of Stac Fada ejecta by Paul Guyett.
Soon I hope to have some thin section GIGAmacros of my own to share… Stay tuned!

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