2 December 2016

Friday fold: Dalradian kinks, crenulations, and folded crenulations on Arran

For the Friday fold, let’s travel to the northern edge of the Isle of Arran in southwestern Scotland, where near the town of Lochranza, you can find Dalradian metagraywackes that display a lovely suite of folds. There are kink bands, like this one:

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And this one:

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And these en echelon kink bands:

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And these:

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But there’s also a more pervasive structural fabric to be seen: symmetrical crenulations:

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And in places these highly crenulated rocks have been folded into a variety of secondary contortions:

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There’s much to be seen in and around Lochranza. I’ll return to this site in future blog posts.

In the meantime, happy Friday!

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1 December 2016

Novels by Ernest Cline

armada rp1 In the past couple of months I listened to the audiobook versions of Ernest Cline’s two novels. They are of a common piece, and so I opt to review them in tandem. There is a feeling I have that I am increasingly at odds with the students I teach in terms of cultural references and common interests. On a field trip recently, I made a joke that referenced Indiana Jones and the Temple of Doom, and it fell utterly flat. Probing for why (I have no shame), I learned that NONE of the students on the trip had seen ANY of the Indiana Jones movies. These films were touchstones for my youth and worldview. Only Star Wars has a higher position in the Bentley pantheon. Another angle: I read a lot, and I don’t get the sense that my students do. When I was in high school and college, I read voraciously outside of class, and many of my friends did too. In the calm, organizational moments before a class began, many of my peers would be reading books. Nowadays, it hardly needs saying, the students are paying attention to their smartphones instead. What books could possibly bridge this generational cultural chasm?

My money’s on Ernest Cline.

Ready Player One, his debut, is set in a dystopian future where most people spend most of their time online in a simulated universe called the OASIS. The creator of this ne plus ultra virtual reality dies, and sets up with his will a competition for his accumulated riches that’s based on exploring the OASIS with a thickly-cultivated sense of 1980’s music, movies, TV, and games. I’m not a gamer myself, but I watched a fair amount of TV in my youth, and I’ve been a constant cinematic consumer throughout my life. And I’m familiar with most of the music referenced, though none of it comes close to the Talking Heads for me. Bottom line: there were a veritable gigatonne of 1980’s pop cultural references that were woven into integral plot developments in this novel, and they are so much fun to revisit in the context of a new cut-throat competition for the biggest pot of money on Earth. Poor boy Wade invests his passion in mastering every little detail of Steven Spielberg*, Atari, Rush, and Japanese monsters. When various trials are presented to him, he has the skills to succeed. Along the way, there’s a fairly traditional romance subplot, but call me a sucker for that sort of thing – it’s just like all the movies I watched in the 1980s!

So what else has the guy written? That was the question as I closed out Ready Player One. It turns out, there’s only one other option at this point: Armada. I checked it out from my library, and just finished it yesterday. I think I liked Armada even better. It’s set more or less in the present day, and the plot hinges on the notion that all of the science fiction movies and video games we’ve been enjoying as a culture are in fact intentionally preparatory. More specifically, two massively multiplayer online games, “Terra Firma” and “Armada,” are specifically designed to train Earthlings for a forecast alien invasion (ground combat and space ‘aerial’ combat, respectively). The protagonist, like that of Ready Player One, lacks a father but discovers that before his father died, he had clued in to this massive cultural conspiracy. The protagonist, Zack, is really good at playing “Armada,” and soon discovers that his dad’s nutty old journals were right, and now he too is being folded in to this effort to fend off Earth’s annihilation by hostile aliens. As with RPO, there’s a ton of pop-cultural tie-ins, though this time the connective tissue runs in the other direction. Star Wars, The Day the Earth Stood Still, Independence Day – those were all propaganda to get everyone up to speed. Fun: Carl Sagan got the funding for the original Cosmos by virtue of his involvement in the cover up. Brief cameos by Seth Shostak, Stephen Hawking, and Neil DeGrasse Tyson. Twists and turns in the plot, and another cliched romance sub-thread, and it’s all good. Overall, a rollicking good time.

I should note that both audiobooks I listened to were read by Wil Wheaton, which is perfect, since the Stand By Me / Star Trek: The Next Generation actor is an exemplar and advocate for geek culture across the decades.

Recommended.

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* Spielberg is directing the movie adaptation of Ready Player One, which I predict will be awesome. Due date: 1.5 years from now.

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30 November 2016

“Drumsticks” of Islay tillite

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One fun thing about examining the Port Askaig Tillite in the field is to find odd-shaped exemplars of the unit lying on Islay’s beaches. My favorites were shaped like wands, or antennae, or perhaps the drumsticks freshly detached from a Thanksgiving turkey… a big clast at one end and then a thin septum of the finer-grained matrix to hang on to:

Here’s an example:

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The shape results from differential weathering of the matrix relative to the large clast. Another example is perhaps even more striking, with an ice-cream-cone morphology:

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I recently learned of a museum in Japan dedicated to rocks that look like faces. Perhaps some Ileach should found a museum dedicated to “drumstick stones”…

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29 November 2016

Islay’s Port Askaig tillite

Have a look at this:

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Pretty uninteresting rock at first glance – massive gray stuff.

But what about those pink bits? What are those?

Turns out those are pebbles and cobbles of granite. Here are a few more:

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These “outsized clasts” that ‘float’ in a deposit of much finer grained sediment qualify this rock as a diamictite.

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There’s more than one way to deposit this blend of clast sizes and make a diamictite (landslide, etc.), but the coolest way is for a glacier to melt and dump its sedimentary load as a pile of till. Later lithification sticks that till together into a new rock, a tillite.

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I think it’s fair to say that all tillites are diamictites, but not all diamictites are tillites.

The diamictites in these photographs are interpreted as tillites. They crop out along the eastern shore of the island of Islay in Scotland. The name of the unit is the Port Askaig Tillite.

Here’s the parking area for the ferry terminal at Port Askaig itself:

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The walls of the roadcut are all Port Askaig Tillite, though the exposures are not especially good there.

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The rock walls there are good, though. They are locally sourced!

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In addition to granitic clasts, carbonate clasts (weathering orange/tan) can also be seen:

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The exposures are better further south along the coast.

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Like many of my favorite diamictites, the Port Askaig Tillite is Neoproterozoic in age, and is cited as evidence of a “Snowball Earth” glaciation then.

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The Port Askaig Tillite is associated with a limestone unit (more on that later) that is interpreted by some workers as a “cap carbonate.”

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This was the only “exceptional” example of bedding that I saw — unfortunately, it was in a boulder loosed from its original in situ orientation.

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Many of the outcrops that are just out of reach of the surf look like this – decorated with a dozen varieties of lichen:

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Here are some field-based GigaPans of outcrops of the Port Askaig Tillite that I saw, as well as front and back views of two specimens I collected on Islay:

Link GigaPan by Callan Bentley

Link GigaPan by Callan Bentley

Link GigaPan by Callan Bentley

Link GIGAmacro by Callan Bentley

Link GIGAmacro by Callan Bentley

Link GIGAmacro by Callan Bentley

Link GIGAmacro by Callan Bentley

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28 November 2016

Scenes from the Wildlife Camera

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Here’s a look at some of the wild critters that have been visiting my yard this year:

The video’s organized in alphabetical order, so it starts with bears, and ends with a walking stick insect.
See how many you can identify!

Plus, here’s a compilation of 125 still photos of black bears from June of 2015:

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25 November 2016

Friday fold: intrafolial folds in Eriboll mylonite

Loch Eriboll in the North-West Highlands of Scotland, east of Durness and west of Scrabster, is a beautiful place.

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It’s also a place of immense importance to the development of geologic thinking. It was here that Charles Lapworth first demonstrated the bizarre stratigraphy of the North-West Highlands resulted from tectonic shuffling along faults that were more or less parallel to bedding (“thrust faults”) and these faults were often marked by sheared-out packages of rock he dubbed “mylonite.” Lapworth chose the neologism mylonite because he wanted to describe his proposed mechanism for their strange fine-grained, highly foliated texture. The grain size reduction relative to nearby undeformed versions of the same rock was because the grains were were “milled” out – in other words, crushed up like wheat in a grain mill. A few examples, showing the very well developed foliation overprinted on various flavors of local bedrock:

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Today, mylonite gets applied a bit more broadly, as it’s also used to include rocks that have seen ductile deformation contemporaneous with their grain size reduction. This is often easiest to spot in multi-mineral assemblages, where the different components of the rock have different rheological responses to being sheared out. Some break and get pulverized; others smear out and flow. The combination of these two responses can produce some of the most beautiful textures in structural geology.

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But the dynamic nature of the deformation along one of these bedding-parallel shear zones had another effect: (1) it developed a profoundly well-defined foliation, but then (2) it deformed it. The foliation in some cases was folded over on itself, producing folds with looooooooooooooooooooooooooong limbs, mostly obscured from view as the various components of the fold were transposed along the plane of foliation. In places, though, isolated hinges of these folds remain visible to the watchful structural geologists, like knots in otherwise smooth-grained wood.

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These are called intrafolial folds, folds caught up in the foliation of the larger body of rock.

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Here are two GIGAmacro images of mylonites that bear intrafolial folds. Check them out:

Link GIGAmacro by Callan Bentley

Link GIGAmacro by Callan Bentley

Happy Friday. May your weekend be restful and rejuvenative.

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24 November 2016

U-turn

Scotland was glaciated during the Pleistocene “Ice Ages:”

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The signatures of glaciation are manifold in a scene like this. Most prominent and easily recognizable is the broad, relatively flat-bottomed U-shaped valley.

Now check this one out:

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That’s a U-turn in a U-shaped valley: the valley is first gouged to the right, then turning around and heading in almost the reverse direction:

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Good things these things flow so slow, otherwise that ice may have gotten whiplash.

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23 November 2016

A conversation with Zack Labe

zlabe_photoYesterday, I mentioned climate change visualizer extraordinaire Zack Labe. As delineated then, he’s a PhD student at U.C. – Irvine in the Earth Systems Science department. He’s producing some really excellent #dataviz on climate change.

Today, I’d like to share a short exchange I had with Zack about his work.

1)      Please give Mountain Beltway readers a sense of your background, leading up to what you’re working on now for your PhD.

My interest in the weather stems back as far as I can remember. I studied atmospheric sciences at Cornell University and have always had an interest in understanding broader connections in the large-scale atmosphere for weather prediction. While the Arctic may seem remote to many living in the tropics and mid-latitudes, there are important atmospheric teleconnections between these two regions that can affect our weather and climate. Changes in the Arctic, such as warming surface temperatures and decreasing sea ice, are happening a lot more quickly than other parts of the globe (“Arctic Amplification”). However, our understanding of these relationships remains very uncertain, especially in the presence of climate change.

My PhD work at the University of California, Irvine is using a combination of observations, reanalysis data, and sensitivity modeling experiments to try to better understand the critical relationships between the Arctic and mid-latitudes with a focus on how changes in sea ice and snow cover may respond or drive the large-scale atmospheric circulation.

2)      At what point did you get involved in the preparation of elegant figures relating to climate data? When did you get involved in social media / outreach?

Climate change science communication is not working. While broader public acceptance continues to grow, there remain significant challenges in how to tell this story. I’ve found that a big barrier exists in our science figures. Many times these plots are full of jargon, unclear labels, and/or poor choices of color schemes. I’ve used social media (Twitter) as an outlet for sharing science data and observations that (I hope) bridges the gap between science and non-science backgrounds.

My goals are to both visualize and explain where science data derives, and how do scientists evaluate, criticize, and analyze this information. Science is not meant to be kept hidden away in the halls of academia, but to share and better understand the world around us. Some of the most questions I get revolve around how can people find science data and read more information about it. I’ve found that climate visualizations provide an avenue that helps allow people to become involved with science and critically assess this information.

3)      How is the data you present in your figures gathered?

All of the sea ice and Arctic climate data is publicly available through sources such as NASA, JAXA, and other meteorological/climate centers. I try to provide a data source link in each of the figures and sometimes an associated Python code script for those interested in replicating their own plots. There is immense amount of freely available climate data, but the challenge is often where to find this information. I am encouraged that science will continue to advance and expand the amount of open access data and code available to the public.

4)      Is what’s happening now in the Arctic anomalous? What about the Antarctic? What’s going on?

The persistent atmospheric circulation from a deep low pressure anomaly over the North Pacific and a record ridge over Eurasia allowed warmer air to advect into the Arctic on both the Pacific and Atlantic sides. Warmer sea surface temperatures and more open ocean waters have also contributed to the slow expansion of sea ice this fall, particularly in the Barents and Kara Seas. As a result of this anomalous atmospheric pattern and the continued warming of the Arctic from climate change, temperatures were able to rise well above normal in addition to record low sea ice extent.

5)      Can you address the suggestion made a few days back that “a broken sensor” was a possible explanation?

During the spring of 2016, the instrument on the DMSP-F17 satellite used for sea ice concentration data by the NSIDC began recording erroneous data. The NSIDC made the transition to the DMSP-F18 satellite passive microwave instrument and provided a consistent and continuous record of sea ice concentration. More information/validation between satellites can be found from the NSIDC at http://nsidc.org/the-drift/data-update/sea-ice-index-processing-resumed-with-dmsp-f18-satellite-data/.

Therefore, the current data from both the Northern and Southern Hemisphere is not affected by any sensor issues. Additionally, there are other tools for sea ice data, including the AMSR2 instrument available from JAXA, which confirm the anomalously low sea ice in the Arctic and Antarctic.

6)      Do you have any predictions for what we can expect to see in the weeks to come?

Sea ice is susceptible to large variability as a result of atmospheric and oceanic interactions. However, as we are already seeing, the high temperatures anomalies are beginning to wane over the Arctic basin. As air temperatures and sea surface temperatures continue to cool, it is likely sea ice extent will continue to expand across the marginal seas.

The persistence of these abnormally high air and ocean temperatures have significantly reduced sea ice thickness across much of the Arctic, and this may play a role going forward into the 2017 melt season. Overall despite large interannual variability, we are continuing to see a long-term reduction in sea ice thickness and the fraction of multi-year ice.

I would echo this point – regardless of whether the anomaly we’ve observed over the past few months turns out to be a one-time incident, there is clear evidence that the long-term trend is toward less sea ice, less sea volume, younger sea ice, and less glacial ice. That trend will stand independent of whether this is a unique incident. We should be concerned at the changes we are observing in this aspect of the cryosphere.

I’m grateful to Zack for taking the time to share his insights here. Do you have any other questions you’d like to pose to Zack? If so, drop them into the comments thread.

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22 November 2016

We are in unprecedented territory with global sea ice

The amount of our planet’s ocean area covered by ice is at an unprecedented low for this time of year. It is the Arctic winter, the long night when no sun shines on that northerly ocean, and yet temperatures there are averaging 10°C above normal. My attention was called to this issue last week thanks to the Twitter feed of Zack Labe, a PhD student in Earth Systems Science at the University of California – Irvine. He makes great graphics showing the latest data on polar climate. Here’s his latest temperature map for the Arctic, for instance:

labeClick for source

Water there is accordingly failing to freeze. Meanwhile, down south, the Antarctic summer is getting cranked up, and that sea ice is melting. When these two polar situations are summed, we see that there is less sea ice on Earth for this time of year than we have ever seen since we started keeping track of it. This graph, not by Zack by by Wipneus (click for source), shows the current situation in the context of the entire record:

nsidc_global_extent_byyear_bClick for source

Zack Labe breaks out each pole independently, if you’d like to see that:

This deviation from the trend of previous years is utterly anomalous. Will it turn out to be a unique diversion that we’ll end up chalking up to the mere vicissitudes of “weather?” Or is this what a tipping point looks like when it is finally reached?

Time will tell.

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21 November 2016

GIGAmacro sample preparation: 3 techniques

Here are three pairs of GIGAmacro images to illustrate a few techniques I’ve used in preparing the samples and the images. The image pairs here illustrate the effects of transparent acrylic coatings, pressure-washing, and post-imaging clean-up in Photoshop.

Let’s begin with a meta-ignimbrite of the Catoctin Formation, cut with a rock saw and polished using a handheld grinding wheel with diamond grit pads, and then with one of the two sides, the second one in this set, sprayed with a layer of clear acrylic “paint.”
Link GIGAmacro by Callan Bentley

Link GIGAmacro by Callan Bentley

Here’s a mylonite, before and after being pressure-washed:
Link GIGAmacro by Callan Bentley

Link GIGAmacro by Callan Bentley

Here’s a pair to show the effects of digital clean-up in Photoshop after the image has been stitched together. Both show a set of three fossils (Khufus, Turitella, and Dentalium) from the Sunken Meadow Member of the Yorktown Formation in Virginia’s Coastal Plain. In the first, a layer called the “alpha channel” exists, automatically generated by the image stitching software I used, Kolor AutoPano Giga, producing the irregular white mess at the top of the image. In the second, I’ve deleted the alpha channel and also deleted many of the white scraps of shell debris lying on the black velvet backdrop.
Link GIGAmacro by Callan Bentley

Link GIGAmacro by Callan Bentley

I’d be happy to answer any questions you might have about any of these techniques. I’d also be eager to read your feedback on the merits of the different ‘treatments.’

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