A Swim Through the Ocean's Future.

Hat tip to the Volcanism Blog for alerting me to this.

Labels: ocean acidfication, volcano

Perusing the USGS page on yesterday's magnitude ~8 earthquake in Samoa, I found a new feature that I had not previously seen on these earthquake data pages: a cross-section! Check it:

The star gives the location of yesterday's temblor some regional context. This is a super-cool visualization of a subduction zone (in this case, the Pacific Plate subducting beneath the Indo-Australian Plate). I'll be using this image in my upcoming "earthquakes" lecture in Physical Geology. What a beautiful way of visualizing the plunge of a slab of oceanic lithosphere!

Labels: art, earthquakes, plate tectonics, websites

There's been a lot of hubbub in the geoblogosphere over the past couple of days about caldera-forming eruptions. The trigger for all the discussion was a report about a really old (Permian) caldera-forming eruption in Italy. This invokes discussion of our modern worry-inducing "supervolcanos," like Yellowstone. There's also a lesser-known place in California, where the USGS maintains a volcano observatory there just like they do with Yellowstone: Long Valley Caldera. This caldera formed ~760,000 years ago, and deposited a lot of ash, collectively called the Bishop Tuff. The Long Valley Caldera's true area is about 300 km², although central sagging has generated ring faults that give it a topographic area of ~350 km². The Bishop Tuff is thickest right around the caldera, but ash from this eruption can be found as far away as Nebraska.

I got to see the Bishop Tuff firsthand the week before last when I spent a week in the Owens Valley as part of a Geological Society of America Field Forum. I was lucky to be introduced to the tuff by Wes Hildreth, a volcanologist at the USGS's Menlo Park office. Wes "wrote the book" on the Bishop Tuff, and shared an immense amount of information and perspective with the Field Forum participants. I am indebted to him for all the information I'm sharing here. Maggie Mangan just took over the reins of the Long Valley Observatory, and she also participated in the Field Forum. I also really benefitted from talking to her about the eruption. (Any errors that you may find here, of course, are my own.)

The Bishop Tuff is the most striking of many volcanic eruptions along this same system. It's the only one that has produced a caldera. It was preceded by dacite and basalt eruptions at 3.5 to 2.5 Ma, and then by rhyolite and obsidian during the appropriately-named Glass Mountain Interval, from 2.1 to 0.8 Ma. (The Glass Mountain Interval is pretty cool in its own right: at least 60 eruptive units, each high-silica rhyolite!) The focus of both of these was further to the northeast. That area is also home to some post-Bishop eruptions, the youngest of which is at Mono Lake (only 250 years ago). In 1989, a dike came within a few km of the surface, and degassed a CO₂ "burp" which killed trees near Mammoth Mountain, which lies on the caldera boundary.

The Bishop Tuff is compositionally similar from bottom to top: it's all rhyolitic pyroclastics, whether it's welded (fused together) or not. Some went north from Long Valley Caldera under the Mono Lake area, while the bulk of it went south towards Bishop, forming the Volcanic Tableland. it has a density of about 1.5 g/cm³.

In this photo, Kim Bishop (yes, that's really his last name) and Peter Lovely (yes, that's really his last name) check out the first of the ashfall deposits, dumped atop lake sediments in a cool outcrop on the southern margin of the Volcanic Tableland, north of Bishop and the Owens River:


A close-up of this contact:

The ashfall portion of the Bishop Tuff has 9 subunits, and you can see the first (F1) and the base of the second (F2) here, overlying the silty lake sediments.

Here's another outcrop, in the Owens River Gorge, where you can see the welded ashflow "caprock" up top, and down below, and outcrop that showcases nonwelded ashfall and ashflow deposits. I've put a box around the area that I'll zoom into in the next photo:


The ashfall deposits are finely stratified and well-sorted, with no reworking. Overlying them, the first of the ashflow (ignimbrite) units shows characteristic poor sorting: big blobs of pumice mixed in with the finer pyroclastics. Most of the ashflow is pinkish in color, but you can see here that the first of it is white, same as the ashfall:

Why pink in the ashflow portion? It's hot when it gets deposited, and heat retention promotes oxidation. The earliest ashflows were dumped atop ashfall (which gets deposited cold), and so likely lost much of its heat downward; hence less oxidation. The entire eruptive seqence is preserved in the Volcanic Tableland north of Bishop. Here, at the southern rim of the Tableland, we're getting the latest flows. The earlier flows didn't make it this far south.

Here's a close-up of that basal ashflow, from the first outcrop. My field notebook is 18 cm "tall," for scale. Note the white color and all the large pumice clasts:

The iron to titanium ratio in these clasts suggests that they erupted at 770 to 800 degrees C. The temperature of the eruption increased as it progressed. This corresponds with an increase in the mafic content of the tephra over the course of the eruption. In the early layers, there's about 77.7% silica, but when you get towards the end of the eruption, you see that number drop to 74%, as well as a doubling of iron content, a quadrupling of the Ca content, and ten times as much magnesium as in the earliest strata.

Here's a close-up of some semi-welded material. This is float, so I don't know precisely where in the sequence it fits, but I would guess the "Ig1" layer, the lower of the two welded ashflows.


And another. One thing I noticed about a lot of the included pumice blobs is that their vesicles were all stretched out into cigar-shaped tubes (prolate), like an L-tectonite. Anyone have any idea what's up with that? I would expect oblate strain ellipsoids (pancake-shapes) here due to post-depositional compaction, but that's not what I noticed...


We made a trip to the lip of the Owens Gorge to look down on the upper ignimbrite (ashflow tuff) layers of the Bishop Tuff:


The first half of the eruptive sequence, dubbed "Ig1" (for "ignimbrite 1") is below the sharp line. In the upper half of the sequence, Ig2, you'll find rhyolite lithics that can be sourced to the earlier Glass Mountain Interval, as well as pyroxene-bearing pumice. You can see here some abortive cooling columns in Ig1:

Likely these don't extend very far down because as soon as they started forming, Ig1 was buried underneath piping hot Ig2 ashflow. This addition of heat disrupted the cooling front and truncated the fracturing process. Sorry I don't have a sense of scale in this photo: it's hard to do when you're photographing the opposite side of a deep gorge. I'd guess these columns are a meter or so across. In one spot, a little downstream (southeast) of here, you can actually see a little ashfall intercalated with these ashflows (it's the F9 ashfall subunit). This, Wes Hildreth told us, is most unusual and quite handy for interpreting the stratigraphy of the Bishop Tuff. The only other place he's seen such a thing is in the Valley of 10,000 Smokes in Katmai, Alaska.

Some close-ups of the Ig2 unit, which is classic "welded" tuff with nice pumice blobs and rhyolite lithics, as well as pyroxene-bearing pumice:


Rhyolite lithic clast in "Ig2" welded Bishop Tuff ashflow deposit:

That's likely from the earlier Glass Mountain Interval, through which the Bishop Tuff erupted.

The "Ig2" layer wasn't the last part of the Bishop Tuff eruptive sequence, but the stuff deposited on top of it was unwelded, and has since been eroded away. In order for a tuff to weld, it needs to be close to 600 degrees C when it stops (this temperature is for rhyolite: it's actually composition and H₂O dependent). But the welding process (essentially superhot glass fragments warp around one another and lock into place) has made for a resistant layer atop the modern Volcanic Tableland, and this layer preserves the weaker layers beneath, preventing them from being eroded (except, say, where a river incises downward through the caprock). It's a nice example of differential weathering. Cosmogenic ¹⁰Be measurements on the upper welded tuff suggest a modern weathering rate of 2 mm/1000 years.


Now here's the thing that I thought was most interesting about the Bishop Tuff: it's big, and it erupted quickly. There are about 200 km³ of ignimbrite (ashflow tuff), another 100 km³ of fallout (ashfall tuff) out to Utah and Nebraska, as well as 300 to 350 km³ of welded tuff that filled the downdropping caldera (2.5 km of subsidence). That's a lot of magma fluffed out and ejected onto the surface! But Wes calculated that this whole sequence, from the first puff of ash descending from above to the last of the sizzling nuee ardentes, lasted a mere 6 days: a single huge eruption! And, Wes added, "on the seventh day, it rested."

Further reading (I particularly recommend taking a look at Figure 5d!):
Hildreth, Wes, and Wilson, Colin, 2007. Compositional Zoning of the Bishop Tuff. Journal of Petrology 48 (5):951-999.

Labels: california, permian, pleistocene, volcano

Awesome: right-handed Anomalocarids!
Elizabeth Kolbert on getting things moving re: climate policy.
The volcanological blogs are all agog over tephra and teeth.
Lockwood tears into sloppy "press release" style "journalism."

Labels: blogs, climate change, evolution, politics, science and society

WHAT: Earth Science in the Spotlight: Engaging the Public

WHEN: Tuesday, Oct. 6, 5:30-8:00 PM; program begins at 6:15 PM.

WHERE: The Front Page Restaurant, 4201 Wilson Blvd., Arlington, VA, Located near Ballston Metro on the ground floor of the NSF building. Parking is available under the NSF building or at Ballston Common Mall.

WHO: Ann E. Benbow, Ph.D., Director of Education, Outreach and Development, American Geological Institute

HOW: Special 1/2 price burgers start at 5:30 PM. Please come early to order table service and socialize. Short presentation begins at 6:15 PM, followed by Q&A. No science background required- only an interest! Cafe Scientifique is free and open to the public. Register online here.

ABOUT THE TOPIC: The news media routinely sound alarms about natural disasters, climate change, and the energy crisis. But who helps the public make sense of these issues? More and more, scientists are stepping up to help ordinary people, from school children to policy makers, understand the earth science behind the headlines. Earth science, after all, encompasses virtually all the sciences, from biology to chemistry to physics. Learn how AGI, an association of 45 member societies across the geosciences, is tapping the expertise of professional geologists, oceanographers, meteorologists, and other scientists to improve education and promote public awareness on such timely topics. Join us for a brief discussion, exciting video and hands-on activities showing how you can play a vital part.

COMING NEXT MONTH: November 3, Mario J. Molina, Ph.D., Nobel Laureate in Chemistry 1995 will speak on ozone depletion in the atmosphere.

Labels: meetings, science and society, teaching

Somehow, I've gotten a lot of reading done over the past six months. A lot of this reading consisted of books on climate change -- more on that in another post. But I wanted to share my thoughts on a few other books:

Sand - Michael Welland [blog]

Awesome. The perfect little book for those interested in geology. Looking at the world through a grain of sand. Very diverse, chock full of fascinating stuff that appeals to the intellect on many levels. Smart, erudite, funny. Recommended.

Stories In Stone - David Williams [blog]

A good read; like reading a compliation of feature stories in EARTH magazine; however, unlike Sand, no single unifying theme ties them all together. The overall idea is that the rocks we make our buildings out of have interesting backstories. The book is organized into a dozen or so chapters, each about a different building stone. Some are common (Indiana limestone), some are rare (petrified wood). All have got interesting stuff going on in terms of their geological history, human tie-ins, and architectural tweaks. If you live or work in a building, it's worth reading.

Your Inner Fish - Neil Shubin

Superb. Learned a ton about evolution's lingering fingerprints on our bodily blueprint. Did you know that the nerve which controls our larynx runs from the brain to the larynx via the heart? This unintelligent design is a vestige of the way our body develops from an embryo -- and can be traced directly to fish. There wasn't as much about Tiktaalik in here as I expected, but just enough to make the point.

Bones, Rocks, and Stars - Chris Turney [blog]

Really interesting, though the chapter on King Arthur didn't do much for me. But the rest of it is a great introduction to the various ways we figure out how old things are (Subtitle: "The Science of When Things Happened"). Great chapters on the orbital forcing of ice ages, carbon dating of Homo florensis (which Turney did), and Pleistocene megafauna extinctions. Recommended.

Glacial Lake Missoula - David Alt

Not so great as a book. Really more of a field guide, but not even all that great on that level. It essentially traces the geologic evidence of GLM "and its humongous floods" from Missoula north, west, south, and west again -- the path of the big Channeled Scablands-forming megafloods. A good resource for specific outcrops that illustrate parts of our understanding of this huge event, but not especially enjoyable to read.

Bretz's Flood - John Soennichsen

Much better -- a lovely biography of J. Harlan Bretz, the geologist from the University of Chicago who first documented the Channeled Scablands and deduced that they must have been carved by an enormous flood. A perfect little portrait of an academic's career. Bretz appears to have been quite a character! I really enjoyed the perspective this gave me on the whole "megaflood" idea.

Labels: books, evolution, floods, geologic time, sediment

I went to the College of William and Mary for my undergraduate geology degree. One of the cherished rights of passage in that department was the "Geology 310" trip -- Regional Field Geology, often of the Colorado Plateau, but in recent years, the faculty have been running field courses to other locations. The program was written up in this fall's issue of the William and Mary Alumni Magazine. Check it out!

Labels: geology, teaching

Kim already gave GSA a shout-out about this, but in the unlikely event any Portland-meeting-attending geobloggers see this first, go register your blog at their "dynamic blogroll."

Labels: meetings, oregon

I spent last week in the Owens Valley of California, attending a GSA field forum on the structure and neotectonics of the Owens Valley and the Volcanic Tableland north of Bishop. It was really cool, and I learned a lot. I'll be sharing images and ideas on the blog in days and weeks to come.

Twenty-four people attended, plus the three conveners: David Ferrill, Alan Morris, and Nancye Dawers. Here's the team getting an orientation on Monday morning, looking west towards the Sierra Nevada. Note the time-honored geology field tradition of using magnets to hold posters and maps to the side of the van:


David discusses the tectonics and geomorphology of the "Eastern California Shear Zone," a transtensional zone between the Sierra Nevada and the typical Basin & Range. This area ranges tremendously in elevation: from Mount Whitney in the Sierras (14,494' elevation) to Badwater in Death Valley (-282'). The lurid colors on this elevation map show that:


A Landsat photo comes out at the next stop, looking northeast towards the Volcanic Tableland:


And yet another image, this one a beautiful side-scanning radar image of the Volcanic Tableland, which David and Alan (here assisted by Wes Hildreth) pulled out at a stop overlooking the Owens River Gorge (a canyon which dissects the Volcanic Tableland):


This image shows east-dipping normal faults as white stripes, and west-dipping normal faults as dark stripes:


This is the main reason we're all here: the young welded ashflow deposits of the Bishop Tuff (760 ka) record brittle strain as a result of the past 760,000 years of extensional and strike-slip tectonics. Due to the low rainfall and this excellent marker unit, you can really get a sense of how such systems operate. The faults are expressed topographically: a lovely marriage of structure and geomorphology.

Our first overview of the Volcanic Tableland, looking northeast from the Sierra Nevada over the fractured Bishop Tuff, towards the White Mountains in the distance:


Here's a Google Map of the Volcanic Tableland, showing the orange upper ignimbrite layer of the Bishop Tuff, and the north-south trending faults which rupture it. Green stripes are the Round Valley (southwest), Owens River (southern border, trending east-west), and Fish Slough (far east, trending north-south):


Here's another Google Marp, zooming in on some of the faults. Conveniently, Google opted for morning sunlight in this image, so it's "color-coded" the same way as the side-scanning radar image I showed you earlier: east-dipping fault scarps are light-colored, while west-dipping fault scarps are in shadow:

(Another very cool thing about this image is the northwest-southeast trending Pleistocene drainage channel -- more on that later!)

Many of the faults in the Volcanic Tableland are arranged in en echelon arrays, reflecting a broader zone of deformation:


In en echelon arrays of these normal faults, we find the individual fault segments are linked up with intermediary flexures of the the ignimbrite layer, called "relay ramps." This was a new term to me, but once I learned it, I saw them everywhere. Here's one atop the Volcanic Tableland:

(It's the shallowly-sloped bit in the middle, dipping towards us, bounded by two west-dipping fault scarps: the intensely-shadowed areas.)

Here, in Fish Slough, we see a couple of 'relict' relay ramps that have gotten cut off as the small fault segments linked up into a larger through-going fault. Pretty cool!


The group descends a relay ramp on their way back from a field excursion to the vehicles:


Annotated version of the photo above:


Relay ramps occur on many scales. This 'scaling' of fault systems (and deformation in general) was a theme at the field forum. Here's a Google Terrain Map of the Owens Valley area. Notice how, just west of Bishop, the Sierra Nevada front jumps to the west? That's a much larger relay ramp, the Coyote Warp Relay Ramp:


Looking west from the first stop at the Sierras, with the Coyote Warp Relay Ramp descending from upper left towards lower right:


Annotated version of the photo above:

That's a little taste to get you started. More geology from the Owens Valley in future posts...

Labels: california, faults, structure, volcano

My colleagues in NOVA's biology department were featured in today's Washington Post, which includes some photos of my building (the Shuler Building) and one of our labs. The point of the article is that community colleges in the DC area are adding classes like crazy to keep up with demand. The weak economy is blamed for the uptick in enrollment. Our student population increased by about 10% this semester. NOVA's numbers tower over other area schools:

Hat tip to Doug Dupin for alerting me to this piece!

Labels: nova, teaching

This is a new, useful tool: an online map that can guide you to rough information about local geology, and then to detailed geologic maps. The National Geologic Map Database appears to be a joint project between the USGS and the Association of American State Geologists. Here's what it looks like when you go to the website:




You can then close the little "About" information tab in the lower right:



Next, grab the screen and scroll to an area that you're interested in:



Double-click or use the "zoom" lever at upper left to zoom in:



Open the "Map Unit Info" tab to select individual map units and learn more about them:



After you do that, clicking anywhere in the map will bring up information about the rock units generally found in that area:



If you need more information, hover over the rock unit name in the "Map Unit Info" tab:



Close the "Map Unit Info" tab and open the "Map List" tab to get a list of all the USGS geologic maps available in your field of view:



Click on one of them to open up a red "footprint" on the map showing the area it covers:



An additional window will pop up with information about the map. Click on the number "2" in this new window to open the map itself:



It opens in a new tab, and is initially quite zoomed-out:



But you can zoom in, of course:



In fact, you can zoom in really far, until you start seeing pixels:



There are some design flaws in the interface, but overall, I think I'm willing to overlook them so I can get access to this sort of information. It strikes me as very, very useful: a rich dataset, waiting to be mined.

Labels: geology, maps, websites

Yet five more of the maps I scanned from my recently-entered-the-public-domain copy of Vernon Quinn's book A Picture Map Geography of the United States. As before, clicking on the image will take you to a bigger version of the map. Enjoy!

Labels: art, books, connecticut, maps, maryland, new york, oregon, washington

Here we have some nice little glacial striations exposed in the Grinnell Glacier cirque in Glacier National Park, Montana. These grooves were carved by pebbles and other clasts within the glacial ice as it flowed over this outcrop of the Mesoproterozoic Helena Formation (part of the Belt Supergroup). Perhaps some of the same pebbles you see in this photo were responsible for acting as carving tools -- though the 'hand' that wielded them, Grinnell Glacier itself, melted away from this point sometime since 1939.

Also of interest to me in this photo is the lingering stain of water around the joint set in the upper right. I'm fascinated at the interplay between physical and chemical weathering, and seeing stuff like this emphasizes how even a simple hairline fracture can help funnel water, with all its destructive effects, deeper into the heart of an outcrop. Weathering is focused on these areas, and in another century this outcrop may look quite different.

Labels: glacial landforms, glaciation, joints, montana, national parks, pleistocene, proterozoic, sediment, snow, weathering

If you haven't seen this yet, please watch it. Nice work, Mr. Balog!

Labels: art, climate change, glaciation, global warming, ice, meetings

George Mason Univerity invites you to attend the first lecture of this season's Vision Series on Monday, September 21, 7:00 PM, in the Center for the Arts. Jagadish Shukla, Distinguished Professor of Atmospheric Oceanic and Earth Sciences, will present "Global Warming: Science, Adaptation and Mitigation". A reception with light refreshments will follow the lecture. The Vision Series lectures are free and open to the public. Tickets are available online, or at the CFA ticket office, or the evening of the presentation. For more information and to reserve tickets, click here.

Labels: climate change, global warming, virginia

As an analogy for how most minerals never get to attain their full habit (hemmed in by surrounding space constraints), perhaps even better than the boxy watermelons I mentioned last December are Buddha-shaped pears!

Labels: analogies, humor, minerals

Five more of the maps I scanned from my recently-entered-the-public-domain copy of Vernon Quinn's book A Picture Map Geography of the United States. As before, clicking on the image will take you to a bigger version of the map. Enjoy!

Labels: art, books, california, georgia, idaho, maps, utah, west virginia

On our hike to Grinnell Glacier this past July in Glacier National Park, I found lots of cool cobbles of float, mainly of the Mesoproterozoic metasedimentary rocks that make up the bulk of the park: the Belt Supergroup. One of these formations, the Helena Formation, is intruded by a diorite sill known as the Purcell Sill. It's a prominent rock unit showing up as a black stripe within the lighter-colored Helena Formation, exposed high on the glaciated walls throughout the park. Occasionally, you'll find pieces of it as float, and I noticed that the higher we climbed up, the more of it we saw. Here's one of my favorites among these pieces of the Purcell Sill:


This cobble shows beautiful slickenlines, small gouges into the rock as neighboring rock ground across its surface, along a fault. These physical gouges are decorated with a chemical accoutrement: the metamorphic* mineral epidote, which is a gorgeous grassy green.

Labels: faults, igneous, metamorphism, minerals, montana, national parks, proterozoic, structure

Labels: art, books, colorado, indiana, louisiana, maps, michigan, new mexico

Took all these images of joint surfaces this summer in Glacier National Park on my Rockies trip. Enjoy!

Appekunny Formation, with two concentric ribs:


Grinnell Formation, showing well-developed hackle fringe (rough area at bottom):


In the lovely fine-grained limestones of the Helena Formation:

Labels: montana, national parks, proterozoic, structure, weathering

Labels: arizona, art, books, delaware, maine, maps, new jersey, pennsylvania

Following on from Sunday's post showcasing new outcrops seen recently along the Billy Goat Trail, here's a cool ptygmatically-folded quartz vein I saw:



Can't quite make it out? The boulder's kind of weathered, so let me highlight it for you:


...and a close-up of the left side, which is better exposed:


That's all I noticed that was new this time around... but next time I'm sure there will be something else. The Billy Goat Trail is the gift that keeps on giving...

Labels: maryland, metamorphism, piedmont, structure

My colleague Ken Rasmussen and I were among ten faculty featured in a video that NOVA-Annandale Provost Barbara Saperstone commissioned to brag to the NOVA Board about all the cool stuff going on at her campus. If you're interested in watching the video (~17 minutes), it can be downloaded here. If you're only interested in the geology portion, fast-forward to 14:57 or so. (They saved the best for last.) Enjoy!

Labels: field trips, movies, nova, teaching

Went for a hike on the good old Billy Goat Trail last Sunday and saw this beautiful outcrop. I love it how every time I walk that trail, I see something new and blog-worthy. Here you see the metagraywacke of the Mather Gorge Formation getting squished and squeezed under conditions of partial melting. Granitic magma (light-colored rock) is leaking out, while the foliated mafic residue (schist chips) are getting strung out and boudinaged under conditions of mountain-building. This granite yeilds late Ordovician isotopic ages (Taconian Orogeny, ~460 Ma).

Seeing an outcrop like this reminds me of making cheese: squeezing the liquid whey (felsic magma) out from the solid curds (higher-melting-temperature solid minerals like those comprising the 'schist chip' boudins). As orogenic forces squeeze from the sides, granite oozes out the top.

I love that there are outcrops where this process is caught in freeze-frame: not all the granite escaped from its migmatitic source rock here; instead the process stopped before it was complete, and through the luck of uplift and exposure by the probing erosion of the Potomac, we get a glimpse of a fundamental process in making the Earth look the way it does. A single outcrop shows rocks that were oceanic sediments, then became metamorphic schist, and now are were transitioning to igneous granite! That's pretty wild. We have caught the rock cycle red-handed.

Labels: analogies, granite, igneous, maryland, metamorphism, piedmont, primary structures

First one to identify this animal* (photographed with my new microscope) wins a GEOLOGY ROCKS bumper sticker... Width of photo is about 2 cm.


* Note, not the entire animal is shown.

Labels: contest, fossils

The first of our monthly science seminar series is coming up at the end of the month:

"Cameras we cannot picture"
Dr. Ravi Athale, Senior Principal Scientist, The MITRE Corporation
Monday, September 28, 2009, Ernst Center Forum, 12 noon - 1pm

Abstract: The world of imaging has evolved from its humble origins as a pinhole camera to its current incarnations of very large (Hubble Space Telescope) and very small (pill cameras that one swallows). Last 10 years, in particular, has seen more rapid growth in our ability to record static and moving images than anytime in human history. This has been enabled by replacing film with semiconductor devices for recording imagers. Dr. Athale argues that as dramatic as this progress has been, the future will bring even more startling and unimaginable changes due to the integration of imaging with equally spectacular progress in computing, communications and storage technologies.

Ravi Athale is Senior Principal Scientist and Department Head, Emerging Technology office at the MITRE Corporation. Over past 30 years he has worked as a scientist, educator and manager in government, academic and industrial institutions. In 2007, he received Leadership Award of the Optical Society of America and Secretary of Defense Medal for Exceptional Public Service. In addition, he is a co-author of a high school engineering textbook published by Prentice-Hall and is a co-founder of company that develops consumer products based on computer generated holograms.

Please join us, if you can!

Labels: art, meetings, nova, science and society, tech

(Parts 1, 2, 3, 4, 5, & 6 of this series...)

Today's episode: The route down the mountain, and the long way back to camp.

After our "summit" of the arete between Hanging Canyon and Cascade Canyon, we begin carefully picking our way back downhill, switching between talus piles and snowfields, and back again:




We popped over the threshold, and started dropping down towards Jackson Hole. As the sun was dropping lower and lower in the sky to the west, we were pretty much in shadow from here on down... but the light still lingered on the highest peaks, like Teewinot Mountain, Mount Owen, and the Grand Teton itself:


By the time we got all the way back down to Jenny Lake, the sun was pretty much gone. However, it was illuminating a tall cloud north of us, sitting atop the Yellowstone area. We joked that this was the big one: Yellowstone had finally blown up and the orange color we were seeing wasn't "alpenglow" but incandescence from the long-awaited eruption of the Yellowstone volcanic center...


It wasn't, though. Just a little jest to take our minds off the fact that we had missed the last ferry across Jenny Lake, and so that meant adding an additional "2" (it sure felt more like 3) miles to our hike. As darkness closed in, we hoofed it along (only Pete had been prepared enough to bring a headlamp). For me, a highlight of this long slog came when Joel and I spotted an animal I'd heard of but never actually seen before: a pika! They are very, very cute animals that live in talus piles and make little squeaky noises. But they're quite elusive, at least in my experience. I've seen plenty of marmots and other alpine rodents, but this was my first Ewok pika.

We eventually got back to the vehicle and rolled back to camp, getting there about 10pm. We wolfed down some dinner, quenched our thirst, and sacked out. What a great day! In spite of being dog tired, I felt mentally rejuvenated and ready to take on the second half of the Rockies trip.

This post concludes the Hanging Canyon series. Thanks for coming along!

Labels: mammals, nova, travel, volcano, wyoming, yellowstone

(Parts 1, 2, 3, 4, & 5 of this series...)

As we were climbing up a steep snowfield, we saw something that made us rush up to the top:


Interpretive sketch:

At first, we thought this was a big isoclinal synform that was cross-cut by a ptygmatically*-folded granite dike, but closer inspection at the "axis" of the "fold" revealed that it was instead just the trailing edge of a big boudin. It pinched down and then swelled again in the downward direction, hidden in this photo by the snowpack. Not quite as cool... but still pretty cool. And I can never say no to ptygmatic* folding, regardless of the setting.

This is also kind of cool:

What you're looking at here is a gneiss, with alternating layers of coarse-grained mafic and felsic minerals. The view of the photo is orthogonal to the plane of foliation, but the boulder has been weathered so that in some places the uppermost mafic layers has been worn away. There's one spot where you can "see through" the mafic layer into the underlying felsic layer (upper right) and another spot where there's a little isolated scrap of the mafic layer where the surrounding material has been weathered away. This reminded me of a larger-scale phenomenon where the same thing happens to thrust sheets: an erosional hole through a thrust sheet into the rock beneath is a tectonic "window" or "fenster" (German for window). An erosional remnant of a thrust sheet is a "klippe." The Grandfather Mountain Window in North Carolina is an example of a fenster. Chief Mountain in Glacier National Park, Montana, is an example of a klippe. So this little boulder gives us a nice physical analogue for regional-scale tectonic/erosional features.

Ahh... what cool stuff to see and think about. But the sun was setting, and we had to head back to camp and the rest of our team... Tomorrow: the story of the long hike home.

________________________________
* Really, more of a "cuspate-lobate" fold, without the parallel limbs that make for a truely ptygmatic fold.

Labels: analogies, art, montana, national parks, north carolina, nova, structure, travel, wyoming

The September meeting of the Potomac Geophysical Society will be held September 17th at the Fort Myer Officers' Club in Arlington, VA in the Campaign Room. This month's talk will be: North Korean Nuclear Test of May 25 2009: Similarities and Differences With Respect to the Initial October 9, 2006 Test, by Jack Murphy (SAIC, McLean, VA).

Abstract:
On May 25, 2009 North Korea announced that it had conducted its second nuclear weapons test. As with the first test, this second explosion was well-detected by the seismic stations of the International Monitoring System (IMS), as well as numerous other international stations operated by the USGS and other organizations. The best relative seismic location for this explosion places it within 2 km of the ground truth location of the initial 2006 test in a mountainous region of northeastern North Korea. Comparisons of the seismic data recorded at common stations from these two tests indicate that the second was approximately four times larger than the first, having an estimated yield in the range from about 2 to 5 kt. While there are many similarities in the observations from the two tests, there are several notable differences. Perhaps the most surprising of these is that there were no reported detections from any of the IMS radionuclide stations. The report of a noble gas (Xe¹³³) detection in Canada tentatively associated with the October 2006 test had led to some optimism that the more complete network of stations operating in 2009 might provide powerful detection capability with respect to clandestine underground nuclear tests. While analyses are continuing, the absence of detections from the May 2009 test has tempered that optimism to some extent. Another unusual aspect of the May 2009 test was the observation of anomalously large long-period surface waves. While the surface waves from the October 2006 were also somewhat larger than expected, the surface wave Ms magnitude value for the May 2009 test places it in the earthquake population on the Ms:Mb discriminant plot, and there has been no convincing explanation offered for this to date. Thus, despite the many years of experience with nuclear test monitoring, there continue to be unanticipated surprises that require in-depth analyses and assessments.

Reception at 6:30. Dinner at 7:30. Talk at 8:30 PM. Allow 15 minutes for security entering Ft. Myer as all civilian vehicles are searched. To ensure access to and from Fort Myer use the Hatfield Gate, open 24 hours a day. If you wish to attend dinner ($25), please make reservations with Joydeep Bhattacharyya at 703-676-4373 or via e-mail. If you wish, please feel free to attend the talk without dinner. Non-members and guests are welcome. Visit the PGS web site at for new meeting announcements, etc.

Labels: earthquakes, korea, meetings, pgs

(Parts 1, 2, 3 & 4 of this series...)

Today we'll look at some of the structural geology photos I took in Hanging Canyon, Teton National Park, Wyoming. These are all rocks of the Archean-aged Wyoming Terrane (or "Wyoming Craton"), one of the most ancient pieces of crust that make up the quilt-like North American continent. They include both metamorphic and igneous rocks that have been suffered enjoyed being deformed by tectonic processes.

Labels: archean, igneous, metamorphism, national parks, nova, structure, travel, wyoming

Parts 1, 2, & 3 of this series are at these links.

Today and tomorrow, I'll share some of the gorgeous Archean rocks that are exposed in Hanging Canyon, Grand Teton National Park, Wyoming. Today: the igneous stuff. Tomorrow: the structural stuff.

There were many pegmatite dikes that we saw along the hike. Here's a lovely one cutting across the metamorphic host rock:


A close up of some big muscovite "books" in the pegmatite:


A couple of parallel pegmatite dikes cutting across granite:


Here's the largest single feldspar crystal I've ever seen in the wild. The crystal starts to the left of my boot and continues for over a foot to the left of that. Its color varies between bluish gray and whitish. Where the left-most and most prominent blue stripe is, that's the edge of this monster megacryst:


Huh... Only four "igneous" photos... I guess I'll make up for that with tomorrow's structural geology post about Hanging Canyon... I have about forty photos of folds and boudins and what-not to share...

Labels: archean, granite, igneous, minerals, national parks, nova, structure, travel, wyoming

Part 1 and Part 2 of this series described the journey up from Jenny Lake to Hanging Canyon. Today, we pop up over the threshold of this hanging valley and see what we can see...



As it turns out, there's some snow up there:


We manage a few clumsy glissades:


And what's going on with this hole?


Aha! A dark rock with low albedo absorbs energy from the sun, releasing it as heat and melting the surrounding snow. Cool!


Times like this, I just love my job:


Ken shows off some glacial striations on the bedrock:


Pointing in the direction of glacial flow:


We then opt to climb up even higher, to peer down into the neighboring valley, the much larger Cascade Canyon...



Steep climb, with tarn in the background; Joel appears to be enjoying himself:


Here's a Google Maps "terrain" view of the area, showing the relative locations of Jenny Lake, Cascade Canyon, and Hanging Canyon.


Wow... Once we got up over that last little knife-edge crest, we had a pretty amazing view.


And what did we see along the way? More on that in tomorrow's post (Hint: pegmatites and old folds)...

Labels: glacial landforms, glaciation, national parks, snow, travel, wyoming

Today, picking up where we left off yesterday, some images from the hike upwards from Jenny Lake to Hanging Canyon...

Joel and Ken take a breather:


The approach to the final lip of Hanging Canyon:


A view down over Jenny Lake and Jackson Hole:

Jenny Lake is dammed by an end moraine (which is characterized by pine trees growing on it here, making for a nice dark stripe around the lake).

We could also see across Jackson Hole to the Gros Ventre valley, where the Gros Ventre lanslide scar was readily visible:


...And lastly, the view to the north, over Jackson Lake (with String Lake in the middle distance):


More tomorrow about what we found once we got up into Hanging Canyon itself... (Hint: it's white and cold and fun to ski on...)

Labels: glacial landforms, mass wasting, national parks, nova, travel, wyoming

One of the highlights of this past summer's Northern Rockies field course was an afternoon set aside as a "choose your own adventure" hike in Teton National Park. Some students opted for Cascade Canyon; others climbed Blacktail Butte. Four of us wanted something really challenging, so we chose Hanging Canyon at the recommendation of my friend Amy Manhart, who lives in Jackson and knows the Tetons like the back of her hand.

We took a ferry across Jenny Lake along with the Cascade Canyon Crew, and then started climbing up. A thunderstorm rolled up Jackson Hole, with much ominous booming and lightning, but we didn't get hit with the storm directly. The climb was very steep, but we entertained ourselves along the way with a geological conundrum: We discussed how best to interpret a hypothetical piece of float that is half granite and half diorite: Is it more parsimonious to guess that the granite represents an intrusion or an inclusion? The implications for the relative dates of the two units are huge: if the diorite is an intrusion, it's younger than the granite. If the diorite is a xenolith (an inclusion) within the granite, then it's older than the granite. Consider the possibilities:



Ultimately, there's no answer to this question without finding an outcrop of the rock in situ, which is why it's entertaining to consider when you're slogging up a 2000 foot hillside. My co-instructor Pete Berquist and I upped the ante by each doggedly defending one of the two indefensible interpretations and sticking to it for the sake of argument. Pete was the xenolith man, whereas I came down fully on the side of the dikes. Our students Joel and Ken were "fortunate" enough to listen to Pete and I bicker about the relative merits of our favored interpretations. Rest breaks came whenever either Pete or I found a boulder along the hillside that showed evidence to support our position. We would stop to consider it, catch our breath, and the resume the uphill climb and the argument. The bad weather passed and the day was beautiful. We were unencumbered by the need to reach a conclusion or acknowledge the obvious: the best interpretation is that such half-&-half clasts "cannot be interpreted."

Here's Pete posing with an obvious dike (I forced him! Ha!):


Here's me posing with an obvious xenolith (Oh well, fair's fair...):


We had a similar ongoing "argument" on the trip about the merits of "Tertiary" versus "Paleogene." I think it keeps students amused to see their professors going back and forth over geologic ideas -- surely if these fellows spend this much energy and thought discussing some geologic question, it must be valid and important... ...right?

More on the Hanging Canyon hike tomorrow...

Labels: archean, geologic time, igneous, national parks, nova, structure, travel, wyoming, xenoliths

Here's two pictures of quartz I took with my new toy, a Nikon camera/microscope/digital-picture-stitcher-togetherer. More to come, clearly. Click on each image to make it bigger.

Conchoidal fractures at the tip of a quartz crystal:

Blue quartz, a distinctive mineral that's found in Virginia's Blue Ridge province:

The blue color is apparently from inclusions of ilmenite and rutile...

Purty, huh? No sense of scale, though. Tough!

Labels: blue ridge, minerals, weathering

PALEONTOLOGICAL SOCIETY OF WASHINGTON

Maryland in the Miocene: Paleoenvironmental History of the Calvert Cliffs
Susan Kidwell, Williams Rainey Harper Professor of Geology
Department of Geophysical Sciences, University of Chicago

Wednesday, Sept. 16, 2009
7:00 p.m., in the Cooper Room, National Museum of Natural History (10th St. and Constitution Ave. in NW Washington, DC)

Meet in the Constitution Avenue lobby at 5:00 p.m. if you wish to join the PSW members for dinner at the "Elephant and Castle," NW corner of 12th & Penna. Ave., NW

Non-Smithsonian visitors will be escorted to the Cooper Room at 6:30 and 6:55 p.m.

Labels: dc, fossils, maryland, meetings, miocene, psw, smithsonian

The fall edition of Walkingtown, DC again features my walking tour of DC geology, "History Before History: the Geologic Saga of Washington, DC." It will be on Sunday, September 20, and is free (but reservations are required; sign up with Cultural Tourism DC, the sponsors of the event). Hope you can join us.

Labels: dc, geology, meetings, piedmont

Last night, I took a group of Honors students to the United States Geological Survey's National Center in Reston, Virginia, for a public lecture by Bruce Molnia about Alaska's disappearing glaciers. The talk was all well & good, but a nice little surprise came afterwards, when Jared noticed a display in the lobby of the Dallas Peck Memorial Auditorium:

That's the classic "ancient Chinese seismograph" featured in so many introductory geology textbooks as the lead-in to their chapters on earthquakes and seismology. Pretty cool to see it in the flesh brass.

The way it works is that each of the little dragon heads projecting off the urn had a little brass ball in its mouth. If it got shaken by an earthquake, that little brass ball would pop out and into the waiting mouth of the little brass frog down below. The frogs aligned with the wave propogation direction would be the ones to be "fed." This implication of the temblor's source direction would allow authorities to direct scouts and relief operations to the appropriate corner of the dynasty.

Neat!

Labels: alaska, earthquakes, gear, glaciation, nova, rept, teaching

We just got a new position approved for our campus Science Learning Center!

Job Title: Science Learning Center Coordinator

Job description: Assist in setting up and coordinating the Science Learning Center. Provide lab help and advising outside of regularly scheduled class and labs. Provide help to science faculty for individual supervised classess, laboratories & undergraduate research. Work with laboratory assistants in reviewing & updating experiments. Organize study sessions and open study hours. Gather needed equipment and supplies; properly store and inventory these materials. Work with the Math, Science, and Engineering faculty, staff, and steering committees.

Degree Requirement: Bachelor’s Degree in Science, or equivalent training and experience. Master’s preferred.

Salary Range: $35,693-$53,345

Apply at our Human Resources page.

Labels: jobs, nova, teaching

First off, I'd like to say a big "Thank you!" to everyone who joined in the basins discussion yesterday after my post comparing depositional basins and structural basins. I haven't had a post generate that level of chewy discussion in a while, and it pleases me to see folks chiming in.

So here's some additional thoughts: yes, structural basins are big synforms wherein the bedding dips in all directions towards the center of the structure. They are the opposite of structural domes. It seemed that this was a sticking point with several readers, who weren't familiar with "structural basin" used in this way. Chris indicated that the term "structural basin" isn't part of structural geology vocabulary in the U.K., and in many ways I agree with him when he says, "calling a structure which was never a site of sediment deposition a 'basin' seems rather silly to me." But that is what our textbooks and lab manuals refer to them as... That's why students get confused, and that was my motivation to draw the graphic delineating the differences. (I didn't invent this term! Ed appears to back me up on this.)

Suvrat called attention to the erosion that I included as part of my structural basin "model," and while that's not necessary for a structural basin to be called a structural basin, I included it to show that there was no basin-like topography necessarily involved. And that word, topography, is likely critical to the discussion. Shame on me for not mentioning it yesterday. (Ed mentioned that's how he distinguishes the two.) Here's the way structural domes and basins are expressed in the second edition of Steve Marshak's textbook Earth: Portrait of a Planet (reproduced here with his permission):


In the uppermost part of the image, you have both topographic and stuctural domes and basins. In the central part of the image, you see erosion-gutted (and differentially eroded) structural domes and basins that are not topographically basinal or domal. Brian asked an excellent question after yesterday's post, which was "where's a good example of a structural basin?" I didn't know of any great ones offhand, so I Googled it, and as it turns out, Wikipedia has a list on their page about "structural basins." (Tragically, the fourth hit on that same search turned up yesterday's blog post! I hate it when that happens.)

And this brings us to the most interesting part of the discussions: Lockwood was the first to say it: "Basins can be both, can't they? i.e., a structural basin can become a locus of deposition." Ah, yes! As my friend John Weidner likes to say about simple geological explanations, "Actually, it's more complicated than that." Are there depositional and structural basins? "Yes...."

"...but actually, it's more complicated than that."

The reality is that many basins are both structural and depositional. I hinted at this yesterday, when I said "[Depositional basins] can also self-perpetuate, as the heavy sediment keeps the crust sagging downward at that location." But I didn't launch into a full-blown discussion then because I was mainly interested in generating crisp thinking in my students: understanding that the term "basin" gets used (at least in our textbooks) to mean two different things, which have similar patterns but independent means of generation. Yes, the reality is that crustal sagging creating a lowspot is itself a structural phenomenon, which then has sediment accumulate atop it, which can encourage through its weight additional sagging, and additional sediment accumulation, and so on. Howard pointed this out in yesterday's comments. The layers at the bottom of such a "hybrid basin" will be structurally deformed at the same time sediment is being deposited at the top of the stack in the resulting topographic low.

So, really, what I outlined yesterday are end-members of a spectrum:


Reality has shades of gray! Yesterday's post was about the "black and white." Today, we discuss the spectrum in between.

How can we tell them apart? The classic test of whether a basin represents a sag in the crust and a hence a paleo-crustal downward flexure is to look at the thickness of the sedimentary layers. If they thin towards the edge and thicken towards the middle, then you've likely got some topographical low, and hence elements of a depositional basin. In contrast, a purely structural downwarp in the strata will not necessarily show any such changes in bedding thickness across the structural basin; so you'll see uniform thickness across (so much as such a thing exists):



Many basins have aspects of both of these -- sometimes they look structural further down and depositional higher up. The lower half of the Marshak illustration above is a map that shows the various basins and domes of the Midwest U.S. (Sometimes the domes are called 'arches' in they're more elliptical in outcrop than circular.) So are these regional-scale basins depositional or structural? Or both? Both, pretty much. These basins do show bedding thickness changes over time, and as I understand it, those times of increasing crustal flexure have been tied to the various episodes of Paleozoic mountain-building on the east coast. The Cincinnati Arch, for example, appears to have developed by the Devonian, since the layers older than the Devonian appear to be uniform in thickness across Ohio, but the Devonian sequence is thinner atop the arch and thickens to the southeast. (I'm no expert on Midwest geology; if someone cares to clarify and/or enlighten, please do!)

Eric made another excellent point: that sometimes we refer to the volume of sedimentary rock that was deposited in a depositional basin as a sedimentary basin. Hence the volume of sedimentary rock comprising the tortured strata of the Valley & Ridge province is sometimes referred to as the Appalachian Basin: not because it's either a depositional or structural basin today, but because it was a depositional basin in the past, before it got folded and faulted. Interestingly, the Marshak map also shows a non-folded, non-faulted Appalachian Basin northwest of the Valley & Ridge province. Hmm. You mean there's one term that geologists apply to two different things?

"No! Say it ain't so!"

Howard asked about the basins of the Basin & Range province. In my parlance, those would be strictly depositional basins -- structurally controlled, yes, but by brittle faults rather than crustal downwarping. They are sites of sedimentary accumulation, but do not show any kind of synformal structure. Thus, they don't qualify as "structural basins." Tricky business! ...Yes, they're basins; yes, they're structurally controlled. But they don't meet the definition for "structural basin."

And lastly, both Eric and Howard noted that there's yet another kind of basin: a drainage basin, a topographical feature through which runoff is collected, essentially synonymous with "watershed." To summarize the difference between a drainage basin and a depositional basin, consider this: a topographical basin which is primarily the site of erosion would be a drainage basin. A topographical basin which is primarily the site of deposition would be a depositional basin. Can a single topographical basin host both erosion and deposition? Definitely! Consider the Mississippi River drainage: eroding in the high country headwaters, depositing in the lowlands nearer the mouth of the river.

Thanks again for all the thoughtful comments, folks.

Labels: appalachian plateaus, appalachians, devonian, sediment, structure, valley and ridge, words

Definitely worth watching for Environmental Geology classes. (from the Times-Picayune)

Hat tip to Lisa for forwarding this to me!

Labels: louisiana, mississippi river, rivers, sediment

One thing I've noticed when teaching Historical Geology at NOVA and GMU over the past four years is that students get confused between basins. There are depositional basins and structural basins, and they're not the same thing, though they both sag downwards in the middle. The other day while driving out to the Blue Ridge for a hike, a lightbulb went off above my head. I knew what I needed was a graphic that explicitly laid out the processes responsible for each structure, and their development over time. I jotted down a reminder to myself on the lid of the Starbucks coffee cup in my car's cup-holder.

When I got home, I translated the scrawled reminder into action. In my spare time over the past couple of days, I've been composing the basin graphic with CorelDraw. Here's what I drew:



Depositional basins result when there's a low spot on the Earth's crust. Water flows into these crustal sags, carrying sediment with it. Gradually, they can fill in. Sedimentary inputs are shown with arrows. (They can also self-perpetuate, as the heavy sediment keeps the crust sagging downward at that location.) Layers stack up according to superposition: oldest on the bottom, youngest on the top.

In contrast, structural basins have a different story. There, we start with an accumulation of sedimentary layers, and then we deform them into a basin shape. This deformation is the result of tectonic stresses which warp the rock layers. Erosion can then attack the downwarped strata, planing the "nested cups" shape down to a roughly horizontal ground surface. Sedimentary outputs are shown with arrows. The resulting outcrop pattern is somewhat like a bull's-eye, with the youngest layers exposed in the middle and the oldest layers exposed on the outer part of the structure.

In a depositional basin, the downward central sag comes first, and the stack of sediment is a result of that sag. In a structural basin, the stack of strata comes first, and the central downwarp is produced second.

________________________________________
If any educators want a larger version of this graphic for use in teaching, let me know. I'll happily e-mail you one. Also, if anyone would suggest any modifications to the graphic to make it more accurate or more useful for communicating these ideas, I'd be happy to get that feedback.

Labels: art, sediment, structure, teaching, words