Labels: art, movies

A new study in Geophysical Research Letters uses C-14 to date the shrinkage of the ice cap on Baffin Island, in Canadian Nunavut. Baffin Island is the fifth largest island in the world, located just west of Greenland.

As the (non-flowing) ice cap withers, it exposes vegetation which has been buried beneath the ice since ancient times. This organic matter can be dated using the relative proportion of isotopes of radioactive carbon-14 and its daughter product, stable nitrogen-14. The oldest date found so far is apparently 350 AD.

The researchers, mostly from the University of Colorado at Boulder, also used measurements of cosmogenic ("made by space") nuclides in the rocks on which the ice cap sat to figure out how long they had been uncovered by the ice. I'm not an expert on cosmogenic nuclide exposure dating, but it works something like a sun tan: how long have the rocks been exposed to the barrage of radiation from the sun? If they've been exposed for a long time, they build up a substantial amount of these "cosmogenic nuclides" that wouldn't be found in an unexposed sample of the same rock. In my local area of mid-Atlantic North America, a study by Paul Bierman, et al. (2004) used cosmogenic berylium-10 to date bedrock terrace levels along Mather Gorge, thereby revealing the incision history of the Potomac River.

However, this is the first time I've heard of carbon-14 used as a cosmogenic nuclide. The authors offer this justification: "In situ cosmogenic radionuclide inventories in rock surfaces provide an integrated record of periods of ice-cover and exposure at a specific site since the end of the last ice age. We utilize in situ cosmogenic 14C due to its short half-life. In situ 14C production is reduced by 85% under 6 m of ice and is completely attenuated under 35 m of ice. Any 14C that had accumulated in rocks prior to the last glaciation would have decayed below our background after 25 ka beneath the Laurentide Ice Sheet." Is this coming from nitrogen in the rocks, the same way carbon-14 is generated in the atmosphere? Or is some other element/isotope serving as the source material which then gets changed upon exposure to the sun? Enlighten me if you know! It builds up specifically in quartz, if that helps at all.

Anyhow, they've found that half the ice cap has melted in the past 50 years. Half. Yep.

References:

Anderson, R. K., G. H. Miller, J. P. Briner, N. A. Lifton, and S. B. DeVogel (2008), A millennial perspective on Arctic warming from 14C in quartz and plants emerging from beneath ice caps, Geophys. Res. Lett., 35, L01502, doi:10.1029/2007GL032057.

Bierman, P., E. Zen, M. Pavich, and L. Reusser (2004). The Incision History of a Passive Margin River, the Potomac near Great Falls. USGS Circular 1264: Geology of the National Capital Region—Field Trip Guidebook, Trip #6.

University of Colorado at Boulder press release on the study.

Labels: canada, global warming, ice

Here's a shot from last week of the almost-full moon hanging over DC's National Cathedral. The view is to the west, which I guess means that I must have taken this picture in the morning, since the moon's face is being illuminated by the Sun. The Sun, of course, rises in the east. And if I can't specifically remember, that probably means I hadn't had my coffee yet, so that definitely makes it a morning shot.

Labels: dc, moon

While prepping for the Climate Change Symposium on Friday, I came across these excellent old quotes about CO2: One is over a hundred years old. The other is over fifty years old. They both remain totally relevant today:

"If the quantity of carbonic acid (CO2) increases (in the atmosphere) in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression."

Labels: CO2, global warming

So this weekend, as part of my ravenous Netflix consumption, I watched Libby, Montana, a documentary which explores the effects of vermiculite mining in the namesake town. The vermiculite in question is augmented with a less desirable mineral: the amphibole known as tremolite. Tremolite grows in a long, fibrous habit, which has been given the name... asbestos. So the deal with Libby is that essentially everyone in town either worked in the vermiculite mine, or was married to someone who worked in the vermiculite mine. A bunch of them inhaled tremolite fibers, both workers and family members. A bunch of them developed lung diseases like asbestosis or mesothelioma. A lot of them died. The movie ends with a moving tribute to the dead. It's some bad stuff. W.R. Grace, the company operating the vermiculite mine, is demonstrably culpable for their employees' deaths.

Tremolite is one of the nastier varieties of asbestos, but not all minerals that happen to grow in that shape are carcinogenic. Some, like chrysotile, (the variety mined at the type locality) have not been found to be as dangerous (by authorities like the USGS). But because many varieties of asbestiform minerals do cause disease, many people (particularly in the litigious U.S.) have opted to ban all minerals of the asbestiform habit. This has resulted in umpteen gazillion public buildings being stripped of their asbestiform minerals, whether or not those particular minerals have been shown to be disease-causing. It's like banning all round candy just because you think that red M&Ms are carcinogenic (which isn't even true). So this brings us to my home institution of Northern Virginia Community College (NOVA). This week, if you were to come visit me in my office in the CF building, here's what you would see (photo).

We're doing asbestos abatement. Amazingly (from a legal standpoint), I'm still allowed to keep working in my office, ten feet away from a what appears to be a major asbestos removal project. The local source is the floor tiles, which look pretty much like linoleum, but are apparently held together with the strong "asbestos" fibers. Which asbestos mineral exactly? Don't know. Probably never will. Last year, they did the same thing in a separate building, the one where my classes are held.

As a P.S., I'll mention that halfway through the day yesterday, I noticed someone put duct tape over the words "Asbestos" and "Cancer and Lung Disease Hazard." No longer that particular danger, apparently...

Labels: minerals, movies, nova

It's funny how one thing leads to another. In promoting our Climate Change Symposium on Friday, I wrote to Cerphe (pronounced "Surf"), probably the best DJ in the world, who's on air in the afternoons on 94.7 The Globe, our DC-area "world-class rock" station that also features a green message. Cerphe wrote back, saying he'd get some mentions on the air this week, and also mentioned that his wife has a small business building green homes. I noticed that the business is headquartered in Bentonville, Virginia, out in the Shenandoah Valley between Massanutten Mountain and the Blue Ridge. And it occurred to me that I've looked at a bentonite layer out there in the Valley (see photo), not too far away from Bentonville. Bentonite is a common clay mineral that in stratigraphic layers is usually interpreted as weathered volcanic ash. (The one pictured above is possibly the "Big Bentonite" that accompanied the onset of the Ordovician Taconian Orogeny in eastern North America.) Could it be that bentonite is named for Bentonville, Virginia? Well, Wikipedia tells me that "The absorbent clay was given the name bentonite by an American geologist sometime after its discovery in about 1890 ...after the Benton Formation in Montana's Rock Creek area." So that took me to the entry on Fort Benton, Montana, which was named for the first 5-term U.S. Senator, Thomas Hart Benton. He was an advocate of westward expansion by the United States, the idea that later was dubbed "Manifest Destiny." So: as near as I can follow, bentonite is a mineral named for a place, which is in turn named for a man. What this has to do with world-class rock and climate change is anybody's guess.

Labels: appalachians, history, montana, volcano

A sizable group of researchers (21; all members of the Stratigraphy Commission of the Geological Society of London) has put forward an idea in this month's issue of GSA Today: they suggest that humans have altered the planet enough that it will show up in the geologic record of the future. They suggest, therefore, that we may have already entered a new geologic epoch defined by human alteration. As a result, they've adopted the name originally suggested by Nobel laureate Paul Crutzen: "the Anthropocene." (Crutzen won in 1995, with two other chemists, for his work on the depletion of the ozone layer in the atmosphere.)

The evidence they offer for this assertion is compelling, but it raises a few questions about how we define these stratigraphic breaks in the geologic record.

Here's the only figure from the paper, a temporal comparison between several lines of data (top to bottom): sea level, average global temperature, atmospheric CO2, terrestrial erosion rates, and human population of the planet.

This is a powerful image. The authors note that climate essentially stabilized in the Holocene, the "long summer" of Brian Fagan's phrasing. In a classic display of scientific understatement, they note that this prolonged period of stable climate "has been a significant factor in the development of human civilization."

How will the rise of humanity be remembered by the geologic record? They note that we've accomplished some major changes to the rate of erosion and sedimentation : "directly, through agriculture and construction, and indirectly, by damming most major rivers, that now exceeds natural sediment production by an order of magnitude." I may be missing something here, but it would seem to me that anthropogenic erosion would produce more sediment due to our land use practices, but that less of that sediment would make it to the sea due to the "sediment trap" effect of dammed reservoirs. I mean, the Colorado River doesn't even make it to the ocean anymore.

Then there's temperature. A quote from the paper: "Temperature is predicted to rise by 1.1 °C to 6.4 °C by the end of this century, leading to global temperatures not encountered since the Tertiary." The high end of that estimate is indeed the sort of temperature change that one would think would leave a profound mark in the geologic record. (I find it interesting to note that a cast of 21 stratigraphers persists in using the outmoded and archaic term "Tertiary," by the way. I guess that's as sure a sign as any the Wernerian Chronology still has some kick left in it.)

I think one of the most compelling arguments made in favor of the Anthropocene is the rapid change in the Earth's biosphere. As the authors of the GSA Today paper point out, we've wiped out the majority of the big terrestrial animals, and concomitant wave of extinctions has rippled through the marine realm. Since changes in fossil biota have been the benchmarks of change in the geologic timescale, it seems certain that our tenure will be marked clearly for future paleontologists to see. Not only are species going extinct, those that survive are migrating to new territories as a result of shifting climate.

I'm pleased that the authors also explored changes to ocean chemistry, which will likely be a major source of information to future geologists. They cite Ken Caldiera and Michael Wickett's 2003 study on ocean acidification (which I blogged about last month) which shows that pH in the world's oceans has already dropped by 0.1 unit, and is predicted to continue acidifying so long as there's excess carbon dioxide to absorb from the atmosphere. Of course, add sea level rise to that (as is predicted via accelerated melting of continental ice sheets), and you've got a distinctive stratigraphic signature.

And I guess that brings me to a point that's been on my mind since I started listing these items. Will these changes persist for a long time, or will they be a small but distinct signature, a la the iridium layer at the K/P (formerly known as the "K/T") boundary? Another way of putting this: are we seeing the beginning of the Anthropocene's modus operandi, or are we seeing the environmental catastrophe which paves the way for a new, different, and (at this time) unpredictable Anthropocene status quo? At this point, we don't know what the Anthropocene will really look like in bulk. While it makes a lot of sense to point out the accelerated rates of change unfolding in so many geological realms, what it all portends for an as-yet-unattained future equilibrium remains to be seen.

I think papers like this are important. It's both broad in scope and displays some excellent thinking outside the box. I'm curious to see what reaction it provokes in the scientific community. Certainly it's getting some press.

* A side note: Does anybody else find GSA Today to be a weird journal? It always has one main article and then a bunch of stuff about meetings, awards, and the like, of interest to members of the GSA. But the articles featured each month are all over the map. Some, like this month's, are potentially ground-breaking works of scholarship. Others, just seem a bit... fringe. Like the one in December about how a team has shared Denver's geologic story with the public. Or the one about a historical critique of Lord Kelvin. Don't get me wrong: both topics are well and good, but if you're putting out only a single article each month that gets mailed to the entire GSA membership, why those? Sometimes I'm just left perplexed and scratching my head.

References:

Caldeira K., Wickett M.E. 2003. Anthropogenic carbon and ocean pH. Nature. v. 425. p 365. doi: 10.1038/425365a
Fagan, Brian. (2004) The Long Summer: How Climate Changed Civilization. Basic Books. ISBN 0465022812
Zalasiewicz J, Williams M, Smith A, Barry TL, Coe AL, et al. (2008) "Are we now living in the Anthropocene?" GSA Today: Vol. 18, No. 2 pp. 4–8. doi: 10.1130/GSAT01802A.1

Labels: CO2, environmental, global warming, stratigraphy

In today's issue of the Washington Post, an article by David Fahrenthold reviews the mixed bag of results that the House of Representatives has achieved in making their half of Capitol Hill carbon neutral. In November, they spent about $89,000 to offset their unavoidable carbon emissions by paying for agricultural acts that sequestered an equal amount of carbon elsewhere. All well and good, at least in theory, but carbon offsetting is a new and weird commodity. It doesn't always work that well. Some of the money went to farmers in North Dakota, to pay them to practice a certain soil conservation technique they were already doing. Some other funds went to a power plant in Iowa that was supposed to produce cleaner energy -- during a trial run that ended a year before the money got there.

Driving around town, I see a decent minority of cars sporting a bumper sticker that says "This car's CO2 offset by TerraPass" or something similar. Despite my strong concern over climate change and the clear connection between CO2 emissions and global warming, I have yet to invest in one of these balancing schemes. I think it's just that it's an unproven system. Mainly through my own ignorance of their practices, I'm not convinced that companies like TerraPass aren't just taking people for a ride. I think that if the U.S. government had some sort of verification procedure whereby carbon offsetting companies could be certified, then I would be more inclined to trust them and get on board. But, as the Post article elucidates, we don't really regulate this business yet in America. They regulate the heck out of it in Europe, but also with mixed results.

It should be noted that despite these examples of offsetting "flubs," the House achieved some real progress with some simple acts that conserve energy: they switched to compact fluorescent light bulbs and ordered the Capitol Power Plant to burn natural gas instead of coal.

Labels: action, global warming, politics

We had some snow the week before last in DC. Here's the view from my apartment out over the National Zoo, draped in a lovely layer of white.

That's Rock Creek in the foreground, a major waterway cutting through DC along a pre-existing zone of weakness called the Rock Creek Shear Zone. Rock Creek Park is the largest urban national park in the United States (twice as large as Central Park, and about 5/3 the size of Golden Gate Park).

Labels: dc, snow

Casey went to Michigan last weekend to hang out with her sisters, and one thing they did was go snowshoeing/sledding at the YMCA camp where they all grew up. When they walked out to the lake, an interesting sight awaited them: a scum of ice balls floating in the water, and (presumably pushed by the wind), collected up along the shore. She brought back these three photos.
It's a neat phenomenon, and I'm not really too sure what to make of it. The question is: are these concentrically zoned features, like oolites, hailstones, or the hematite concretions seen in Friday's post? Or are they fragments of lake ice that got broken up and then rounded due to abrasion and jostling against one another in the waves? I'm guessing that the first hypothesis is correct, but unfortunately I don't have any way to test it from here in DC.

Some observations: the ice balls are pretty well sorted, pretty spherical, and well rounded. The ice balls are packed closer together closer to the shore. There also seems to be a size gradient from larger ice balls close to shore (right, in the image below) to smaller ice balls out into the open water of the lake (left, in the image below). If this isn't just a trick of the camera's perspective, could this correspond to increased growth due to closer packing (and thus more time lifted up out of the water into the cold Michigan air) close to the shore?
Finally, I note that in some areas, multiple ice balls have clumped together into a larger entity, as some oolites will do. This cohesion between ice balls is potentially the first step for making a solid layer of ice that will extend out from the shore over the whole lake.

Anyone else ever seen anything like this? What's going on?

Labels: ice, michigan

A couple of near misses are predicted in the coming days: tomorrow, an asteroid about 150 meters long is expected to zoom by Earth at a distance half again as far as the Moon. The next day, Mars is supposed to get a near miss. This was originally reported as a "possible collision," but detailed study of the trajectory since that announcement suggests it's merely going to be close. National Geographic has more details.

Labels: astronomy

Breaking News: Series Of Concentric Circles Emanating From Glowing Red Dot

Labels: earthquakes, humor, tv

Today my piece for Geotimes on geological travels in Northern Ireland went up on their website. You can check it out here.

Labels: northern ireland, websites

Outside of Shamokin, Pennsylvania, is a coal strip mine that has had the coal stripped away. Under the coal was a Pennsylvanian (in the time sense of the word) carbonaceous shale (the Llewellyn Formation), which is now preserved in lovely undulating Appalachian folds. Thanks to the removal of the coal, these fold surfaces appear in three dimensions -- a rarity for structural geologists like myself. The area is known as "The Whaleback" because of one anticline (center) with a shape that evokes a surfacing cetacean:

I went to the Whaleback last fall on a fossil-hunting trip with the The Calvert Marine Museum Fossil Club. In today's post, I'll take a look at the structure, and in a later post, I'll show you some photos of the fossils themselves. Here's some of the guys on the trip:

At the north end of the excavation, a cross-sectional view of the absent upper levels is preserved, showing this syncline. It once continued towards the camera's perspective in the air, a downflung fold between the Whaleback anticline and the neighboring anticline which made up the background "wall" in the first photo.
Okay, that's it for today. Tune in soon for the fossiliferous sequel.

Labels: appalachians, structure

Last night at the year's first meeting of the Geological Society of Washington, Derek Schutt of the National Science Foundation gave a talk entitled "The Yellowstone hotspot and how it got that way." Derek mainly focused on the evidence for there indeed being a mantle plume under Yellowstone, possibly caused by the destabilization of the core-mantle boundary layer when subducted Farallon lithosphere sank down to the bottom of the mantle.

But the thing that he said that really caught my attention has to do with one of the weird aspects of Yellowstone. Yes, to the southwest of Yellowstone's modern caldera is the Snake River Plain, a series of ancient calderas which overlap one another, getting older and older the further to the southwest you travel, until you get to the oldest one at 17 Ma. That part of it looks pretty much like a classic hotspot track, a la Hawaii. But there's a weird aspect to Yellowstone that doesn't fit the traditional hotspot stereotype: starting at that same 17 Ma caldera/"rift," another series of eruptions propagated away to the west/northwest, including the voluminous Columbia River flood basalts and leading to the Newberry Caldera, which Derek described as "the largest basalt dome in the United States." (See the map above, from Schutt's collaborators Gene Humphreys and John Hernlund.)

So, the question is: What's up with that? It kind of looks like two hotspots heading in different directions. Is this linked to the stretching of the western U.S. via the Basin and Range? Derek pitched another idea, which is based on the thickness of the lithosphere (crust + uppermost mantle). His idea is summarized in the diagram below, which I drew this morning based on my rough sketch of the diagram he put up on the screen at GSW last night. (My apologies to Derek if I've gotten any of the details wrong.)

The basic idea is that the North American lithosphere is thicker to the east, under Yellowstone, which Derek (admittedly loosely) defined as the Wyoming Craton. He suggested that the lithosphere was thinner to the west under Newberry and the Columbia River Plateau, since those were accreted terranes added to North America during the Mesozoic. The mantle plume came up underneath the thicker lithosphere, and punched a hole through right above it (Yellowstone), but part of the plume slid upwards and westwards towards the thinner lithosphere, where it broke through in multiple locations, producing first the Columbia River flood basalts and then later the eruptions culminating in Newberry. I like the idea, and the picture Derek showed is elegant. I can picture this happening, if the suggested lithosphere thicknesses are true. The question is, are they? I don't know enough about that region of the country (yet) to assess the validity of this model. I wanted to use this blog post to share the notion, and see what people think. If you're familiar with that area, please clue me in to the details.

An additional difference between Yellowstone and Columbia River/Newberry (CR/N) is that Yellowstone's magma is rhyolitic and CR/N's magma is basaltic. Rhyolitic magma is a lot more explosive than basalt, and indeed Yellowstone's eruptions have been among the most powerful observed in the geologic record. (The Huckleberry Ridge tuff, which erupted from Yellowstone 2.1 Ma, is deposited over something like half of the Lower 48!) CR/N, on the other hand, appear to be gentler eruptions more like Hawaii's oozing of basalt. I suppose this too can be explained by Derek's model: partial melting of the more-felsic crust under Yellowstone (as hot plume magma heats that thicker slab of continental crust), but a shallower Moho to the west, producing mafic magma a shorter vertical distance from the surface.

PS -I must also add that it was great to meet Tuff Cookie of Magma Cum Laude at the meeting. If there had been one more of us there, it could almost have been a geology blogger's conference.

Labels: gsw, yellowstone

Whole Foods stores have decided to phase out the use of plastic bags in their stores, aiming to be rid of the nasty things by Earth Day. Bravo! The sea turtles thank you. Let's use that (petroleum-derived) plastic for something else.

Labels: environmental

The Accretionary Wedge is a every-once-in-a-while compendium of geology blog posts on a particular theme. This episode is about geological misconceptions, mostly, but also a bit about pie. Yes, pie. Check it out here.

Labels: blogs, geology

Last week, I posted my first of these images. Today I follow up with another spot in the same state as last week's A.W.o.G.E. Annotations are described in detail below. The first one to correctly identify the location wins a "GEOLOGY ROCKS" bumper sticker. The contest is open not just to my students but to the whole world (though I'm hoping someone in the U.S. wins it so I don't have to pay some outrageous postage to send the winner their bumper sticker!) Last time the winner was helped along by comparing the Google Earth image to photos on my website, but I don't have any photos of this area up on the website, so it ought to be more challenging!

Labels: contest, google

It appears that researchers have located a volcano under a thick mantle of Antarctic ice. They found the volcano's approximate position by mapping a layer of ash and glass shards within the glacial ice. The volcano erupted in or around 325 B.C., say Hugh Corr and David Vaughan, based on their study. (Both men work for the British Antarctic Survey.)

They initially detected the layer of volcanic debris through airborne radar-reflectance measurements. (At first they thought the reflective layer was the bedrock at the bottom of the ice, since it provided such a strong reflection.) Then they looked at the thickness of snow overlying this layer and correlated the ash deposit with eruption-linked acid-rich snow strata in ice cores that were taken in adjacent areas. The image here shows the radar-wave reflectance profile.

(According to my rough calculations, the vertical exaggeration of the cross-section is about 6x. )

This has been billed as the first time we've seen clear evidence of a volcano pushing its way up through the ice sheet in Antarctica, though similar eruptions have been observed in historical times in Iceland (like Grimsvotn in 2004). However, just this past weekend I watched an episode of the PBS series NOVA, which showed scientists working on a big ice coring project near what they interpreted to be a sub-ice volcano. There was a big depression, and ice was flowing into the depression (downhill) from all directions. Ergo that ice had to be going somewhere. NOVA's scientists posited it was being melted, and that meltwater was greasing the skids of the bottom of multiple ice streams which were cruising out of that area of the ice sheet. (These ice streams are just faster-flowing areas of the ice sheet, like currents zooming through ocean water, sometimes 50x as fast as the "background" rate of flow.)

The show got me thinking about another study, coincidentally also published in Nature Geoscience, although this one was in the inaugural January issue. It's a study of the Kennicott Glacier, in Alaska's Wrangell-St. Elias National Park:

The study was conducted by three researchers, all associated with the Institute of Arctic and Alpine Research: Timothy Bartholomaus, Robert Anderson & Suzanne Anderson. They measured a bunch of variables on the Kennicott Glacier, seeing which of them correlated with a rise in the glacier's speed. They found that an annual flood event from Hidden Creek Lake (HCL in part d of the diagram, orange line) occurred at the same time as the glacier's maximum speeds during the measured interval, the maximum discharge of the (downstream) Kennicott River, and a maximum electrical conductivity of the water in the Kennicott River (the bedrock beneath the glacier is halite-bearing). As this whopper of a graphic shows, Not only does the glacier speed up its horizontal motion during the flood (part b), but the whole thing actually rises up vertically too! (part c) Also, Donoho Falls Lake (DHL in part d of the diagram, blue line) downstream experiences a huge surge in water as the flood passes over it. Conductivity spikes during this same interval. Bartholomaus and the two Andersons propose that when the ice dam of the lake gives way and all that water surges into the glacier's channel, it overwhelms the capacity of the sub-glacial network of channels & raises the pore pressure of water within the ice. This extra pressure "inflates" the space between glacial ice & underlying bedrock, and the whole thing slides like an air hockey puck. At least, as long as the super-high pressure lasts. Once the flood ebbs, pore pressure in the glacier drops back down to levels that are easily counteracted by friction. The glacier slows once more to a "normal" pace.

This is very reminiscent to me of studies done on how an increase in pore pressure along a fault plane can trigger movement along that fault. When I took structural geology in college, the professor described an example from Colorado (I think) where the Army (I think) was injecting nerve gas down into the ground to get rid of it. The nasty nerve gas was dissolved in water, and the periodic injections of this solution correlated with a series of earthquakes (movement) along a previously-unknown subterranean fault. The injections increased fluid pressure in the pore space of the rock, and that "inflated" the space between the fault blocks, and the relatively minor shear acting on them was then enough to get the two to slide. I won't get into the whole Mohr Circle here, but I do recommend you check out the famous Beer Can Experiment to get an idea of how an increase in fluid pressure can cause an otherwise "stuck" fault to slide. Anyhow, I guess the base of a glacier is essentially a big fault, with one kind of rock below and another (ice) above. Same phenomenon, in other words, but different geologic context.

The Bartholomaus + 2 Andersons study also has some big global warming implications. The recent surge noted in Greenland's glaciers (e.g. Zwally, et al., 2002) may be explained by higher rates of surface melting (due to elevated Arctic air temperatures) which then produces lots of meltwater, which flows down through the glaciers to the bottom via meltwater channels which plunge through the ice. Via the mechanism explained above, the great ice sheet atop Greenland is reduced more rapidly than without the surface melting. One of these meltwater channels was featured prominently on the cover of the June 2007 issue of National Geographic.

So, with that, I think I'll end this blog post -- my thoughts went from volcanoes to ice streams & subglacial meltwater to fault slippage to global warming. I reckon that's just about enough... just about... but I also noticed something else...

A tangent about publication: The Corr & Vaughan findings will be published in the second issue of the new spinoff journal Nature Geoscience, but they were posted online over the weekend in advance of the actual print publication of that issue. An article in the New York Times alerted me to the study. I'm not surprised that Nature, like the Proceedings of the Royal Society, has taken to hatching specialty sub-journals to convey more articles each month. (An "about the journal" page appears on their website, if you're curious.) The image shown here with this post is from the Times, not the actual Nature Geoscience article.

References:
Hugh F. J. Corr & David G. Vaughan. (2008) "A recent volcanic eruption beneath the West Antarctic ice sheet." Nature Geoscience. Published online: 20 Jan. 2008. doi:10.1038/ngeo106

Timothy C. Bartholomaus, Robert S. Anderson & Suzanne P. Anderson. (2008) "Response of glacier basal motion to transient water storage." Nature Geoscience 1, 33-37. Published online: 20 December 2007 doi:10.1038/ngeo.2007.52

H. Jay Zwally, Waleed Abdalati, Tom Herring, Kristine Larson, Jack Saba, & Konrad Steffen. (2002) "Surface melt-induced acceleration of Greenland Ice-Sheet flow." Science 297, 218-222. doi: 10.1126/science.1072708

Also see:
Kenneth Chang. "Scientists find active volcano in Antarctica." The New York Times. Published online: 21 Jan. 2008.

Labels: antarctica, global warming, tv, volcano

I watched a cool documentary the other night about the Canadian photographer Edward Burtynsky. The film is called Manufactured Landscapes. (It's available from Netflix.)

It follows Burtynsky mostly through China (with asides to Bangladesh and North America) as he photographs of places where humankind has indelibly altered nature to produce landscapes that are at once disturbing and utterly beautiful. By trailing Burtynsky, the documentarians film the landscape through his eyes, as well as showing his still photos. Burtynsky maintains a website with some of his best images available in an online gallery. It's a remarkable ensemble. I recommend that you check out this visionary photographer.

Labels: art, environmental, movies

The Maine Geological Survey maintains a terrific website with lots of information about the state's umpteen gazillion geological locales.

I feel like you could run a virtual field trip to Maine with the wealth of quality information and and images they have on this site. It's all well illustrated with lots of photos of structures and geologic contacts.

Learn more about the granite dikes at Pemaquid Point Lighthouse.

Or learn about where to find pillow basalts.

Or check out the giant purple crystals at Mount Apatite.

Or check out the distinctive dark feldspars of Maine's only "shonkinite".

It's all there, plus much, much more! Enjoy.

Labels: geology, maine, websites

Plans are coming together for the big NOVA Climate Change Teach-In, scheduled for the week after next. Each of the six different campuses of Northern Virginia Community College are participating in one form or another. Starting on Wednesday night (Jan. 30), there are opportunities to learn about climate change and its implications for our society. Webcasts, lectures, and in-class teach-ins on Thursday the 31st will lead up to the biggest event, held at my own Annandale campus. This will take the form of a series of short lectures and a panel discussion from 12pm to 3pm on Friday, February 1. Plus we're going to serve cookies! Under the leadership of the College-wide Green Committee, on which I serve, NOVA's events are part of a larger nation-wide teach-in involving over 1400 schools.

More information about the multiple events can be found at the Green Committee's website.

If you're in the DC Metro area, you are invited to attend any of these events. They are free and open to the public. Also, for the Manassas lectures and the big Annandale event, surface parking regulations will be waived. There's no excuse not to attend. Of course, if you're one of my students, then I expect to see you there!

Labels: action, global warming, nova

A paper in the new issue of Proceedings of the Royal Society announces the discovery of fossil evidence of the largest rodent yet recorded by science. The fossil reported is a skull, found in Uruguay. Of course, South America is home to the largest living rodent (the capybara, Hydrochoerus hydrochaeris), and it's no surprise that the continent should also have been home to the largest fossil rodent. The reason is that South America was a hotbed of mammalian evolution from about 65 million years ago (Ma), when it separated from North America, until about 3 Ma, when it reconnected with North America via the narrow Isthmus of Panama.

The new species, dubbed Josephoartigasia monesi, is closely related to another large extinct rodent called Phoberomys pattersoni as well as an extant (still living) species known as a pacarana (Dinomys branickii). The image at right, from the paper, shows a reconstruction of the head of J. monesi and a comparison with a pacarana.

P. pattersoni (from Venezuela) is estimated to have weighed about 700 kg, while J. monesi's bulk (extrapolated from the relative size of the skull) must have been about 1000 kg, a full metric ton.

As a continent hosting an independent trajectory of mammalian evolution, South America offers a beautiful contrast to Australia. Both continents were isolated from other continents for tens of millions of years, and their particular blend of mammals (& other species) evolved into unique & interesting forms. The South American experiment ended when it reconnected to North America at 3 Ma. At that time, mammals from North America trooped southward through Panama, and mammals from South America trooped northward. This flux of biodiversity is referred to as the Great American Faunal Interchange, and it dramatically reshaped South America's mammal assemblage. Saber-toothed cats (Smilodon sp.) was one of the turistas from the north, and it likely fed on big fat critters like J. monesi.

Other southward-bound groups included deer, bears, squirrels, rabbits, raccoons, and camelids (which went on to diversify into llamas & their kin). Northward-bound groups colonizing North America were fewer in number: the armadillos, the opossum, ground sloths (now extinct), and porcupines. Today, about 50% of South American mammal species have a North American origin, while only 20% of North American mammals have a South American origin. One of the reasons suggested for this lopsided distribution was that North America had been periodically connected to Eurasia (both east and west) via landbridges during the Cenozoic, and therefore North American mammals had been continually tested against the biggest continent's most competitive species. The North American mammals had already been forced to prove their mettle. South American mammals were living a life of blissful ignorance & luxury, and they experienced a rude awakening when their neighbors from the North came stampeding in. The competition between the two groups resulted in a lot of extinctions, and one of those appears to have been J. monesi. The fossils were found in a sedimentary unit usually interpreted to be about 2 Ma.

The image below shows the sheer size of the J. monesi skull by comparing it to a handheld rat. (Maybe a Norway rat? I can't tell, and the image from New Scientist doesn't specify the species.) It's a pretty extreme difference, of the same order of magnitude as the difference between an elephant and a hyrax.


Evolution can be really fruitful given a sufficient easing of competitive pressure. Island biogeography gives us some weird creatures (Komodo dragons, dwarf elephants, and Homo florensis come to mind as three Indonesian examples) if isolation is maintained over time. This new discovery from South America confirms the larger pattern by showing us that gigantism has happened in the rodent family, too. Discoveries like this (and the recent giant ape reported from China) prompt me to imagine other possible evolutionary trajectories: what about giant bats, or mouse-sized whales? Could evolution produce arboreal deer, or bears the size of Chihuahuas? I welcome your thoughts & creative speculations on potential record-breaking mammals.

Reference: Rinderknecht, Andres, and Blanco, R. Ernesto. The largest fossil rodent. Proceedings of the Royal Society, B. doi:10.1098/rspb.2007.1645 Published online.

For those without a subscription to the Proceedings, you can check out New Scientist's write-up of the research here.

Labels: evolution, fossils

Baked goods occupy a central role ("roll?") in my style of teaching geology. In honor of National Pie Day and Accretionary Wedge #5, I hereby offer a run-down on my favorite baked-good analogies. As the pie chart above conclusively demonstrates, some baked goods are more versatile teachers than others and get therefore merit more class time.

I invoke pancakes to describe oblate shapes in deformed clasts (cigars, which are not a baked good, exemplify prolate shapes).

Muffins (especially the pop-over variety) are squat stand-ins for laccoliths.

Snickers bars offer a terrific way for students to grasp the concept of differential weathering. In class, I pass out to little bite-sized Snickers, and ask students to suck on them. (No chewing! We're trying to demonstrate chemical weathering here, not physical weathering!)They quickly learn that some ingredients are more stable than others.

A pint of Ben & Jerry's gets drawn on the board every semester in Physical Geology when we discuss the carving of alpine glacial landforms. Everyone has had the experience of buying a pint of Ben & Jerry's and finding it too hard to eat. As they wait for it to thaw, people insert their ice-cream scoop (or their spoons) into the top of the pint and carve downward and outward, towards the edge of the container (where the Chunky Monkey has lost more heat and is therefore easier to carve). Working around the container, repeated scoops leave a point of hard ice cream in the middle, surrounded by curved scoop surfaces. This is a lot like a glacial horn, surrounded by the headwalls of several cirques.

I mentioned raisin bread in Tuesday night's Historical Geology class, when discussing the principle of relative dating by inclusions. If you're going to bake raisin bread, which of the following seems like the better recipe? (A) Bake a loaf of bread, then grow some grapes, dry them out, & teleport them individually to positions evenly distributed throughout the loaf of bread. (B) grow some grapes, dry them out, and mix the raisins into the dough, THEN bake it into bread. Well, my teleporter's always in the shop, so I'm going with the second recipe. The raisins have to pre-exist the bread in order to be included in it.

Bob Lillie of Oregon State University gave me this idea: Oreo cookies are composed of a stack of three layers with brittle/ductile/brittle rheologies. This can serve as an analogy for the lithosphere, asthenosphere, and mesosphere. You can even break up the upper cookie bit and slide the pieces around on the white filling. If you're clever, you can produce rift zones, subduction, and even crude mountain building this way.

Chunky cookies (like these classics from Pepperidge Farm) offer a nice contrast between cookie and ingredient. You can tell where the cookie starts & stops, but you can also tell within the cookie where the chocolate starts & stops, and where the pecans start & stop. The analogy is an important one that I draw early on for my Physical Geology students: the difference between a mineral and a rock. Minerals are like the ingredients (chocolate chunks, pecans, etc.). Rocks, being an aggregate of many mineral grains, are like the cookie. Minerals are the ingredients that make up rocks.

And that brings us to cake, by far the most frequently invoked baked good in my introductory geology lectures. Cake is good for so many reasons. First off, there's the stratigraphy of cake: frequently it's a layered structure. Second, broken cakes are not doomed: they can be stuck back together by sealing fractures with frosting. Third, the different rheology of the frosting layers versus the cakey layers makes them ideal for explaining thrust faults that travel over a "greased skid" of less competent rock. (This is my favorite way of explaining the Blue Ridge Thrust Fault, for instance.)

Ironically, pie itself has not so far merited inclusion in this cavalcade of calories. Can you think of a geologic concept that pie helps illustrate? If so, leave your suggestion in the comments area below.

Labels: food, teaching

Last year's temperature data is in, and it's no surprise that it was the second-warmest year ever, since human beings began measuring temperature. To be precise, 2007 is tied with 1998 for second place in the rankings for warmest. (2005 was the warmest year on record.) NASA, which released the data today, posted some nice analysis, animations and graphics on their website. Check it out here.

Labels: global warming

On Monday at noon, I went to the Russell Senate Office Building on Capitol Hill to attend a seminar organized by the American Meteorological Society.

The speakers were: David Archer of the University of Chicago and Ralph Keeling of Scripps (son of Charles David Keeling, also of Scripps). In two months, the Keeling curve (started by the father, maintained by the son) turns 50 years old. Probably more than any other graph, the Keeling curve is responsible for convincing people of the reality of CO2 buildup in our atmosphere.

Click on the picture at left to get a full-sized PDF of CO2 data from multiple measuring stations (not just Mauna Loa), all showing the same thing. The concentration varies with the seasons (more CO2 is pulled out during the northern- hemisphere summer; less in the northern winter), but overall the amount of this gas is increasing.


The seminar was titled "Natural CO2 Sinks and their Policy Implications: A Closer Look at Where Current CO2 Levels are Headed, in Historical Context." The two scientists gave an outstanding pair of back-to-back presentations, detailing the enormity of climate change we are now committed to.

The image that stuck most in my mind is this one: measurements of atmospheric oxygen (O2) from Cape Grim, Tasmania (Australia).

If volcanoes were the source of all that CO2 building up in our atmosphere, you would expect oxygen measurements to stay static (or at least not to vary beyond normal seasonal variations: the zig zags). But that's not what researchers have found. Instead, the pattern seen in the graph above is clear: oxygen levels are declining in lock-step with CO2's rise. The reason is simple: when we burn fossil fuels, we oxidize hydrocarbons. We can't burn a fossil fuel without oxygen. Oxygen is consumed by the process, and that oxygen is then paired up with carbon to generate CO2. The process is so simple, but the implications are profound. This graph makes clear that human burning of fossil fuels is the source for atmospheric CO2 rise. This is mankind's fingerprint on global warming.

I might also add that it was cool to run into Michelle Arsenault and Linda Rowan at the seminar.

AMS seminar series.

Labels: CO2, global warming, oxygen

The favorite pastime of the geoblogosphere appears to be "Where On Google Earth?" (example 1, example 2, example 3) ...Who am I to buck such a trend? But I've also gotta give it my own spin: so I hereby introduce Annotated "Where On Google Earth?" The difference is that in my version, the game gives you a chance to learn something new about me (via the annotations) while exploring some cool places.

Here are your clues: (A) West of this line is a major Mesozoic batholith. Location (B) is a peninsula where I camped for a week and a half. (C) is a dam which produced the lake that the image is centered on. (D) shows a prominent shadow below a cliff formed by a Paleogene ("Tertiary") basalt flow.

Since today is my first day of classes for the semester, I'm going to make this a contest. The first of my students to deduce the location of this image by naming the lake and the mountain range that hosts it, will win a GEOLOGY ROCKS sticker. Geoblogospheroids, you can guess too, but my students are allowed to check your answers and then adopt them as their own to win the prize. It's kind of like one of those celebrity game shows, or the weekly bigwig- plays- for- a-random- person- getting- Carl- Kasell- on- their- home- answering- machine dealio on "Wait, Wait: Don't Tell Me!" The contest is open... see some of you in class in a few hours!

Labels: contest, google

I was struck by the visual similarity of these two round graphics from the Science section of today's Washington Post. The first shows the circuitous path taken by the Mercury Messenger spacecraft, which is scheduled to fly by the innermost planet in about 2 hours from the time I'm writing this:


The second image shows the changing ice situation in Antarctica on a cool combination of ice-flow velocity map and ice loss/gain bar graph, wrapped around the edge:

Labels: art, global warming, planetary geology

Labels: google, maps

In preparation for this summer's rafting trip down the Grand Canyon with my father & two brothers, I checked out the book An Introduction to Grang Canyon Geology from the NOVA library. The author is L. Greer Price. It's a slim little book, in full color, with lots of little boxes inserted amid the main text. These boxes explore smaller subtopics like stromatolites or rock color. The main text emphasizes the chronological sequence of steps to create the bedrock of the Canyon, and then a detailed discussion of how rock structure and erosional effects combine to carve the land into a shape as varied as the Grand Canyon. It's a book a lot like the one I'm working on for the C&O Canal.

I've visited the Grand Canyon four times, so I've managed to get a lot of the upper stratigraphy down. I picked up this book to bulk up my understanding of the deeper gorge (where my family & I will be spending our time in June). While a lot of the book was geological boiler-plate about plate tectonics and superposition, I learned some new details. For instance, I had no idea the Cenozoic was represented at all in the Canyon, but apparently the remains ("still pungent") of a Shasta Ground Sloth were discovered in Rampart Cave (a cave in the Mauv Limestone) in the western Canyon.

The writing style is balanced. I could see how the author struggled with being technically accurate but also accessible to the wide audience he was writing for: the Mazatzal Orogeny (~1.7 Ga) is described, but it's not called the "Mazatzal Orogeny." Another example would be in describing Mesozoic subduction on the west coast, Greer swaps out the technically-correct name Farallon plate for the more recognizable "Pacific" plate, even if that's not technically correct.

The book is short (59 pages), and it's 50% pictures -- an easy read in an afternoon.

Labels: books, grand canyon

In last week's issue of Science, Paul Silver (of DC's own Department of Terrestrial Magnetism at the Carnegie Institution) and Mark Behn (formerly a post-doc at Carnegie, and now at Woods Hole in Massachusetts) published a paper putting forward an intriguing idea: maybe plate tectonics proceeds in fits and spurts.

Silver and Behn note that most of the world's subduction zones are located in the circum-Pacific belt, and that the Pacific is getting smaller over time. (Subduction destroys oceanic crust, and since the Earth presumably isn't increasing or decreasing in volume, subduction in the Pacific is balanced by seafloor spreading elsewhere, like the Atlantic.)

The Pacific is "predicted" to close in about 350 million years, assuming that the tectonic plates continue to move at about the same rate they're moving now. The death of the Pacific would come as the Americas smash into eastern Asia and Australia, raising up a Himalayan/Appalachian style mountain belt. Silver and Behn posit that this would basically end subduction on planet Earth for a time. This was a startling idea to me at first, but then I thought, "Why not?" Then I thought, "I wish I'd thought of that."

My understanding of mountain belts comes from the Appalachians, which built up in three successive episodes called orogenies. Check out the diagram below (from the excellent textbook Essentials of Geology by Steve Marshak, that I use in my Physical Geology course at NOVA) and follow along so you can see why this new concept startles me a bit (but in a good way):

There used to be a big ocean basin off the "east" coast of North America that closed via subduction over the course of the Paleozoic Era. This extinct ocean goes by the name of Iapetus. This was not a simple event: it was more like a pile-up on the highway than a simple head-on collision. This ancient ocean basin was not just empty ocean. It also included islands and small chunks of continental crust ("microcontinents" like modern-day Madagascar). First a subduction zone developed out there in the ocean, closing a portion of it. This brought a chain of volcanic islands closer & closer to North America. The islands hit North America (around 460 million years ago), in a mountain-building event called the Taconian ("Taconic") Orogeny. Once that had happened, a new subduction zone developed on the ocean side ("outboard") of the islands/accreted terranes. That began to close another part of the Iapetus Ocean. Around 360 million years ago, that episode of subduction ended when a microcontinent (dubbed Avalonia) smacked into North America. This collision caused more mountains to rise: the Acadian Orogeny. Then yet another subduction zone, outboard of the newly accreted Acadian terrane, kept the closure of the Iapetus Ocean going, until finally the continent on the other side of the ocean (Africa) smashed into North America, raising more mountains. This is the Alleghenian Orogeny (sometimes spelled "Alleghany"), which really crumpled up the landscape, starting around 300 million years ago. The moment the Iapetus died was the moment Pangea was born.

I go into all this because the model of plate tectonic convergence the Appalachians display is one that says collisions between plates don't stop the overall convergent forces. As soon as one subduction zone is snuffed out, a new one develops outboard of the continent, where the weaker, denser oceanic crust gets shoved downward.

But does it actually work that way all of the time? Silver and Behn suggest maybe not. Maybe it's an "on-again, off-again" affair. They cite among their evidence an earlier orogeny, the Grenville Orogeny, which sutured together many continents at a much earlier time (about a billion years ago). When that collision had ended, the supercontinent Rodinia was born. Silver and Behn note a lack of volcanic activity around the world for hundreds of millions of years after the Grenville Orogeny (most volcanoes are caused by subduction). Rodinia did eventually break up amid much volcanic activity (including the eruption of the mid-Atlantic's infamous Catoctin Formation), and giving birth to the Iapetus Ocean basin in the process -- but that didn't happen for a long time after Rodinia got assembled. What gives? Does that mean subduction was inactive during that period?

They also offer a modern example: India and the Himalayas. 20 million years ago, India was a microcontinent out in the Indian Ocean, with a pavement of oceanic crust separating it from Eurasia. India moved north, the oceanic crust got subducted, and eventually India plowed into Eurasia, raising the Himalayas. But why hasn't a new subduction zone developed south of India? That would be what would happen if India's orogeny were following the Appalachian example.

Maybe plate tectonics has periods of intense activity (lots of subduction), but then has periods where it's "clogged up," and the movement of the plates slows. Eventually heat builds up in the underlying mantle (the source of plate movement) to the point where the mantle begins to convect more vigorously, and the plates start getting dragged around again. It's kind of a cool notion. I'd be interested to hear what you think about it. Please post any thoughts you have in the comments section below.

The whole idea reminds me of the concept of punctuated equilibrium, a model of biological evolution which bucked the long-standing notion (originated by Darwin himself) that evolution proceeded slowly and methodically over time. Thanks in part to an eye-opening appreciation of the Earth's immense age, the prevailing wisdom was that evolution was gradual, smooth.

Then (in 1972) Niles Eldridge and Steve Gould published a landmark paper that suggested otherwise. Instead of "gradualism," they argued, changes in populations of living organisms may have happened suddenly, experiencing a lot of change in a short period of time. Once equilibrium was achieved, the new status quo was preserved as a non-dynamic scene for a long time. (See image at left, which came from Wikipedia).

They cited the fossil record as their primary evidence: most of the change seen in fossils is a sudden switch of biological "regimes," with new fossils showing up, lasting a while, and then abruptly vanishing. I'm oversimplifying here, but I hope the analogy is clear: if evolution can do it, why not plate tectonics? Is there any reason to think plate tectonic motion couldn't happen in spurts of more activity followed by periods of quiescence? Ponder it...

Reference: Silver, Paul G., and Behn, Mark D., 2008, Intermittent plate tectonics?: Science, v. 319, p. 85-88, doi: 10.1126/science.1148397.

For those without a subscription to Science, you can read the press release about Silver and Behn's work that Carnegie put out by visiting their website.

Labels: appalachians, evolution, iapetus, plate tectonics

Sir Edmund Hillary, the first man to summit the tallest mountain on Earth, has died. When I think of him, I think of an explorer cut from an ancient cloth. They don't make 'em like that any more. He was one of the good ones. Rest in peace, Sir Ed.

National Geographic's obituary.

PS - As John McPhee likes to point out, the summit of Mount Everest is made of marine limestone.