Georgia Perimeter College professor Pamela Gore sent me these photos yesterday of some interesting structures she found in the snow in her yard. She was away for the storm itself, so she didn't watch them forming, but the morphology suggested linguoid ripple marks to her. If that's accurate, the current direction (wind direction) was from the north. Take a look at her photos below, and here's some photos for comparison.





Two shots that are zoomed and cropped from the image above:




Pamela e-mailed me again this afternoon to say that, "Looking at them in daylight, they look like they were formed by impacts of snow [clumps] from trees, landing at an angle and causing folding on the 'downstream' side."

What do you think? Are these linguoid ripples? Any sedimentologists want to chime in?

Labels: georgia, primary structures, snow

Here's an iPhone shot of the view out the back of my house:

Labels: dc, snow

Dawn in DC: a blue grey hazy light filters down from the sky, just enough to illuminate the falling snow. I know that I'm not alone when it comes to being a bit tired of this snow. This is our sixth day in a row of being hemmed in. It's pretty profound, and the masses are starting to murmur with their frustration.

I'm astonished at how paralyzed the city is. It's really stunning. The federal government has been shut down every day this week, and according to the Office of Personal Management, it's costing $100 million a day in lost productivity. I was shocked to see that the Post Office didn't deliver mail at all on Saturday. What? The "Neither rain nor sleet nor snow nor dead of night..." crew called in frozen?

The snow has been falling all night, and not even once did I wake up to the sound of plows scraping their way down the street. I don't get it: where are the snowplows? Walking over to Woodley Park yesterday to ease the cabin fever, the weather was fine (as it was Sunday and Monday), and yet the streets were ankle-deep in grey slush. The sidewalks were usually in better condition than the streets: individuals' efforts to improve their small stretch of the common space were effective. But the city's response to the snow has been quite lackluster, from my perspective. I'd be more sympathetic if I saw them out there working, but I haven't observed a single snowplow plowing. (To be fair: I did see one snowplow, blade in the air, spreading salt. Also, I've been spending most of my time indoors, but I can see and hear the road.)

Salt supplies are running low, says the rumor mill. I believe it. Patience is running low, too. I'm at least thankful that here in the city, we haven't lost power, unlike many of my friends, colleagues, and students out in the suburbs.

Yesterday, when I was reflecting on people's thinking about the storm, I mentioned Haiti. I'd like to bring that up again today, and explore it from a different angle. The earthquake in Haiti was horrible and devastating, but it was (a) predicted, and (b) the equivalent of a large-magnitude earthquake that could occur elsewhere, like the Pacific Northwest or California. Yet it was really, really bad in Haiti, while the same magnitude quake, at the same depth, the same distance from San Francisco wouldn't be nearly as destructive. Why? Simple: the people of San Francisco are more prepared for earthquakes. A nation as rich as the United States, and a state as (formerly) wealthy as California, has the power to study earthquakes and their causes, to pass laws requiring buildings to be structurally capable of standing up to serious shaking, and the power to enforce those laws. Haiti's populaiton isn't so lucky: their unreinforced masonry buildings collapse readily when they get sheared; people die as a result.

Which brings me back to DC. While it's no Port-au-Prince, it's a big freaking mess that's not getting cleaned up anytime soon. This same snowstorm could hit Minnesota or South Dakota or Anchorage and I don't think anyone would really bat an eye. When I lived in Homer, Alaska, storms like this seemed to come around once a month or so. The difference was that people there had four-wheel-drive (and knew what that meant, unlike some of my SUV-driving neighbors inside the Beltway), studded tires, experience driving in snow, and a prepared attitude. The weather was the same; we just dealt with it better up there. Many private trucks had plows on front, and it was seen as a civic duty to plow out the road if you were the first one to drive down it after a storm*.

The culture of the DC area is as unprepared to deal with snow as Homer would be to deal with 100 degree F heat and 100% humidity. DC deals with mugginess like that every summer, though, so though it's a pain, it's not a catastrophe. Each area develops precautions and procedures based on the variations that nature typically throws its way. We make predictions based on the past. When something novel arrives, chaos breaks out, official services get disrupted, and it's up to the individual citizens to clean up the mess and look after one another.

Nature doesn't make disasters, in other words. We do.
____________________________________
* One time in Homer, I drove my pickup truck (which did not have a plow) down the road after about 2 feet of snow had fallen. I was the first one there, and I just charged on through. After I had gone about half a mile, my engine died. Surprised, I got out and shuffled forward to pop the hood. The entire engine block was surrounded by snow! As I was driving forward, there was nowhere for the snow to go except into the airy interstices under the hood. There was so much snow that the engine's air intake was blocked. I cleared it out (poking it with an ice axe I kept in the car) and started the engine up again, no problem. Then I drove on to work.

PS - Here's a gallery of images from the Washington Post.

Labels: alaska, dc, earthquakes, haiti, snow

People see the most interesting things in the world around them. Some people see Stephen Hawking's initials in the universe's microwave background radiation. Others seek patterns in the clouds or lines on a palm. People are hard-wired to look for meaning in patterns. Not all patterns have meaning, but many do. Geologists, for instance, pay a lot of (legitimate) attention to patterns in ancient sediments: these patterns, called primary structures, give information about current flow direction, exposure to air, and the presence of living organisms. Others can orient us to which way was "up" when the sediments were deposited. Cross-bedding, mudcracks, and bioturbation are some examples of patterns with meaning. Seeing a dog's face in a rock exposure is an example of a pattern that lacks meaning, as surely as if one saw the same dog's face in the meaningless blobs of ink in a Rorschach test.

Lately, I've been thinking about the human predisposition for perceiving meaning in patterns.

The week before last, I gave a presentation at a local middle school about climate change. Before my talk, one of the teachers came up to me to ask if I thought that global warming could have triggered the earthquake. He whispered conspiratorially, "There have been a lot of earthquakes lately!" I said no, because (1) I couldn't think of a plausible mechanism for that to work in Haiti* and (2) there are perfectly good tectonic reasons for the Haiti earthquake, and (3) there haven't been more earthquakes lately than usual, at least not in any significant way.

As I type these words, the first snowflakes are falling in the second major snowstorm to hit Washington, DC, in less than a week. The first, dubbed Snowmageddon or the Snowpocalypse, dumped more than 18 inches of snow on the capital city. The city does not respond well to that amount of snow: schools shut, the government closed, and there were insane panicked runs on groceries at the area's stores. The new storm, dubbed Snoverkill, adds insult to injury with another 6 to 16 inches predicted. The schools I teach for, NOVA and GMU, have both been closed since last Friday. The way it's looking now, I'm not going to be working again until this coming Friday -- a full week lost due to the white stuff.

What's interesting to me is how people react to the snow. I mean this on two levels: one is the obvious fact that both the culture and infrastructure of Washington, DC, are quite poorly equipped to deal with a couple feet of snow. However, that's not as interesting as the way the snow serves as a reflection on people's mental states. Some people look at the two big snowstorms coming back to back and say, "Where's global warming now?" Others look at the same two storms, with fear that this is the new paradigm like The Day After Tomorrow, and say, "See what climate change hath wrought?" The thing is, they are both wrong.

Weather is not climate, even when two weather events occur in the same week. Tamino calculates that you need about 14 years of temperature data to tease out the long-term trend. Nine years isn't enough, and one week isn't enough. Yet people notice the "clumping" of these data: "two storms in one week! That's a pattern! It must therefore be significant! If it's significant, it's therefore reflective of a common cause, and that common cause is the one I have already decided to be true. Therefore these two storms are evidence of global warming / global cooling**" (depending on who you're listening to).

The thing is, data are clumpy. There is going to be noise in the data. When it comes to snowstorms, the noise is the weather. The noise is superimposed upon a longer-term trend. That trend is the climate. Likewise with earthquakes: no one expects earthquakes to occur with a periodicity regular enough to set to music. Earthquakes of a certain size have a certain probability of occuring in a given period of time, but there's no guarantee that one will occur. If you calculate the average number of earthquakes during a given period of time, and then compare any period of time to that average, your comparison time period will either have more earthquakes than the average or less earthquakes than the average. Ditto for snowstorms: some winters will be more snowy. Some winters will be less snowy.

There are exceptions, such as earthquakes triggered by other earthquakes, or a common cause. The recent earthquake storm at Yellowstone is sufficiently constrained in time and space to suggest that it indeed is a group related by a common cause (though it does not show a magmatic signature, another case of people seeing what they want in the data). Haiti's aftershocks play the same game, though not every earthquake that occurs in Haiti is necessarily connected to the big shock.

Anyhow, this stuff has been on my mind this week. The world is one big Rorschach blot, and humans see what they want in it. We are psychologically all too likely to jump from pattern recognition (noticing clumps in data) to conclusions (often pre-determined), without taking the time to really analyze whether there is in fact a trend present, and if that trend is significant, and if there is a logical causal mechanism to explain that trend.

We are a species that seeks meaning: some augur the future from tea leaves, while others engage in science and reason. Some methods of gaining access to meaning are themselves meaningful. Others are meaningless. Both surround us.

Stay warm out there.
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* Though potentially up in Greenland it could work due to glacial melting causing unloading on the crust, changing the stress field that's keeping a fault locked in place.
** It's probably also worth pointing out that snow does not equal temperature. It's precipitation. People are visually susceptible to the sight of snow: it registers more than numbers.

Labels: analogies, climate change, dc, movies, nova, primary structures, science and society, snow

You may have heard that D.C. got some snow this weekend. (It's true.) We went for a walk this morning to check out what the snowed-in city looked like. Here are a few photos...





This is fun:


K Street, home of the lobbyists:


Group of robins hanging out at National Geographic HQ:


The White House gets whiter:


A magnolia tree in Jackson Square, not doing so well:

(Magnolias seem particularly susceptible to losing limbs via heavy snow...)

Photogenic trees:




Washington Monument:


Up-side-down Diplocraterion? Or just where someone sat in the snow?


This trace fossil is more obvious; Bicyclus, clearly:


The National Mall (Smithsonian's Natural History Museum at left, Capitol Building at right):


Doppelganger week for the Capitol:


Cold Triceratops:


Snow decorates the trees in front of the FBI building:


Pennsylvania Avenue:


Callan checks on the snow depth:


Guess this roof isn't very well insulated...


Some structures... Here's a set of two normal faults in a snow stratum atop a hedge:


(Glove for scale, of course.) Here's a different angle on these extensional structures:


(Because GMU classes were canceled on Friday, I assigned my structural geology students to make some structures in the snow -- like Kim's example, perhaps, or perhaps like this hedge, but really limited only by their own imaginations...)

Here's a different one:

That's a sheet of snow being driven downward by gravity, sliding over a roof (fault-like) but then arching up at the tip (this would look 'antiform' if it were rotated 90 degrees...). Kind of like a compressional antiform transitioning into a thrust fault, a common 'structural ingredient' in fold and thrust belts the world over.

Some more normal faults, including en echelon arrays like we saw last September in the volcanic tableland north of Bishop, California... These are viewed from the bottom -- they are forming in snow atop the glass roof of the pagoda-thingy that covers the Columbia Heights metro escalators. Notice too the color difference (due to more or less snow) from the peak of the pagoda (where the faults are -- an area of "crustal" thinning) to the bottom (where the snow is thickest).


Finally, if you haven't already seen it, check out this time-lapse image of the snow accumulating! And here's one from Greg Willis, who has shared videos on this blog before... Enjoy!

Stay warm out there, everyone...

Labels: dc, dinosaurs, fossils, humor, smithsonian, snow, structure

The final segment of day 3 in Torres del Paine National Park was crossing through John Gardner Pass and heading down the other side, being treated to our first view of the Grey Glacier.

Here's me huffing and puffing up the final snowfield below the pass:


...And then we were there! This is the highest point on the Grand Circuit. An "iron woman" trail runner took our photo atop the Pass:


The surrounding scenery spoke very clearly of recent glaciation, like these horns:


And it was here that we first got a look at the immense Grey Glacier...


Annotated panorama shot of the Grey Glacier:
It is an impressive thing, this massive tongue of ice. Sourced in the South Patagonian Ice Field, the Grey Glacier is the largest in Torres del Paine, and effectively divides the Paine Massif from the main chain of the Andes (visible on the other side). I've noted a promontory of bedrock poking up through the ice (a "nunatak") at left, and the position of a tributary glacier at right. I was quite struck by the 'deflation' of the Grey Glacier, as marked by the disparity between the current top of the glacial ice and the line where vegetation begins.

A closer look at the tributary glacier:


Crevasses galore, and a 'blue hole' where a stream is feeding into the base of the glacier:


A few more shots. It's very photogenic. I don't have anything to say about these. Just enjoy:








Peaks of the Paine massif enconced in ice and snow:


We camped that night at Paso Campground. It was Christmas Eve, and we drank some Gato vino tinto and made a delicious fish stew for dinner. We went to bed at dark, but our campground neighbors did the European / South American thing by staying up late celebrating with one another. At midnight they sang their final song and drank their last swig of whiskey, and then there was peace and quiet... so at least half the night was silent!

Labels: chile, glacial landforms, glaciation, ice, national parks, patagonia, snow, south america, travel

From Puerto Natales, we took a bus with other backpackery types north to Torres del Paine National Park, the main object of our trip. It was a bit rainy when we left the bus and walked off into the park, aiming to complete the Grand Circuit, a 7-day, 100-km hike around the Paine Massif. Heading down the trail:


Google Map of the Paine Massif, the main focus of the national park:

It's a little offshoot of the main Andean cordillera, a relatively isolated block of mountains rising from the Patagonian steppe. The park is named for some towers ("torres" in Spanish) in the eastern part of the massif. The word "paine" ("pie-nay") apparently means "light blue" in the pre-Spanish native language. This is apparently because many of the lakes (so prominent in these maps) are light blue in color due to the large influx of suspended glacial "milk."

Here's the specific route we took (approximately) in blue:

We hiked in a counter-clockwise direction.

So we started off over in the eastern part of the park, headed north by northwest. We were hiking through steppe, with the snow-covered mountains rising to the west:


...But wait, what's that on the horizon?

Guanacos! These are camellids -- related to the better-known llamas of Peru.

Thumbs-up for guanacos!


The rocks of Torres del Paine are mainly Cretaceous-aged turbidites (shale, graywacke, and conglomerate), intruded by granitic magma in the Eocene. All along the whole trip, I was drooling over the many beautiful graded beds I saw. Here's the first photogenic graded bed I found, with the paleo-top of the bed at the top of the photograph:


These rocks of the Cerro Toro Formation were deposited in the Magallanes Basin, a Cretaceous to Paleogene retroarc foreland basin. Brian Romans of Clastic Detritus shared some information with me before I went down to Patagonia, and I am indebted to him for the insights I gleaned from that sharing. However, any errors in identification or interpretation are my own. According to the model of Romans, et al. (2009)*, a fold and thrust belt was operating to the west, and an elongate north-south oriented submarine trough flexed downward east of that during the Cretaceous. Mud and sand and gravel flowed into this sedimentary basin mainly from the north in three phases which can be contrasted readily with one another in terms of depositional style and confinement of depositional area. These three phases of deposition correlate to different facies, and are exposed well in the area north of Puerto Natales due to subsequent deformation and uplift (not to mention recent deglaciation).

I'm a structural geologist, and deformation is what I am all about, but I honestly didn't expect to see much structure when in Torres del Paine. (I was eagerly anticipating the graded bedding, though!) So it was somewhat shocking to see some very deformed turbidites on that first day of hiking. Here's me standing on the edge of the Paine River, surrounded by tilted turbidite strata:


...And this stuff was really messed up:


Zoomed-in, you can see some severe folding and faulting having shuffled up these rocks:


We hiked about six or seven miles that first day, and camped at a place called Seron. The park has set up these dozen or so campgrounds where you are allowed legally to camp. Some are free, some cost a few bucks. Seron cost about $8 per person to camp there, but we got hot showers with that cost: Nice! The sun set on our first day, and we slept well.


More soon, on our second day of hiking...
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* Romans, B.W., Fildani, A., and Hubbard, S.M., 2009. "Controls on Deep-Water Stratigraphic Architecture," in Stratigraphic Evolution of Deep-Water Architecture: Examples of controls and depositional styles from the Magallanes Basin, southern Chile, SEPM Field Guide No. 10, p. 7.

Labels: chile, cretaceous, eocene, mammals, maps, national parks, paleocene, patagonia, primary structures, rain, sediment, snow, south america, structure, travel

Can you guess which of these Google Maps is (a) Greenland, (b) Australia, (c) Antarctica, and (d) Utah?

Labels: antarctica, australia, contest, greenland, ice, salt, snow, utah

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

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

From NASA's Earth Observatory:

Labels: nova, snow

For the penultimate post in my Ecuador travel series, I hereby recount the story of climbing the mountain called Iliniza Norte (16,997 feet above sea level: the tallest peak I've ever summitted).

We began by driving up from the town of Chaupi, where we were staying at a hostel, to the trailhead above treeline in the paramo ecosystem...


We had hoped for awesome weather, but as with our previous peak bagging in Ecuador, the clouds were here too, making a ceiling that we headed up into...




Heading up into the clouds; the valley below fades away...


...and we start to see snow.






We went up a long, steep snowfield for probably two hours... It was frustrating going: take one step forward, slide two steps backward. The snow got thicker and thicker...

Eventually, when we got close to the summit, we got off the snowfield and onto some rocks. I was surprised to feel how my energy spiked at the prospect of rock-scrambling. The long slog up the snowfield was boring and repetitive, but this was totally engaging as a physical/mental workout. Here's Lily and Diego climbing up:



At the summit, there's a steel cross with various doodads attached...


This is the highest point above sea level I've ever experienced. When I stood on the summit, my head was above 17,000 feet in elevation!



Silly video of the summit team making celebratory noises:


Then Diego said, "I think we go down now, because of thunders."

The guy knows his stuff: as soon as he had said this, we heard a ba-boom from off in the white clouds somewhere... Yikes. Okay, time to head down.

Descending the rocks:


When we got to the snowfield, another peal of thunder sounded, and this one was louder than the first one. The snowfield, fortunately, made for easy going -- we essentially skied down it. It was pretty exciting... Flashes of lightning, booms of thunder (sometimes within a microsecond of one another), adrenaline pumping, running/sliding/skiing downhill as fast as we could.

We did not get hit by lightning.

After we got below cloud level (and into a valley where we felt a little less exposed to lightning strikes), we could see that the lower elevations had gotten some frozen precipitation too: a mix of snow and hail:











When we got back to the vehicle, we found it covered in hail:


Now for the adventure after the adventure: driving down a steep, twisting, muddy mountain road that's coated with hail and host to numerous roaring streams of runoff. It was almost as intense as descending the snowfield amid lightning bolts: the vehicle slid and knocked against a mud embankment at one point, and it was all seriously sketchy. Diego said he had never seen anything like it.

Here's some video of a raging torrent of meltwater/runoff flowing over a road surface that's decorated with white hailstones:



We did not crash the car.

Back safely at the hostel, we took hot showers and drank beer and congratulated ourselves for clearly being such daring adventurers. Whew... the next morning, we took our weary selves back to Quito.

One more Ecuador post to go... on lichens... stay tuned.

Labels: ecuador, ice, mountains, snow, south america, travel, volcano

In prepping for a mass wasting lecture this week in Environmental Geology, I checked out YouTube's "avalanche" offerings. Found a couple of cool videos:

Cheesy music on this one...

French skiers chatting on this one...

Labels: mass wasting, snow

Yesterday was our first big snowfall (well, "big" by DC standards) of the year. We got around 3 inches total, but then last night that got covered and compacted by a layer of freezing rain. Here's the scene yesterday morning around 8am from my apartment, looking west over Beach Drive, Rock Creek Park, and the National Zoo (movie is 30 seconds long):



The College was open, though, so in we all trooped. Here's the campus as viewed from Little River Turnpike:



And a few shots of the snow-laden campus...




The snow continued into the afternoon, with predictions of freezing rain for the evening. I had my Physical Geology class, but then the word came down from on high* that NOVA would be closing at 2pm. So, no lab, and no Environmental Geology. We all trooped home to our various classes.

* NOVA has put together an impressive new emergency alert system. It automatically sends e-mails, sends text messages to our cell phones, and (as I found out yesterday in the middle of my Physical Geology lecture) causes a window to open up on all campus computers saying "ALERT: The College will be closing today at 2pm due to snow." I was in the middle of a PowerPoint slide showing why weak bonding in mineral crystal lattices cause cleavage, and BAM suddenly there was a flashing alert up on the screen. Instantaneous notification for the entire class. Another one was open on my computer when I got back to my office. Pretty effective, I think.

Labels: dc, nova, snow

Ed Adam's "cold lab" (which I toured this past summer as part of my "Examining Life in Extreme Environments" class at Montana State University) gets mention in an article in today's New York Times. They also profile some of Adams' experiments setting off avalanches at Bridger Bowl, in the Bridger Range north of Bozeman. Worth a read. Some cool photos, too.

Labels: ice, mass wasting, montana, msse, snow

Labels: appalachians, climate change, global warming, new york, rain, sediment, snow

Here's a satellite image of the Caribbean from early Friday morning:



Gustav's still moving northwest through the Caribbean, and set to enter the Gulf of Mexico by about midnight tonight, or early tomorrow morning. As you may have heard, everyone's getting ready for the worst-case scenario. Louisiana governor Bobby Jindal has already declared a state of emergency, and President Bush gave him a similar federal declaration. I'll be watching this one pretty closely over the next few days.

Another phenomenon that's manifesting itself over the coming days and weeks is the melting of the Arctic sea ice pack. As Al Gore noted in his speech the other night, the worst case scenario for melting of this sea ice has the Arctic ocean ice free sometime late in the term of the next president (but that's a worst case scenario). Certainly, the trend over time is towards less and less of the Arctic frozen. I follow the fluctuation of sea ice area on the website The Cryosphere Today (University of Illinois), which provides satellite data, graphs, maps, and animations of the areal extent of polar sea ice. Here, for example, is a graph showing the area of the Arctic Ocean covered by sea ice over the past year:



Last year, of course, it hit a record low, and there's still a few weeks to go before it starts freezing up again (mid-to-late September is the time of the minimum). Open Mind did an excellent post examining the trend here, although the pattern is also observable on this long-term graph from Cryosphere Today. Here's another one, from the National Snow and Ice Data Center at the University of Colorado, that gives a half-century of context to the graph above:

In case DC-area folks didn't hear about it, there's also been some recent flooding in the southwest. (Geoblogospheroids will be well aware of it already, thanks to excellent coverage from Lee Allison at Arizona Geology.) I swam in that canyon this summer, just above the confluence with the Colorado River, and so this caught my attention more than an equivalent story would have about flooding someplace I hadn't been.

In addition to these larger-scale phenomena, there's a more local kind of weather I'm watching too: it's actually started raining in DC, for the first time since I got back on August 1! (A perplexed Achenblog on this odd situation). Time to bust out the umbrella.

Labels: hurricanes, ice, news, rain, snow

...No kidding!

This photo was taken in early June, when I drove through Yellowstone for the first time this summer... there was still snow eight feet deep along Sylvan Pass at that time!

Labels: snow, travel, wyoming, yellowstone

The geoblogosphere spawns semi-monthly collections of blog posts on a particular theme, and this time around, Dr. Lemming is hosting with the theme of "things that make you go Hmmmm." The idea here is to write a blog post about something you don't understand in geology -- a mystery. Here's my contribution:

When I was in graduate school at the University of Maryland, I started hearing about a crazy notion that the entire planet had frozen over in the past. Apparently, multiple streams of evidence (chemical, isotopic, geologic, and magnetic) suggested that during the Neoproterozoic era of geologic time, the planet experienced a mega-Ice Age. There were even glacial deposits within a few degrees from the equator. If you've got glaciers operating within a few degrees of the equator, some scientists argued, then that means the Earth would have been entirely sheathed in ice. Its reflectivity ("albedo") would have been so high that most (~85%?) of incoming solar radiation would have been reflected back out into space, and that would have made the planet even colder, promoting more snow and ice. This positive feedback cycle would have reached a tipping point if the planet were covered in ice from the poles to approximately 30 degrees latitude: once it got that white, the "runaway albedo" feedback would have reached a tipping point, and wham, you've got a planet that looks like a great big snowball.

This led Joe Kirschvink (of Cal Tech) to dub this episode of glaciation the "Snowball Earth," which is about as catchy a name as a scientific hypothesis is every likely to get. The idea was then heavily promoted by Paul Hoffman (of Harvard), who was seeing strange stratigraphic patterns during field work in Namibia. Among the evidence Hoffman eventually accumulated for the Snowball were the following: "dropstones" (boulders, presumably dropped by icebergs into fine-grained offshore marine deposits, squishing the layers beneath them); conformable stratigraphy of "tropical" carbonate topped by glacial tillites, topped by more "tropical" carbonate; carbon isotope anomalies in overlying "cap" carbonates indicating a massive inorganic dumping of precipitated CaCO3; delicate crystal fans (some meters tall) precipitated rapidly in the post-Snowball ocean; and the temporary reappearance of banded iron formations (BIFs), which had not been seen since the Paleoproterozoic (and indicated an anoxic ocean, such as one sealed beneath a layer of ice).

When Kirshvink pitched the initial hypothesis, he also proposed how the Snowball could have ended (in a deliciously short, non-peer-reviewed paper): he noted that just because the surface of the planet was frozen, that would have meant diddly to plate tectonics. Radiogenic heat from the Earth's interior would have continued to drive plate tectonic processes, and that meant subduction would have continued, beneath the icy rime. If subduction continued, that meant that volcanoes would have continued to erupt, and as Iceland and Antarctica show us today, volcanoes can erupt underneath glaciers. This is important because volcanic outgassing has a substantial percentage (~15%) of carbon dioxide (CO2), and CO2 absorbs reflected infrared radiation: it's a greenhouse gas.

But with the entire surface of the planet frozen, what would have happened to this degassed CO2? If the planet's surface is frozen solid, that means the hydrologic cycle would be shut down, and the usual means of removing CO2 from the atmosphere (e.g. photosynthesis & also deposition of carbonate sediments like limestones) would be non-functional. Any CO2 emitted by volcanoes would therefore likely linger in the atmosphere, building up in concentration over time. Eventually, Kirshvink suggested, it built up to levels that caused global warming which compensated for the ice albedo effect, and the absorption of all that radiation by the CO2 melted the Snowball.

As evidence for this audacious idea, Kirshvink pointed to the cap carbonates: all that limestone ("cap carbonate") deposited on top of the glacial units needed a lot of CO2 to be dissolved in seawater (and a lot of Ca+ too). The cap carbonates, it was suggested, represented the stratigraphic removal of all that built-up CO2 from the atmosphere. Once the levels of CO2 were drawn down to a non-hothouse level, the cycle could repeat itself. Modeling calculations suggest that it would take about 5 million years of CO2 buildup to melt the Snowball.

And this is what I don't get: if you've got an atmosphere full of CO2, I can see how that would melt the Snowball. But wouldn't it then acidify the ocean (with carbonic acid, like we're seeing today), making calcite dissolve, rather than be precipitated? If the ocean is undersaturated with respect to CaCO3, then that ocean should not host accumulations of limestone. How could the voluminous worldwide cap carbonates be deposited in an acidic ocean?

On the Snowball Earth website, a list of suggested reasons why Snowball Earth could not have happened are listed, along with Hoffman, et al.'s scientific rebuttals. But when they come to the question of acid oceans and the deposition of cap carbonates, you can almost see them shrug: "These are serious criticisms," they note. Hmmmmm.

Post-script: The idea is intriguing not merely scientifically, but also in terms of the way science gets done: by people, sometimes people with outsized personalities. Paul Hoffman promoted the idea with an "evangelical zeal" (according to Gabrielle Walker, who wrote a book about the whole idea and the scientists involved). Hoffman's relentless pushing of the idea ruffled a good many feathers. Some scientists fought back, motivated in part by these chafing interpersonal dynamics. There's nothing like a little scientific controversy, and this is what Walker's book focuses on, more than the details of Snowball science.

When I found that Jay Kaufman (of UMD-College Park) was interpreting a local diamictite(near Aldie, VA) as a Snowball Earth tillite (and the overlying marble layer as a cap carbonate), I thought "this could make a great class." Last spring, I applied for and received a grant from the Virginia Community College System to develop a 2-credit class for NOVA utilizing these local rocks as a gateway to understanding the Snowball Earth hypothesis. I offered the class for the first time last summer, and I'll be offering it again this summer in August. We were fortunate to get rock samples from Virginia's two putative Snowball deposits as well as a suite of samples on loan from Gene Domack of Hamilton College. These "Snowball Suite" samples include tillites and dropstones from Namibia, Greenland, Mauritania, and Canada, as well as international BIFs and cap carbonate samples. I have to tip my hat to Dr. Domack and his colleagues: making these samples available is a terrific service in support of geoscience education.

Labels: climate change, CO2, geology, global warming, nova, snow, snowball earth, teaching

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