This is beautiful: That's an image by Chris Waythomas of the USGS, hosted by the Alaska Volcano Observatory website. It shows a cutbank (river-eroded alluvium deposit) along Rust Slough, south of the Drift River Oil Terminal, northeast of Redoubt Volcano. The sediments exposed were deposited on March 22, 2009 by a lahar (volcanic mudflow). The lahar deposit is 2.5 m thick. When I saw this image tonight (as I was searching for another shot), I was particularly struck by the subrounded clasts of ice in the mud. Here is ice acting the part that chunks of rock usually play. Technically, ice is a mineral, and so these chunks are sedimentary clasts much like any other... But to me there's something distinctly different about seeing ice cobbles and pebbles included in a sedimentary deposit. On a planet as warm as Earth, this sort of thing isn't likely to be preserved in the geologic record. It would melt! ...And that gets me thinking about other planets and planet-like objects, like Titan. The Huygens probe took pictures of sedimentary clasts, presumably of ice, on the surface of that moon. Other cold locations could have CO2 ice ("dry ice"): That makes for the sort of rock specimen that would be really difficult to keep on your shelf as a 'deskcrop'...

An additional thought: how could the former presence of icy clasts have influenced the geologic record? Perhaps ice clasts were an integral part of a deposit as it was laid down... but then later the ice melts away. How could we detect and control for this?

Labels: alaska, CO2, ice, satellite imagery, sediment, volcano

You'll recall that our sixth day in Torres del Paine National Park had us hiking east from the Paine Grande Lodge. We hiked up over a ridge dividing Lago Pehoe from another turquoise-colored lake, Lago Nordenskjold:


At the so-called Italian Camp, we dropped our packs, and went for a small side hike. We turned to the north, and hiked up the French Valley:

The object of this day-hike was to see some glacier calving. The French Valley is famous for this: you sit back and watch, and big chunks of ice spall off the glaciers, crashing hundreds of feet below onto the rocks. A few seconds later, a sound like thunder reaches you: it was this that we came to experience.

Anybody seen a glacier around here? Rumor is that it was JUST here!

[The line demarcating vegetation above from bare rock below shows former height (and presence) of the glacier.]

Here's a look at the amphitheatre where our glacial show would be performed:


As the clouds cleared a bit, we could see an astonishingly thick cornice of snow/ice atop the mountain peaks. All the valleys up top had been filled in and smoothed off, and there was this white rim atop the black rock. The cornice is probably 40-100 feet thick in this photo:


An annotated photo of the area where we were observing the action:

What happened here was that a much larger glacier (see the vegetation line back a few photos) ablated away, splitting into two upper disconnected feeder glaciers, and a lower glacier which is now semi-buried in rocky debris (talus) and ice spalled off the upper glaciers.

A closer look at the annual growth layers revealed in the lower part of the glacier:


We soon saw some calving events. They were quite cool. Big booming noises, ice explosions seen through binoculars, eating chocolate and almonds. We were happy. Then we heard a roaring noise, like an airplane going overhead. We looked at the glaciers: nothing. What was making that noise? Then, from above, we saw it: coming down out of the clouds was a huge billowing white mass. Apparently, it was coming down from the cornice of snow atop the mountain. An avalanche! An honest-to-goodness avalanche! I have never seen one before; I was giddy at the spectacle. It looks just like a turbidity current, people, but it is white!

It was a magical thing to witness: watching it spread out and poof outward in hundreds of little round turbulent vortices. Everyone in the valley cheered: "YEAHHHH!!!!!"

Tough act to follow... but: Just east of us were the rugged Cuernos del Paine, a series of glacial horns made more photogenic by the pink stripe running through their middles, like a WWF Championship Belt:


This pink stripe is a granitic intrusion, approximately 12 Ma (Miocene*). Here is another photograph of the Cuernos, where the granite is very obvious:


We walked along the north shore of Lago Nordenskold towards the Cuernos campground...


Across the lake, some nice folds were visible:


The Cuernos campground is in this little nook. A lovely place to spend an afternoon and our final night in the park:


And it has very nice views of the Cuernos del Paine:


Seeing the Cuernos was the fulfillment of a decades-old dream for me. I think I saw them in an REI catalog (or perhaps a Patagonia catalog, hmm?) back when I was in college, and thought, "Wow. There's a place on Earth that really looks like that? I gotta go... someday." What I didn't expect then, and was pleased to see now that I was there, was the excellent evidence of stoping, one of the processes by which magma chambers enlarge their size and intrude into other rocks. Stoping is where chunks of the wall rock ("host rock" or "country rock") are broken off by inquisitive fingers of magma, and the liberated blocks (now xenoliths) drop into the magma chamber. Here, you can see (white arrows) some of these splurtles of granite working their way into cracks at the top of the magma chamber:


If these fingers of granite connect up, they separate the block of rock beneath them from the country rock (a form of physical weathering, like root wedging!). More dense than the surrounding magma, the resulting xenoliths sink. If the magma is still rather fluid, the xenoliths may now pile up on the floor of the intrusion. If it's getting to be mushy and semi-crystalline, their downward flow may be retarded, like a slice of banana trying to sink through thick oatmeal. As the granite crystallizes into rock, those xenoliths will be trapped somewhere between the ceiling (source area) and the bottom. Check out the diversity of xenolith positions (white arrows) displayed on this Cuerno:


Great looks at stoping here: some have fallen, some are still beginning to fall. I could easily have spent another two days just hiking along this contact, looking at this intrusive relations.

We spent our final night in the park enjoying the sounds of a nearby waterfall, nature's white noise machine. Only one more day in Torres del Paine...

Labels: chile, glacial landforms, glaciation, granite, ice, igneous, miocene, national parks, patagonia, south america, travel, weathering, xenoliths

On Boxing Day morn (Dec. 26), we woke at Refugio Grey, and took our camp stove outside. Just for a lark, we walked over to the shore where an iceberg had beached itself, and popped off a chunk to melt and make coffee:

You haven't really had coffee until you've had coffee made with water that's been locked out of the hydrologic cycle for 14,000 years!

With warm coffee and a granola bar apiece, we walked over the small peninsula where Regugio Grey is located to the bay on the other side. There, a flotilla of icebergs had rafted up against the peninsula. We decided to spend a little bit checking them out, before heading out on the day's (short) hike to the next refugio. We had it all to ourselves:


The icebergs varied tremendously in size, shape, color, and texture.


So, presented with a wealth of icebergs like this, what would you do? If you answered "put one on my head!" then apparently you think the same way that we do:


Silliness expended and coffee consumed, we grabbed our packs and hit the trail again. Today's destination was the Paine Grande Lodge. It wasn't an especially long hike, and it was essentially parallel to Lago Grey for most of the distance. Here's some more icebergs, further down the lake:


One geological site that really caught my attention was this sweet outcrop showing gorgeously folded turbidite layers. To give a sense of scale, each of those green bushes is about 1 meter in diameter:


Here's (white arrow) the Paine Grande Lodge, on the shore of a new lake (you can tell by the color), Lago Pehoe.


Closer in shows the detail of this nice, modern facility:



It was our second night indoors, and while it was a bummer that we had to share our room (6 bunks) with 4 other people, one 'up' side was that the Paine Grande took credit cards, which mean that the pisco sours were on Callan and Lily!

This is the lounge, with a nice woodstove and great views of the landscape for birdwatching or just sitting back and feeling satisfied. We spend a while hanging out here, particularly as a few rain squalls moved through.

The usual routine followed: dinner, bed, dawn, coffee, hiking... on to Day 6!

Labels: chile, glaciation, ice, patagonia, south america, structure, travel

Christmas day in Torres del Paine National Park: We packed up our gear at Paso Campground, and hit the trail in the rain. It rained on us for about an hour as we walked south, parallel to the downstream flow of the Grey Glacier, a huge gleaming presence to our right. Occasionally, the trail exited the forest as we had to cross deep ravines, like this one:


Snowmelt coming off the Paine Massif carved these ravines, and the park service had placed ladders in a few key locations, like this one:


Some people didn't like the ladders very much:


Once we got far enough along, we could see the terminus of the Grey Glacier:

Umm, wow.

Slightly different photo composition, with a tree in the foreground:


Nothing but terminus:


Looking south-ish, down the axis of Lago Grey:

Our destination for the evening was Refugio Grey, located on the far side of that first little hook-shaped peninsula.

Iceberg in Lago Grey:


Refugio Grey:

This was our first night spent under a roof on this trip. After three nights in a tent (me with a flat Therm-a-rest), it was quite luxurious to indulge in hot showers and a mattress! We also had a superb Christmas dinner behind those plate-glass windows, eating pork loin and drinking Gato and watching icebergs float by. It was pretty freaking cool.

That afternoon, we went for a walk down the beach, checking out the rocks. There were nice sedimentary structures and nice tectonic structures. Here's some trace fossils seen on one of the bedding planes of the turbidite strata:

I saw a fair amount of bioturbation in the turbidites, but this was without question the best exposure I saw.

Here's a tight little anticline:


Callan takes a nap in a little synclinal bed:


Flame structures with palimpsest glacial striations:


And another set, a few feet over to the right (same bed):

There appear to be some burrows here, too (the little circles of sandstone in the mudstone below the main sandstone contact).

We slept well that night. I was especially pleased by the fact that it rained for half the night (since I was sleeping indoors).

Labels: chile, fossils, glaciation, ice, patagonia, primary structures, south america, structure, travel

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

Wow. Very cool. Literally.

Hat tip to Al Rasheed. Thanks Al!

Labels: antarctica, australia, ice

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

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

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

Paul Hoffman is speaking next Wednesday (April 22) at the Geological Society of Washington; I've just recieved word that his topic has changed from Snowball Earth to "The Pleistocene glacial controversy and the discovery of climate warming and crustal dynamics." I'm curious to see what Hoffman has to say about the 160-year old controversy as to whether there had been recent "Ice Ages," and how that relates to his currently-controversial ideas about the Snowball. Whatever he says, it's likely to be thought provoking.

Labels: geologists, glaciation, gsw, ice, pleistocene, science and society, snowball earth

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

Cool idea. Check it out.

Labels: art, blogs, climate change, global warming, ice, oceans

Last month, when hiking Iliniza Norte, a 16,997' volcano in Ecuador, we got up near the summit and began scrambling over the rocks there. Conditions were cold and snowy, and I was pleased to see some beautiful ice formations in protected nooks in the rock. These crystals of ice had a gorgeous branching pattern...



To show this branching pattern close up, here's Lily's gloved hand holding two such crystals (fused together). They look like squirrel tails!



The backdrop of oxidized porphyritic andesite (hosting lichens) isn't bad either.

Labels: ecuador, ice, minerals, travel

The International Year of Planet Earth may have declared a list of "the Earth's ten most spectacular places." At least that's what they're saying at the Discovery Channel's new Discovery Earth site, where they have a rundown of all ten (with photos). (No mention of it at the IYPE site, though: It may be that the Discovery Channel is just highlighting ten of the many, many U.N. World Heritage sites... their language is unclear as to who decided on these particular ten.)

Regardless, the photos will whet your appetite. With my visits in bold, they are:

• The Giant's Causeway, Northern Ireland (posts on NOVA Geoblog)
• Wadi Al-Hitan (Valley of the Whales), Egypt (Eric's been posting on this recently)
• Lake Baikal, Siberia (deep, big)
• Komodo National Park, Indonesia (big monitor lizards; my friend Kenny has been)
• Grand Canyon, Arizona, USA (posts on NOVA Geoblog)
• Ilulissat Icefjord, Denmark (glacial beauty)
• Wulingyuan, China (quartzite pillars and indigenous fauna)
• Surtsey, Iceland (46 years old this year)
• Central Amazon, Brazil
• Great Barrier Reef, Australia

Labels: antrim coast, asia, australia, china, fossils, giants causeway, glaciation, grand canyon, ice, reefs, south america, travel, water resources

The day before Inauguration, I decided to celebrate George Bush's last day in charge of my country by taking a walk in the woods. Okay... that wasn't really my motivation. I was just procrastinating writing up my Structural Geology labs for the coming semester. Anyhow, for one reason or another, I took a stroll in the woods.

I brought my rootin' tootin' new camera with me, and took a few photos. I've got four things to show you: (1) some differential weathering, (2) some kink banding, (3) some cool effects in frozen soil, and (4) a critter.

(1) To start, check out this close-up photo of a stone bridge where the Klingle Valley merges with the Rock Creek Valley:


Several of the (local) stones used in the bridge are weathering at a faster rate than the mortar (cement) that holds them together. As a result of this differential erosion, the less-stable rocks are recessed into the face of the bridge:



Here's another one, where you can see that not all minerals are equally stable at Earth surface conditions. The large central quartz augen stands out in high relief as the micaceous & feldspathic schist around it weathers away.



Yet another: recessed about an inch into the bridge:



That's not all I saw. I also re-discovered the location of some kink bands along the Rock Creek Park bike path:



These kink bands are similar to the ones that Spring 2008 Honors student Victoria measured and analyzed in Broad Branch (also in Rock Creek Park), but these ones are in a different location, further south in the park.



What's worth noting about these kink bands is that they overprint the regional foliation of these schistose rocks. In order to do that, the force that generated the foliation must have been coming from one direction (call it east-west), causing the mineral grains to line up at right-angles to that stress. That allignment is what we call foliation. Later, a new generation of deformation came in from a different direction (call it north-south, approximately parallel to the foliation), kinking the pre-existing foliation. For more on kink bands in DC, see my "DC rocks" page.



(4) One of the disadvantages to hiking in Rock Creek Park in the winter is that it's pretty monochromatic. One of the advantages is that with all the leaves off the trees, it's a lot easier to see new stuff. It's great woodpecker-watching weather, for instance. I saw five woodpeckers of two species that day. Also, it makes it a lot easier to see where the trails are. I saw a new trail that I had never walked before, and so I decided to check it out. I'm glad I did. One thing that I saw that is pretty cool is this effect in frozen soil:



When water freezes, it expands in volume by about 9%, and that shows up here as the upper layer of wet soil froze, it expanded in all directions, pulling away uniformly from two large cobbles of quartzite. It almost makes it look like the quartzite cobbles shrunk in their "sockets," but really it's the "sockets" that got larger.

(4) Lastly, I was doubly glad to have taken the new trail because it was a "road less travelled" kind of deal. I was the only one there. As I trod along, suddenly I heard a scampering noise. It was a critter! It ran up a little gully and then paused as still as a stump, looking at me:



Can't see it? Try this zoomed-in shot:



It's a red fox! Vulpes vulpes, one of two wild canids we have in Rock Creek Park. Pretty good sighting -- only the fourth time I've seen one here (and I spend a lot of time in this park). And every one of those times was in the winter. Again, it's having those clean leaf-less views that allows hikers to see stuff like this.

Labels: critters, dc, ice, mammals, national parks, structure, weathering

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

An article posted last hour on washingtonpost.com by Joel Achenbach examines an upcoming paper in Science that explores the idea of an impact triggering the Younger Dryas glacial advance as well as ending the Clovis culture and triggering the extinction of the Pleistocene megafauna. The evidence is nanodiamonds in sedimentary deposits from 12,900 years ago. Read the article, and wonder how Joel Achenbach finds out about this stuff a day before it's published. How does he get his hands on this article with enough time to compose a newspaper piece about it, but the rest of us have to wait until tomorrow to read the original paper?

Labels: anthropology, climate change, critters, diamonds, ice, news, sediment

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

Two weeks ago, my friend Lily took a hike up Mauna Loa. Lily teaches science at a middle school on the big island of Hawaii, and we became friends this summer at MSSE Dino Camp. I would think that living on the island of Hawaii would have some major disadvantages over time (my guess is that I'd get cabin fever living on an island), but you can also imagine that it would have some major advantages too.

In addition to live volcanic activity, surfing, exotic birds, and just general paradise-like conditions, add this to the list: climbing a tropical volcano to see giant frost crystals forming on top! Here's an image she took at sunrise, looking west over the summit caldera:



Mauna Loa is the largest volcano on the planet Earth. Rising 5 kilometers from the Pacific seafloor to sea level, then an additional 4 kilometers to its summit, Mauna Loa has an estimated volume of 80,000 cubic kilometers! It's big.

Because it's so tall, the weather at the top is much colder than the tropical sultriness at the beachfront resorts. Lily and her hiking partner found this out when they camped out on top, and woke to find that overnight, giant crystals of frost had grown spike-like from the tops of the exposed cobbles and boulders of basalt. I don't have a sense of scale here, but I'm guessing these are a centimeter tall or so... Here's a close-up of the lower-left corner of the upper image:



Pretty cool, eh? Literally. Maybe Hawaii has more variety than I had assumed. I think this calls for a field trip to investigate!

Thanks to Lil for sharing the photo!

Labels: hawaii, ice, volcano

A bunch of articles in today's issue of Nature use precise measurements of the composition of glacial air bubbles to extend the record of atmospheric gases (and airborne dust) back to 800,000 years before present. (Previously, the record "only" went back to 650,000 years before present.) Fully eight glacial cycles are seen in the new, expanded dataset. These new findings are all part of the European Project for Ice Coring in Antarctica (EPICA), and they offer some new insights, as well as additional confirmation of the close link between climate and past fluctuations in CO2 and CH4. Check it out.

Labels: climate change, CO2, global warming, ice

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

My friend 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 some 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, lakes, michigan