Labels: alaska, climate change, global warming, humor, oil

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

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

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

Neat!

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

After we had collectively collected a hundred pounds of samples from Mineral Hill, the final stop on the University of Maryland petrology trip was in scenic Ellicott City, Maryland, where we visited the Ellicott City Granodiorite (map to outcrops).

Like everything else on this trip, the ECGD is intimately tied in with the Taconian Orogeny (late Ordovician; caused by the collision of ancestral North America with a volcanic island arc in the Iapetus Ocean basin). However, unlike the Port Deposit Tonalite we looked at early in the trip, this one crystalized from magma at 435 +/- 15 Ma (U/Pb in zircon). It is not only much younger than the PDT, but it's also pretty young even for the Taconian Orogeny, which reached its peak around 460 Ma.

It's more potassic than the Port Deposit Tonalite, as these K-spar 'megacrysts' show:


This potassium feldspar 'megacryst' shows internal growth laminations, as small mafic bits got caught up in the growing feldspar crystal, which consumed and included them:

Not only does this help us see how the feldspar crystal's habit is a reflection of its internal structure, but it's also an example of the principle of relative dating by inclusions, expressed in a single mineral crystal! Pretty cool.

As with the PDT, xenoliths may be seen in the ECGD:


Parts of it are equigranular, and parts of it are highly foliated:


And of course my eye is always drawn to the structures, like these small faults offsetting dikes of granite which cross-cut the ECGD:




The real prize with the Ellicott City Granodiorite is to view first-hand the magmatic epidote it bears:


Most epidote is metamorphic. However, as Zen and Hammerstrom (1984) showed that epidote could also crystalize from a late-phase magma as the melt interacted with hornblende at high pressures (8 kbar; roughly 30 km depth). You'll note in the photo above the intimate association between the epidote and the hornblende. (I'm not super-confident on my titanite identification, by the way; this rock also bears similar-looking allanite. Please correct me if I'm clearly wrong.) E-an Zen has guest-posted to this blog before, and once upon a time he tasked me with searching for magmatic epidote near Haines, Alaska, in 2006. I didn't find any, but it did pique my interest. So it felt good to be able to finally see some of this rare beast. I was surprised to find it locally, considering the the original magmatic epidote paper referred mainly to west coast plutons from California to Alaska. I was also suprised because of the tremendous depth of crystallization it implied: 30 kilometers down? Wild! I collected a sample for the NOVA lab.

Thanks again to Rich Walker and Roberta Rudnick for graciously hosting me on this trip. I learned a lot, and I'm greatful for the opportunity to expand my local outcrop knowledge.

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Reference:
E-an Zen and Jane M. Hammarstrom (1984). "Magmatic epidote and its petrologic significance." Geology, September 1984. Volume 12, no. 9, p. 515-518. DOI: 10.1130/0091-7613.

Labels: alaska, maryland, metamorphism, minerals, structure, xenoliths

One of my students, Rob M., forwarded this photo to me over the weekend:



He tells me his dad took it along the coast of Alaska. Pretty cool shot. Unlike most of the photos on this blog, you can click through to get a big version.

Thanks to Rob and his dad for permission to share the photo here!

Labels: alaska, glacial landforms, glaciation

This image came to my attention the other day via Lutz's Geoberg blog. It's one of the high-res images provided by the newly-launched satellite, the GeoEye-1, which is supplying new images to Google*. The image shows a marginal lake associated with an alpine glacier in Kenai Fjords National Park, Alaska (just south of Seward):


The top of the above image is not north; it's southwest. Mentally rotate it, and you can see that the resolution is a lot better than the current level on Google Earth and Google Maps:


The thing that struck me about the new GeoEye image, aside from its beauty, is the distinct pattern of iceberg sizes in the lake: freshly calved off the glacier, the biggest icebergs are close to their source, while further away the icebergs are smaller. This pattern struck me as being analogous to sediment. Fresh from its source, sedimentary particles are at their largest size, and the further away they travel, the more weathering they experience. This weathering (in particular of the physical variety) tends to break them down into smaller pieces. Adjacent to an orogenic belt, for instance, you tend to find deposition of sedimentary particles shed off the uplifting mountains. As a general rule, these are of the largest sizes and the greatest volume closest to the source, and then particle size and stratum thickness both diminish with increasing distance from the orogen.

For a North American example, consider the Catskill Clastic Wedge, a tick pile of sediments shed off the late Devonian Acadian Orogeny along the east coast. Here's a cross-sectional view** (pre-Alleghany Orogeny deformation) of the wedge, running from the Bay of Fundy west to Michigan:


Same pattern! Coarse stuff, and more volume of stuff, close to the source. Finer stuff, and less volume of stuff, further from the source. Just like the iceberg, except the weathering of the icebergs is mainly thermal, while the weathering of the sediments is physical, accompanied by depositional sorting by the transporting currents of water.

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* An original version of this post misidentified Google as the owners of the GeoEye-1, as opposed to the company called GeoEye, which sells images to Google. Thanks to Bruce Haley for the correction. (updated 8:14AM eastern time on Dec. 9, 2008)
** Image redrawn (by me) from an original in Prothero & Dott (2003).

Labels: alaska, analogies, art, canada, glacial landforms, glaciation, maine, michigan, mountains, new york, satellite imagery, sediment

Andy Revkin's Dot Earth blog alerted me to a significant milestone in Arctic melting: There is a continuous circle of water around the Arctic now: the Northwest Passage (north of North America) and the "Northeast Passage" (a.k.a. the Northern Sea Route, north of Eurasia) are both open at the same time, for the first time in recorded human history. The last time the Northern Sea Route was open was 2005, but the Northwest Passage wasn't open then. The Northwest Passage opened up last summer (2007), but the Northern Sea Route wasn't open then. This year is the first time in human history that you could sail a boat completely around the North Pole through open water... but you'd have to have a pretty fast boat (because it's going to start freezing up again within a couple of weeks).

The last month's worth of retreating sea ice data is shown in this animation loop.

Article in the Independent (U.K.)

Press release by the National Ice Center (Sept. 5):

"As of September 4, 2008, the Northern Sea Route (Northeast Passage) appears 'open'. According to the World Meteorological Organization (WMO), open water is defined as areas with less than 1/10th ice concentration (WMO Sea-Ice Nomenclature, 1970). National Ice Center (NIC) analysis of Synthetic Aperture Radar imagery suggests a 10-15km wide area of open water that winds along the Taymyr Peninsula and through the Laptev Sea. Even with small openings, currents from the north could clog openings again quickly, in the same fashion that has opened the sea ice lead in a matter of days. A sea ice lead is any fracture or passage-way through sea ice which is navigable by surface vessels. There are also substantial amounts of dangerous multi-year ice present in the area. Shallow or uncharted bathymetries may present additional hazards in those areas where ice concentration is reduced. Current charting of bathymetry from the International Bathymetric Chart of the Arctic Ocean (IBCAO) suggests depths between 10-20 meters along the Taymyr Peninsula and 20-30 meters through the lead in the Laptev. This is the first recorded occurrence of the Northwest Passage and Northern Sea Route both being open at the same time. The NIC will continue to monitor this area and will report on any changes in the status of polar navigation routes."

UPDATE: You may also be interested in the fate of some specific ice shelves: "Rapid Retreat: Ice Shelf Loss on Canada's Ellesmere Coast," a well-illustrated update from NASA's Earth Observatory.

Labels: alaska, canada, climate change, global warming, russia

A new study in Current Biology looks at mitochondrial DNA evidence from 160 woolly mammoth fossils on both sides of the Bering Land Bridge, and finds that the beasts trooped east from Asia into North America, and then marched back again 40,000 years ago, at which point the Asian mammoths slid into decline and extinction. The interpretation by the study's authors is that the North American prodigal mammoths returned to the mother country and possibly wiped out their Asian cousins.

The original article on the Current Biology* site. *Link wasn't working quite right this morning...
Scientific American's treatment of the story.
An article in the New York Times reviewing the study.

Labels: alaska, critters, fossils, mammals, pleistocene, russia

There's been some interesting articles in my media subscriptions lately. Thought I'd use today's post to share.

In the June National Geographic, a study of the geology of Stonehenge reveals the source of the monoliths ("polyliths?") there. They came from the Preseli Mountains of Wales. That's a long journey for such big rocks. Also in the same issue is an eye-popping pictorial piece on sea slugs. You must check it out, because it features dozens of David Doubilet images like this one:

WIRED's cover story this month is about environmental "heresies": ideas that supposedly environmentalists aren't supposed to like, but need to happen. The basic premise is that "only cutting carbon matters," and so they come up with some interesting recommendations like: (1) use A/C more, and heating less, (2) "screw the spotted owl" (don't worry about the loss of biodiversity), and (3) buy a used Geo Metro rather than a new Prius. I found this last of particular interest, as it recounts a web rumor that it took less carbon to make a Hummer than a Prius, and therefore Hummers were more environmentally friendly. (The Prius' battery has a lot of high-carbon-cost nickel in it.) WIRED breaks it all down into BTUs, and runs the numbers. According to their analysis, it takes the Prius 100,000 miles to catch up (i.e. be more carbon-efficient) than an old Toyota. Bummer... Big bummer. (At least the Hummer bit has been debunked.)

As usual, Smithsonian had a bunch of interesting pieces in it. Almost everything in there catches my imagination. It's a very well done magazine.

The New Yorker had a couple of articles, too: In their recent "innovators issue," Alex Ross profiled John Luther Adams, the man responsible for the mesmerizing "the place where you go to listen" in the Museum of the North at the University of Alaska, Fairbanks. If you haven't ever been there and find yourself in Fairbanks, I would recommend this museum highly, and this one room / art installation in particular: it plays certain notes and tones and changes the lighting depending on what the aurora, seismic activity, and other Earth processes are doing. And Margaret Talbot profiled Irene Pepperberg, who raised the parrot Alex and taught him to talk. This article explores the insights into intelligence gained from this serendipitous longterm experiment.

On the commodities front, the New York Times reports today that thieving biofuellers are stealing vegetable oil in Oregon, and that guano stocks are being closely guarded in Peru. Telling quote from the latter: "Before there was oil, there was guano, so of course we fought wars over it," (Pablo Arriola).

Labels: alaska, birdies, environmental, mollusks, news, prius, wales

Labels: alaska, travel