Yesterday, I took a three Honors students and a colleague to Difficult Run, Virginia. This is a hiking trail that goes from Georgetown Pike, in the tony neighborhood of McLean, Virginia, down through a deep, steep river valley to the Potomac River.

As noted a couple days ago, the trail is right across the Potomac River from my beloved Billy Goat Trail. In a recap from that post, here's a map of the area... Feel free to switch it to "satellite" view.



Some discussion of the bedrock geology of Difficult Run can be found here, in an excellent field trip guide by Scott Southworth (USGS) and colleagues that's part of Excursions in Geology and History (Frank Pazzaglia, editor).

We began our trip by meeting up with Doug Dupin of the Palisades Museum of Prehistory, who joined us for our exploratory geohike. We walked a short distance down the trail and found a big (abandoned) quarry where it was rumored there was a good fault. This is one of these pieces of information that I heard somewhere, at some point. I couldn't find it in any literature, so maybe I heard it in discussion when I taught at George Mason University for a year between grad school and when I got my position at NOVA. Anyhow, I had never actually checked it out...

...So our first order of business was to review the criteria for identifying a fault: What would we look for? Fault breccia, fault gouge, slickensides, hydrous mineral veins, and of course, offset. However, here in the Virginia Piedmont, it's rare to have a good marker unit to compare on opposite sides of the fault: usually it's just schist on one side, schist on the other. In some places, you could add the presence of a fault scarp to that list, but being as how this was an old quarry, geomorphic features like that didn't seem likely. So our search focused on the search for fault breccia, fault gouge, veins of odd minerals, and slickensides.

A few minutes in, we found some slickensides on this boulder of float:

This is a boulder of migmatitic phyllonite, with a wavy texture due to mylonitic flow at depth. (The picture doesn't show this very well at all, though you can see faint undulations 'cascading' from the top of the photo towards the bottom. It's much clearer in cross-section.) Anyhow, the 'slicks' are a faint upper-left to lower-right lineation seen on this surface, one or two degrees off from the orientation of the ballpoint pen. The surface you're looking at here was a fault plane at some point in its history. Ballpoint pen for scale.

We did eventually locate the fault, uphill from this boulder. It was characterized by a zone of fault gouge (pulverized rock), three inches wide to a foot wide in places, and highly oxidized (presumably by oxygen-rich meteoric waters percolating along this fractured surface)... but there were no good marker units to judge the total offset.

Here's a different section through a similar rock (though I wouldn't apply the "phyllonite" textural description to this one). Instead of looking at the plane of foliation here, we're looking at a surface which is perpendicular to the foliation plane(s)....

Here in this image, you can see two cleavages... One which runs roughly upper-left to lower-right through the photo, defined by gneissic banding including bands of granite (light-colored; late Ordovician in age... Taconian Orogeny). A second cleavage runs roughly left-to-right through this photo. This second cleavage overprints the first. The overall interpretation is that the first cleavage developed due to lower-left-to-upper-right compression, forming the foliation defined by alternating bands of different compositions of minerals in an upper-left to lower-right direction. The second cleavage formed due to compressive stress sub-parallel to the pre-existing foliation, deforming it into a series of tight folds. The limbs of these folds line up parallel to one another, defining the second-generation, overprinting cleavage. Can anyone else add to this interpretation? Dime for scale.

Along Difficult Run itself, the outcrops were all relatively recently scoured (in 1972 by Hurricane Agnes), so there are some good exposures. As I noted earlier this week, the area shows some nice exposures of granite pegmatites (keys, and the edge of the Pazzaglia volume, for scale):


On our field trip yesterday, we took at closer look at these beautiful pegmatites, and the associated amphibolite bodies. Take a look at this close-up... Dime for scale.

What's going on here? You've got a beautiful (euhedral/subhedral) example of an orthoclase feldspar ("potassium feldspar") crystal amid a bunch of quartz. But look closer at the feldspar crystal... this sucker has been fractured in many places, and it's shot through with very small veins of quartz. Somehow, as this pegmatite dike was cooling, the earlier-crystallizing feldspar was broken and intruded by the presumably-still-fluid silica-rich magma. Anybody able to expand on this interpretation and shed some light on how this all played out? Or contradict it and give a different story to explain this relationship?

In the neighboring amphibolite, we checked out these cool ridges of resistant rock which are centered on thin fractures. Here, you see a couple of intersecting joint sets, each of which was the "plumbing system" for silica-rich hydrothermal fluids (my interpretation). These silica-rich hydrothermal fluids impregnated the surrounding amphibolite with quartz, which made the immediately-adjacent areas more silica-rich, and hence more resistant to weathering and erosion: Hence, now that they've made it to the surface, they're weathering out in high-relief. Dime for scale.


A bit further downstream, Doug showed us a 'cave' (central dark area, just to the right of the waterfall) between the bedrock and a big slab of sloughed-off migmatitic metagraywacke:

We each edged into the 'cave' to the end, where Doug has shown that a distinctly-rectangularly shaped hole admits a direct beam of sunlight during the fall and spring equinoxes. From the inside, it's a striking arrangement, enough to make you wonder whether it's anthropogenic. However, from the outside I was unconvinced that the hole's position was anything other than natural. Doug's initial intepretation of the site was strongly influenced by the fact that there are some unambiguous petroglyphs a short distance away from here, and based on this proximity, I think it's acceptable to infer that Native Americans may have visited this cave. However, I interpreted the opening to be completely natural, with no need to invoke anthropogenic modification in any way.

We hiked on along a ridge overlooking Mather Gorge, sighting a fox and an accipiter (Coopers? Sharp-shinned?) and a few vultures, and returned to the parking lot as the sun dipped low in the sky. On the way back to campus, Honors students Ana and Hope fed us Swiss cookies and cheese & crackers. Altogether, it was a pretty great way to spend a November afternoon...

Labels: birdies, faults, field trips, granite, igneous, metamorphism, ordovician, piedmont, rivers, virginia

On Saturday, June 14, I drove from Fort Collins, Colorado northwest across Wyoming, ending up just west of Cody in Shoshone Canyon.

Here's a few photos I took along the way:

Hogbacks (or "incipient hogbacks?") north of the Interstate (not sure whether this qualifies as the Laramie Mountains or the Medicine Bow Range, or some other range altogether).

Regardless, what you're seeing here is what happens when tilted sedimentary strata are incised by streams. The stream valleys develop at regular intervals along the slope, and notch the sedimentary layers, which themselves have different resistances to erosion. As a result, these triangular-shaped slabs end up poking up along the flanks of the mountains (the Flatirons outside of Boulder, Colorado, are perhaps the best known example).

The Wind River Range appears in the distance. Seeing big bad mountains makes me happy.


Road trip man!


The Prius at the southern (upstream) end of Wind River Canyon, between Shoshoni and Thermopolis:


...And looking downstream (north):


Unconformity between Archean basement rocks and overlying Cambrian sandstone:


The Wind River:


An outcrop on the way north, somewhere south of Meeteetse. Got some cool green concretions here, and coasted downhill for more than ten miles:


Camp at the end of the day. This is at Buffalo Bill State Park, between Cody and the eastern entrance to Yellowstone (Sylvan Pass, subject of a photo I put up yesterday). The body of water seen here is the Shoshone Reservoir. I enjoyed a pleasant evening here of drinking wine, writing a letter, and watching grebes in the water.


Dark clouds came over later, hastening nightfall over the park. Note the addition of the rainfly to the tent. Turns out we just got a sprinkle, no real downpour.


Life on the road is (was) good. Months later, it makes me happy to look at these photos and think about rolling along across the great North American continent, checking stuff out, seeing new places. Classes start on Monday for me, and I'll be locked down in DC for a bit... a fair trade, it seems to me, if my job allows me to go out and see places like these during the summers.

Labels: birdies, travel, wyoming

I left Bozeman on Saturday morning, and drove for about seven hours. I headed south through Ennis, Montana, along the western side of the Madison Range, passing by the Madison Earthquake Site landslide (from the 1959 Hebgen Lake earthquake), and then south into Idaho. I went through Island Park, Idaho, site of the caldera of one of the three big recent eruptions of the Yellowstone volcanic center. Then into northern Utah, where I got a glimpse of the Great Salt Lake. I headed up into the Wasatch Range to spend the night, just east (and several thousand feet above) Ogden, Utah. I did some birding on the reservoir there, observing the mating rituals of both the woodcock (amazing humming noise produced during flying dives) and the western grebe (neck bobbing following by synchrnonous running across the water).

The next morning, I headed west from there, into the basin, across a range, into another basin, across another range -- you get the idea. I initially intended to go hunt for trilobite fossils in the Wheeler Shale in the House Range, but the 20-mile dirt road rattled me (quite literally) and I turned around after only four miles. I got spooked: what would happen to me if the Prius broke down out here? It's really quite desolate country. I've only ever had that feeling once before, when my Dad and I drove across the Namib Desert. It's a mix of agoraphobia and anxiety over feeling inept at repairing mechanical things, like Prii and other automobiles. I chickened out -- no trilobites for me. But there was a consolation in Great Basin National Park, which was where I headed that afternoon. I did a short hike there in the Snake Range, and toured Lehman Caverns there (my third guided cave tour in two weeks!). I had my best campsite of the trip at Great Basin: montane forest, with a gurgling stream running fifteen feet from my tent. Lovely.

When I woke up, I packed up the car and coasted downhill for eight miles into the town of Baker, Nevada, where I had a great breakfast and coffee at a little cafe there. Then up and over the Snake Range, and down the next valley to the west, south for 93 miles of some of the most empty country I've ever seen in America. In an hour and a half of driving, I saw only 20 vehicles. I crossed back into Utah, and then made my way south to the edge of the Colorado Plateau, and drove up into Zion National Park. Zion is a great canyon cut into a series of sedimentary rocks. The last time I was here, 13 years ago, I walked up the Narrows, and my first order of business was to repeat that hike. There's a new shuttle system in the park now, so after parking at my campsite, I hopped on a shuttle into the park and rode it to the end. I waded into the Virgin River and shuffled upstream. In the Narrows, the Virgin River has cut down through the Navajo Sandstone, but not quite down into the weaker underlying Kayenta Formation, and so the canyon is deep but narrow. (Downstream, when it gets deep enough to tap into the Kayenta, it undermines the sandstone cliffs, and the valley widens.) "Hiking" here is one of the more unique outdoor experiences I've had. Being immersed in the cool river, surrounded by towering rock walls -- it's magical. The further upriver you hike, the less people there are, and it's like a cathedral. I went up and around several entrenched meanders, and marvelled at the alcoves, cross-bedding, and variety of cobbles in the riverbed.

Today, I'm staying in the park and heading up to Angel's Landing, a legendary hike in its own right. Tomorrow morning, bright and early, I'm off to Las Vegas to pick up my Dad and brothers for our Grand Canyon rafting trip. Not sure if I'll be able to post again until after I get out.... late next week.

Labels: birdies, fossils, grand canyon, idaho, montana, national parks, stratigraphy, travel, utah

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

Okay, so we've all heard what a stinker the new movie 10,000 B.C. is, right? I actually went to see it, on Geotimes' nickel, along with a couple of other scientists so we could assess the scientific validity of the film for the magazine. Afterwards, I went to enter my own "review" into Netflix (2 stars out of 5) and I noticed there was another "10,000 B.C." film in the Netflix library: "L.A. 10,000 B.C.," a program from the Discovery Channel that examined the natural history of the Los Angeles area during that same time. I decided to check it out, and last night I watched it.

My brief review: It's not really a traditional natural history program. Instead it takes fossil evidence and uses it as a starting point for a "reality T.V." style stunt program. They take three L.A. stunt actors and "train" them to be Ice Age hunter-gatherers. Then they build pneumatic robots to mimic the teratorn and Columbian mammoth, and the stuntmen and women have to battle them. No joke. This resulted in some cool visuals, though: the mammoth crushing a ten-pound can of tomatoes and having all that red spray everywhere (mimicking the head of a Clovis hunter). And the footage of the stuntman being tossed thirty feet through the air by the "angry" robot mammoth was kind of cool too.

But you can't really call that a nature program. There were some cool facts presented, but the majority of the film was devoted to sensationalism of the encounters between humans and these Pleistocene species. The film was also very repetitive, taking half an hour's worth of material and stringing it out into 1.5 hours. It appeared to have been designed so anyone channel-surfing could get an orientation as to what the program was all about regardless of when they tuned in. That's kind of lame if you're watching the whole thing from start to finish, methinks.

Labels: birdies, cenozoic, mammals, movies, tv

The New York Times reviewed a new book about birdwatching this weekend. If you can agree with the statement, "I can't think of any activity that more fully captures what it means to be human in the modern world than watching birds," then you might enjoy Jonathan Rosen's The Life of the Skies. The review (by Robert Sullivan, who wrote the book Rats, which has the best cover of any book ever) is astonishingly well-connected (in the Internet sense of the word): it weaves in allusions to Robert Frost, Jack Kerouac, and Theodore Roosevelt. I haven't read The Life of Skies yet, but it is now on my list.

I love running into birds. The other morning, when it was relatively warm, Casey and I went for a walk in the Zoo, and saw a pair of red-shouldered hawks (wild, not caged) building a nest in one of the big old orthern red oak trees there. It was cool to see: they were collecting sticks several feet long and doing short fly-hops through the canopy as they maneuvered into their nest site. Today, we went back and looked for them again, but there weren't there. Maybe out hunting?

In DC, the winter weather persists. It was cold and windy this weekend, and daylight savings time didn't help much. Soon, (very soon, I hope), the weather will warm and the birds will return. Right now, there's nothing to look at except rocks, cold rocks. Some of my Honors students and I got out in the field today to do measurements for their various projects, and when the sun was out, it was pretty nice. Still fleece and jeans weather, but you can sense spring is on the way.

Labels: birdies, books, nova, teaching

I have a confession to make. Geology was not my first love: birds were. I spent one summer in college watching cattle egrets. That research project helped me get into ornithology, & I've kept "birding" as a hobby ever since. Even these days, I don't usually manage to get through a geology field trip without pointing and shouting "Look! There goes a pileated woodpecker!" (or a Cooper's hawk, etc.) Birds are everywhere, and they're great.
Accordingly, I was pleased to get these photos Friday from my colleague, NOVA biologist Bill Gorham.

This is a female cardinal (Richmondenis cardinalis). She has a unique look: her head is white! Bill calls her Ms. Whitey.

He tells me that the bird "has been a visitor in my yard for over a year. Last winter she just had a white 'collar' around her neck, then during the summer her whole head gradually whitened."
Bill continues: "I understand the term 'leucistic' applies because it is certainly not albinism but a loss of all pigments in certain areas... I would have to guess that the progressiveness has something to do with maturity. She mated and had chicks this past summer but I think she was a youngster last winter. She is also a member of a local tribe of cardinals that get bald every summer in July and August. First it was just one male (who we called 'Baldy') but now there are several males and several females. I don't think it is mites; I think it is some kind of heat response. When they molt in the fall they get a full head of feathers again."

A few points to be made here: (1) I like sharing images of natural oddities, which is why I'm posting these images [with Bill's permission] here; (2) I like having colleagues who share images of natural oddities [I like the fact I'm part of a community of people at NOVA who are curious about the natural world] and (3) I want to know what the heck is going on with this bird: I think it's weird that it's progressive whitening like Bill describes. I mean, I can see a certain region of the cardinal embryo mutating a gene (which subsequently gets copied & copied) leading to albinism in certain portions of the body (which then remain constant over the bird's life), but I find it truly odd that the area lacking pigment has increased over time. That's remarkable! If anyone has any insights into this "rare bird," let's hear it...

Labels: birdies, evolution, nova