Yesterday, I took my Audubon Society / USDA Grad School "Natural History Field Studies" students on a field trip to examine the bedrock geology of Washington, DC. We had a good time: beautiful weather, great attitudes, and even luck with parking! I guess because it's Memorial Day weekend, a lot of people have left town. One of the great challenges of urban geologizing is finding room for those infernal cars...

Here's a photo of the group at Chain Bridge, DC, on Sunday morning:

That class ends on Monday night, bridging the gap between my NOVA spring and summer semesters. It's been a good run -- thanks, folks!

Labels: dc, field trips, piedmont, teaching

This map was in this morning's Washington Post. The red dots are currently-existing coal-fired power plants. The black dots with the central stars are proposed future coal-fired power plants.

Labels: CO2, coal, dc, environmental, nova

This is how good it is to be a professor on summer break: Yesterday afternoon, after composing yesterday morning's epic account of my Massanutten trip, I toodled on over to the Palisades Museum of Prehistory to (a) drink beer and (b) talk rocks with the museum's curator, Doug Dupin.

The Palisades Museum of Prehistory is in far western Northwest DC, near the Dalecarlia Reservoir and Sibley Hospital. There, you'll find a neighborhood called the Palisades, and in the Palisades, you'll find Doug Dupin's house. In Doug's backyard, you'll find what appears to be a nice shed. Turns out, this is the museum. It's a long story, but basically it boils down to this: Doug was a cartographer, but a contract went sour, and so he was staying at home with a lot of time on his hands. He decided to grow some grapes to make wine, and store that wine in a self-dug wine cellar. He started digging the hole, and encountered arrowheads, pot sherds, and other artifacts. He got intrigued, and decided to showcase the findings atop the wine cellar in a self-made museum.

If you want more details, the Washington DC CityPaper profiled Doug in a 2006 article. A good read; I recommend it.

Doug is a great guy -- pursues what he's interested in, be it homebrew, viniculture, skateboarding (he once rode the length of the C&O Canal on a self-made board -- read about it in this New York Times Magazine article), or archaeology.

Doug attended my "Walkingtown, DC" walking tour of DC's geologic history, and brought along a few odd rocks for me to identify. At the end of the tour, he invited me over to see his museum. Yesterday, I finally got the chance to do that. We cracked open a couple bottles of Dogfish Head 60-minute IPA and started browsing his collection of found prehistoric objects. Doug was very interested in my analysis of rock types (apparently archaeologists use a different set of terminology for describing what rock types projectile points are made out of).

On his own property and in neighboring areas of the Palisades, Doug has found hundreds and hundreds of objects, many of them beautifully worked arrowheads of flint, quartzite, and rhyolite. There are also some oddballs that don't fit with the human prehistory theme: a 1791 coin bearing the image of Louis XVI, crystals of amethyst and gypsum, old glass bottles, rounded river cobbles, and anything else that caught his attention. One of the most astounding things I saw yesterday was a huge woolly mammoth tooth. Doug told me a friend of his found it in the Potomac River while canoing (I think he said near Seneca Creek, but that was a beer and a half in, so maybe I've got that wrong). But there it was, a fully ridged mammoth molar; unmistakable. I hadn't heard of previous mammoth finds in our area, but I guess it's not surprising they were here.

Anyhow, I had a great time, and I recommend that everyone in the DC area make an appointment with Doug to go check out his collection and support his project.

Labels: cenozoic, dc, history, mesozoic, museums, piedmont, tourism

Latest gage information from the Potomac River near Little Falls. Looking out my window at Rock Creek this morning, I can see the water is way up, moving fast, and the color of teh tarik.

DC (and many other surrounding municipalities) are under flood warnings this morning as a result. The Washington Post's Capital Weather Gang is impressed by it all.

(Fortunately Saturday's field trip happened to be scheduled between downpours.)

Labels: dc, floods, rain

Morning, folks. I awake to a challenge from Chris at GoodSchist, to show where my local bedrock was at the time of Pangea's incipient breakup. (I think Chris chose the late Triassic, 220 Ma, since Ron Blakely's map of that time shows New Zealand clearly in the south.) It's an interesting time for the rock beneath Washington, DC. After have just experienced ~50 million years of crunching between North America and Africa, DC's tortured bedrock is now being stretched as Africa begins to pull away again. A series of rift valleys mark the stretching of the crust, shown clearly in the map as a series of NE-SW oriented lakes along the axis of the Appalachian orogen.

DC's future location is between two of those rift valley lakes: one to the east, one to the west. If I owned DC real estate during the Triassic, I'd be very interested in this process, because one of those rift valleys is going to become a new ocean basin, and one isn't. The one that isn't is destined to stop opening and fill in with dirt. It will be a failed rift valley, an aulacogen of sorts.

The question is: which one is the weakest link? If the one to the west breaks open, that will be the new Atlantic Ocean basin, and DC will stay hitched to Africa. If the one to the east breaks open, that will be the site of the Atlantic, and DC will stay hitched to North America.

As it turned out, the eastern rift was the one that connected up with other rifts to the northeast and southwest, and became the young Atlantic. The western rift, known as the Culpeper Basin, stopped stretching open, and got filled in with sediment. DC stayed attached to North America, and that's the way it is.

Labels: culpeper basin, dc, geology, mesozoic, piedmont, plate tectonics

Three-quarters of the way through my Physical Geology final exam this afternoon, the room shook and a low rumble propagated through our building. The students, many of whom were in the area on 9/11, instantly looked up with a very concerned "Was that a bomb?" look on their faces. To assuage their fears, and because I've previously heard similar rumbles coming from our HVAC ducts, I told them that it was just the cooling system, and not to worry.

Turns out I was wrong: it was a small earthquake with an epicenter about 1 km from here (we're about 1 km west of Annandale proper, and the USGS suggests it was 2km southwest of Annandale; see map below).

Almost on the epicenter of our own little quake! For us east-coasters, that's a big deal!

WTOP reported on it (Thanks to Ron Schott for forwarding me this link).

Here's the USGS quake page on the event.

Here's the Maryland Geologic Survey's seismometry. (source of image above, which is in Eastern Standard Time, not Daylight)

Here's the Washington Post's (brief) treatment of it.

I've gotta say, Ron Schott's up on it -- within an hour of the seismic event, he had e-mailed Tuff Cookie and I to ask about it. Pretty prompt! Thanks, Ron.


Update: Here's the Google Map showing the epicenter (green arrow). I've circled the building where I was giving the exam in the green circle:

Also: Here's the intensity map as it looked after I logged on and completed the "Did You Feel It?" survey:

Labels: dc, earthquakes, nova

It started raining in DC on Sunday, and it basically hasn't quit since then. Rock Creek is running high and frothy, and the Potomac has about seven times as much water in it today as it did 36 hours ago. The USGS has only one gauging station on the Potomac in the Piedmont -- at Little Falls, approximately on the DC/Maryland border. Here's what that gage's data (available free online from the Survey) tells us (as of last evening) about the river's recent discharge trend:

Labels: dc, nova, piedmont, rivers, sediment, water resources

Later this month, I'm leading a tour for "Walkingtown, DC" a twice-annual event sponsored by Cultural Tourism DC, a nonprofit organization. My tour is called "History Before History: the geologic saga of Washington, DC." I'll be leading the tour on both Saturday, April 26, and Sunday, April 27, from 1-4pm. If you're in the area, consider coming along. We'll be discussing the deposition of sediments in the Iapetus Ocean, generation of an accretionary wedge, the Taconian Orogeny, the Rock Creek Shear Zone, emplacement of the Georgetown Intrusive suite, and finally the erosion of the young Appalachian mountains and the deposition of dinosaur-fossil-bearing river gravels atop the unconformity: the Potomac Group. As a bonus, we'll even visit a thrust fault which ruptures the unconformity at the intersection of Adams Mill Road and Clydesdale Place, NW. It's a nice little jaunt through prehistory. However, this hike was extremely popular last year: we had ~300 people show up! So I've asked Cultural Tourism DC to institute a reservation system this time around: I'm limiting participation to 30 people per day. Act now to reserve your place by calling or e-mailing Cultural Tourism DC.

Here's two pictures of the mad crowds last spring. I get the heebie-jeebies just thinking about it:

Labels: action, dc, dinosaurs, geology, granite, metamorphism, sediment

I've already introduced you to two of my Honors students' field projects. Now for the last of the three -- Jason's project on the strained metaconglomerate of Klingle Road. Klingle Road is a "road" in D.C. that was damaged by a storm some years back, and never repaired. Some people have started using it as a park, while others clamor for the road to be fixed. Geologically, it's interesting because it exposes a rock unlike any other nearby: a distinctly foliated metaconglomerate. Because I am so clever, I call it the Klingle Road Metaconglomerate. It's part of the "Laurel Formation," which is one of many flavors of metagraywacke / accretionary wedge complex that make up the bulk of the Piedmont in this area. Here's some of the squished clasts that Jason is interested in:

We know these rocks got heated up a fair bit. How do we know this? Well, they flowed out into elongated shapes all oriented in the same direction for one (see the additional photos here). The outcrop is peppered with clusters of little plus-shaped protuberances: they are clusters of sericite (cryptocrystalline muscovite) in the shape of staurolite porphyroblasts. Staurolite is a reasonably high grade metamorphic mineral, and when we see the three-dimensional shape of staurolite, but it's been turned into relatively-low-grade sericite, it's an indication of "retrograde metamorphism." Basically, after hitting the peak of its particular metamorphic conditions (high temperature and pressure, growing staurolite), the rock is readjusting to lower temperatures and pressures, and those staurolite crystals are reacting to a mineral that's more stable at those lower temperatures and pressures: sericite.

But anyhow -- back to the metaconglomerate. It's made of clasts, and those clasts have been stretched. The question is: how much have they been stretched. Sometimes when strain estimates are made, we assume an initial sphere shape, and then measure the lengths of the various axes of the resulting ellipsoidal shape (the "strain ellipsoid"). But is the assumption of initial sphericity valid? Jason is testing this issue by measuring the axes of cobbles and pebbles from the metaconglomerate as well as loose cobbles and pebbles found in nearby Rock Creek. We want to get a sense of how ellipsoidal cobbles are before they experience orogenic shortening/stretching. Here's a shot of Jason, Spencer, and Victoria measuring cobble axis lengths on a gravel bar near the National Zoo:

And a shot of the crew close-up:

And, just for fun, here's one more shot from Victoria's field area on Broad Branch. We hiked up to the contact with the Kensington Tonalite (a ~464 Ma felsic intrusive rock -- essentially a granite) and found a series of small waterfalls over this resistant rock unit. In the sequence of cascades were a series of deep pools. I submerged myself in one of them:

Labels: appalachians, dc, field trips, nova, piedmont, sediment, structure, teaching

Picking up with my series of posts introducing the work my Honors students are doing this semester: today we'll take a look at Spencer's project, which involves field work on a bedrock terrace (strath) of the Potomac River near Chain Bridge (which can be seen in the background of this photo). As before, ignore the datestamp in the lower-right of the photo. These pictures were taken last week, not in 2004.

This is in the westernmost corner of DC's "diamond" shape. The bridge leads across the river into Arlington, Virginia. As you can see, there's a lot of rock exposure here -- the sort of thing we go crazy over here in the east. As noted before, this is metagraywacke (sometimes metamorphosed to schist, sometimes to gneiss, sometimes just strongly foliated, and sometimes so lightly metamorphosed / deformed that it even preserves original sedimentary structures like graded bedding. The interesting thing about the Chain Bridge locality is that in amongst the metagraywacke are big chunks of other rock types. I'll refer to these as "clasts." Some geologists have interpreted them as sedimentary deposits; others as "olistoliths" (tectonically emplaced chunks in an accretionary wedge complex). Spencer is in charge of documenting the variety of these clasts, in hopes that it may tell us something about their ultimate source. Here's a big elongate clast of gneiss:

We had a good little field routine going: Victoria and Jason would go scout out clasts, and then mark their location with a chalk arrow. Then Spencer would document each clast's lithology and characteristics (e.g. foliation at an angle to regional foliation) and then photograph it. Once he'd photograph it, he "checked it off" with chalk. All of this chalk graffitti gets washed away with the next big rainstorm.

Some of the clasts are no longer in their original condition. The one below, for instance, bears a multitude of garnets, metamorphic minerals which reflect how the clast's original composition reacted to the higher temperatures and pressures of Appalachian mountain-building.

Another thing we saw a lot of in the Chain Bridge locality is erosional features related to the incision of the Potomac River into bedrock. Here's Jason showing off a pothole that drilled all the way through one outcrop:

Next time, we'll take a look at Jason's project.

Labels: dc, field trips, geology, nova, sediment, teaching

It's almost cherry blossom season, so that means it's also time for the annual DC Environmental Film Festival. For two weeks, lots of interesting films are hosted by dozens of libraries, theaters, embassies, NGOs, and the like. Many of them are free. If you live in the DC area, this is an excellent opportunity to see some movies that you won't otherwise get access to. Even if you're not in the Capitol area, you can check out some of these films: this year, several of the films (like tonight's snow leopard movie) are available for watching free via the Internet. Enjoy!

Labels: dc, environmental, movies

DC Metro area residents, you're hereby invited to join me (NOVA) or Phil Justus (NRC) or Michelle Arsenault (NSF) on a geology hike along the Billy Goat Trail, a popular and rugged hiking trail upstream from DC on the Potomac River, downstream from Great Falls. Michelle and Phil and I take turns leading this excellent hike. You'll learn about the Iapetus Ocean, Appalachian mountain-building, and the incision history of the Potomac River. You'll see potholes, amphibolites, metagraywacke, migmatite, and the mysteriously-straight Mather Gorge. The Park Service has just posted the spring schedule online here. Reserve your space today!

Labels: appalachians, dc, geologists, piedmont

Today was the artist's reception at the National Academies of Science for Camille Seaman's exhibit of photographs entitled "The Last Iceberg." I took a break from writing a paper for my MSSE class and went down to check it out.

One of my geology honors students, Spencer, showed up too, and we checked out Seaman's glowing icebergs set against dark backgrounds. There were some really stunning images, but the exhibit was rather small -- only fifteen or so separate pictures.

If you're not in the DC area, you can check out a slideshow of images from the exhibit at Seaman's website. Enjoy!

Also, while I was there, I went upstairs to see the excellent "Monkey Portraits" exhibit by Jill Greenberg. As with "The Last Iceberg," only a selection of images was shown -- a total of ten or so. But man, what an amazing ten images! I'll put just one up here, entitled "Undecided":

Labels: art, climate change, dc, global warming, primates

Labels: art, dc, ethanol, global warming, humor, politics

In the spirit of the day, check out this article about mating at the National Zoo, here in DC (and a literal stone's throw from my apartment window).

Among the information featured:
when two females cheetahs are housed together, one or both females will shut down their ovulation, which makes it impossible to breed them until they are again separated.

Shanthi, the baby Asian elephant (who's now almost as big as her mom), was the result of artificial insemination. I remember visiting the Zoo shortly after Shanthi was born, and seeing video footage of her birth. Wow! Kablooey! That's a big package to drop!

The male Panamanian golden frog (pictured), which is extinct in the wild, will attach itself to the female for up to 120 days to make sure he's the one to fertilize her. Talk about clingy!

Also, you may be interested to know that some lowland gorillas will mate face-to-face, as the Wildlife Conservation Society reported this week, and was subsequently promoted by National Geographic.

Labels: dc, evolution

Starting today, DC police are monitoring live images from surveillance cameras in many parts of the city. The District has 73 cameras, with live feeds from 54. The Washington Post published this map showing where they are (supposedly the locations were chosen in historically high crime areas). They also have an article about the new system. My 'hood of Adams-Morgan gets two, it looks like...

Anyhow, I always love maps, so I thought I'd share this one.

Labels: dc, maps

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

Labels: dc, moon

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