The routine

It’s that time of year for me… summer’s here, and I’m winding up my duties at NOVA in preparation for some travels. We leave Sunday night for two weeks in Turkey, followed by my regional field geology course in Montana (also two weeks), followed by some family time and mountain climbing in New Hampshire (three weeks), including hiking the Presidential Range.

This summer, as I have done for the past several summers, I’ll be subletting my home while I’m gone. Among the many disadvantages of living in DC (high taxes, high crime, lots of noise, all those politicians), this is a big advantage: you can sublet your apartment soooooo easily. It’s a cinch! The city’s government and nonprofit sectors draw in swarms of interns every summer, and I’ve been very fortunate to find great subletters via Craigslist to come pay my rent/mortgage and take care of my cat while I’m away.

The first summer I did this was the most extreme: I was gone for three months in 2006 on a road trip up to Alaska and back; but since then I’ve subletted for at least two months each summer, mainly while I was out west. The 2010 summer is the shortest sublet I’ve so far had: a mere seven weeks. Still, the routine each summer is roughly the same: stock up on cat food and litter, pack up my clothes and store them somewhere (mom’s attic; my office at NOVA), clean the place up, and then clear the heck out. The packing has been more complicated this year since I’m essentially packing for three trips with overlapping gear needs all at once. But it’s a nice annual tradition: right about the time that DC gets to be sweltering hot and humid, I can decamp for exotic locales and cooler climes. I feel very lucky not only to travel like this, but also to have my home and cat cared for in my absence, and bring in cash to pay the mortgage, too. It’s a sweet deal.

More immediately, I’ll be in an all-day workshop starting tomorrow night, and through Sunday. It’s a SERC workshop on the role two-year colleges like NOVA play in geoscience education. Between that and packing, this might be the last you hear from me for a while.

Blogging will likely be light around here for the next two months as I’m flitting about. I’ll do my best to log on and post some travelogues when I can, but I can’t promise too much. When I have phone service (will my iPhone work in Turkey?), I can offer a series of short posts to my Twitter account. Beyond that, you’re on your own!

At the edge of the intrusion

Mountain Beltway reader Greg Willis attended my colleague Ken Rasmussen’s Triassic Rift Valley field course last weekend, and sent me this photo of the view inside the Luck Stone diabase quarry in Centreville, Virginia:

Here’s an annotated version:

Both photos are enlargeable by clicking on them (twice).

This quarry chews into rock right along the contact between a mafic igneous intrusion and lake sediments that formed when water pooled in a low-lying continental basin that formed during the breakup of Pangea. This rift valley, the Culpeper Basin, is just one prominent basin in a whole series of Triassic grabens and half-grabens that run through the Piedmont north and south of here, including all the way to the Bay of Fundy.

A similar environment can be seen today in east Africa, where a modern rift valley hosts similar lake deposits and mafic igneous rocks:

If you were to drop maybe half a kilometer below the surface of the Afar region, you’d see a similar situation to the one that produced Greg’s quarry photo ~200 million years ago.

Visiting the Centreville quarry is by permission of the Luck Stone corporation only; the best way to see it is by signing up for Ken’s course the next time it rolls around!

A new river graphic

I really appreciated the feedback everyone contributed regarding the river evolution graphic I posted a week and a half ago. The latest offering is from Kyle House, who linked to a couple of nice summary images derived from Stanley Schumm. Because the images were low-resolution, and black and white, I decided to do some re-drafting. Here’s one (click through twice for full size version):

And here’s the original:

Images like this (and the previous, obsolete “river evolution” image) are central to the way I teach — a nice summary picture that compares variables. This one is more complex than I consider ideal, but I think it will do the trick.

I’d like to thank everyone who contributed to the discussion. I felt that this episode was a great example of how blogging benefits its practitioners. By putting my earlier graphic online, I got valuable feedback that corrected the erroneous and oversimplified way I was teaching about fluvial geomorphology. It was great to get critiques from both geomorphological and educational perspectives. That feedback has lead me to do some deeper thinking about that topic, and to change the way I teach it. Thanks – on behalf of myself and my future students!

Now for the new image… what would you critique here? (…either in terms of Schumm’s original ideas, or my redrawing of them…)

EDIT: Michael M. pointed out in the comments that several of the arrows were too low contrast to be legible. Funny, those colors totally aren’t what they looked like in the Corel Draw drafting stage! Anyhow, I’ve darkened them up a bit in this version:

Harpers Foldry

Cleaning out the backlog of photos I haven’t popped up here yet… Here’s three shots from last weekend, of folds (some kinky) which deform Harpers Formation foliation, just south of Harpers Ferry, West Virginia:

hf_3

hf_2

hf_1

The Harpers is a Cambrian-aged lagoonal mudrock, dated via Olenellus trilobites in Pennsylvania. It is part of a transgressive sequence that followed Iapetan rifting of the mid-Atlantic, and was later deformed during Alleghanian mountain-building. That’s when the pronounced foliation was imparted, and when that foliation was folded (also overturned). There are plenty of nice exposures of kink folds in this charismatic rock throughout historic Harpers Ferry. Check it out if you’re ever there on a history field trip.

Taking your requests

In a week, I’ll be in Turkey.

This is very exciting: Turkey has tons of cool geology, and a modicum of cool history as well. Anyone have any suggestions for stuff I should do/see/visit while there? Anything you particularly want to see geoblogged? Any “assignments”?

Lily and I only have two weeks, so we will be sticking to western Turkey (Mount Ararat will have to wait), so bear that in mind.

I’ll be back in Turkey in October for the Tectonic Crossroads conference, and (I anticipate) at a later time, too: I really want to climb Mount Ararat, but I figure I’ll need at least a week to get out there, climb the mountain, and get back to civilization. So: that will have to wait.

Top Ten Park meme

Lockwood started it. He grabs two new lists from National GeographicOur Amazing Planet“: the Ten Most Visited National Parks and the Ten Least Visited National Parks. Says he: Bold the ones you have visited, and italicize the ones you’ve never heard of before.

Most visited:
10: Glacier
9: Acadia
8: Grand Teton
7: Cuyahoga Valley (what? the river that caught fire? that one?)
6: Rocky Mountain
5: Olympic
4: Yellowstone
3: Yosemite
2: Grand Canyon
1: Great Smoky Mountains

Least Visited:
10: City of Rocks NR, Idaho
9: Cumberland Island NS, Georgia
8: Florissant Fossil Beds NM, Colorado
7: Chiricahua NM, Arizona
6: Tonto NM, Arizona
5: Dry Tortugas NP, Florida (one of the coolest places I’ve ever been, and unfortunately, also one of the national parks most threatened by the Gulf oil spill)
4: Katmai NP & Preserve, Alaska
3: Kalaupapa NHP, Hawaii
2: Hagerman Fossil Beds NM, Idaho
1: Russell Cave NM, Alabama

Overturned bedding at Maryland Heights

The Lilster & I drove out to Harpers Ferry, West Virginia, today, and crossed the Potomac River to hike up to the overlook at “Maryland Heights,” which is what they call the Blue Ridge north of the river. On the way uphill, I noticed this nice example of Harpers Formation bedding and cleavage dipping in the same direction (~east):

Note that the cleavage is dipping more gently than the bedding: this suggests that the bedding is overturned. No big shocker here: that’s the standard interpretation for the western edge of the Blue Ridge province; but it’s nice to see some meso-scale evidence of the regional structure.

Duke Stone

I wrote last fall about my visit to the Duke Quarry, home of a charismatic metavolcanic rock used to face buildings on the campus of Duke University in Durham, North Carolina.

Here’s a sample of the “Duke Stone” that I brought back to NOVA, cut, polished, lacquered, and scanned. It’s quite lovely. You can click through (twice) for the biggest version:

Gorgeous, isn’t it?

DC fossil website is now live

Chris Barr’s informative website of the “Accidental Museum of Paleontology” that can be found in D.C. building stones is now live. You should go and check it out, and if you ever visit the city, you can use it as a guide for your tourism.

The LaHood Conglomerate

The Belt Supergroup is a series of sedimentary strata laid down in the Belt Sea, an inland sea (like modern Hudson Bay) that existed in the northwestern (by present coordinates) part of ancestral North America during the Mesoproterozoic era of geologic time. Estimates of the absolute age of these rocks range from 1470 to 1400 Ma. Mostly, it’s siltstones (argillites) and limestones, including the multicolored strata so gloriously displayed at Glacier National Park in Montana. But there are some coarser units, too. My favorite is the LaHood Formation, which is a beautiful diamictite well exposed in the canyon of the Jefferson River just east of Cardwell, Montana.

Check out this gorgeous rock (sawn, polished, lacquered, and scanned):

Here it is again, rotated by 90°:

You can click through (twice) for both of these images to get big versions if you want more details. The prominent pinkish clast in the upper scan is a myrmekitic granite, and the prominent grayish clast in the lower scan is marble. These are pieces of the Archean basement complex (Wyoming Terrane), such as we see exposed in the Gallatin Range or the Beartooth Plateau. Note their well-rounded shapes: these cobbles traveled some distance before reaching their depositional location. You can also see pebbles of potassium feldspar, milky quartz, and rock fragments, all set in a dirty sandstone matrix.

Because of the coarse grain size, especially relative to other Belt units, the LaHood conglomerate is interpreted to have been deposited along the southeastern shore of the Belt Sea. Here’s a sketch from my field notebook (from 2008) showing this basic depositional interpretation:

belt

While some of the sediment has been sourced to Montana rocks, I am told that some of it comes from some other landmass, maybe Antarctica or Siberia, indicating their possible paleo-proximity to what is today the northern Rocky Mountains, USA.

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