Hole-in-the-Ground

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Here are a few photos of "Hole-in-the-Ground" (yes, that's its real name). It's a maar -- a relic of a volcanic explosion -- out in Eastern Oregon, about an hour southeast of Bend off Highway 31.

The name is accurate: It's a very large, and very beige, hole in the ground. It looks a bit like a meteor crater, but it isn't, sadly. It's pretty damn big, no matter what created it.

The USGS quotes a couple of sources about the place:

From: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., Contribution by Lawrence A. Chitwood

Hole-in-the-Ground is a nearly circular maar with a floor 150 meters below and a rim 35 to 65 meters above original ground level. Its diameter from rim to rim is 1,600 meters. The volume of the crater below the original surface is only 60 percent of the volume of ejecta. Only 10 percent of the ejecta is juvenile basaltic material. Most of the ejected material is fine grained, but some of the blocks of older rocks reached dimensions of 8 meters. The largest blocks were hurled distances of up to 3.7 kilometers from the center of the crater. Accretionary lapilli, impact sags, and vesiculated tuffs are well developed.

From: Heiken, et.al., 1981, A Field Trip to the Maar Volcanoes of the Fort Rock-Christmas Valley Basin, Oregon:
IN: Johnson and Donnelly-Nolan, (eds.), 1981, Guides to Some Volcanic Terranes in Washington, Idaho, Oregon, and Northern California: USGS Circular 838.

According to Lorenz (1971):

Hole-in-the-Ground is a volcanic explosion crater or maar located in Central Oregon on the edge of Fort Rock basin. At the time the crater was formed between 13,500 and 18,000 years ago a lake occupied most of the basin and the site of the eruption was close to the water level near the shore. The create is now 112 to 156 meters below the original ground level and is surrounded by a rim that rises another 35 to 65 meters higher. ...

The crater was formed in a few days or weeks by a series of explosions that were triggered when basaltic magma rose along a north-west-trending fissure and came into contact with abudnant ground water at a depth of 300 to 500 meters below the surface. After the initial explosion, repeated slumping and subsidence along a ring-fault let to intermittent closures of the vent, changes in the supply of ground water, and repeated accumulations of pressure in the pipe.

The Forest Service also describes the place, with nearly (but not entirely) identical words:

Hole-in-the-Ground is a volcanic explosion crater or maar located on the west edge of the Fort Rock basin. The floor of the crater is at an elevation of 4340 feet and the surrounding area has an elevation of about 4650 feet. The crater is approximately 1370 m (4500 ft) east-west by 1675 m (5500 ft) north-south. The crater was probably formed in a few days or weeks by a series of explosions due to rising basaltic magma coming into contact with abundant ground water at depth. The magma may have been rising along the fault that is exposed in the crater walls. After the initial explosion, repeated slumping and subsidence along a ring fault led to intermittent closures of the vent, changes is the supply of ground water, and repeated pressure buildup. The layering visible in the rim records the pulsing of the eruption.

The surrounding area is full of volcanic oddities. Nearby there's another maar called "Big Hole", and a bit to the east you'll find "Crack in the Ground" and "Fort Rock" (more about the latter in a future post). Further north you'll find Newberry Caldera, the Lava River Cave, and much more. If you're spending a day or two, doing a volcano-themed tour or something, you might as well stop by and check this one off the list. The WP article linked to above has an aerial photo, and the USFS page links to a couple more. It does look a lot more interesting from the air, but since neither I nor my car can fly, that information isn't terribly useful. Waymarking also offers a few photos of the place.

The gravel side road off Highway 31 is pretty washboardy in parts, so if you're afraid to, uh, "mar" your vehicle or your busy travel schedule, you could also skip this one and you'd be fine, probably. There's a trail down into the hole, but I figured I'd seen enough and headed off to Bend after this to find a hotel and a bite to eat (more about which here).

If you search for info on the place, like I'm doing, you'll actually encounter quite a few academic papers mentioning it. Apparently it's a well-studied example of a maar, probably due to its relatively convenient location. Here's an interesting recent paper mentioning it: UNDERSTANDING MARS AT THE MICROSCALE BY IMAGING TERRESTRIAL ANALOGS: THE HANDLENS ATLAS. The researchers visited a few volcanic sites in Eastern Oregon and took microscopic photos, attempting to better understand what the microscopic imagers on the Mars rovers are observing. Kewl. This was mentioned on a recent episode of Oregon Field Guide, but I always prefer the original source materials when they're available.

Oh, and for your further entertainment here's a rather odd page arguing Hole-in-the-Ground is somehow electrical in origin, just like the Grand Canyon. Oh, and the events of ancient mythology. And gravitational lensing. And sand dunes on Mars. And the Big Bang. WTF!? Who knew? Color me skeptical, as you always can, but the whole site really sets off my crank alarm bells.