Geo 365: March 19, Day 78: Hole-In-The-Ground

Dana admires Hole-in-the-Ground, a classic maar on the tableland to the west-northwest of Fort Rock. There's a foot path to the bottom from this point- you can see it to Dana's left. However, most geology people probably are aware of the problem of hikes that start downhill: the easy part is when you're fresh, the hard part comes when you're not. So I used to tromp down with kids, but didn't on this trip. (It's a serious slog, coming back up that slope, roughly 400-500 feet  (correction- closer to 200 meters or more, looking more carefully at the guide linked in the next paragraph, so maybe a bit less than) 700 feet vertical, and relentlessly steep.)

The reason I chose this photo as an introduction to Hole-in-the-Ground can be seen above that little tree past and to the left of the central playa, on the opposite wall. The offset in that layer of basalt marks a fault which bisects this crater, and it's thought that this was the weak feature that allowed the basaltic magma to migrate upwards at this spot. More detailed information on HIG can be found in USGS Circular 838, at mile 25.1 in this road log.

In one of those nice little bits of synchronicity, @Cmdr_Hadfield tweeted yesterday, "What is this little perfect round hole in Africa? Likely in Ethiopia near 7.99N, 37.19E. pic.twitter.com/G57OBpL1j7" I replied,"@Cmdr_Hadfield Given location- not too far off axis of rift- & water, guessing maar. Funny, just looking at another: http://www.flashearth.com/?lat=43.410204&lon=-121.198268&z=15.6&r=0&src=msl" And a few minutes later, I was able to pin it down in FlashEarth: "@Cmdr_Hadfield Yep, definitely looks like a maar- explosive interaction between magma and groundwater, steam blasts hole open." and "@Cmdr_Hadfield location, oriented ~same, scale ~same, as your photo http://www.flashearth.com/?lat=8.04363&lon=38.351359&z=12.7&r=74&src=msl Maar def.: http://en.wikipedia.org/wiki/Maar" However, my comments got no reply, so I don't know if he saw them.

Photo unmodified. August 20, 2011. FlashEarth Location. (You can see the fault on the crater wall in that view, almost directly across from the center cross hairs.)