HOLE-IN-THE-GROUND

'Hole-in-the-Ground' is a large maar (explosion crater) in the Fort Rock Basin of Lake County, central Oregon, northeast of Crater Lake, near Oregon State Route 31.
It is about 1,600 meters (nearly a mile) across, a little longer N-S than E-W. Its floor is about 150 meters below the surrounding ground level and has a rim that rises 35 to 65 meters (about 110 to 220 feet) above, the highest point on the east side. The crater formed during the late Pleistocene, between 13,500 and 18,000 years ago, at which time the Fort Rock Basin was a lake and the location was near the shore. Basaltic magma intruding near the surface flashed ground water to steam, which blew out overlying rock and soil, along with some juvenile material. As material slid into the hole formed, it closed the vent and the process repeated, eventually forming the huge hole.^[2] Blocks as large as 8 meters in size were flung as far as 3.7 km from the crater.^[3]
To the west of Hole-in-the-Ground is an even bigger maar, 1,820 meters (about 6,000 feet), but older and more eroded, called Big Hole.

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References

1. Deschutes & Ochoco National Forests - Hole-in-the-Ground Volcano
2. A Field Trip to the Maar Volcanoes of the Fort Rock - Christmas Lake Valley Basin, Oregon
3. Volcanoes of North America, , Charles A., Wood, Cambridge University Press, ,

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