Big Hole (Oregon)

Eastern edge of the Big Hole, Oregon

Big Hole is a large maar crater in the Fort Rock Basin, Lake County, Oregon near the Oregon Route 31, northeast of Crater Lake. It has a diameter of 1,820 m and is 91 m deep. Big Hole is located near the smaller but better preserved Maarkraters Hole- in-the- Ground.

Description

The crater is surrounded by a 24 to 30 m thick ring of tuff. The Tuffablagerungen extend beyond 1.8 to 2.5 km above the crater rim and are - possibly due to the prevailing wind direction during the eruption - on the northeast side of the powerful, where they form the Big Hole Butte. The tuffs were deposited in 5-100 cm thick layers, one formed by landslides winding stratification show places ( Convolute Bedding, see photo above) and consist of lapilli - tuff and tuff breccia containing sideromelane, a volcanic glass hyaloklastisches. Often, volcanic bombs of basalt, which can reach up to 2.5 m in diameter. The proportion of nichtvulkanischem host rock is low.

Ground levels in the crater indicate that there has been a collapse of rock floes in a cavity formed during the phreatomagmatic explosion, which could explain the size of the maar. Similar processes have also led to the emergence of large Eifelmaare, such as in the case of sea fields Maar or Dreiser Weiher.

Surroundings

Big Hole is part of the volcanic Cascade Range ( Cascade Range), which extends from northern California to southern British Columbia. The base of the Cascade Range consists of fragments of the Earth's crust that have been added since the Paleogene by the subduction of the Juan de Fuca plate to the west coast of North America ( accretion ). Since about five million years ago volcanic activity caused by the melting of the subducted crust is particularly active. Due to the influenced by crustal material composition of the ascending magma ( andesite and dacite ) volcanic activity is often explosive.