Fort Rock Basin
Fort Rock, Fort Rock Basin
The Fort Rock Basin, and Fort Rock - Christmas Lake Valley Basin, is a former lake basin in the U.S. state of Oregon, which existed from the late Pliocene to the late Pleistocene. The Maarfeld of the Fort Rock Basin covers more than 30 phreatomagmatic landforms that are scattered over an area of more than 4,000 square kilometers.,
Origin of volcanism
The Fort Rock Basin 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.
Moffitt Butte
Moffitt Butte is a cut-up of the erosion of basaltic tuff ring. It has a diameter of 1.400 m and is 122 m high. Moffitt Butte is not connected to a lake basin, as is the case with Fort Rock and Hole-in- the-ground, but with the rise of magma into an aquifer. A number of Tuffringen between Moffitt Butte and the Fort Rock Basin is strung on a line that could correspond to an early drainage line between the Fort Rock Basin and the adjacent La Pine Basin. The crater floor of Moffitt Butte is about 80 m above the surrounding plain. A small volcanic chimney of 520 m in diameter, surrounded by a tuff ring, located on the southwestern edge of the Moffitt Butte. The crater of a small chimney is filled with solidified lava that has leaked from a volcanic Dyke at its northwestern edge.
Table Rock
Table Rock is the eroded remnant of a tuff volcano, which today is in the form of a symmetrical cone, which measures about 360 m by a base diameter of 1.530 m and its peak at 360 meters above sea level. The cone has a cover made of flat -lying basalt, which once filled the crater. Erosion has removed the original volcanic cone, so that the former lava lake in the crater remained. Volcanic Dykes extend north and south of the former lava lake. The tuffs are made on the lower flanks of the cone mainly from palagonitischen lapilli, near the summit this Palagonittuffe are overlain by massive ash layers with volcanic bombs, which bear witness to the violent ejective volcanic activity that took place prior to the filling of the crater with lava.