Fort Rock Basin

Fort Rock Basin
	Fort Rock , Fort Rock Basin
height	1500 m mean altitude, altitude range 1,320 - 1,716 m
location	United States ( Oregon , United States )
Mountains	Cascade Range (Cascade Range)
Coordinates	43 ° 18 ′ 0 ″ N , 121 ° 0 ′ 0 ″ W Coordinates: 43 ° 18 ′ 0 ″ N , 121 ° 0 ′ 0 ″ W
Type	Maar area
Age of the rock	50,000 to 100,000 years
Last eruption	about 50,000 years ago

The Fort Rock Basin , also Fort Rock - Christmas Lake Valley Basin , is a former lake basin in the US state of Oregon that existed from the late Pliocene to the late Pleistocene . The Fort Rock Basin maar field comprises more than 30 phreatomagmatic landforms 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 extends. The subsurface of the cascade chain consists of fragments of the earth's crust that have been added to the west coast of North America ( accretion ) by the subduction of the Juan de Fuca plate since the Paleogene . For about five million years, the volcanic activity caused by the melting of the subducted earth's crust has been particularly brisk. Due to the composition of the rising magma ( andesite and dacite ), which is influenced by the crust material, volcanism is often explosive.

Moffitt Butte

Moffitt Butte is a basaltic tuff ring that has been cut up by erosion . It has a diameter of 1,400 m and is 122 m high. Moffitt Butte is not associated with a lake basin, as is the case with Fort Rock and Hole-in-the-Ground , but with the rise of magma into a groundwater- bearing layer. A series of tuff rings between Moffitt Butte and the Fort Rock Basin are strung on a line that might correspond to an early drainage line between the Fort Rock Basin and neighboring La Pine Basin. The crater floor of Moffitt Butte is about 80 m above the adjacent plain. A small volcanic vent, 520 m in diameter, surrounded by a tuff ring, sits on the southwest flank of Moffitt Butte. The crater of the small vent is filled with solidified lava that emerged from a volcanic dyke on its northwestern edge.

Table rock

Table Rock is the eroded remnant of a tuff volcano, which today has the shape of a symmetrical cone with a base diameter of 1,530 m and its top at a height of 360 m about 360 m. The cone has a lid made of flat basalt that once filled the crater. The erosion has removed the original volcanic cone, leaving the former lava lake in the crater. Volcanic dykes extend south and north of the former lava lake. On the lower flanks of the cone, the tuffs consist essentially of palagonitic lapilli ; near the summit, these palagonite tuffs are covered by massive layers of ash with volcanic bombs , which testify to the violent ejective volcanic activity that took place before the crater was filled with lava.

Major volcanoes of the Fort Rock Basin

Surname	height	Coordinates	Type	Last eruption
Big hole	1,447.8 m	43 ° 26 ′ N , 121 ° 19 ′ W.43.425280555556 -121.31221944444 1447.8	Maar	probably 20,000 years ago
Black Hills	1558 m	43 ° 10 ′ N , 120 ° 41 ′ W.43.167126 -120.686188	Tuff ring / lava lake
Boat-Wright Ranch		43 ° 18 ′ N , 121 ° 11 ′ W.43.294825 -121.180476	Tuff ring
Flat top			Tuff ring / lava lake
Flatiron	1,354 m	43 ° 21 ′ N , 120 ° 52 ′ W.43.344344 -120.86669	Tuff ring / lava lake
Fort Rock	1,431 m	43 ° 22 ′ N , 121 ° 4 ′ W.43.37 -121.06 1431	Tuff ring	50,000 to 100,000 years ago
Hole-in-the-Ground		43 ° 25 ′ N , 121 ° 12 ′ W.43.41 -121.2 1431	Maar	50,000 to 100,000 years ago
Horning Bend		43 ° 18 ′ N , 121 ° 2 ′ W.43.30788 -121.030798	Tuff ring
Moffitt Butte		43 ° 31 ' N , 121 ° 26' W43.51 -121.44	Tuff ring / lava lake	50,000 to 100,000 years ago
Reed rock		43 ° 21 ′ N , 120 ° 44 ′ W.43.342658 -120.740776	Tuff ring / lava lake
Ridge 28		43 ° 28 ′ N , 121 ° 26 ′ W.43.473851 -121.426392	Tuff ring
St. Patrick Mountain	1,764 m	43 ° 7 ′ N , 120 ° 35 ′ W.43.117776 -120.589371	Tuff ring / lava lake
Sand rock	1,405 m	43 ° 22 ′ N , 120 ° 19 ′ W.43.37 -120.32	Tuff ring	50,000 to 100,000 years ago
Seven-Mile Ridge	1,324 m	43 ° 13 ′ N , 120 ° 43 ′ W.43.22488 -120.721335	Tuff ring
South Green Mountain		43 ° 21 ′ N , 120 ° 42 ′ W.43.350398 -120.705414	Tuff ring
Table Mountain	1,387 m	43 ° 24 ' N , 120 ° 51' W.43.397439 -120.850296	Tuff ring / lava lake
Table rock		43 ° 10 ′ N , 120 ° 53 ′ W.43.17 -120.88	Tuff ring / tuff cone / lava lake	50,000 to 100,000 years ago
Wastina		43 ° 18 ′ N , 121 ° 11 ′ W.43.294825 -121.180476	Tuff ring
Wildcat Butte		43 ° 18 ′ N , 120 ° 20 ′ W.43.299697 -120.330505	Tuff ring

Individual evidence

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q Oregon Volcanoes - Fort Rock Basin Maar Field. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , January 9, 2004, accessed September 19, 2008 .
^ RV Fisher, NV Peterson, GH Heiken: A Field Trip to the Maar Volcanoes of the Fort Rock - Christmas Lake Valley Basin, Oregon. In: Geological Survey Circular 838: Guides to Some Volcanic Terrances in Washington, Idaho, Oregon, and Northern California. United States Geological Survey , March 28, 2006, accessed September 19, 2008 .
↑ Jurgen Kienle, Charles A. Wood: Volcanoes of North America . Cambridge University Press, 1993, ISBN 0-521-43811-X , pp. 203-204 .
^ Gerhard H. Eisbacher: North America . In: Geology of the Earth . 1st edition. tape 2 . Ferdinand Enke Verlag, Stuttgart 1986, ISBN 3-432-96901-5 .
^ ^A ^b Oregon Volcanoes - Moffitt Butte Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , January 9, 2004, accessed September 20, 2008 .
^ ^A ^b Oregon Volcanoes - Table Rock Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , November 26, 2003, accessed September 20, 2008 .
↑ Volker Lorenz: Some Aspects of the Eruption Mechanism of the Big Hole Maar, Central Oregon . In: Geological Society of America Bulletin . tape 81 , no. 6 . Geological Society of America , 1970, pp. 1823-1830 , doi : 10.1130 / 0016-7606 (1970) 81 [1823: SAOTEM] 2.0.CO; 2 .
^ Oregon Volcanoes - Fort Rock Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , December 24, 2003, accessed September 20, 2008 .
^ Oregon Volcanoes - Hole-in-the-Ground Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , December 24, 2003, accessed September 20, 2008 .
^ Oregon Volcanoes - Sand Rock Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , January 9, 2004, accessed September 20, 2008 .

[USFS-1] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q Oregon Volcanoes - Fort Rock Basin Maar Field. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , January 9, 2004, accessed September 19, 2008 .

[USGS838-2] RV Fisher, NV Peterson, GH Heiken: A Field Trip to the Maar Volcanoes of the Fort Rock - Christmas Lake Valley Basin, Oregon. In: Geological Survey Circular 838: Guides to Some Volcanic Terrances in Washington, Idaho, Oregon, and Northern California. United States Geological Survey , March 28, 2006, accessed September 19, 2008 .

[Wood-3] Jurgen Kienle, Charles A. Wood: Volcanoes of North America . Cambridge University Press, 1993, ISBN 0-521-43811-X , pp. 203-204 .

[4] Gerhard H. Eisbacher: North America . In: Geology of the Earth . 1st edition. tape 2 . Ferdinand Enke Verlag, Stuttgart 1986, ISBN 3-432-96901-5 .

[USFS_MB-5] A ^b Oregon Volcanoes - Moffitt Butte Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , January 9, 2004, accessed September 20, 2008 .

[USFS_TR-6] A ^b Oregon Volcanoes - Table Rock Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , November 26, 2003, accessed September 20, 2008 .

[Lorenz-7] Volker Lorenz: Some Aspects of the Eruption Mechanism of the Big Hole Maar, Central Oregon . In: Geological Society of America Bulletin . tape 81 , no. 6 . Geological Society of America , 1970, pp. 1823-1830 , doi : 10.1130 / 0016-7606 (1970) 81 [1823: SAOTEM] 2.0.CO; 2 .

[USFS_FR-8] Oregon Volcanoes - Fort Rock Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , December 24, 2003, accessed September 20, 2008 .

[USFS_HIG-9] Oregon Volcanoes - Hole-in-the-Ground Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , December 24, 2003, accessed September 20, 2008 .

[USFS_SR-10] Oregon Volcanoes - Sand Rock Volcano. In: Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service , January 9, 2004, accessed September 20, 2008 .