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Broken Top
Elevation 9,175 ft (2,796.5 m) [1]
Prominence 2,175 ft (662.9 m) [1]
Location
Location Deschutes County, Oregon, USA
Range Cascade Range
Coordinates 44°04′58″N 121°41′59″W / 44.0828931°N 121.6997595°W / 44.0828931; -121.6997595Coordinates: 44°04′58″N 121°41′59″W / 44.0828931°N 121.6997595°W / 44.0828931; -121.6997595 [2]
Topo map USGS Broken Top
Geology
Type Stratovolcano
Age of rock Pleistocene
Volcanic arc/belt Cascade Volcanic Arc
Last eruption About 100,000 years ago [3]

Broken Top is an extinct, glacially eroded stratovolcano in Oregon state[4], part of the extensive Cascade Range. Located south of the Three Sisters peaks, the volcano, residing within the Three Sisters Wilderness,[5], is 20 miles (32 km) west of Bend, Oregon in Deschutes County. Eruptive activity stopped roughly 100,000 years ago, and currently, erosion by glaciers has reduced the volcano's cone to where its contents are exposed.

Contents

Geology

Broken Top. USGS image.

Due to extensive erosion, the contents of Broken Top's cone are exposed, and allow volcanologists to classify Broken Top as a complex stratovolcano.[4] Its initial eruptions during the Pleistocene, consisting of basaltic andesite lava, contributed to a base shield. The center of this edifice consists of agglomerate, which was oxidized, and intrusive dikes and geologic sills.[4] Erratic eruptions continued afterward, erupting silicic lava. Much of the current cone is occupied by mafic flows of andesite, dacite, rhyodacite, and pyroclastic flows; these deposits extending from the subordinate volcano to the summit.[4] The volcanic crater, now 0.8 km, was most likely subsidized.

Wilderness

Broken Top resides in the Three Sisters Wilderness, which makes up 242,000 acres of the Willamette National Forest. About the area, there are geologic features such as Collier Glacier, Rock Mesa, Collier Cone, and Yapoah Crater.

Permits for average entry are distributed, free, from Memorial Day (May 31)–Halloweeen (October 31).[6] To gain access to the Obsidian area of the wilderness, special entry is required, for both day and overnight hikers.[6] These passes are distributed only at McKenzie Ranger District in Willamette Forest and Sisters Ranger District in Deschutes Forest.[6] The administration disallows any vehicle entry.

See also

References

  1. ^ a b "Broken Top". Peakbagger.com. http://www.peakbagger.com/peak.aspx?pid=2420. Retrieved 2009-06-30. 
  2. ^ "Broken Top". Geographic Names Information System. U.S. Geological Survey. http://geonames.usgs.gov/pls/gnispublic/f?p=gnispq:3:::NO::P3_FID:1138649. Retrieved 2008-03-31. 
  3. ^ "Broken Top Volcano". Deschutes & Ochoco National Forests. USDA Forest Service. 2003-11-26. http://www.fs.fed.us/r6/centraloregon/geology/info/volcanoes/brokentop.shtml. Retrieved 2008-03-18. 
  4. ^ a b c d Wood, Charles A.; Jűrgen Kienle (1993). Volcanoes of North America. Cambridge University Press. p. 183. ISBN 0-512-43811-X. 
  5. ^ "Three Sisters Wilderness". Willamette National Forest. United States Forest Service. 2004-07-29. http://www.fs.fed.us/r6/willamette/recreation/tripplanning/wilderness/threesisters.html. Retrieved 2008-05-18. 
  6. ^ a b c "Wilderness Permits". United States Forest Service. May 24, 2006. http://www.fs.fed.us/r6/willamette/general/passespermits/recpasses/wilderness.html. Retrieved July 6, 2009. 

External links

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