Fort Rock Basin

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Fort Rock Basin
Elevation 1,320 - 1,716 m[1]
Location Oregon , USA
Coordinates 43°18′N 121°00′W / 43.30, -121.00[1]
Type maar field
Age of rock 50,000 to 100,000 years[2]
Last eruption 50,000 years ago[2]

Portions of this article include public domain text from the USFS Deschutes & Ochoco National Forests - Crooked River National Grassland.

The Fort Rock Basin - Christmas Lake Valley basin is a former lake basin that existed from late Pliocene through late Pleistocene time.[3] The Fort Rock Basin Maar Field includes over 30 hydrovolcanic landforms of spread over an area of 4,000 square kilometers.[2][1]

Contents

[edit] Moffitt Butte

Moffitt Butte is a dissected basaltic tuff ring, 1,400 m (4,600 ft) in diameter and 122 m (400 ft) high. Moffitt Butte is not associated with a lake basin, as is the case for Fort Rock and Hole-in-the-Ground, but rising magma probably encountered permeable aquifers beneath the cone. A line of tuff rings between Moffitt Butte and the Fort Rock Basin are located roughly along what would have been an early drainage route between the Fort Rock Basin and the La Pine Basin. The crater floor of Moffitt Butte is about 80 m (260 ft) above the surrounding plain. A smaller vent and small tuff ring, 520 m (1,700 ft) in diameter, are located on Moffitt Butte's southwestern flank. The crater of the smaller vent is filled with lava that issued from a dike on its northwest edge.[4]

[edit] Table Rock

Table Rock is an erosional remnant of a tuff cone, which at present is a symmetrical cone about 1,530 m in diameter at the base, tapering to a diameter of about 360 m at a height of 360 m above the surrounding plain. The cone is capped with flat-lying basalt which once filled the crater, but erosion has modified the original cone, exposing the once-ponded basalt lava lake. Dikes extend north and south of the crater lava lake. On the lower flanks of the cone, the rocks are mostly palagonite lapilli-tuff. Near the summit, the uppermost palagonites are overlain by massive cinders and bombs from fire-fountaining that preceded the filling of the crater with lava.[5]

[edit] Notable Vents

Name Elevation Location Last
eruption
Big Hole[2][6] - - possibly 20,000 years ago
Black Hills[2] - - -
Boat-Wright Ranch[2] - - -
Flat Top[2] - - -
Flatiron[2] - - -
Fort Rock[7] - 43°22′N 121°04′W / 43.37, -121.06 50,000 to 100,000 years ago
Hole-in-the-Ground[8] - 43°25′N 121°12′W / 43.41, -121.20 50,000 to 100,000 years ago
Horning Bend[2] - - -
Moffitt Butte[4] - 43°31′N 121°26′W / 43.51, -121.44 50,000 to 100,000 years ago
Reed Rock[2] - - -
Ridge 28[2] - - -
St. Patrick Mountain[2] - - -
Sand Rock[9] - 43°22′N 120°19′W / 43.37, -120.32 50,000 to 100,000 years ago
Seven-Mile Ridge[2] - - -
South Green Mountain[2] - - -
Table Mountain[2] - - -
Table Rock[5] - 43°10′N 120°53′W / 43.17, -120.88 50,000 to 100,000 years ago
Wastina[2] - - -
Wildcat Butte[2] - - -

[edit] See also

[edit] References

  1. ^ a b c Wood, Charles A.; Jűrgen Kienle (1993). Volcanoes of North America. Cambridge University Press, pp. 203-204. ISBN 0-512-43811-X. 
  2. ^ a b c d e f g h i j k l m n o p q Oregon Volcanoes - Fort Rock Basin Maar Field. Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service (2004-01-09). Retrieved on 2008-05-17.
  3. ^ Heiken, G. H.; R. V. Fisher and N. V. Peterson (2006-03-28). A Field Trip to the Maar Volcanoes of the Fort Rock - Christmas Lake Valley Basin, Oregon. Geological Survey Circular 838: Guides to Some Volcanic Terrances in Washington, Idaho, Oregon, and Northern California. United States Geological Survey. Retrieved on 2008-05-17.
  4. ^ a b Oregon Volcanoes - Moffitt Butte Volcano. Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service (2004-01-09). Retrieved on 2008-05-17.
  5. ^ a b Oregon Volcanoes - Table Rock Volcano. Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service (2003-11-26). Retrieved on 2008-05-17.
  6. ^ Lorenz, Volker (1970). "Some Aspects of the Eruption Mechanism of the Big Hole Maar, Central Oregon". Geological Society of America Bulletin 81 (6): 1823–1830. Geological Society of America. doi:10.1130/0016-7606(1970)81[1823:SAOTEM]2.0.CO;2. 
  7. ^ Oregon Volcanoes - Fort Rock Volcano. Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service (2003-12-24). Retrieved on 2008-05-17.
  8. ^ Oregon Volcanoes - Hole-in-the-Ground Volcano. Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service (2003-12-24). Retrieved on 2008-05-17.
  9. ^ Oregon Volcanoes - Sand Rock Volcano. Deschutes & Ochoco National Forests - Crooked River National Grassland. United States Forest Service (2004-01-09). Retrieved on 2008-05-17.
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