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map showing location of Mount Okmok. Image source: Cameron, Cheryl, courtesy of the Alaska Volcano Observatory / Alaska Division of Geological & Geophysical Surveys
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Latest news:
Okmok volcano
One of the most active volcanoes in the Aleutian island chain (Alaska)
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Volcano type |
Central shield complex with nested caldera |
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Location |
Aleutian islands, 1383 km (859 mi) from Anchorage, 53.397° N / 168.166° W |
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Summit elevation |
1073 m (3520 ft) |
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Last eruptions |
1817, 1824, 1878(?), 1899, 1931, 1935, 1936, 1938, 1943, 1945, 1958, 1960, 1981, 1983, 1986, 1997, 2008 |
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Typical eruption style |
Explosive and effusive |
Background:Okmok Volcano is one of the most active volcanoes in the Aleutian chain. It consists of a complex of shields truncated by a caldera and several active vents inside the caldera, which have built small cones and lava flows.
Okmok's caldera was formed by at least two collapses following catastrophic pyroclastic eruptions, at around 8200 y B.P. and 2400 y. B.P.
Within the caldera, the oldest volcanic deposits are brecciated pillow lavas and pyroclastic rocks once deposited in a caldera lake. The lake attained a maximum depth of about 150 m and the upper surface reached an elevation of about 475 m, at which point it overtopped the low point of the caldera rim. A small shallow lake near the outlet of the caldera is all that remains today. Three dissected tuff cones may have been produced by eruptions beneath the former caldera lake. Other cinder cones occur atop pillow lavas; such cones apparently breached the surface of the former lake. Cinder cones and associated lava flows that are younger than the caldera lake are identified by structures and textures characteristic of subaerial eruption. The documented eruption of 1945 occurred at a cinder cone near the southwest caldera wall; this cone may have been the site of all historical activity of Okmok volcano. Hot springs and fumaroles occur both within Okmok caldera and at Hot Springs cove, 20 km to the southwest.
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Source: abbreviated from AVO (http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Okmok)
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