The 2008 phreatomagmatic eruption of Okmok volcano, Aleutian Islands, Alaska: Chronology, deposits, and landform changes

Alaska Division of Geological & Geophysical Surveys Report of Investigation RI 2015-2
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Abstract

Okmok volcano, Aleutian Islands, Alaska, explosively erupted over a five-week period between July 12 and August 23, 2008. The eruption was predominantly phreatomagmatic, producing fine-grained tephra that covered most of northeastern Umnak Island. The eruption had a maximum Volcanic Explosivity Index (VEI) of 4, with eruption column heights up to 16 km during the opening phase. Several craters and a master tuff cone formed in the caldera as a result of phreatomagmatic explosions and accumulated tephra-fall and surge deposits. Ascending magma continuously interacted with an extensive shallow groundwater table in the caldera, resulting in the phreatomagmatic character of the eruption. Syneruptive explosion and collapse processes enlarged a pre-existing lake, created a second, entirely new lake, and formed new, deep craters. A field of ephemeral collapse pits and collapse escarpments formed where rapid groundwater withdrawal removed material from beneath capping lava flows. This was the first significant phreatomagmatic event in the U.S. since the Ukinrek Maars eruption in 1977.

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Additional publication details

Publication type Report
Publication Subtype Other Government Series
Title The 2008 phreatomagmatic eruption of Okmok volcano, Aleutian Islands, Alaska: Chronology, deposits, and landform changes
Series title Alaska Division of Geological & Geophysical Surveys Report of Investigation
Series number RI 2015-2
DOI 10.14509/29405
Year Published 2015
Language English
Publisher Alaska Division of Geological & Geophysical Surveys
Publisher location Fairbanks, AK
Contributing office(s) Volcano Science Center
Description Report: 53 p.; Vector Data Set
Country United States
State Alaska
Other Geospatial Aleutian Islands, Okmok volcano
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