1817 INTRACALDERA ERUPTION OF OKMOK VOLCANO, ALASKA: TRANSITION FROM HYDROMAGMATIC TO STROMBOLIAN ACTIVITY
Okmok Volcano consists of a 10-km-diameter, late-Holocene caldera on Umnak Island in the eastern Aleutians, 1400 km southwest of Anchorage (Byers, 1959). The most recent eruption in 1997 (Patrick et. al, 2003) was predominantly strombolian in character, producing a basaltic-andesite lava flow within...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.528.6608 http://kiska.giseis.alaska.edu/kasp/kasp04/abstracts/neal.pdf |
| Summary: | Okmok Volcano consists of a 10-km-diameter, late-Holocene caldera on Umnak Island in the eastern Aleutians, 1400 km southwest of Anchorage (Byers, 1959). The most recent eruption in 1997 (Patrick et. al, 2003) was predominantly strombolian in character, producing a basaltic-andesite lava flow within the caldera and a localized scoria and ash fall. Recent geologic mapping has confirmed, however, that since caldera-formation ~2050 14C yrs BP (Beget and Larson, 2001), far more violent eruptions from vents within the caldera have impacted all flanks of the volcano with tephra fall, ballistics, pyroclastic surges and flows, and lahars. An example of these is the 1817 eruption. Reevaluation of the historical and geological record suggest that this event included opening hydrovolcanic activity that produced significant pyroclastic fall and surge deposits extending down the north and east flanks of the volcano. Later stages of this eruption involved strombolian lava fountaining and production of several lava flows. 1817 vents form a 4-km-long arc that parallels the base of the north caldera wall and include a 50-70-m-deep, elongate maar crater that excavated pre-existing tuff cone deposits. Terrace morphology and flood deposits less than 200 14C yrs BP indicate a related flooding event down Crater Creek that drains the caldera, consistent with historical accounts of Aleut village inundation at the |
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