English: Okmok volcano occupies most of northeastern Umnak Island, in the eastern Aleutian Islands, Alaska. The last eruption of Okmok started on July 12, 2008 as an explosion eruption. The opening explosions consumed a portion of intracaldera Cone D within the east-central sector of the caldera, reaming several new craters into the caldera floor. Eruptive activity began only a few hours after a subtle increase in the rate of earthquakes followed by a short swarm sequence, both noted only in retrospect.

Over the next 5 weeks, several hundred million cubic meters of tephra and lahar deposits blanketed much of northeast Umnak Island. Within the caldera, nearly continuous hydrovolcanic explosions accumulated many tens of meters of wet, mostly fine-grained tephra. Explosive activity completely disrupted existing groundwater and standing water bodies within the caldera, formed new lakes, and constructed a new tephra cone about 100-200 m (330-660 ft) high. Photo: Janet Schaefer, Aug 11, 2013.

Learn more about Okmok at bit.ly/okmok

1. USGS #science #volcano #Alaska #Okmok #eruption #Aleutian #landscape #waterfall