On August 6, 2008, a vigorous seismic swarm was detected in the vicinity of Kasatochi volcano in Andreanof Islands. Starting at 15:00 UTC on August 6, the intensity and frequency of the earthquakes rapidly increased resulting in ~1,100 events located over the course of 48 hours during the most energetic part of the swarm. The largest earthquake, magnitude 5.8, occurred about 27 hours into the sequence and about 3.5 hours before the first aerial ash discharge from Kasatochi was detected by the Alaska Volcano Observatory through satellite data.

This discharge was followed by two more explosions, also detected via satellite monitoring. The 3rd explosion consisted of nearly continuous ash emissions and declined in frequency and intensity through ~22:00 UTC on August 8. The seismic swarm intensity started to decline at ~18:00 UTC on August 8, and continued to decline through the end of August.

Last Modified: April 19, 2024