Following apparent explosive activity and a resultant small ash cloud on February 18, 2012, the Alaska Volcano Observatory elevated the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY for Kanaga Volcano in Alaska's Aleutians. Volcanic tremor had been detected on the local seismic network at Kanaga, followed by numerous small events for about an hour. Short-lived explosive activity was suspected, and the unrest was corroborated by AVHRR satellite data that showed a small -- 8 kilometer in length -- ash plume, detached and of unknown altitude, drifting northeast of the volcano.
This new unrest indicates a possibility for sudden explosions of ash to occur at any time, and ash clouds exceeding 20,000 feet above sea level may develop. If a large, explosive, ash-producing event occurs, the local seismic network, satellite ash alarms, infrasound and volcanic lightning will alert AVO to the new activity.
Kanaga Volcano occupies the northern corner of Kanaga Island, one of the most southerly members of the central Aleutian chain. It is a symmetric composite cone 1,307 meters high and 4.8 kilometers in diameter at sea level, built of interbedded basaltic and andesitic lava flows, scoria layers, and pyroclastic rocks. Kanaga Volcano last erupted 1994-1995 when observed eruptive plumes were relatively dilute, rising to altitudes of less than 3 kilometers and dropping ash onto the flanks of the volcano. At least two significant ash plumes were recorded over the course of this eruption: the first, to ~7.5 kilometers occurred on February 21, 1995 and the second on August 18,1995, when an eruption cloud reached ~4.5 kilometers. A light dusting of ash fell on the community of Adak and air traffic was disrupted due to continuing low-level activity and cloudy conditions which prevented visual approaches to the Adak air field.
For more information about Kanaga Volcano, visit http://www.avo.alaska.edu.
PHOTO CAPTION/CREDIT: Kanaga Volcano viewed from the west, with Mount Moffet, Adak and Great Sitkin in the background. Photo by C. Read, courtesy of AVO/USGS.