AVO/USGS Volcanic Activity Notice

Volcano: Shishaldin (CAVW #1101-36-)

Current Volcano Alert Level: ADVISORY
Previous Volcano Alert Level: NORMAL

Current Aviation Color Code: YELLOW
Previous Aviation Color Code: GREEN

Issued: Tuesday, January 6, 2009, 3:28 PM AKST (20090106/0028Z)
Source: Alaska Volcano Observatory
Notice Number: 2009/A2
Location: N 54 deg 45 min W 163 deg 58 min
Elevation: 9373 ft (2857 m)
Area: Aleutians Alaska
Volcanic Activity Summary: AVO has detected a significant thermal anomaly and a slight increase in earthquake activity at Shishaldin Volcano on Unimak Island in the eastern Aleutians. Together, these observations indicate a departure from background conditions at Shishaldin. AVO is raising the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. There is no indication that an eruption is imminent or certain, although the potential for an eruption has increased. AVO will continue to monitor the volcano closely.

Recent Observations: [Other observations] Over the past 24 hours, several satellite passes over the volcano have recorded strong thermal signatures over the summit of the volcano. Such intense thermal anomalies are fairly rare for Shishaldin. Over the past 36 hours, AVO seismic networks have recorded a small but significant number of earthquakes below the volcano. AVO has received no reports of unusual steaming or activity at the volcano from airline pilots or residents of the lower Alaska Peninsula or False Pass, the nearest community. Steaming from the summit crater is quite common, however.

Hazard Analysis: [General hazards] Higher thermal output and small earthquakes could increase the possibility of rock and snow avalanches on the steep cone. Sudden steam explosions could also produce minor amounts of ash and blocky ejecta on the slopes of the volcano.

In the event this unrest leads to an explosive eruption, primary hazards would be ash clouds, minor ash fall in nearby communities, and lahars that could reach the sea.

A complete description of these hazards during future eruptions of Shishaldin Volcano can be found online at: http://www.avo.alaska.edu/pdfs/RI_2002_4.pdf

Remarks: Shishaldin volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetric cone with a base diameter of approximately 10 miles (16 km). A small summit crater typically emits a noticeable steam plume with occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, erupting atleast 28 times since 1775. Most of Shishaldin's eruptions have consisted of small ash and steam plumes, although the most recent eruption in April-May 1999 produced an ash column that reached a height of 45,000 ft above sea level.

Contacts: Peter Cervelli, Acting Scientist-in-Charge, USGS
pcervelli@usgs.gov (907) 786-7497

Jon Dehn, Acting Coordinating Scientist, UAFGI
jdehn@gi.alaska.edu (907) 474-6499

Next Notice: A new VAN will be issued if conditions change significantly or alert levels are modified. While a VAN is in effect, regularly scheduled updates are posted at http://www.avo.alaska.edu

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.