ALASKA VOLCANO OBSERVATORY DAILY UPDATE
U.S. Geological Survey
Thursday, December 12, 2019, 12:45 PM AKST (Thursday, December 12, 2019, 21:45 UTC)

SHISHALDIN VOLCANO (VNUM #311360)
54°45'19" N 163°58'16" W, Summit Elevation 9373 ft (2857 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

A short-lived explosion from Shishaldin Volcano occurred earlier this morning at 7:10 AKST (16:10 UTC) and produced an ash cloud to about 25,000 feet above sea level, drifted to the NW and dispersed after a couple of hours. The eruption cloud is visible in a series of GOES satellite images from 16:30 until about 18:00. Three lightning strokes were detected by the Worldwide Lightning Location Network (http://wwlln.net/) between 07:15 and 07:17 AKST (16:15-16:17 UTC). Consistently elevated surface temperatures were seen in satellite data yesterday afternoon and overnight through clouds. The SIGMET issued by the National Weather Service earlier this morning has been cancelled. The ash cloud was associated with a 3-minute period of elevated seismic tremor. Tremor continues to be observed in seismic data at this time indicating that surficial eruption processes are continuing.

Episodic explosions and lava flow front collapses resulting in low-level ash plumes can occur with little warning.

Shishaldin is monitored by local seismic and infrasound sensors, satellite data, web cameras, a telemetered geodetic network, and distant infrasound and lightning networks.

SEMISOPOCHNOI VOLCANO (VNUM #311060)
51°55'44" N 179°35'52" E, Summit Elevation 2625 ft (800 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Seismicity remains elevated at Semisopochnoi over the past 24 hours. Tremor bursts and small explosions have been observed in seismic data today. An 50 mile (80 km) long steam and gas plume (possibly containing volcanic ash) was observed in satellite data from yesterday and today and may contain small amounts of ash.

Semisopochnoi is monitored with an on-island seismic network and remotely by satellite and lightning sensors. An infrasound array on Adak Island may detect explosive emissions from Semisopochnoi with a slight delay (approximately 13 minutes) if atmospheric conditions permit.

CLEVELAND VOLCANO (VNUM #311240)
52°49'20" N 169°56'42" W, Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

No eruptive activity at Cleveland has been detected in local seismic or infrasound data over the past day. No activity was observed in satellite data over the past 24 hours.

Episodes of lava effusion and explosions can occur without advance warning. Explosions from Cleveland are normally short duration and only present a hazard to aviation in the immediate vicinity of the volcano. Larger explosions that present a more widespread hazard to aviation are possible, but are less likely and occur less frequently.

Cleveland volcano is monitored by only two seismic stations, which restricts AVO's ability to detect precursory unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption may be possible using a combination of seismic, infrasound, lightning, and satellite data.

OTHER ALASKA VOLCANOES

Information on all Alaska volcanoes is available at : http://www.avo.alaska.edu.

For definitions of Aviation Color Codes and Volcano Alert Levels, see: http://www.avo.alaska.edu/color_codes.php

SUBSCRIBE TO VOLCANO ALERT MESSAGES by email: http://volcanoes.usgs.gov/vns/

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CONTACT INFORMATION:

Kristi Wallace, Acting Scientist-in-Charge, USGS
kwallace@usgs.gov (907) 786-7497

Janet Schaefer, Acting Coordinating Scientist, UAFGI
janet.schaefer@alaska.gov (907) 322-4085

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.

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