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AVO/USGS Volcanic Activity Notice

Volcano: Semisopochnoi (VNUM #311060)

Current Volcano Alert Level: WATCH
Previous Volcano Alert Level: WARNING

Current Aviation Color Code: ORANGE
Previous Aviation Color Code: RED

Issued: Monday, September 20, 2021, 8:12 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A817
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: Ash emissions from the ongoing eruption at Semisopochnoi continue at a decreased rate. Over the last few hours, activity has consisted of discrete explosions that occur about once an hour and produce small ash clouds that rise to 10,000 to 15,000 feet above sea level and are currently drifting to the northwest. This represents less significant ash emissions and we are therefore lowering the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH.

Activity at Semisopochnoi remains elevated and ash emissions could increase again at any time.

Please visit the NWS Alaska Aviation Weather Unit for current information about the volcanic ash cloud forecast. https://www.weather.gov/aawu/sigmets

Recent Observations:
[Volcanic cloud height] 10,000 to 15,000 ft. asl
[Other volcanic cloud information] Small ash clouds are drifting NW
[Lava flow/dome] none
[Lava flow] none

Remarks: Semisopochnoi is monitored by a local seismic and infrasound network, local web cameras, regional lightning and infrasound sensors, and satellite data.

Contacts: Michelle Coombs, Scientist-in-Charge, USGS
mcoombs@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAF
dfee1@alaska.edu (907) 322-4085

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.

VOLCANO ALERT LEVELS

NORMAL
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

ADVISORY
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

WATCH
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.

WARNING
Hazardous eruption is imminent, underway, or suspected.

AVIATION COLOR CODES

GREEN
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

YELLOW
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

ORANGE
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].

RED
Eruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].