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VOLCANO ACTIVITY NOTIFICATION

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(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued: (20210416/0024Z)
(3) Volcano: Semisopochnoi (VNUM #311060)
(4) Current Color Code: ORANGE
(5) Previous Color Code: ORANGE
(6) Source: Alaska Volcano Observatory
(7) Notice Number: 2021/A160
(8) Volcano Location: N 51 deg 55 min E 179 deg 35 min
(9) Area: Aleutians
(10) Summit Elevation: 2625 ft (800 m)
(11) Volcanic Activity Summary: Satellite data suggests ash emissions from Semisopochnoi volcano have been ongoing since early this morning and are continuing. The ash cloud extends up to 217 mi (350 km) southeast of the volcano with heights up to 20,000 feet (6 km) above sea level. Based on the length and height of the ash plume and ongoing nature of ash emissions, AVO is issuing this update; the Color Code/Alert Level remains at ORANGE/WATCH. AVO will continue to monitor the situation.
(12) Volcanic cloud height: 20,000 feet above sea level. or less.
(13) Other volcanic cloud information: continuous ash cloud extends 350 km from volcano.
(14) Remarks: Semisopochnoi is monitored by satellite data, regional infrasound, and lightning detection instruments. An infrasound array on Adak Island may detect explosive emissions from Semisopochnoi with a slight delay (approximately 13 minutes) if atmospheric conditions permit.
(15) Contacts: Aaron Wech, Acting Scientist-in-Charge, USGS
awech@usgs.gov (907) 786-7497

Jessica Larsen, Acting Coordinating Scientist, UAF
jflarsen@alaska.edu (907) 322-4085
(16) 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

AVO/USGS Volcanic Activity Notice

Volcano: Semisopochnoi (VNUM #311060)

Current Volcano Alert Level: WATCH

Current Aviation Color Code: ORANGE

Issued: Thursday, April 15, 2021, 4:24 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A160
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: Satellite data suggests ash emissions from Semisopochnoi volcano have been ongoing since early this morning and are continuing. The ash cloud extends up to 217 mi (350 km) southeast of the volcano with heights up to 20,000 feet (6 km) above sea level. Based on the length and height of the ash plume and ongoing nature of ash emissions, AVO is issuing this update; the Color Code/Alert Level remains at ORANGE/WATCH. AVO will continue to monitor the situation.


Recent Observations:
[Volcanic cloud height] 20,000 feet above sea level. or less.
[Other volcanic cloud information] continuous ash cloud extends 350 km from volcano.

Hazard Analysis:
[Ash cloud] continuous ash cloud extends 350 km from the volcano and up to 20,000 feet above sea level.
[Ashfall] Ashfall is expected on the flanks of the volcano and onto marine waters under the ash cloud southeast of the volcano.

Remarks: Semisopochnoi is monitored by satellite data, regional infrasound, and lightning detection instruments. An infrasound array on Adak Island may detect explosive emissions from Semisopochnoi with a slight delay (approximately 13 minutes) if atmospheric conditions permit.

Contacts: Aaron Wech, Acting Scientist-in-Charge, USGS
awech@usgs.gov (907) 786-7497

Jessica Larsen, Acting Coordinating Scientist, UAF
jflarsen@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].
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Page modified: January 4, 2021 11:16
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