(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA) | |
(2) Issued: | (20210920/0558Z) |
(3) Volcano: | Semisopochnoi (VNUM #311060) |
(4) Current Color Code: | RED |
(5) Previous Color Code: | ORANGE |
(6) Source: | Alaska Volcano Observatory |
(7) Notice Number: | 2021/A811 |
(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: | Ash emissions from the ongoing eruption at Semisopochnoi have increased in frequency and intensity. Satellite images show an ash cloud at an estimated altitude of 15,000 ft. above sea level extending approximately 60 miles (100 km) to the southeast through 05:00 UTC. Explosions have been observed throughout the day and increased sulfur dioxide gas emissions have been observed in satellite data this afternoon. These observations represent an increase in eruptive activity and Aviation Color Code and Volcano Alert level are being increased to RED/WARNING. Increasing high clouds over Semisopochnoi will likely obscure satellite views of ash emissions within the hour. Seismic and infrasound monitoring will continue to provide notice of ongoing explosive activity, however it cannot determine the height or extent of ash emissions. The Alaska Volcano Observatory will continue to closely monitor all available data. Please visit the NWS Alaska Aviation Weather Unit for current information about the volcanic ash cloud forecast. https://www.weather.gov/aawu/sigmets |
(12) Volcanic cloud height: | 15,000 ft. asl |
(13) Other volcanic cloud information: | Ash and sulfur dioxide observed in satellite extending 60 miles to the SE |
(14) Remarks: | Semisopochnoi is monitored by a local seismic and infrasound network, local web cameras, regional lightning and infrasound sensors, and satellite data. |
(15) Contacts: | Michelle Coombs, Scientist-in-Charge, USGS mcoombs@usgs.gov (907) 786-7497 David Fee, Coordinating Scientist, UAF dfee1@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 |