USGS Volcano Notice for Aviation - DOI-USGS-AVO-2023-09-05T12:41:31-08:00

(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20230905/2046Z)
(3) Volcano:	Shishaldin (VNUM #311360)
(4) Current Color Code:	RED
(5) Previous Color Code:	RED
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2023/A1360
(8) Volcano Location:	N 54 deg 45 min W 163 deg 58 min
(9) Area:	Aleutians
(10) Summit Elevation:	9373 ft (2857 m)
(11) Volcanic Activity Summary:	Correction to previous VAN/VONA issued at 12:31 PM AKDT. Alert Level remains at WARNING. An explosive eruption from Shishaldin began at ~08:30 AKDT (1630 UTC) following a several-hour increase in seismicity and produced an extensive ash cloud that moved towards the south-southeast at an estimated altitude of 32,000 ft (9.7 km) above sea level. Around 19:00 AKDT (1900 UTC) seismic amplitude decreased rapidly, and the altitude of the ash emissions as observed by satellite also decreased to an estimated altitude of ~15,000 ft (4.5 km). At 12:00 pm AKDT (2000 UTC), the lower-altitude ash cloud extended for ~75 miles (125 km) towards the east. The Aviation Color Code and Volcano Alert Level remains at RED/WARNING. The National Weather Service has issued a SIGMET for the ash cloud (https://www.weather.gov/aawu/sigmets), and a Special Weather Statement and a Marine Weather Statement has been issued for possible trace ash fall on Unimak Island and on nearby marine waters, respectively. Based on previous eruption cycles, significant ash emissions are likely to continue for several hours. Pyroclastic and mudflows are likely on the immediate flanks of the volcano. Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite images to detect eruptions.
(12) Volcanic cloud height:	15,000 ft
(13) Other volcanic cloud information:	Estimate based on winds and satellite obs.
(14) 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 660 ft. (200 m) wide funnel-shaped summit crater typically emits a steam plume and occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, with at least 54 episodes of unrest including over 26 confirmed eruptions since 1824. Most eruptions are relatively small, although the April-May 1999 event generated an ash column that reached 45,000 ft. (14 km) above sea level.
(15) Contacts:	Matt Haney, Scientist-in-Charge, USGS mhaney@usgs.gov (907) 786-7497 David Fee, Coordinating Scientist, UAFGI dfee1@alaska.edu (907) 378-5460
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