USGS Volcano Notice for Aviation - DOI-USGS-AVO-2023-08-04T13:48:44-08:00

(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20230804/2207Z)
(3) Volcano:	Shishaldin (VNUM #311360)
(4) Current Color Code:	RED
(5) Previous Color Code:	RED
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2023/A1215
(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:	Eruptive activity continues at Shishaldin Volcano, with continuous ash emissions, strongly elevated surface temperatures, and high levels of seismic tremor. A continuous ash plume extends to the east-northeast with two branches visible in satellite imagery and confirmed by passing aircraft. The volcanic cloud extends up to ~112 miles (~180 km) from the volcano, with its top as high as 31,000 ft (9.4 km) above sea level. Additionally, a gas-rich but less ash-laden volcanic plume is also drifting to the southeast. The National Weather Service has issued a SIGMET for these ash clouds, a Marine Weather Statement and a Special Weather Statement for trace ash on marine waters and land areas downwind of Shishaldin Volcano. The color code and alert level remain at RED/WARNING. 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:	31,000 ft. (9.4 km) above sea level
(13) Other volcanic cloud information:	lower plume drifting NE, higher plume E
(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 Loewen, Acting Scientist-in-Charge, USGS, mloewen@usgs.gov, (907) 786-7497 Ronni Grapenthin, Acting Coordinating Scientist, UAFGI, rgrapenthin@alaska.edu, (907) 378-5460
(16) Next Notice:	Should volcanic activity change significantly, a new notice will be issued.