USGS Volcano Notice for Aviation - DOI-USGS-AVO-2023-07-23T03:48:19-08:00

(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20230723/1218Z)
(3) Volcano:	Shishaldin (VNUM #311360)
(4) Current Color Code:	ORANGE
(5) Previous Color Code:	RED
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2023/A1123
(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:	Volcanic activity has significantly declined at Shishaldin Volcano. Seismic tremor began declining from a peak at 12:30 am AKDT (08:30 UTC) and is and is currently at low levels. Significant ash eruption notably decreased in satellite data around 1:30 am (09:30 UTC). Satellite data continue to indicate elevated surface temperatures at the summit associated with lava erupting at the surface and possible low-level ash emissions below regional cloud tops which are currently at around 20,000 ft. (6 km) above sea level. A sustained ash plume with a height of 37,000 ft. (11 km) above sea level erupted between 11:20 pm AKDT on July 22 (07:20 UTC on July 23) and 12:30 am on July 23 (08:30 UTC on July 23). Around this time plume height decreased to around 15,000 ft. (4.5 km) above sea level. A detached plume is currently drifting to the northeast along the Alaska Peninsula. The National Weather Service has issued a SIGMET for this ash cloud, as well as a Marine Weather Statement and an Ashfall Advisory that were issued for areas that might expect ashfall associated with this eruption. Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. The local monitoring network has been partially impaired over the last few weeks due to telecommunications issues but seismic stations and web cameras south of the volcano were brought back online on July 19. 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:	unknown, below 20,000 ft. (6 km) above sea level
(13) Other volcanic cloud information:	Main eruption cloud detached and drifting to the northeast, see current NWS SIGMET.
(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:	Chris Waythomas, Acting Scientist-in-Charge, USGS, cwaythomas@usgs.gov, (907) 786-7497 David Fee, Coordinating Scientist, UAFGI, dfee1@alaska.edu, (907) 378-5460
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