Strong eruption at Shishaldin ends, Aviation Color Code lowered to Orange, Alaska

Strong eruption at Shishaldin ends, Aviation Color Code lowered to Orange, Alaska

Ash cloud produced by the strong eruption at Shishaldin volcano, Aleutian Islands, Alaska at 14:10 UTC on January 7, 2020, reached 10 km (33 000 feet) above sea level before midnight UTC. Volcanic ash tops were raised from previously reported 7.6 km (25 000 feet) due to pilot reports received at 23:14 UTC; with low to medium confidence. Seismicity and ash emissions decreased significantly shortly after 21:00 UTC.

A sharp but brief increase in seismicity was detected before the eruption, followed by observations of a volcanic cloud drifting to the northeast at about 5.7 km (19 000 feet) a.s.l., the Alaska Volcano Observatory (AVO) reported. 

Seismicity waned for a few hours, followed by a subsequent increase. 

Image credit: Copernicus EMS/Sentinel-2

Shishaldin at 22:09 UTC on January 7, 2020. Image credit: Copernicus EU/Sentinel-2, Antonio Vecoli

Shishaldin at 14:090 UTC on January 7, 2020. Image credit: Copernicus EU/Sentinel-2, Antonio Vecoli

During this increase in intensity, the volcanic cloud increased in altitude to about 7.6 km (25 000 feet) a.s.l. and appeared to increase in ash content, prompting a change in Aviation Color Code to RED and Alert Level to WARNING at 21:33 UTC.

Satellite views showed strongly elevated surface temperatures and web camera views showed incandescence. Volcanic lightning was detected in the cloud and volcanic infrasound was detected at regional stations.

Seismicity has decreased significantly shortly after 21:00 UTC, as well as ash emissions, prompting AVO to lower the Aviation Color Code back to ORANGE and Alert Level to WATCH at 04:17 UTC on January 8.

Trace fallout of ash is expected in the communities to the northeast, potentially up to Sand Point.

Seismicity is currently low and satellite data suggest continued low-level eruptive activity.

It is, however, possible for more explosive activity to resume with little warning.

Geological summary

The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high (9 379 feet), glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island.

The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition.

Remnants of an older ancestral volcano are exposed on the west and NE sides at 1 500 -1 800 m (4 920 - 5 900 feet) elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows.

Frequent explosive activity, primarily consisting of strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century. (GVP)

Featured image: Shishaldin on January 7, 2020. Credit: Copernicus EMS/Sentinel-2

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