Short-lived explosion at Shishaldin, heightened level of unrest, Alaska

A short-lived explosion occurred at Shishaldin volcano, Alaska, U.S. at 16:10 UTC (07:10 LT) on December 12, 2019.

The eruption lasted about 3 minutes and produced an ash cloud up to 6 – 7.6 km (20 000 – 25 000 feet) above sea level, moving W-NW at 83 km/h (52 mph). In addition, three lightning strokes were detected, AVO reports.

Shishaldin remains at Aviation Color Code ORANGE and Alert Level WATCH.

The volcano remains at a heightened level of unrest and explosions may occur with little warning, AVO said.

Shishaldin is monitored by local seismic and infrasound sensors, satellite data, a web camera, a telemetered geodetic network, and distant infrasound and lightning networks.

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 18^th century. (GVP)

Featured image: Shishaldin on November 1, 2019. Credit: ESA/Sentinel-2, Antonio Vecoli