Increased seismicity, alerts raised for Shishaldin volcano, Alaska

The Alaska Volcano Observatory is raising the Aviation Color Code to YELLOW and the Alert Level to ADVISORY at Shishaldin Volcano, the observatory said 21:09 UTC on July 12, 2019. The last eruption of this volcano took place in 2015 (VEI 1).

This change is based on increased seismic activity over the past few weeks, accompanied by elevated surface temperatures at the summit in satellite data.

A pilot also observed incandescence in the summit crater during a recent overflight.

These observations represent a departure from normal background activity at Shishaldin, but do not necessarily indicate that an eruption will occur, 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.

Shishalding on August 15, 2018. Image credit: Matt Loewen, USGS/AVO

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 1500-1800 m 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 credit: Loewen Matt, USGS/AVO