Lava flows, large lahar at Shishaldin volcano, Alaska

Lava flows, large lahar at Shishaldin volcano, Alaska

Satellite data from the past day show that lava now fills the Shishaldin's summit crater and is beginning to flow over the northern crater rim in two locations, the Alaska Volcano Observatory reported at 20:07 UTC on October 24, 2019.

One 200 m (600 feet) long lava flow has melted snow and produced a large ~2.9 km (~1.8 miles) long lahar extending down the north flank reaching ~1 230 m (~4 000 feet) elevation and a smaller lava flow has caused a ~1 km (~0.6 mile) long lahar down the northeast flank.

Spatter from low-level explosive activity is accumulating around the crater rim and melting snow, as well.

Steam emissions from strombolian eruptive activity in the summit crater of Shishaldin Volcano as seen from the NW. Credit: USGS/AVO

Photograph of a steam plume at Shishaldin taken by an ACE Air Cargo pilot from flight AER963 into Cold Bay on October 21, 2019. Credit: USGS/AVO, Ben Mosier

This activity has coincided with strongly elevated surface temperatures, elevated seismicity, and infrasound detections.

There has been no evidence of any significant ash-bearing volcanic plumes over the past day in cloudy satellite imagery and web camera views.

Shishaldin's Volcano Alert Level is at Watch and the Aviation Color Code at Orange since October 17, 2019. Satellite observations indicated a lava effusion event starting on October 13.

Steam emissions from eruptive activity in the summit crater of Shishaldin volcano as seen from the SE, on October 21, 2019. Credit: 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 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: Steam emissions from eruptive activity in the summit crater of Shishaldin volcano as seen from the SE, on October 21, 2019. Credit: USGS/AVO

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