A swarm of earthquakes started at Semisopochnoi volcano on June 9 and escalated on June 12 at approximately 20:00 UTC, the Alaska Volcano Observatory (AVO) reported yesterday.
The continuation of this anomalous seismic activity prompted AVO to raise the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. No eruptive activity is currently indicated.
AVO is closely monitoring the situation and will issue further updates as conditions change.
Semisopochnoi volcano is monitored by a 6-station seismic network as well as satellite imagery. Five of the seismic stations on Semisopochnoi are currently operational. The telemetry system for the Semisopochnoi stations, located on Amchitka Island, was just repaired in late May.
Remote Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The volcano is dominated by an 8-km (5-mile) diameter caldera that contains a small lake and a number of post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene.
The last known eruption of Semisopochnoi occurred in 1987, probably from Sugarloaf Peak on the south coast of the island, but details are lacking.
Another prominent, young post-caldera landform is Mount Cerberus, a three-peaked cone cluster in the southwest part of the caldera. The island is uninhabited and part of the Alaska Maritime National Wildlife Refuge. It is located 65 km (40 mi) northeast of Amchitka Island and 200 km (130 mi) west of Adak.
Featured image courtesy of Roger Clifford
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