Monday, June 16, 2014

Alaska Volcano Semisopochnoi Raised To Yellow Alert

Semisopochnoi, a remote volcano island in Alaska's Aleutian arc, has begun experiencing heightened seismicity, leading AVO to raise its alert status to Yellow (watch). No eruption has yet occurred, however given the escalating seismicity, the possibility of an eruption is growing. On June 13th, AVO reported the following (not much has changed).

"A swarm of earthquakes at Semisopochnoi volcano that started at 10:00 AKDT (18:00 UTC) on June 9 escalated yesterday, June 12, at approximately 12:00 AKDT (20:00 UTC). The continuation of this anomalous seismic activity through the night prompts 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. Semisopochnoi Island is located 65 km (40 mi) northeast of Amchitka and 200 km (130 mi) west of Adak in the remote western Aleutian Islands. The last eruption of Semisopochnoi occurred in 1987."

Today's update indicates that the situation is about the same:

"The earthquake swarm at Semisopochnoi volcano that started on June 9 and escalated on June 12 continues. No eruptive activity is currently indicated and nothing was observed in cloudy satellite images over the past day."

Image of Semisopochnoi webicorder from AVO.

In the above image, you can see quakes that indicate fracturing of rock and magma dike intrusion into the shallow crust. The USGS earthquake indicator has detected at least one quake above mag 2.0 within the caldera. It is unknown at this time if or when the volcano may erupt, and which vent it may choose to use. 

The Smithsonian GVP indicates that most historical eruptions have occurred from a SE cone within the caldera known as Cerberus, although two other cones were considered to have possibly erupted in historical time by Coats (1950); Sugarloaf, and Lakeshore Cone. 

This now brings the current number of Alaskan volcanoes on alert status to 5:

Cleveland (Yellow)
Shishaldin (back up to Orange, after new eruptive activity was detected on webcam and satellite)
Pavlof (Orange; it is still having large eruptions)
Veniaminof (Yellow; activity has decreased, however seismicity remains above background)
Semisopochnoi (Yellow; has not yet erupted, but seismicity is high)

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