Thursday, August 30, 2012

Alaska's Little Sitkin Volcano Stirs

AVO is reporting that seismic activity has picked up at Little Sitkin volcano in the Aleutian Arc. Little Sitkin is one of the farthest volcanoes from mainland Alaska, and is about halfway from Alaska to Russia's Kamchatka peninsula. The volcano does not have a record of historical eruptions, however evidence on the island suggest it may have erupted early last century. A series of sharp and frequent quakes has rattled the island, and has prompted AVO to raise the aviation code from unassigned to "Yellow" (advisory).

AVO's statement is below:

"At approximately 19:15 AKDT (04:15 UTC) last night, a swarm of high-frequency earthquakes began at Little Sitkin Volcano. 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 changes.Little Sitkin is monitored by a 4-station seismic network as well as satellite imagery. Little Sitkin Island is located 35 km (21 mi) northwest of Amchitka and 320 km (200 mi) west of Adak in the remote western Aleutian Islands. The last eruption of Little Sitkin is questionable and may have been in the early 1900s."

The Smithsonian GVP characterizes the volcano here:

"Diamond-shaped Little Sitkin Island is bounded by steep cliffs on the east, north, and NE sides. Little Sitkin volcano contains two nested calderas. The older, nearly circular Pleistocene caldera is 4.8 km wide, may have once contained a caldera lake, and was partially filled by a younger cone formed mostly of andesitic and dacitic lava flows. The elliptical younger caldera is 2.7 x 4 km wide; it lies within the eastern part of the older caldera and shares its eastern and southern rim. The younger caldera partially destroyed the lava cone within the first caldera and is of possible early Holocene age. Young-looking dacitic lava flows, erupted in 1828 (Kay, in Wood and Kienle 1990), issued from the central cone within the younger caldera and from a vent on the west flank outside the older caldera. Fumarolic areas are found near the western coast, along the NW margin of the older caldera, and from the summit crater down the southern flank for a 1 km distance."

With activity at this volcano now being closely watched, this brings the number of Alaskan volcanoes currently being monitored to three. Cleveland volcano has been having small to minor eruptions for about a year now, and Mt Iliamna was raised to Yellow alert following a series of very shallow quakes, and increased fumerolic activity, however no eruption has happened at Iliamna following what AVO suspects was a minor magma dike intrusion. This brings the total volcanoes in Alaska showing activity to three at this time. 

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