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AVO reported on 25 November that for several weeks seismicity beneath young volcanic vents on Tanaga Island decreased significantly from levels recorded in early October.

Satellite images of the island showed no anomalous temperatures or evidence of ash emissions.

AVO reported that based on the decrease in earthquake counts and frequency of tremor episodes, the likelihood of an eruption had diminished.

Therefore, AVO downgraded the Concern Color Code from Yellow to Green.

The Alaska Volcano Observatory (AVO) detected an increase in seismic activity beneath Tanaga beginning on 1 October 2005, with 15-68 earthquakes occurring daily.

Previously, less than one earthquake had occurred per month since the seismic network was installed in 2003.

The earthquakes were centered roughly 2 km NE of the summit at depths of 10-20 km below sea level.

The largest event was M 1.7, with most earthquakes at M 0.5-1.5.

Tanaga was at Concern Color Code Green on 5 October.

During 5-7 October, there was a marked increase in the rate of seismicity.

The located earthquakes ranged in magnitude from 0.5 to 1.9 and ranged in depth from 6 to 12 km beneath the summit.

In response, AVO raised the Concern Color Code to Yellow on 7 October.