AVO reported that intermittent tremor and low-frequency earthquakes recorded at Shishaldin over the past week had gradually become more regular and consistent during 10-11 July. Strongly elevated surface temperatures at the summit were identified in satellite images during 10-11 July. The Volcano Alert Level was raised to Advisory (the second level on a four-level scale) and the Aviation Color Code was raised to Yellow (the second color on a four-color scale) at 1439 on 11 July, but AVO noted that the increased activity may or may not lead to an eruption.

Geological Summary. The symmetrical glacier-covered Shishaldin in the Aleutian Islands is the westernmost of three large stratovolcanoes in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." Constructed atop an older glacially dissected edifice, it is largely basaltic in composition. Remnants of an older edifice are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is covered 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. A steam plume often rises from the summit crater.

Source: US Geological Survey Alaska Volcano Observatory (AVO)