AVO reported that the effusive and explosive eruption at Shishaldin continued during 9-15 August. Seismicity was generally low during 9-14 August with a few local earthquakes detected on some days; no significant explosive activity was observed in seismic or infrasound data. Elevated surface temperatures were observed in satellite images caused by a small lava flow at the summit. Minor steam-and-gas emissions were visible in webcam or satellite images, though weather clouds sometimes prevented views. At 1827 on 14 August AVO noted that seismic tremor had steadily increased during the afternoon and erupting lava at the summit was evident in a satellite image. Explosion signals began to be detected at 0200 on 15 August. By 0335 satellite images showed an ash cloud drifting NE at 7.6 km (25,000 ft) a.s.l. and lightning was detected in the vicinity of the volcano. The ash cloud drifted 100 km NE over the Bering Sea and may have risen as high as 11 km (36,000 ft) a.s.l. Seismicity was significantly elevated during the eruption but had declined by 1322, though levels continued to indicate ongoing, low-level activity; a pilot reported that ash emissions continued, rising as high as 4.9 km (16,000 ft) a.s.l. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

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)