AVO reported that a minor increase in seismicity was first detected at Gareloi on 19 May. Beginning on 27 May the rate and size of small volcanic earthquakes increased and was sustained at that level. On 8 June AVO raised the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory based on seismicity rising above baseline levels. Sulfur dioxide emissions had been identified in satellite images the past week, though they were consistent with measurements recorded in previous years. No other changes were evident in satellite or webcam views.

Geological Summary. The 8 x 10 km Gareloi Island, the northernmost volcano of the Delarof Group at the western end of the Andreanof Islands, consists of a stratovolcano with two summits and a prominent SE-trending fissure. The fissure was formed during an eruption in 1929 and extends from the southern summit to the sea. Steep sea cliffs that are cut into rocks of an older, eroded center are found on the SW coast, and submarine deposits of three debris avalanches produced by edifice collapse are found offshore. Young lava flows cover the older volcano from the summit to the coast along three broad axes trending NW, ENE, and S. The 1929 eruption originated from 13 craters along a 4-km-long fissure. Phreatic explosions were followed by the ejection of glassy pumice, lapilli, scoria, and older blocks, as well as by the emission of four short, steep lava flows, one of which reached the SE coast.

Source: US Geological Survey Alaska Volcano Observatory (AVO)