AVO reported that during 2-6 August no activity at Bogoslof was observed in mostly cloudy satellite images, and no activity was detected in seismic, infrasound, or lightning data.
An explosive eruption began at 1000 on 7 August, following more than an hour of increased seismicity.
A pilot reported that an ash cloud rose to an altitude of 9.8 km (32,000 ft) a.s.l., prompting AVO to raise the Aviation Color Code (ACC) to Red and the Volcano Alert Level (VAL) to Warning.
The eruption lasted about three hours, and was longer lived than most of the events in the eruptive sequence that started in December 2016.
At 1341 AVO noted that the ash plume had formed a continuous cloud which stayed attached to the volcano and drifted S.
The ACC was lowered to Orange and the VAL was lowered to Watch on 8 August.
Satellite images acquired on 8 August showed a significant expansion of the island towards the N with thick tephra deposits around the vent area forming a new crater lake.
Source: US Geological Survey Alaska Volcano Observatory (AVO)