Clear indicator that an eruption occurred

In a satellite image from 26th August 2015 obtained from the Earth Explorer website, I noticed that the east flank of Mount Michael volcano was stained grey which strongly indicates that an eruption took place. I am under the opinion that this was ashfall from an eruption which may have took place maybe a few days to a week ago.

Ash stained east slope of the volcano on Saunders Island. SOURCE: Landsat 8/USGS/NASA.