The Alaska Volcano Observatory on Wednesday raised the level Cleveland Volcano to advisory from unassigned.
There is no real-time seismic network at the volcano, located 939 miles southwest of Anchorage on an uninhabited island. Officials are not able to track local earthquake activity related to volcanic unrest.
Short-lived explosions with ash clouds or plumes exceeding 20,000 feet above sea level are frequent on Cleveland. It last showed signs of unrest last summer, with a small ash emission and lava flows on its upper flanks.
The observatory says the last significant eruption of the 5,676-foot volcano began in February 2001 and eventually produced a lava flow that reached the ocean. Source