The Alaska Volcano Observatory today raised the level to advisory status.
There is no real-time seismic network at the volcano. Scientists say unrest there is frequent, and short-lived explosions with ash plumes up to 20,000 feet can occur without warning and may not be detected by satellites.
Cleveland is about 940 miles southwest of Anchorage, on a remote and uninhabited island in the Aleutians chain.
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. There were minor eruptions in January, June and October 2009.
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