Unalaska, AK – This weekend, Mount Cleveland showed yet more signs of activity. The volcano, located in the central Aleutians, has been fairly active this summer and it released a seven-kilometer plume containing ash and steam on Sunday morning.

Steve McNutt is a research professor at the University of Alaska-Fairbanks and a coordinating scientist at the Alaska Volcano Observatory. Here's what he can make out from the satellite imagery of the volcano.

"Satellite images showed a weak plume, possibly containing ash, in the vicinity of Cleveland Volcano," says McNutt. And this is not completely in isolation. The remote sensing data from several different sensors has showed over the last couple of weeks an increase in thermal anomalies. So that means when the satellites are flying straight overhead looking down in the volcano they see evidence of increased heat in the summit area"

Two weeks ago, AVO placed Cleveland on watch, and upped its status to yellow. But on Friday, AVO moved the volcano down to unassigned. Now, it's back on yellow and will be for some time, due to the difficulty of monitoring the volcano.

"The trouble with Cleveland is that it seems to be mildly active a lot of the time, and about half a dozen times a year it has these small to moderate eruptions with an ash plume up in the 15,000 to 20,000-foot range," says McNutt. "And because we don't have any monitoring equipment on it guesstimate when conditions are favorable."

Cleveland frequently emits ash, and plumes like this are released about six times a year. McNutt says that AVO is keeping a close eye on the volcano but that increased thermal activity doesn't necessarily mean a major eruption is on the way. Still, even small plumes could spell trouble for air travel and inconvenience nearby boats.

"The effects would be fine ash in the air, a little bit of ash fall on the ground," says McNutt. "For example, fishing boats in the vicinity might have had some ash fall on their decks. Airplanes flying locally would have noticed the sulfur smell and ash hitting the windshield. Part of the reason for our advisories is to keep local aircraft away."

Among the communities potentially affected are Nikolski and Atka, which receive air service from Unalaska. Trans-Pacific jet shouldn't be affected by a plume like this, since they fly at much higher elevations. The ash that erupted on Sunday drifted easterly, and McNutt said that AVO has not heard of any damage caused by the activity.