ANCHORAGE, Alaska: A remote Alaska volcano has spewed an ash cloud 15,000 feet (4,500 meters) into the air.

The Alaska Volcano Observatory says satellite images show the ash cloud drifting Thursday from Cleveland Volcano in the Aleutian Islands.

The observatory has raised the aviation alert level based on the presence of the cloud.

Scientists throughout much of 2011 have monitored activity in the crater at the summit of 5,675-foot Cleveland Mountain on an uninhabited island 940 miles (1,512 kilometers) southwest of Anchorage.

The ash cloud was spotted 50 miles (80 kilometers) from the mountain moving east-southeast. The observatory says in a release that satellite data indicates the cloud come from a single explosion event.

The observatory says more explosions could send ash plumes above 20,000 feet (6,000 meters).