On Wednesday the 20th July 2011 the Alaska Volcano Observatory issued an advisory warning on Cleveland Volcano in the Aleutian Islands, following the detection of thermal anomalies in satellite data. Since then the weather has prevented further satellite observations, and the warning remains in place.
Cleveland is located on the uninhabited Chuginadak Island, 1500 km southwest of Anchorage, and 75 km from the nearest settlement, Nikolski on Umnak Island, a village of 39 people. Due to its remote location it it seldom visited, and does not merit a network of seismometers, so there is not data available other than that from satellites.
Cleveland Volcano, in a remote part of the Aleutian Islands.
Cleveland has a history of sudden, explosive eruptions, it's last major eruption, in February 2001, threw ash 12 km into the air and produced a lava flow that reached the sea, so it is considered a hazard to aircraft.
Cleveland is a stratovolcano, a volcano formed by layers of ash and lava deposits with a classic cone shape. It rises 1730 m above the sea level, and is about 8 km across at the base. It shows little sign of erosion, and is probably no more than 10 000 years old. Due to its location it is completely treeless, and has little vegetation of any sort on its flanks, making its shape particularly notable.
An arial photograph of Mount Cleveland.
The Aleutians are a volcanic island arc, formed where the Pacific Plate is being subducted beneath the North American Plate; the arc actually continues onto land as the Aleutian Range, a string of volcanic mountains on the Alaskan Peninsula. As the Pacific Plate sinks into the Earth it is heated and partially melted; lighter minerals then rise up through the overlying North American Plate, forming volcanoes.
How volcanoes are formed by oceanic plate subduction.
See also Recent Eruptions on Mount Etna, New Submarine Volcanoes found in the South Sandwich Islands, and Volcanoes on Sciency Thoughts YouTube.