On Saturday 18 February 2012 a network of seismic sensors on Mount Kanaga, on Kanaga Island in the Aleutian Island Chain, Alaska, detected an outburst of Earthquake activity that lasted about an hour, according to the Alaska Volcano Observatory. Subsequently a small plume was detected drifting northeast of the island by the NOAA-15 weather satellite.
Satellite image of Mount Katanga, taken in 2002. Taken from the International Space Station with the E4 Kodak DCS760C Electronic Still Camera. NASA/Earth Observatory.
Mount Kanaga is a 1307 m high stratovolcano (cone shaped volcano) located at the northern tip of Kanaga Island in the Central Aleutians. It sits inside the older Kanaton Caldera, and has erupted a number of times since it was discovered by Europeans in 1763, the most recent significant eruptive cycle having lasted from December 1993 to August 1995, and produced a number of volcanic plumes, some of which reached 4500 m in height. Much of northern Kanaga Island is covered by layers of ash and pumice up to 7 m thick, with soil layers trapped in between, but it is not certain if all this material was produced by Mount Kanaga or whether volcanoes in neighboring islands contributed.
The Aleutian Islands are located on the boundary between the Pacific and North American Plates. The Pacific Plate is being subducted beneath the North American Plate in the Aleutiam Trench to the south of the Islands. As it sinks into the Earth's interior it is partially melted by the heat from the planet's core, the some of the melted material then rises up through the overlying North American Plate as magma, forming the volcanoes of the Aleutian Island Arc.
See also Is Mount Cleveland, Alaska, about to erupt? and Volcanoes on Sciency Thoughts YouTube