An aerial photograph shows the Cleveland Volcano during the time a small lava flow, or dome, was accumulating in the summit crater as the 660 foot (182.88m) wide summit crater emits a white, largely steam condensate cloud in this Aug 8, 2011 file photo. The remote volcano in Alaska's Aleutian islands erupted early on Dec 29, 2011 spouting an ash cloud 15,000 feet(4572m) into the sky and prompting an air-traffic alert, scientists said. [Photo/Agencies]

A true-color satellite image of Cleveland Volcano collected by the Worldview-2 sensor on Oct 7, 2011. The summit of the volcano is mostly snow-covered, and the growing lava dome is seen as the dark feature in the center of the image. Some snow-free ground is observed on the southern upper flanks of the volcano, just south (below) of the crater. A faint steam and gas plume is observed moving towards the northeast (upper-right). [Photo/Agencies]

A drifting ash cloud from a small eruption of Cleveland Volcano is pictured in this annotated NOAA satellite image taken December 29, 2011. The ash cloud is the yellow and orange feature located on the southwest tip of Umnak Island. The brief explosive eruption began at around 4:15 AM AST, and the cloud had drifted 35 miles to the east at an altitude of about 15,000 above sea level by the time is was observed in this satellite image. [Photo/Agencies]