Okmok Volcano, in Alaska’s Aleutian Islands, released a continuous plume of ash and steam in early July 2008. According to the Alaska Volcano Observatory, the eruption began at 11:43 a.m. ADT (19:43 UTC) on July 12, releasing an ash cloud some 9,000 to 10,500 meters (30,000 to 35,000 feet) above sea level. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image on July 13, 2008. In this image, the volcano’s summit peeks through a break in the cloud cover. Both a steam plume (on the right) and an ash plume (on the left) emanate from the volcano. The steam is snowy white like the nearby clouds. The ash is slightly darker. The blue-green color of the nearby ocean water may result from volcanic ash fall.
Comprising the northeast end of Umnak Island, Okmok is a shield volcano with a low, broad shape that resembles an ancient warrior shield. The volcano is 35 kilometers (22 miles) wide, and has two 10-kilometer- (6-mile-) wide overlapping calderas from ancient eruptions. Eruptions have been recorded at Okmok since 1805.