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Toba Caldera, Sumatra
02.23.07
 
Toba caldera in Sumatra, Indonesia Image above: The Toba caldera in Sumatra, Indonesia. Click to view high resolution image. Image credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team.

The Toba caldera in Sumatra, Indonesia, produced the largest volcanic eruption in the last 2 million years. The caldera, a large, basinlike depression resulting from the explosion or collapse of the center of a volcano, is 30 by 100 kilometers, or about 19 miles by 62 miles, and has a total relief of 1,700 meters or slightly more than 1 mile.

The caldera probably formed in stages: large eruptions occurred 840,000, 700,000 and 75,000 years ago. The eruption 75,000 years ago produced the Young Toba Tuff, with an estimated volume of 2,800 cubic kilometers, or nearly 672 cubic miles. By comparison, Mt. St. Helens erupted about 1 cubic kilometer, or .24 cubic mile, of ash. In places around the caldera, the tuff is more than 600 meters, or more than a third of a mile, thick. Ash fall from the eruption covers an area about half the size of the U.S. Toba and other stratovalocanoes in Sumatra are related to the subduction of the Indian Plate under the Eurasian Plate. This ASTER image was acquired on Jan. 28, 2006.