Magma On The Move Beneath Yellowstone

[MORTARDUDE]

http://www.sciam.com/article.cfm?cha...3083414B7F0000

Magma On The Move Beneath Yellowstone



Image: NATIONAL PARK SERVICE

Much of Yellowstone National Park is a giant collapsed volcano, or a caldera. In an enormous eruption roughly 640,000 years ago, this volcano spit out around 240 cubic miles of rock, dirt, magma and other material. Around 70,000 years ago its last eruption filled in that gaping hole with flows of lava. The area has enjoyed an uneasy peace since then, the land alternately rising and falling with the passing decades. New satellite data indicate that this uplift and subsidence is caused by the movement of magma beneath the surface and may explain why the northern edge of the park continues to rise while the southern part of the caldera is falling.
Charles Wicks, Daniel Dzurisin and their colleagues at the U.S. Geological Survey studied radar images of the caldera captured by the European Space Agency's ERS-2 satellite during two passes over the park. Using a technique called interferometry--whereby radar measurements from two different vantage points are combined to give a measure of height--the scientists confirmed measurements on the ground that showed the land rising. But the images also revealed that a roughly 12-mile-wide circle of land centered at the northern rim of the caldera is still rising while land to its south is sinking. The source of that uplift, according to data revealed in today's Nature, lies more than seven miles underground.