for National Geographic News
Molten rock flowing beneath Yellowstone has been causing the national park to rise and fall, scientists say.
Periodic uplifting and settling has occurred here over the last 15,000 years.
A new model helps explain the latest episode of rapid surface rise and increased geyser activityfrom 1997 to 2003in the volcanically active region in the western United States.
Much of Yellowstone National Park lies in the crater of a massive volcano, formed in a landscape-altering eruption 640,000 years ago. The crater, or caldera, measures some 28 miles wide by 47 miles long (45 by 75 kilometers).
Subsequent lava flowsmost recently 70,000 years agofilled in much of the blasted-out crater, disguising the area's volcanic identity (related site: volcano photos, facts, and virtual eruptions).
Since the 1970s scientists have known that the Yellowstone volcano remains highly active. (See "Yellowstone Volcano: Is 'the Beast' Building to a Violent Tantrum?" .)
But the precise relationship between volcanic activity deep underground and Yellowstone's well-known network of geysers and other geothermal features has long been a puzzle for geologists.
Now a study by scientists with the U. S. Geological Survey (USGS) and the Yellowstone Volcano Observatory attributes changes in both surface terrain and geyser behavior to flows of magma, or molten rock, 9 miles (15 kilometers) below the Earth's surface.
"We're not sure yet if this is a normal episode or not," said Charles Wicks, a geologist at the USGS Western Region headquarters in Menlo Park, California.
Wrinkles and Cracks
Using satellite-based radar, Wicks and his colleagues were able to map small changes in surface elevation continuously across a wide area.
The new, detailed view of the Yellowstone crater shows a surface in constant motion, rising and falling in different locations and over fairly short intervals of time. From earlier surveys, scientists know that the caldera floor raised about 7 inches (18 centimeters) from 1976 to 1984 and then settled back about 5.5 inches (14 centimeters) from 1985 to 1995.
SOURCES AND RELATED WEB SITES