Friday, November 9, 2007

The Earth moves fast in Yellowstone

Quick, look down! The ground is moving!

Can't feel anything? That's because the movement of the Earth's surface is usually pretty slow by human standards. North America, for example, is floating around the planet at about 2 centimeters per year, as fast as your fingernails grow. The Earth's surface is in constant motion, squishing up mountains as land masses run into each other, stretching open deep underwater, and sliding down under continents to be melted by the planet's hot interior. If you could watch Earth's 4.5 billion year history in fast-forward, it would bustle with activity. In your lifetime, though, most of the changes will be too slow to see, other than the occasional abrupt events like earthquakes and volcanoes.

But not in Yellowstone National Park. Yellowstone is one of the most geologically active places in the world, providing unique opportunities to observe change happen fast enough to notice in a lifetime. Small earthquakes rumble through more than once a day (on average); hot water and steam burble from the ground and then shift to a new spot; geysers erupt regularly then stop, or lie dormant and suddenly start again; and according to new findings just released by the University of Utah, the ground swells and recedes like a slowly breathing giant.

In the course of 2.5 years, from July 2004 to December 2006, the Utah geologists used satellites to measure the exact elevation of the caldera, or giant volcanic crater, that lies within the Park, both by bouncing radar beams down and back up to orbit, and by communicating with receivers stationed on the ground. In that time, the land rose 18 centimeters (7 inches), growing faster than your average human child, and three times faster than anyone had seen it grow before.

The scientists attribute this quick expansion to a pancake-shaped blob of molten rock the size of Los Angeles, gurgling six miles underground. This blob of magma originated as part of a "hotspot," or gigantic plume of hot molten rock, that starts 400 miles beneath Earth's surface, travels up through the Earth's layers, then spreads out to a 300-mile pool lying 30 miles underground. From there, hot magma sometimes breaks off, rises up, and fills a chamber below the Park. It's the heat from that chamber that powers Yellowstone's geysers and keeps it so geologically active, and the magma is likely responsible for the recent uplift.

One thing the scientists say for sure is that it's not a sign of an imminent eruption. So if you want to see our Earth systems in action, pack your bags and head for the Park.