For nearly 130 years, visitors have flocked to the world's oldest and largest national park to see its unparalleled array of geysers, mud pots, and hot springs.
Now, the vulcanism that drives these attractions is itself drawing renewed scrutiny.
This week, representatives from the United States Geological Survey, the University of Utah, and the US National Park Service met in Yellowstone National Park to pin down details for a new Yellowstone Volcano Observatory - a network of sensors around the park designed to track volcanic activity and assess the hazards such activity may pose.
"The new observatory will improve our efforts to monitor Yellowstone's extraordinarily large and long-lived volcanic system," notes Robert Christiansen, a USGS scientist who will head the observatory. He adds that while scientists see no imminent threat of eruption, an observatory will put his agency "in a better position to warn of any future hazardous activity."
The new observatory, he explains, takes advantage of existing instrument networks run by the USGS, the University of Utah, and the National Park Service. It is the fifth of a series of observatories monitoring volcanic activity in Hawaii, Alaska, the Cascades in the Pacific Northwest, and in California's Long Valley, east of the Sierra Nevada mountains.
Typically, volcanoes erupt along boundaries formed as one plate in the earth's crust burrows beneath another in a continuous process of crustal recycling.
Occasionally, however, mixtures of molten and solid material form hot spots beneath a crustal plate. As the plate moves over the hot spot, magma can punch through, leaving a trail of volcanoes. If the magma is rich in basalt, it tends to burp and bubble up through cones and fissures, spreading out in a scorching ooze that cools to form new crust. The Hawaiian Island chain and its volcanoes, for example, are forming this way. In other cases, however, hot spots can feed magma rich in silicates into subterranean chambers that erupt explosively, spreading hundreds to thousands of cubic kilometers of ash over continent-size distances.
Yellowstone's hot spot is thought to have formed 16 million years ago. Eruptions have generated a string of large depressions, or calderas, that stretches southwest from the park into southeastern Oregon and northern Nevada.
Although researchers have crisscrossed the Yellowstone region since 1872, the area drew increasing scientific interest following a magnitude 7.5 earthquake at Hebgen Lake, Mont., in 1959.
Studies of the area after the quake, the largest in the intermountain region in recorded history, showed that during the past 2 million years, the Yellowstone hot spot has fueled three catastrophic blasts roughly 600,000 years apart. Each explosive eruption spread hundreds to thousands of cubic kilometers of ash over continent-size distances.
Indeed, Ashfall State Park in Nebraska has yielded camel, rhino, and horse fossils - the remains of Pleistocene animals buried in ash from one of Yellowstone's eruptions.
Each blast also left a enormous crater, or caldera, that later filled in with lava, ash, and sediment deposits. The most recent explosion, which occurred 640,000 years ago, left a caldera 28 miles wide, 47 miles long, and more than 1,000 feet deep.
Researchers have identified at least 30 smaller silicate eruptions on the Yellowstone Plateau since the last catastrophic eruption.
One of the observatory's first tasks will be to assess Yellowstone's geological hazards, notes Manuel Nathanson, scientist in charge of the USGS office in Menlo Park, Calif. But researchers face some practical problems in pulling such an assessment together, he adds.
"Intervals between eruptions are humongously long," Dr. Nathanson says.
Moreover, the area's intense hydrothermal activity can lead to events unlike those found in many other volcanic zones. He notes that quakes in the area have triggered new geysers. Quakes also are thought to touch off hydrothermal explosions, which result when deposits of superheated water under high pressure suddenly lose pressure, allowing the water to violently expand and blast free of the surface.
As if to underscore the Yellowstone Caldera's restlessness, researchers from the USGS compiled satellite data they published in 1998 that showed the caldera's two domes rising alternately as magma or other hot fluids moved into and out of formations some 8 kilometers beneath the caldera.
(c) Copyright 2001. The Christian Science Monitor