Likewise, the eruption of Mt. St. Helens in 1980 was a volcanic sneeze compared to what scientists say America will experience one day. And a mysterious four-inch-high bulge in the ground of central Oregon is, so far, little more than a conversation piece.

The eruption of pent-up energy will cover half the United States in ash, in some places up to 3 feet (1 meter) deep. Earth will be plunged into a perpetual winter that would last years. Some plant and animal species will disappear forever.

Even humans could be pushed to the edge of extinction. Anthropologists suggest it won't be the first time.

But well before such a calamity, warning flags will likely show up on the computers of geologists around the world who monitor an increasingly useful stream of satellite data.

What they see is often illuminating. Sometimes it is just plain frightening.

Geologists have long known that the 10,000 hot springs and geysers in Yellowstone National Park are evidence of magma, hot molten rock below the surface. And they know that long ago the region experienced colossal eruptions on a scale never seen in recorded history.

But an important question has evolved in recent years: Is Yellowstone dying or just hibernating?

In the July 2001 issue of the journal Earth and Planetary Science Letters, University of Wisconsin geologists Ilya Bindeman and John Valley report new evidence indicating "a high probability of a future catastrophic eruption sometime within the next million years, and possibly within the next hundred thousand years."

Analyzing minerals that serve as time capsules of past catastrophes, Bindeman and Valley have found support for other studies suggesting Yellowstone goes nuts every few hundred thousand years. They also propose a reason why: An epic hot spot.

Hot magma welling up from below acts like a burner, the researchers say, melting surface rock and forming giant chambers of lava that build up over long periods. Eventually, the chambers burst and release their fury.

Yellowstone's volcanism is dying, these researchers say, but it has at least one last gasp in store.

The new geologic evidence adds to satellite data showing that the treasured park straddling Idaho, Montana and Wyoming is destined to obliterate its own beauty. Not to mention that of a few surrounding states.

Chuck Wicks of the U.S. Geological Survey uses a relatively new satellite technique called satellite radar interferometry to watch the ground rise, fall and morph around volcanoes and other volcanically active areas. While the Global Positioning System can also show ground movement, it does so only for locations where a monitor is in place on the ground.

But with radar interferometry, geologists map the topography of an entire region, then watch it change over time.

In 1997, Wicks and his colleagues used the technique to document uplifts at Yellowstone, which means the lava below was pushing its way to the surface. "Yellowstone is alive and very active," Wicks said.

But no one can say if or when it might become dangerously active. If a volcano is like a hibernating bear, however, then it may well be volcanic springtime in Yellowstone.

"Super explosions, about 1,000 times more material erupted than Mt. St. Helens in 1980, happen about every 600,000 years at Yellowstone," Wicks says. "And it's been about 620,000 years since the last super explosive eruption there."