Scientists have predicted that the world's largest volcano beneath Yellowstone National Park in Wyoming could erupt for the first time in 600,000 years and wipe out 66 percent of the United States.
Researchers monitoring Yellowstone National Park's Caldera said that has it been rising at a record rate since 2004 - its floor has gone up three inches per year for the last three years alone, the fastest rate since records began in 1923.
"It's an extraordinary uplift, because it covers such a large area and the rates are so high. At the beginning we were concerned it could be leading up to an eruption," the Daily Mail quoted Bob Smith as telling National Geographic.
"Once we saw the magma was at a depth of ten kilometres, we weren't so concerned. If it had been at depths of two or three kilometre we'd have been a lot more concerned," he added.
Robert B. Smith, professor of geophysics at the University of Utah, added, "Our best evidence is that the crustal magma chamber is filling with molten rock. But we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates again."
Since the most recent blast 640,000 years ago there have been around 30 smaller eruptions, the most recent of which was 70,000 years ago.
"Clearly some deep source of magma feeds Yellowstone, and since Yellowstone has erupted in the recent geological past, we know that there is magma at shallower depths too," said Dan Dzurisin, a Yellowstone expert with the U.S. Geological Survey at Cascades Volcano Observatory in Washington State.
"There has to be magma in the crust, or we wouldn't have all the hydrothermal activity that we have.
There is so much heat coming out of Yellowstone right now that if it wasn't being reheated by magma, the whole system would have gone stone cold since the time of the last eruption 70,000 years ago," he added.