An eruption of a supervolcano in Yellowstone National Park would leave no place to escape to, as it would deposit ash as far afield as Los Angeles, New York and Miami, a study has revealed.
A volcanic eruption is considered to be a supereruption if it ejects in excess of 240 cubic miles of eruption material into the atmosphere.
The Yellowstone region, with a giant pool of hot, partly melted rock beneath, has experienced three such eruptions in the past, at around 2.1 and 3.1 million years ago, and again around 640,000 years ago.
Right now there is no geologic activity suggesting such a giant eruption anytime soon, but scientists curious about the effects of such an event have simulated it using computer models.
The computer model, dubbed Ash3D, uses data about historical patterns of winds across the U.S. to calculate how much ash would fall and where as a result of a Yellowstone supereruption.
Cities in the region of Yellowstone would be covered with several feet of ash; in the Midwest ash deposits could be several inches deep, and even U.S. cities on the two coasts would receive at least a fraction of an inch of ash, the researchers reported in the journal Geochemistry, Geophysics, Geosystems.
The computer models suggests that ash from a supervolcano eruption would be less affected by prevailing winds than ash from a smaller eruption might be, researchers said.
During very large volcanic eruptions, the models show, the expansion rate of the leading edge of the ash cloud can be greater than the average ambient wind speed, creating an outward expansion that can drive ash more than 900 miles upwind to the west and crosswind to the north and south.
"In essence, the eruption makes its own winds that can overcome the prevailing westerlies, which normally dominate weather patterns in the United States," says USGS geologist and study lead author Larry Mastin.
"This helps explain the distribution from large Yellowstone eruptions of the past, where considerable amounts of ash reached the west coast," he says.
Geological studies have found ash from the three previous Yellowstone supereruptions over thousands of square miles of the western and central United States and Canada, in a bull's eye pattern with the eruption site at its center.
"These model developments have greatly enhanced our ability to anticipate possible effects from both large and small eruptions, wherever they occur," says study co-author Jacob Lowenstein.