THREAT: A supervolcano eruption ejects debris more than 1,000 cubic kilometers (240 cubic miles) in volume from the Earth. Only a handful of such volcanos exist on the planet, and most are at the bottom of the ocean.
A nearly fatal decline in the human population 75,000 years ago is blamed in part on the Toba supervolcano, which erupted on the island of Sumatra, blowing out more than 670 cubic miles of ash and pumice. Yellowstone National Park rests on enormous craters from three supervolcano eruptions in the past 2.1 million years. Together they blew out enough material to coat half of North America.
REALITY: The U.S. Geological Survey puts the annual odds of the Yellowstone supervolcano erupting again at about 1 in 730,000 -- the average time between its previous eruptions. This probability is roughly similar to that of a large (1 kilometer) asteroid hitting the Earth," USGS explains on its website.
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