Student' s Book International Hot Spot Level 5:

By coincidence just at this time NASA decided to test some new high-altitude cameras by taking photographs of Yellowstone, copies of which some thoughtful official passed on to the park authorities on the assumption that they might make a nice blow-up for one of the visitorsБЂ™ centers. As soon as Christiansen saw the photos he realized why he had failed to spot the caldera: virtually the whole park-2.2 million acres-was caldera. The explosion had left a crater more than forty miles across-much too huge to be perceived from anywhere at ground level. At some time in the past Yellowstone must have blown up with a violence far beyond the scale of anything known to humans. Yellowstone, it turns out, is a supervolcano. It sits on top of an enormous hot spot, a reservoir of molten rock that rises from at least 125 miles down in the Earth. The heat from the hot spot is what powers all of YellowstoneБЂ™s vents, geysers, hot springs, and popping mud pots. Beneath the surface is a magma chamber that is about forty-five miles across-roughly the same dimensions as the park-and about eight miles thick at its thickest point ...»