At Yellowstone and some other volcanoes, some scientists theorize that the earth's crust fractures and cracks in a concentric or ring-fracture pattern. At some point these cracks reach the magma “reservoir,” release the pressure, and the volcano explodes. The huge amount of material released causes the volcano to collapse into a huge crater—a caldera. (Illustration based on Smith, R. B., and Siegel, L., 2000, Windows into the Earth; New York, Oxford University Press.)
Did You Know?
There were no wolves in Yellowstone in 1994. The wolves that were reintroduced in 1995 and 1996 thrived and there are now over 300 of their descendents living in the Greater Yellowstone Area.