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Yellowstone National ParkSeeing the park from horseback gives visitors a chance to cover ground off the beaten path.
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Yellowstone National Park
Caldera
Yellowstone's caldera
 
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.)
Summer Crowd at Old Faithful.  

Did You Know?
At peak summer levels, 3,500 employees work for Yellowstone National Park concessioners and about 800 work for the park.

Last Updated: July 11, 2007 at 16:45 EST