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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
Fumaroles and How They Work
A fumarole emits a jet of hot steam in Porcelain Basin.
Black Growler Steam Vent
Norris Geyser Basin

Fumaroles, or steam vents, are hot springs with a lot of heat, but so little water that it all boils away before reaching the surface. At places like Roaring Mountain, the result is a loud hissing vent of steam and gases.
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.

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Last Updated: July 26, 2007 at 17:40 EST