"Yellowstone National Park " a Yellowstone National Park Travel Page by sunnywong

Yellowstone National Park is America's first and foremost National Park. It is home to some 10,000 thermal features, over 500 hundred of which are geysers. In fact, Yellowstone contains the majority of the worlds geysers. Within Yellowstone's thermal features can be seen the product of millions of years of geology at work. Much of Yellowstone sits inside an ancient volcanic caldera (the exploded crater of a volcano). The last major caldera forming eruption occurred 600,000 years ago. For hundreds of thousands of years following that, subsequent lava flows slowly filled in most of the caldera. Even now, in some places, nearly molten rock resides as little as 2-5 miles below the surface. Heat from the volcanic activity makes its presence known by heating ground water and creating the therma features we now see. The four basic types of thermal features present in the Park are geysers, hot springs, fumaroles, and mudpots. Many of these are concentrated in Yellowstone's major geyser basins: Upper, Midway, Lower, Norris, West Thumb, Shoshone and Heart Lake.