Old Faithful is probably the most popular and well known feature at Yellowstone. It is not the biggest
or the most regular geyser in Yellowstone, but it is the biggest regular geyser. The interval between
eruptions is not uniform as generally believed. The eruptions can be predicted based on the length
and intensity of the preceding eruption. Old Faithful erupts every 35 to 120 minutes for 11/2 to 5
minutes. Its maximum height ranges from 90 to 184 feet.

Visitors awaiting the eruption.


Old Faithful as it begins to erupt


Half of the world's geothermal features are in Yellowstone, fueled by constant volcanic activity.
Lava flows and rocks from volcanic eruptions cover most of the land area of Yellowstone.

The park is home to one of the world's largest calderas with over 10,000
thermal features and more than 300 geysers.









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