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Geysers

January 1, 1971

A geyser is a special type of hot spring that from time to time spurts water above ground. It differs from most hot springs in having periodic eruptions separated by intervals without flow of water. The temperature of the erupting water is generally nearly at boiling for pure water (212°F or 100°C at sea level). Some geysers erupt less than a foot high, and a few geysers erupt to more than 150 feet. Some small geysers erupt every minute or so, but other geysers are inactive for months or even years between eruptions. Contrary to popular opinion, most geysers are very irregular in their behavior, and each is different in some respects from all others. Among the major geysers, only a few such as Old Faithful in Yellowstone National Park are predictable enough to satisfy an impatient tourist. But even for Old Faithful the interval varies from about 30 to 90 minutes between eruptions, with an average interval of about 65 minutes.