Which natural geyser in Wyoming erupts regularly every 90 minutes on average?

Old Faithful is the natural geyser in Wyoming that erupts regularly every 90 minutes on average. It stands in Yellowstone National Park’s Upper Geyser Basin, where underground heat from the Yellowstone volcanic system warms groundwater until pressure forces boiling water and steam through a narrow vent.

The geyser was named during the Washburn-Langford-Doane Expedition in 1870 and was the first geyser in Yellowstone to receive a name. Its reputation comes from predictability rather than size: eruptions usually last about 1½ to 5 minutes and can send thousands of gallons of water roughly 100 to 180 feet into the air.

The 90-minute figure is an average, not a strict timetable. Intervals can vary widely, and the next eruption depends partly on how long the previous one lasted. Beehive Geyser and Giant Geyser are also Yellowstone landmarks, but they erupt less predictably. Steamboat Geyser is taller, yet far less reliable.