Old Faithful is a cone geyser located in Wyoming, in Yellowstone National Park in the United States. Old Faithful was named in 1870 during the Washburn-Langford-Doane Expedition and was the first geyser in the park to receive a name. It is also called the most predictable geographical feature on Earth erupting almost every 91 minutes.
Eruptions can shoot 3,700 to 8,400 US gallons (14,000 to 32,000 L) of boiling water to a height of 106 to 185 feet (32 to 56 m) lasting from 1.5 to 5 minutes. The average height of an eruption is 145 feet (44 m). The highest recorded eruption was 185 feet (56 m). Intervals between eruptions can range from 45 to 125 minutes, averaging 66.5 minutes in 1939, slowly increasing to an average of 90 minutes apart today.The time between eruptions has a bimodal distribution.