Old Faithful, for one, is a GEYSER, a type of hot spring that periodically erupts jets of water and steam into the air. It is located in Yellowstone National Park in Wyoming, United States, and is one of the most famous geysers in the world. Old Faithful was named by members of the 1870 Washburn-Langford-Doane Expedition and is not the largest or most regular GEYSER in the park, but it is the most predictable. It erupts every 35 to 120 minutes, with an average interval of about 90 minutes.