This cone-type geyser in the Upper Geyser Basin of Yellowstone National Park is the namesake for the Giant Group of geysers (Bijou Geyser, Catfish Geyser, Mastiff Geyser, the "Platform Vents," and Turtle Geyser.) The Giant Geyser's Platform is a raised stone structure that incorporates all these geysers. Giant is notable for its spectacular and sporadic eruptions as well as for its massive cone of geyserite which stands about 12 feet tall. The Giant Geyser enters a state of dormancy from time to time with no eruptions for years at a time. The reasons for this variability are unknown. Hot periods last only a few minutes and when the hot period ends activity on the Platform returns to normal. When Giant erupts the action can be pretty dramatic, lasting about an hour and sometimes reaching over 250 feet. The Giant Geyser is about 100 feet between the loop trail and the Firehole River and it's viewable from a bit off the main path.