GREGORY DIMIJIAN / SCIENCE PHOTO LIBRARY GREGORY DIMIJIAN / SCIENCE PHOTO LIBRARY
Steam trails rising from geysers at dusk. These geysers of the Black Sand Geyser Basin consist of deep wells in geothermal rock fissures. Somewhere near the base of each well is a large chamber. The water in the chamber is heated by the surrounding rocks until it is well over normal boiling point, but is prevented from boiling by hydrostatic pressure. The heating also causes the water to expand, spilling from the lip of the well. At a critical point, the decreasing hydrostatic pressure allows the superheated water to boil spontaneously and erupt. The term geyser comes from the Icelandic "geysir" meaning gusher. Photo- graphed in Yellowstone National Park, USA.
Model release not required. Property release not required.