SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
Grand Geyser. Historical artwork of men fleeing in fright from an eruption of Grand Geyser, Yellowstone National Park, USA around 1880. A geyser consists of a deep well-like fissure in geothermal rock. At the base of the fissure is a large water- filled chamber which is heated by the surrounding rocks until it is well over normal boiling point. However it is prevented from boiling by the immense water pressure. The heating also causes the water to expand, so that it spills from the lip of the fissure. At a critical point, the loss of water reduces the pressure to a point where the superheated water boils spontaneously and erupts.
Model release not required. Property release not required.