A hot spring which at regular and irregular intervals thrown a jet of hot water and stream into the air; sometimes the jet rises to a heights of 100 to 200 feet. It occurs in a volcanic region.
         From the mouth of the geyser, a tube penetrates deeply into the earth, and fills with water, which percolates through from the surface. The water near the base of this tube is considerably heated by hot lava, but the tube is long and narrow that convection cannot take place freely; the temperature of the water down below thus continues to rise, the boiling point of the water is relatively cool.
     At the same time, the boiling point of the water at the base of the tube is raised by pressure, and the temperature has to reach well above 100 degrees centigrade before steam is formed. When this does take place, the water above is forced upwards and flows away. The sudden reduction of the pressure at the bottom of the tube lowers the boiling point of the water, and the latter is now rapidly converted into steam, which forms in such volume that the entire column above it is ejected well into the air. The action of geyser is thus intermittent. The best-known geysers are those of New Zealand, Iceland, and Yellowstone National Park, U.S.A. The famous Old Faithful geyser of Yellowstone National Park used to erupt with great precision every 66 and half minutes, but is now acting with less regularity and at longer intervals.
      Geyserite is a siliceous deposit produced from hot spring or geyser, while sinter is a mineral deposit from a hot spring or geyser, which sometimes occurs in mounds, cones, or terraces. There are two principal kinds, calcareous sinter and siliceous sinter, depending on composition. The former is often known as travertine, the latter as geyserites