Geysers
Views of the Wonderland or Yellowstone Park. Courtesy of the Montana Historical Society Research Center via Big Sky Country Digital Network.
Geysers are hot springs with constrictions in their “plumbing,” usually near the surface, that prevent water from circulating freely to the surface, where heat would normally rise to escape. As the water circulates, the temperature and pressure rise. Increased pressure exerted by the enormous weight of the overlying water prevents the water from boiling. As the water rises, steam forms. Bubbling upward, the steam expands as it nears the top of the water column. At a critical point, the confined bubbles actually lift the water above, causing the geyser to splash or overflow. This decreases pressure on the system, and violent boiling results. Tremendous amounts of steam force water out of the vent, and an eruption begins. Water is expelled faster than it can enter the geyser's plumbing system, and the heat and pressure gradually decrease. The eruption stops when the water reservoir is depleted or when the system cools, and the process begins again.
There are two types of geysers: cone and fountain geysers. A cone-type geyser has a narrow constriction close to the geyser's vent. During eruptions, the constriction acts like a nozzle, causing the water to jet in great columns. The cone is formed by the constant deposition of silica around the geyser's vent. A fountain-type geyser has a large opening at the surface that usually fills with water before or during an eruption. Fountain type geysers are the most common type of geyser and can range in size from very small to very large.
