HOT SPRING

also called Thermal Spring, a type of spring that issues water at temperatures substantially higher than the air temperature of the surrounding region. Most hot springs result from the interaction of groundwater with magma (molten rock) and magmatic gases or with solidified but still-hot igneous rocks at shallow depth. Some thermal springs, however, are not related to volcanic activity. In such cases, deep circulation of water is thought to carry the water to the lower parts of the terrestrial crust, where the temperature of rocks is high because of the normal temperature gradient of the Earth. A type of hot spring known as a geyser (q.v.) spouts intermittent jets of water and steam. Many hot springs that are not geysers exhibit periodicity: some manifest periods of agitation or violent boiling, while others alternately discharge water and gas. A tremendous amount of heat is released by hot springs, and various applications of this geothermal energy have been developed. In certain areas, buildings and greenhouses are heated with water pumped from hot springs, and in others, water from such sources is used for heating soil to enhance crop production and for seasoning lumber. In a few countries (e.g., Iceland, Japan, and the United States), electricity has been generated with high-temperature steam from geysers.