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| Sunday, 28 August 2005 |
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Junior Observer |  |
| News Business Features Editorial
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Earth's natural water heaters
But how does this happen, you might wonder. As molten materials deep in the earth cool down, they give off water vapour and carbon dioxide. This hot vapour then finds its way upward through the cracks in the rocks, cooling as it goes, until it condenses to become water. Finally, it gushes from the ground as a hot spring. This water may be pure and clear, but it is rich in mineral salts dissolved from the rocks it has passed through on its way to the surface. As water cools around the edges of the spring, the minerals form crystals and grains. These build up into beautiful rock layers shaped like waves, basins and terraces. The water coming from a hot spring is heated by geothermal heat, that is heat from the interior of the earth. In general, the temperature of rocks within the earth increases with depth. The rate of temperature increasing with depth is known as the geothermal gradient. If water percolates (filters) deeply enough into the crust, it will be heated as it comes into contact with hot rocks. The water from hot springs in non-volcanic areas is heated in this manner.
If the water becomes so hot that it builds steam pressure and erupts in a jet above the surface of the earth, it is called a geyser; if the water only reaches the surface in the form of steam, it is called a fumarole; and if the water is mixed with mud and clay, it is called a mud pot. Note that hot springs in volcanic areas are often at or near the boiling point. People have been seriously burnt and even killed by accidentally or intentionally entering these springs. Warm springs are sometimes the result of hot and cold springs mixing, but may also occur outside of geothermal areas, such as Warm Springs, Georgia (frequented for its therapeutic effects by polio-stricken former U.S. President Franklin D. Roosevelt, who built the Little White House there).Because heated water can hold more dissolved solids, warm and especially hot springs also often have a very high mineral content, containing everything from simple calcium to lithium, and even radium. Because of both the folklore and the proven medical value some of these springs have, they are often popular tourist destinations, and locations for rehabilitation clinics for those with disabilities. The countries most famous for hot springs are Iceland and New Zealand. The onsen (a Japanese word for "hot spring") plays a notable role in Japanese culture and is one of the most popular tourism industries there. |
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You must have heard about the hot water springs in Mudunagala and
Trincomalee. There are thousands of famous hot springs all over the world.
A hot spring or hydrothermal spring is a place where warm or hot water
gushes from the ground. This happens on a regular basis for at least a
predictable part of the year, and is significantly above the ground
temperature. 
In volcanic zones, water may be heated by coming into contact with
magma (molten rock). The high temperature gradient near magma may cause
water to be heated so much that it boils or becomes superheated. 
