Thermal and Mineral Springs

2.9.2 Thermal and Mineral Springs

Thermal springs can be divided into warm springs and hot springs depending on their temperature relative to the human body temperature of 98 ◦

C: hot springs have a higher and warm springs a lower temperature. Warm springs have temperatures higher than the average annual air temperature at the location of discharge. Stearns et al. (1937) give a detailed description of thermal springs in the United States. Meinzer (1940) pro- vides the following illustrative discussion regarding the occurrence and nature of thermal springs:

F or 37 ◦

An exact statement of the number of thermal springs in the United States is, of course, arbitrary, depending upon the classification of springs that are only slightly warmer than the normal for their localities and upon the groupings of those recognized as thermal springs. A recently published report lists 1059 thermal springs or spring localities. Of these 52 are in the East-Central region (46 in the Appalachian Highlands and 6 in the Ouachita area in Arkansas), 3 are in the Great Plains region (in the Black Hills of South Dakota), and all the rest are in the Western Mountain region. The States having the largest number of thermal springs, according to the listing in the report, are Idaho 203, California 184, Nevada 174, Wyoming 116, and Oregon 105. The geyser area of Yellowstone National Park, however, exceeds all others in the abundance of springs of high temperature (29). Indeed, the number of thermal springs in this area might be given as several thousand if the springs were counted individually instead of being grouped. . . . Nearly two-thirds of the recognized thermal springs issue from igneous rocks-chiefly from the large intrusive masses, such as the great Idaho batholith, which still retain some of their original heat. Few, if any, derive their heat from the extrusive lavas, which were widely spread out in relatively thin sheets that cooled quickly. Many of the thermal springs issue along faults, and some of these may be artesian in character, but most of them probably derive their heat from hot gases or liquids that rise from underlying bodies of intrusive rock. The available data indicate that the thermal springs of the Western Mountain region derive their water chiefly from surface sources, but their heat largely from magmatic sources. . . . The thermal springs in the Appalachian Highlands owe their heat to the artesian structure, the water entering the aquifer at a relatively high altitude, passing to considerable depth through a syncline or other inverted siphon and reappearing at a lower altitude; in the deep part of its course the water is warmed by the normal heat of the deep-lying rocks.

The term mineral spring (or mineral water for that matter) has very different meanings in different countries, and can be very loosely defined as a spring with water having one or more chemical characteristics different from normal potable water used for public supply. For example, the water can have an elevated content of free gaseous carbon dioxide (naturally carbonated water), or high radon content (“radioactive” water—still consumed in some parts of the world as “medicinal” water of “miraculous” effects), or high hydrogen sulfide content (“good for skin diseases” and “soft skin”), or high

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dissolved magnesium, or simply have total dissolved solids higher than 1000 mg/L. Some water bottlers, exploiting a worldwide boom in the use of bottled spring water, label water derived from a spring as “mineral” even when it does not have any unusual chemical or physical characteristics. In the United States, public use and bottling of spring and mineral water is under the control of the Food and Drug Administration and such water must conform to strict standards including source protection.