Springs often issue from the sides of valleys ([Fig. 212]), the bottoms of which are below ground-water level. They are especially likely to issue at the surface of relatively impervious layers, and where the valley slopes cut joints, porous beds, or other structures which allow free flow of ground-water.
Fig. 212.—Diagram illustrating positions, a and b, favorable for springs.
Springs are classified in various ways, and these several classifications suggest characteristics worthy of note. They are sometimes said to be deep and shallow. The “deep” spring, as the term is ordinarily used, is one which issues with great force, and with something of upward movement, and the “shallow” spring, one which issues with little force, and without upward movement; but the spring which issues with force is not necessarily deep, nor is the one which issues with little force necessarily shallow. The idea involved in this grouping would be better expressed by strong and feeble. Springs are also classified as cold and thermal, the latter term meaning simply that the temperature is such as to make the springs seem warm or hot. The temperature of thermal springs ranges up to the boiling-point of water. Between deep springs and shallow ones, and between cold springs and thermal, respectively, there is no sharp line of demarkation. Again, some springs are continuous in their flow, while others are intermittent. Most intermittent springs flow after periods of precipitation, but dry up during droughts (see [p. 202]). Springs are also classified as mineral and common. Mineral springs, in the popular sense of the term, are of two types: (1) Those which contain an unusual amount of mineral matter, and (2) those which contain some unusual mineral. Springs are especially likely to be called mineral if the substances which they contain, have, or are supposed to have, some medicinal property. All springs which are not “mineral” are “common.” This classification is not altogether rational, for all springs contain more or less mineral matter, and many springs which are “common,” contain more mineral matter than some springs that are “mineral.” Mineral springs are themselves classified according to the kind and amount of mineral matter they contain. Thus saline springs contain salt; sulphur springs contain compounds (especially gaseous) of sulphur; chalybeate springs contain iron compounds, especially the sulphate; calcareous springs contain abundant lime carbonate, etc. These various mineral substances are extracted from the rock, sometimes by simple solution, and sometimes by solution resulting from other chemical change. The salt of saline springs is usually extracted from beds of salt beneath the surface. Lime carbonate, one of the commonest substances in solution in ground-water, is dissolved from limestone, or derived by chemical change from rocks containing other calcium compounds. Thus lime feldspars, by carbonation, give rise to lime carbonate. The chalybeate waters often arise from the oxidation of iron sulphide, a mineral which is common in many sedimentary rocks. The iron sulphate is itself subject to change in the presence of the ubiquitous lime carbonate. From this change iron carbonate results, and this is usually quickly altered to iron oxide, which, being relatively insoluble, is precipitated. About chalybeate springs, therefore, iron oxide is frequently being deposited. Medicinal springs are those which contain some substance or substances which have, or are supposed to have, curative properties.
Mineral matter in solution.—The number and variety of mineral substances in spring water is very great, and the amount of solid matter in solution varies widely. Some of the hot springs of the Yellowstone Park contain nearly three grams (2.8733) of mineral matter per kilogram.[108]
The composition of various spring and well waters is shown in the accompanying table, which gives some idea of the range of mineral substances commonly in solution in ground-water.
Geysers.—Geysers are intermittently eruptive hot springs. They occur only in volcanic regions (past or present) and in but few of them. Active geysers are virtually confined to the Yellowstone Park and Iceland, though they formerly existed at other places. Those of New Zealand have but recently become extinct. The great geyser region of the world is the Yellowstone Park, where there are said to be more than sixty active geysers.
The cause of the eruption is steam. The surface-water sinks down until, at some unknown depth, it comes into contact with rock sufficiently hot to boil it. The source of the heat is not open to inspection, but it is believed to be the uncooled part of an extrusive lava flow, or of an intrusive lava mass. From what was said on pp. [216] and [217] it is clear that geysers do not have their origin in water which sinks down to the zone of great heat, where the increment of heat is normal.
The water of a geyser issues through a tube of unknown length. Whether the tube is open down to the source of the heat is not determinable, but water from such a source finds its way to the tube. Water may enter the tube from all sides and at various levels from top to bottom. The heating may precede or follow its entrance into the tube, or both. So far as the water is heated after it enters the tube, the point of most rapid heating may be at the bottom of the tube or at some point above. If the temperature of the source of heat were high enough to convert the descending water into steam as fast as it enters the tube, the steam would escape continuously, though there would be no geyser; but if the rock is only hot enough to bring the water to the boiling-point after some lapse of time, and after some water has accumulated, an eruption is possible.
| Waters | Artesian well | Artesian well “Glacier Spouting Spring” | Artesian well[110] | Manitou Spring | Opal Spring | Sulphur Spring | Hot Spring | Hot Spring | Boiling Spring | Warm Spring |
|---|---|---|---|---|---|---|---|---|---|---|
| Location | Lexington, Ky. | Saratoga, N. Y. | Sheboygan, Wis. | Manitou, Col. | Yellowstone National Park | Los Angeles, Cal. | Hot Sp. Station, C. P. R. R. | Ward’s Ranch, base of Granite Mts., Nev. | Shaffer’s Ranch, Honey Lake Valley, Cal. | Warm Spring Sta. B. & B. R. Mono Basin |
| Date | ...... | 1872 | Feb. 1876 | ...... | ...... | ...... | ...... | ...... | ...... | ...... |
| Analyst | R. Peters | F. A. Cairns and C. F. Chandler | C. F. Chandler | Oscar Loew | H. Leffman | Oscar Loew | T. M. Chatard | T. M. Chatard | T. M. Chatard | T. M. Chatard |
| References | Ky. Geol. Surv., N. S., Vol. V, p. 189 | Am. Chemist, Nov. 1872, p. 164 | Am. Chemist, 1876, p. 370 | U. S. G. S. W., 100th M.. Vol. III, p. 618 | U. S. Geol. & Geog. Surv. Id., Wyo. Ter., 1878, p. 393 | An. Rep. U. S. G. S. W., 100th M., 1876, p. 195 | Ante, p. 49 | Ante, p. 53 | Ante, p. 51 | Bulletin No. 9, U. S. Geol. Survey, p. 27 |
| Sodium, Na | .09227 | 4.72640 | 2.0398 | .45164 | .4615 | .10424 | .7743 | .3554 | .3040 | .6116 |
| Potassium, K | .00919 | .35806 | .1285 | .05980 | ...... | Trace | .0669 | .0191 | .0094 | .0630 |
| Calcium, Ca | .02136 | .94050 | 1.0739 | .44400 | .0344 | .50600[111] | .0305 | .0367 | .0121 | .0589 |
| Magnesium, Mg | .01805 | .53470 | .2352 | .05860 | ...... | .0010 | .0034 | .0004 | .0604 | |
| Barium, Ba | ...... | .01848 | Trace | |||||||
| Strontium, Sr | Trace[112] | .00057 | ||||||||
| Lithium, Li | Trace | .01078 | .0003 | .00039 | ...... | Trace | ||||
| Iron, Fe | Trace[113] | .00341 | .0027 | Trace[114] | ...... | Trace | ||||
| Manganese, Mn | ...... | ...... | .0009 | ...... | ...... | Trace | ||||
| Chlorine, Cl | .07465 | 7.47400 | 4.2730 | .24850 | .7496 | Trace[115] | .9697 | .2396 | .2070 | .2272 |
| Bromine, Br | .04661 | .0025 | ||||||||
| Iodine, I | .00060 | Trace | ||||||||
| Fluorine, Fl | ...... | Trace[116] | ||||||||
| Carbonic acid, CO2 | .12160 | 5.82603 | .1792 | 1.11001 | ...... | .03516 | ...... | Trace | ...... | .5787 |
| Sulphuric acid, H2SO4 | .03218 | .00234 | 2.0318 | .20696 | .0325 | .16140 | .3555 | .3901 | .3492 | .3131 |
| Phosphoric acid, H3PO4 | Trace | .00005 | .0004 | ...... | ...... | Trace | ||||
| Boracic acid, H3BO3 | Trace | Trace | ||||||||
| Alumina, Al2O3 | ...... | .00770 | .0022 | ...... | ...... | Trace | .0010 | ...... | ...... | .0018 |
| Silica, SiO2 | .00940 | .01174 | .0080 | .02010 | .7680 | Trace | .2788 | .1136 | .1310 | .1220 |
| Hydrogen in bicarbonates, H | ...... | .09713 | .0030 | |||||||
| Organic substances | Trace | Trace | Trace | ...... | ...... | Trace | ||||
| Oxygen, O | ...... | ...... | ...... | ...... | ...... | ...... | .0194[117] | .0255[117] | .0080[117] | .0325[117] |
.37870 | 20.05910 | 9.9814 | 2.60000 | 2.0460 | .80680 | 2.4953 | 1.1834 | 1.0211 | 2.0692 | |
| Carbonic acid, CO2 | ...... | 2.015[118] | ...... | ...... | ...... | In excess | Trace | |||
| Sulphuretted hydrogen, H2S | ...... | ...... | ...... | ...... | ...... | 0.5000 |