HOT SPRINGS Analyses of the Waters of The Hot Springs of Arkansas Geological Sketch of Hot Springs, Arkansas

GEOLOGICAL SKETCH OF THE HOT SPRINGS DISTRICT, ARKANSAS.

The question whether the hot springs are changing in character and will eventually either cease flowing or become cold springs is of both popular and scientific interest. The evidence seems to show that there is a very small decrease in temperature since they were first examined, now nearly a century ago. The temperature recorded by Dunbar and Hunter in 1804 for the larger spring was 150° F., and another had a temperature of 154°. In 1859 the springs were carefully examined by David Dale Owen, State geologist. A more accurate map was published by William Glasgow, jr., in 1860 from careful instrumental surveys, together with records of temperature and outflow.

Since then many changes have been made about the springs, all of which have been dug out and inclosed in masonry arches, with the consolidation of two or more springs into one in some instances, the development of new outflows by digging wells or sinking pipes, and the drying up of adjacent natural outflows. For these reasons all the springs now existing can not be positively identified with those shown on the earlier maps, but a majority of them are so correlated without doubt.

Temperatures.—The comparison of the old records mentioned with those recently made shows that the highest temperature known to-day is 147° F., as against 154° in 1804, and 150° by Glasgow and 148° by Owen in 1860. In a number of springs there is a decline of 2° since the latter date. Such a slight difference might, however, be due to differences in the manner or place of taking the temperatures, or the instruments used in the earlier years may not have been accurate. It is noteworthy that Owen's highest temperature, taken in 1859 with a standardized thermometer, was 148°, and that recorded now is 147°. In other words, the temperature is decreasing so slowly that the change is almost imperceptible in half a century. In one instance, that of the Alum spring, there is a very marked decrease in temperature, and as this is the only spring on the west side of the creek, there is no doubt of its identity. In 1804 this had a temperature of 132°. In 1859 its temperature was 133°, according to Owen, and to-day it is but 114.8°.

Amount of outflow.—The comparison of outflow is more difficult. According to Dunbar and Hunter the largest spring had an outflow of 11 quarts in 11 seconds in 1804, corresponding to 22,100 gallons per day, and the 4 largest springs had an outflow of 165 gallons per minute, or 237,600 gallons per day. Dr. Owen gives no measurements, but Glasgow gives the discharge of each spring—a total of 317 gallons per minute, or 450,480 gallons per day, as compared with 850,000 gallons per day at the present time. As the writer has shown elsewhere, the spring water is of meteoric origin, like most spring water, and probably varies somewhat from year to year, corresponding to variation in annual rainfall at some previous year, so that no definite comparison can be made with the early records, except to state that the volume of water discharged is very much greater. Supposing a practically constant amount of heat applied, this of itself would mean a slightly lowered temperature. In this connection attention should be called to the well put down by Maj. Torney, United States Army, in the Army and Navy Hospital, which is capable of yielding the amazing amount of 350,000 gallons per day without affecting but one very small spring (No. 40 of the list).

From a consideration of all these facts it is concluded that the springs are losing their heat so slowly that the loss is almost inappreciable.

Amount of mineral matter carried in solution by the waters.—No essential difference in the composition of the waters can be detected by a comparison of the analyses made for Owen and Larkin (1859) or Dr. Branner, of the State geological survey in 1889, with the elaborate and careful analyses made by the National Government. The waters are remarkable more for their purity than for their mineral contents. The material in solution consists mainly of silica, calcium, and bicarbonates. The total mineral matter discharged by all the springs amounts to about 250 tons a year. The annual removal of this amount of material from the earth's interior to the surface must ultimately result in the formation of large cavities.