Geological Survey Bulletin 395 Radioactivity of the Thermal Waters of Yellowstone National Park

PURPOSE OF THE REPORT.

During the summer of 1906 we conducted a series of field tests for the United States Geological Survey with the object of determining the radioactive properties of the thermal waters of the Yellowstone National Park. In connection with the field work, samples of deposits formed by the springs, some typical rock specimens, and a number of water residues were obtained. In this bulletin the quantitative data of the investigation are presented in a series of tables. An account of the methods of experiment in both field and laboratory precedes the presentation of results, and a discussion follows. We have indicated a possible application of some of the data to a geologic question—the age of some of the spring deposits; but no systematic attempt has been made to relate the facts of radioactivity to the hydrography of the region or to the geology of the park. Since our experiments were conducted chiefly from the chemist's point of view, we have limited our discussion to pointing out the more important characteristics and relations of the data, and comparing them with data on radioactivity in other regions of hydrothermal activity.

PLATE I. GROTTO GEYSER.

WATERS IN YELLOWSTONE PARK.

The thermal waters of the national park are classified by Arnold Hague under three heads, on the basis of incrustations formed by the springs and chemical analyses of some of the waters made by Gooch and Whitfield:^a (1) Calcareous waters carrying relatively large quantities of calcium carbonate in solution; (2) siliceous acid waters which usually carry free acid in solution and possess an astringent taste; (3) siliceous alkaline waters. In all, about 4,000 hot springs are found in the park and about a hundred geysers.

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aGooch, F. A., and Whitfield, J. E., Analyses of waters of the Yellowstone National Park: Bull. U. S. Geol. Survey No. 47, 1888.

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There is but one important group of calcareous waters in the park, namely, Mammoth Hot Springs, near the northern boundary. In the course of their underground flow these waters pass through Jurassic and Cretaceous limestones and become charged with carbon dioxide and mineral matter, which is deposited as travertine. A series of terraces extend more than a mile up a valley and to a height of 1,300 feet. The springs of this locality differ considerably in temperature, the maximum being 74° C., about 18° under the boiling temperature of water at this altitude.

Acid waters occur in the following localities among those we visited: Norris basin, Shoshone basin, Heart Lake basin, Crater Hills, Tower Falls, Mount Washburn, Mud Volcanoes near Yellowstone River, and Grand Canyon of the Yellowstone.

Alkaline waters predominate in the regions of geyser activity. These waters deposit an incrustation of amorphous silica. Springs of this class were tested at Upper and Lower Geyser basins, Excelsior basin, Shoshone basin, Heart Lake basin, and West Thumb of Yellow Stone Lake.

SCOPE OF THE INVESTIGATION.

The field tests extended over a period of two months, during which all the principal basins of thermal activity were visited. The spring waters examined embrace the different types found in the park and include water from a number of cold springs. The aim was to test one or more of each type at each basin visited. Wherever gases were evolved from a spring, these also were tested for their radioactive properties. About eighty quantitative tests were made of waters and forty of gases, besides nearly ninety tests of gases largely of a qualitative nature. In the laboratory some fifty solids, consisting of spring deposits, water residues, and rock samples, were examined quantitatively for the radium content.

GENERAL PLAN OF WORK.

The determinations for radioactivity were all made by the electrical method. Several electroscopes of the C. T. R. Wilson type, as modified in some details by Doctor Boltwood and ourselves for this kind of work, were employed in both field and laboratory tests. The procedure in the field was generally as follows: A qualitative test for radium and thorium emanation was first conducted on the escaping gas from the spring. This was followed by a quantitative determination of the radium emanation present in the gas. Meanwhile a sample of the spring deposit was collected and a sample of water taken. Incidentally the temperature of the water was taken and its reaction toward litmus paper tested. At the field laboratory the quantity of radium emanation in the sample of water collected was determined, after which the water was evaporated to dryness. The residue thus obtained and the sample of deposit made by the spring were subsequently examined for their radium content in a chemical laboratory.

ACKNOWLEDGMENTS.

The United States Geological Survey defrayed the greater portion of the expense connected with the field tests of this investigation. The Northern Pacific Railway furnished transportation between St. Paul and Gardiner, Mont. The University of Missouri and Butler College loaned most of the scientific apparatus used in the field tests, and the determinations of radium present in the spring deposits and rock samples were conducted in the chemical laboratories of these institutions. The field work came under the direction of C. W. Hayes and Arnold Hague, of the United States Geological Survey. Doctor Hague also placed at our disposal several specimens of typical rocks, which were used in determining the radium content of rocks. Maj. John Pitcher, U. S. Army, extended numerous facilities that materially aided in the field experiments. Capt. William H. Forsythe, U. S. Army, collected several samples of travertine for us at Mammoth Hot Springs. The noncommissioned officers stationed at the military posts throughout the park assisted in various ways.