Geological Survey Professional Paper 1180 Grinnell and Sperry Glaciers, Glacier National Park, Montana: A Record of Vanishing Ice

This report summarizes information resulting from observations and surveys relating to Grinnell and Sperry Glaciers, in Glacier National Park, Mont. (fig. 1), during 1887-1969. The assembled information records the changes in these glaciers since their discoveries, and provides a basis for future studies. Descriptions of the glaciers by the area's earliest explorers and visitors contrast with observations made in recent years.

SUMMARY OF INVESTIGATIONS

The first measurable data relating to the glaciers resulted from the U.S. Geological Survey's topographic mapping in 1900 and 1901 of the Chief Mountain 30-minute quadrangle (scale 1:125,000, contour interval 100 feet).

William C. Alden (1914) described the glaciers and discussed the glacial phenomena he observed there in the summers of 1911-13.

George C. Ruhle, Park Naturalist, started terminal-recession measurements of Grinnell, Sperry, and other glaciers in 1931. Annual measurements were made by the National Park Service through 1944, and measurements for Grinnell and Sperry have been made since 1945 by the U.S. Geological Survey in cooperation with the Park Service.

James L. Dyson, former Ranger-Naturalist, topographically mapped Grinnell Glacier in 1937 and Sperry Glacier in 1938. He remapped in 1946 the entire Grinnell Glacier and the terminal (lower) part of Sperry Glacier.

Aerial photographs of most glaciers in the Park were made in 1950 and 1952 through the cooperative efforts of the National Park Service, the Glacier Natural History Association, and the American Geographical Society. From the 1950 photographs, the U.S. Forest Service mapped Jackson Glacier (southeast of Sperry Glacier), and the U.S. Geological Survey mapped Grinnell and Sperry Glaciers at a scale of 1:4,800.

From 1950 and 1960 aerial photographs of both Grinnell and Sperry Glaciers, the U.S. Geological Survey prepared 1:6,000-scale comparison topographic maps. The slight change during the intervening 10 years suggests that such frequent remapping is unnecessary.

The U.S. Geological Survey published in 1968 7-1/2—minute quadrangle maps, scale 1:24,000, of the quadrangles in Glacier National Park. Grinnell Glacier is in the Many Glacier and Logan Pass quadrangles; Sperry Glacier is in the Mount Cannon, Lake McDonald East, and Logan Pass quadrangles.

A series of terrestrial photographs of the two glaciers taken with a phototheodolite during 1956-68, provide a good comparative record.

With few exceptions, changes in surface elevations of the two glaciers have been determined annually during late August or early September by measuring profiles of their surfaces along established lines. Data on surface movement have been obtained for Grinnell and Sperry Glaciers since 1947 and 1949, respectively.

Annual precipitation in the Grinnell Glacier area has been measured at two storage-precipitation gages installed in August 1949 and August 1955 by the U.S. Weather Bureau in cooperation with the National Park Service.

A gaging station installed by the U.S. Geological Survey in August 1949 on Grinnell Creek just below the outlet of Grinnell Lake (east of area shown on plate 1) provides continuous record of runoff from the glacier and its enclosing cirque and some records of precipitation and temperature. An auxiliary gaging station (pl. 1), installed in 1959 on the outflowing stream within about 1,000 feet of the glacier, operates during the summer and early fall; freezing conditions make it inoperative by October or November, and trail conditions make it not readily accessible until the following late June or early July.

ACKNOWLEDGMENTS

The National Park Service staff in Glacier National Park cooperated fully and assisted in the surveys and investigations. Matthew E. Beatty, Park Naturalist 1944-55, and his successors, H.B. Robinson, 1956-57, and Francis Elmore, 1958-70, by their interest and enthusiasm contributed greatly to the program. Donald H. Robinson, Assistant Park Naturalist, actively assisted in 1947-56. The National Park Service furnished saddle and pack animals for transporting personnel and equipment and gave me invaluable access to office files of historical information.

R.A. Dightman, then State Climatologist for Montana, furnished data from the two storage precipitation gages in the Grinnell Glacier area.

Gerald M. Baden, of Fullerton Junior College, California, and former seasonal Ranger-Naturalist in the park, furnished data on the specific ages of trees that have grown in areas from which the glaciers have receded.