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

The climate of Glacier National Park was studied in considerable detail by Dightman (1956, 1967). He noted the pronounced differences in precipitation which reflect the extremely rugged mountain terrain. For example, annual precipitation at Babb (fig. 1), the northeast entrance to the park, is now about 20 inches, whereas precipitation over Grinnell Glacier is estimated to be about 150 inches; this 130-inch increase occurs within a lateral distance of 15 miles and an altitude rise of 1,700 feet. Prior to discovery of Grinnell Glacier in 1887 and Sperry Glacier in 1897—when both glaciers were considerably larger than they are now—precipitation undoubtedly was even greater and temperatures were lower.

FIGURE 1.—Index map of the central part of Glacier National Park, Mont., showing location of Grinnell and Sperry Glaciers. Base from U.S. Geological Survey Cut Bank 1° x 2° quadrangle map, 1960-68. (click on image for a PDF version)

The earliest recorded climatic observations near Glacier National Park were in 1897 at Kalispell. Shown in figure 2 are values for annual precipitation, mean annual temperatures, and cumulative departures from the mean for Kalispell, West Glacier, and Summit. Precipitation and temperature data for certain pairs of years from 1915 to 1953 (table 1) were selected to illustrate the pronounced variations in successive years. Recording of precipitation, temperature, and streamflow in the Grinnell Glacier basin began in 1949 (discussed under precipitation and runoff of Grinnell Glacier). Precipitation and temperature data for Sperry Chalets, July and August, 1960-69, are given in table 2.

FIGURE 2.—Annual and mean precipitation and temperatures, and cumulative departures from the means, for three recording stations in the Glacier National Park area, Montana. Dashed line indicates mean. Kalispell, elevation 2,971 feet; 1897-70. West Glacier, elevation 3,154 feet; 1926-1970. Summit, elevation 5,213 feet; 1936-1969. (click on image for a PDF version)

TABLE 1.—Selected precipitation and temperature records for Summit, West Glacier, and Kalispell illustrating variations for successive years.

TABLE 2. — July and August 1960-69 temperatures and precipitation at Sperry Chalets, Mont., elevation 6,500 feet

(Data supplied by R.A. Dightman, U.S. Weather Bureau, Helena, Mont. July 1964 values based on observations from July 4 to July 31)

The station at Summit, highest of the three stations and on the Continental Divide at the south edge of the park, is 1,000 feet lower than and 35 miles south-southeast of Grinnell Glacier and 2,000 feet lower than and 30 miles southeast of Sperry Glacier. Nevertheless, the record from Summit closely reflects the climatic variations at the two glaciers.

The individual precipitation and temperature measurements for the three stations show no obvious similarity in pattern, but the curves for cumulative departure from means do show similar trends. The greatest negative departures from mean precipitation were in 1941, 1944, and 1947; a trend of increasing precipitation is evident for 1948 to 1969.