Elevation Range: Approximately 2300-2600 meters
Location: Latitude: 48°37'19.53"N, Longitude: 113°45'24.50"W
Area: 2014 = 0.8 km2
Sperry Glacier occupies a broad, shallow cirque situated just beneath and west of the Continental Divide in the Lewis Mountain Range of Glacier National Park, Montana. This northeast facing glacier is wider than it is long relative to its flow direction and spans about 300 m in elevation with a median altitude of 2450 m. It ranks as a moderately sized glacier for this region, which contains the second highest concentration of glaciers in the U.S. Rocky Mountains. The glacier is in a ~4 km2 hanging cirque, and in 2014 it had an area of 0.80 km2, making Sperry Glacier the smallest of the benchmark glaciers.
Due to its position on the Continental Divide the glacier is influenced by both maritime and continental air masses. However, given its position on the western and predominantly windward side of the Continental Divide, Pacific storm systems dominate the weather. These bring heavy precipitation and moderate temperatures as warm, moist Pacific fronts collide with and lift over the Rocky Mountains. Temperature and precipitation patterns in northwest Montana are marked by strong altitudinal gradients. For valley sites at about 1000 m, mean temperatures for July, which is generally the warmest month of the year, are typically 15-17°C (59-63°F); they are roughly half that for mountain sites at 2500 m (Finklin, 1986). Annual precipitation averages 580 mm on the western and eastern edges of Glacier Park, but over 2500 mm at higher elevations in the Park's interior near the Continental Divide.
In 2005, the USGS Climate Change in Mountain Ecosystems (CCME) program established a glacier monitoring strategy in northwest Montana with the goal of assessing long-term changes to the region's glaciers. Through this monitoring program researchers also aimed to evaluate the hydrologic and ecologic effects of glaciers in Glacier National Park. Sperry Glacier was chosen as the benchmark study glacier due to its history of previous research, physical characteristics, and accessibility.
Sperry became the focus of extensive field research starting in 2005 as scientists employed standard glaciological methods (Ostrem and Brugman, 1991) to estimate glacier-wide seasonal and annual surface mass balances. Snow depths and densities are measured in the spring when the glacier's balance is at a maximum. Ablation stakes are also installed at this time and then checked periodically during the summer melt season with a final check in early autumn at the balance minima. With similar goals and methodologies, the Sperry Glacier mass balance project joined the established USGS Benchmark Program in 2013. The addition of Sperry to the long-established mass balance monitoring projects in Alaska and Washington will facilitate a broader understanding of glacier dynamics, hydrology, and glacier response to climate change.
Direct field measurements are combined with weather data and imagery analyses to calculate the seasonal and annual mass balance of each glacier. Access all the data here.
In June 2006 the Sperry Glacier weather station (48° 37' 24.1932" N, 113° 45' 53.4347" W) was installed at an altitude of 2450 m on a rocky outcrop about 100 m from the western edge of the glacier. Sensors measured air temperature, wind speed and direction, incoming solar radiation, and relative humidity. It became apparent that the 2 m mast height was not sufficient as the station was buried every winter and typically did not melt out until June. In some years the sensors were damaged so severely by snowpack creep that they needed replacing. During years with exceptionally heavy snowfall, such as in 2011, the station did not melt out until late July. The station was abandoned in 2012 due to these issues and there are no data for that year. But in 2013, the station was re-installed and recorded data for most of the June through September ablation season. In September 2014 a new station was installed in the same location with a 4 m mast and fitted with new instruments including a net radiometer, a new power system, and satellite telemetry. The taller mast should keep the sensors above the snowpack surface during the winter allowing the station to remain operational year round.
There are complete records of daily average temperature for the months July and August 2006-2011 and 2013. Most of the ablation on the glacier occurs during these two summer months. For the period of record, the mean July-August daily average temperature was 9.7° C (50° F) with a maximum daily average of 19.1° C (66° F) and minimum of -2.1° C (28° F). Precipitation at the glacier has not been measured directly. Snowfall is the dominant form of precipitation and usually accumulates starting in September or October and continues through May or June. The nearest weather station with precipitation data is the Flattop SNOTEL located 25 km northeast of and 530 m lower than the Sperry station. Average yearly precipitation here from the years 1980-2010 was 1.70 m (67 in). Snowpack measurements made in June when the glacier is near peak accumulation reveal precipitation is likely much higher on the glacier. Values of 2.50 meters (98 in) of snow water equivalent to 3.00 m (118 in) are common. However the accumulation patterns on Sperry are not fully understood and it is unclear what percentage of these deep snow packs owe their existence to precipitation versus how much snow is transported onto the glacier by wind and avalanches.
Current data available from the Sperry weather station includes:
- Air Temperature
- Relative Humidity
- Wind Speed
- Wind Direction
At this time, stream discharge for Sperry Glacier is not measured. The glacier's broad expanse creates numerous discreet runoff streams which make gauging this glacier a challenge. Runoff data are not available for this glacier.
The glaciers of Glacier National Park have been the focus of visitor and scientific interest since before the park was established in 1910. Because it is relatively easy to access, Sperry Glacier has one of the most extensive records of historic data and measurement in the region. The earliest photo of the glacier dates back to 1894 and the earliest map was created in 1901. William Alden, a geologist for the USGS, explored the glacier and published the first scientific measurements and descriptions in the early 20th century (Alden, 1914; Alden, 1923). The glacier's retreat was documented by Dyson (1948) and the USGS and NPS conducted annual measurements of the glacier in the mid-20th century, including the installation of ablation stakes, measurements of flow speed and direction, and plane-table mapping that resulted in a detailed topographical map of the glacier with terminus locations from 1913-1969 (Johnson, 1980) (Reardon, et al, 2008). The progression of glacier retreat has been documented using satellite imagery and aerial photos (Key, et al., 2002), repeat photography, and annual GPS mapping of margins and terminus since 2003 by the USGS — CCME glacier monitoring program. Other parameters, such as depth measurement through the use of ice radar, GPS velocity measurements, and the determination of elevation profiles were included at the beginning of the monitoring program in 2005 in collaboration with Joel T. Harper of the University of Montana, Missoula.
Repeating Elrod's photograph from the same photo point was impossible since he shot from the elevated perspective of the glacier's surface. The terminus of the glacier has retreated beyond the field of view, but these images give a sense of the glacier's extent and mass early in the 20th century.
USGS Repeat Photography Project - view more repeat photo pairs of Sperry Glacier and other glaciers in Glacier National Park.