Benchmark Glacier: Sperry

Glacier Monitoring Research

Monitoring and Assessing Glacier Changes and Their Associated Hydrologic and Ecologic Effects in Glacier National Park

Topographic characteristics:

• Its location -- near the center of the region and within 3-10 km of 6 other glaciers in most heavily glaciated part of region -- representative of the region’s climate.
• It occupies a shallow cirque in a large hanging valley just below and west of the Continental Divide, on the northeast slope of Gunsight Mountain. Ice extends above the bergschrund (~2600 m) to just below the east summit (2800 ft) of Gunsight Mountain. Several small lakes and remnant ice bodies sit in the hanging valley below the current terminus, where the glacier has receded from its Little Ice Age maximum. The remnant ice is to the north and west, between Gunsight and Edwards Mountains.
• Sperry is probably the glacier in the park with the strongest climate signal and the least noise from local topography. Nonetheless, local terrain and climate are still strong influences. The largest contribution to accumulation is winter snowfall, but avalanching below rock walls/ slopes on its east and south sides (< 50% of upper perimeter) is still an important process in the accumulation regime. Similarly, shading by the rock wall appears to influence ablation rates during the summer.
• Its configuration allows straightforward longitudinal profiles for mass balance measurements.
• Its flow and area are not disrupted by icefalls or proglacial lakes that cause calving.
• There is a large elevation change between terminus and bergschrund (~300 m).
• It is drained by several streams which do not join until after falling out of the hanging valley, making streamflow measurements difficult.

Previous research and monitoring:

Sperry has one of the most extensive records of historic data and measurements in the region.

• Johnson (1980) includes a detailed topographical map of the glacier with terminus locations from 1913-1969. Other studies at the time include ablation stakes and flow direction and rate estimates.
• Carrara (1987) dated ash in the terminal moraines using C14 dating.
• Key, et al (2002) used remote sensing (Landsat) to document recession of Sperry Glacier.
• Manly established control points for soft copy/ remote sensing in 2001.
• The USGS Glacier Field Station mapped the glacier terminus in Sept. 2003
• The USGS Glacier Field Station has repeated numerous historic photos of the glacier.

Accessibility:

• Sperry is accessed by a 16 km trail running from Lake McDonald Lodge to an observation point just above the glacier terminus. The distance makes day trips for field work difficult.
• The glacier is not heavily crevassed, can be accessed from almost anywhere along its broad terminus, and allows straightforward travel in most places below the bergschrund.
• A cabin and other park facilities at Sperry Chalet (5 km SW) provides a base for extended trips. Park horsepackers regularly supply Sperry Chalet from the spring through early fall, allowing for transport of field gear much of the distance.
• Access to and travel on the glacier is relatively free of avalanche hazard in late spring.

Measurements (year completed):

• Mass balance measurements (2005, 2006)
• Ice radar measurements of depth (2005)
• GPS velocity measurements and elevation profile(s) (2005)
• Installation of weather station for measuring meteorological data (June, 2006)
• Continued repeat photography (ongoing since 1998)
• GPS mapping of margins/ terminus (2003, 2005)
• Remote sensing (1998)