Benchmark Glacier: Sperry

Science Center Objects

Sperry Glacier was chosen as the benchmark glacier for the glacier monitoring studies, due to the combination of its topographic characteristics, historic data, and access. Annual mass balance measurements began in 2005. Sperry Glacier joined the long-established USGS Benchmark Glacier Research program in 2013 where common field and analysis methods enable regional comparison and improved understanding of glacier response to climate change.

Sperry Glacier margins 1998, 2005, and 2015.

Sperry Glacier margins 1998, 2005, and 2015.
(Public domain.)

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 m) 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.
  • 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.


  • 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 (Annual, 2005 - current)
  • Ground penetrating ice radar (2005, 2008, 2017)
  • 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, 2005, 2007, 2013)
  • Remote sensing (1998, 2003 - current)