Glaciers contain about three quarters of the world’s fresh water and cover about 75,000 square kilometers of the U.S. The United States Geological Service (USGS) has been running the Benchmark Glacier program since the late 1950s to track glacier mass balance. Repeat measurements at four selected sites are used in conjunction with local meteorological and runoff data to measure the glaciers’ response to climate change.
Results from South Cascade Glacier in Washington and Gulkana and Wolverine glaciers in Alaska provide the longest continuous record of North American glacier mass balance. In 2005, Sperry Glacier in Montana was added to the program, allowing changes in glacier mass in the principal North American climate zones to be tracked.
South Cascade Glacier in Washington experiences some of the highest precipitation levels in the lower 48 states of the USA, exceeding 4500mm per annum in some places. Data was first collected from this glacier in 1959.
Gulkana Glacier can be found along the southern flank of the eastern Alaska range. It experiences a continental climate, with large temperature ranges and precipitation that is more irregular and lighter than that experienced in coastal areas.
Wolverine Glacier is also located in Alaska, but is found in the Kenai Mountains on the coast. The maritime climate has low temperature variability and regular, heavy precipitation. Data collection at both Gulkana and Wolverine glaciers began in 1966.
Sperry Glacier is located in the Lewis Range of Glacier National Park in Montana. The climate of the region is influenced by both maritime and continental air masses, but Pacific storm systems dominate. These systems result in moderate temperatures and heavy precipitation, which vary strongly with altitude.