GLACIERS OF THE AMERICAN WEST

 

Scientific study of the glaciers in the American West (exclusive of Alaska) did not begin until September 1871 when glaciers were first “discovered” on Mt. Shasta, California by the King Expedition sponsored by the War Department.  Only six states have appreciable glacier cover (Colorado, Wyoming, Montana, California, Oregon, and Washington), most of which occur in National Parks. Glaciers cover about 587.4 km² of the American West as of about 1960, of which about 71% are located in Washington State.  The largest glacier is Emmons Glacier on Mt. Rainier, 11.2 km².  The average size of a glacier (those that exceed 0.1 km²) in the North Cascades National Park, one of the most heavily glaciated regions of the west, is 0.37 km².

 

Glacier altitudes rise with decreasing latitude as one would expect with warmer climates to the south.  Generally speaking the glaciers in the northwestern part of the US West are more numerous and exist at lower elevations (~2000 m) compared to glaciated areas in the drier regions to the southeast (Wyoming, Colorado) and the warmer regions to the south (California), ~3000 m.  Glaciers in Montana, which is drier than the Northwest, but cooler than the northwest, are about ~2500 m. 

 

In the past few decades the glaciers have been receding, continuing a trend from the Little Ice Age.  The magnitude of area shrinkage varies.  For the North Cascades National Park (Washington), between 1957 and 1997 the shrinkage of 321 glaciers averaged 7%.  For about the same period of time in Glacier National Park (Montana) the shrinkage for two glaciers was about 33%.  This range in values seems to be broadly consistent with changes elsewhere in the west.

 

Detailed measurements of glacier mass balance from South Cascade Glacier, located in the North Cascades of Washington show a general mass loss and retreat since 1958, the start of observations.  The mass loss accelerated starting in 1976 due to a change in atmospheric circulation patterns which reduced winter snow accumulation and reflects in the global trend of mass balance variation.