20th-century variations in area of cirque glaciers and glacierets, Rocky Mountain National Park, Rocky Mountains, Colorado, USA

Abstract

Comparison of historic maps and aerial and ground-based photographs for the small cirque glaciers and glacierets of Rocky Mountain National Park in the northern Front Range of Colorado, USA, indicates modest change during the 20th century. The glaciers retreated through the first half of the 20th century, advanced slightly from the mid-1940s to the end of the century and have retreated slightly since. High interannual variability in area and temporal gaps in data complicate the trends. Local climate records indicate a lack of systematic change between 1950 and 1975, but significant warming afterwards. Local topographic effects (e.g. wind redistribution of snow and avalanching) are important influences. These small glaciers respond to changes in regional climate; summer temperature alone is a good predictor of the mass balance of Andrews Glacier (r= -0.93). Spring snowfall is also an important factor. That winter precipitation is not statistically significant supports the notion that these small glaciers gain much snow from wind drift and avalanching, making winter snow accumulation almost indifferent to variations in direct snowfall. Less than expected glacier retreat may be due to increased summer cloudiness.