The response of Rae Glacier to climate variations, Canadian Rocky Mountains
Lawby, Carolyn Patricia
The purpose of this research was to document the response of a cirque glacier to historical climatic fluctuations. It focuses on the climatic sensitivity of Rae Glacier, a small cirque glacier located in the front ranges of the southern Canadian Rocky Mountains. Results from field work completed in the summers of 1990 and 1991 are used to describe the physical characteristics and glaciological nature of the glacier. Aerial photographs and field observations are used to develop a retreat chronology and to provide information on historical volumetric ice losses and changes in the areal extent of the glacier. This information is then used along with a proxy mass balance record to evaluate the response of Rae Glacier to historical temperature and precipitation variations. Rae Glacier has down-wasted considerably and its ice front has retreated approximately 530 m since the Little Ice Age. Terminus retreat rates have varied from over 9.5 m/a in the 1940s to less than 2.5 m/a in the 1980s. It is estimated that the glacier presently consists of approximately 9.3 x 107 m3 of ice, which represents a volumetric loss of 75% since the beginning of this century. If the current trend of negative mass balances continues, Rae Glacier is expected to disappear within the next thirty-five years. Four different methods (Memory Length, Volume Time-Scale, Longitudinal Stress Gradient Coupling, and Kinematic Wave theory) are used to calculate the response times of the glacier. Rae Glacier's measured lag time is between 5 and 10 years indicating that a change in mass balance will be seen at the terminus in a relatively short period of time. Computed response times ranged from approximately 40 to 300 years suggesting two separate scales of response. Three of the estimated response times are of the order of decades. The longest response time is derived from the Memory Length method and corresponds to ice residence times in the range of 100 to 1000 years. The results of this research indicate that Rae Glacier is still adjusting to climatic fluctuations initiated at the end of the Little Ice Age. If Rae Glacier is allowed to attain a steady state without another superimposed mass balance change, then the longer theoretical response time calculated in this paper should be observed.