Abstract

A deductive analysis of the processes responsible for cirque formation leads to a model that describes cirque development through time. In this model, cirque volumes increase as the third power of time, although observed variations in cirque size also reflect pre-glacial erosion, as well as the average rate of surface recession/lowering.

The deductive findings are extended via analysis of 23 cirques from a part of the Sangre de Cristo Mountains, south-central Colorado. The assumption that glacier-occupance times are proportionately adjusted to topoclimatic situation leads to the conclusion that average rates of cirque erosion exhibit at least a fourfold (possibly as much as an order of magnitude) range within a given massif. The notion that cirque-development rates depend on bed-rock resistance is supported by a statistically significant inverse relationship between estimated erosion coefficients and average bed-rock joint spacing.

Allometric analysis of a 15-cirque subsample (the cirques were chosen because they exhibit similar erosion susceptibility) lends credence to the hypothesis that headwall recession has been more rapid than cirque-floor lowering within the study area. However, allometric enlargement cannot by itself account for observed values for the ratio cirque length:cirque depth. The results imply that pre-glacial topography strongly influences observed variability in glacial morphometry.

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