USING GLACIAL DISPERSAL PATTERNS TO UNDERSTAND THE SPATIAL DISTRIBUTION OF SUBGLACIAL QUARRYING

Quarrying in the subglacial environment produces coarse-grained sediment, maintains bed roughness, and creates tools for abrasion. Despite the importance of the process, much remains unknown about the basic mechanics, controlling mechanisms, and rates of quarrying. Determining the large scale spatial distribution of quarrying along a flowline is a vital step in understanding the relationship between process mechanics, ice dynamics, and the geologic record.

Three linear functions for the spatial distribution of quarrying along a flowline were tested using glacial dispersal patterns preserved in the glaciated valleys in the Sawatch Range of Colorado and in the Appalachian Ice Complex of the South Mountain Batholith region of Nova Scotia. The functions are simple forms of three unique distributions; a distally increasing case where quarrying is concentrated in the marginal area, a distally decreasing case where quarrying is concentrated at the beginning of the flowline, and a constant case where quarrying is uniform along the flowline. Computer models were developed to predict dispersal patterns based on the spatial distribution of quarrying, the bedrock distribution, and the flow history of the study areas. Modeled dispersal patterns were statistically compared to observed patterns to identify the best fit.

The distally increasing distribution of quarrying was found to best predict the dispersal patterns of both study areas. Dispersal patterns in the Sawatch Range were found to be created during the advance phase with minor modification during the retreat phase. Dispersal patterns of South Mountain Batholith areas were found to be the result of the last phase of glaciation with little inheritance from previous phases. The agreement between the valley glacier study and the ice complex study suggests that the glaciological controls on quarrying or that the quarrying mechanisms are independent of the size of the ice mass. The increasing intensity of quarrying in the marginal area is likely due to increased frequency and magnitude of water pressure changes in subglacial cavities.