Geospatial analysis of controls on subglacial bedform morphometry in the New York Drumlin Field - implications for Laurentide Ice Sheet dynamics

摘要

The outline and trend of 6566 subglacial bedforms in the New York Drumlin Field have been digitized from digital elevation data. A spatial predictive model has been used to extend values of bedform elongation over an area measuring 200 km x 110 km. The resulting surface is used in conjunction with depth-to-bed rock data and an assumed duration of ice residence to test three proposed controls on bedform elongation. Upon comparison, the resulting display of morphometry is best explained by differences in ice velocity across the field of study. The existence Of Multiple zones of fast-moving ice located along the southern margin of the Laurentide Ice Sheet is implied by the observed patterns of bedform elongation and orientation. We present two interpretations that are consistent with the observations. First, enhanced basal sliding caused by decreasing effective pressure near a calving margin is suggested as a possible mechanism by which localized fast ice flow is initiated and maintained. Second, topographically controlled ice streams likely occupied the fjord-like troughs of the Appalachian Upland northern rim. Contrary to previous understanding of the Laurentide Southern margin in New York State, the resulting palaeoglaciological reconstruction illustrates a dynamic mosaic of ice stream and/or outlet glacier activity.