DO LONG SUBGLACIAL BEDFORMS INDICATE FAST ICE FLOW? - A CASE STUDY FROM NEW YORK

Although drumlins and other subglacial bedforms are well-studied features, controls on their formation and morphometry have remained elusive. Of current interest is the hypothesis that long bedforms (length:width ratios >=10) indicate fast ice flow, and perhaps the location of past ice streams. The research presented here explores this hypothesis by analyzing drumlins from the New York drumlin field. A subset of 548 drumlins between Oneida Lake and Lake Ontario was digitized using 10-m grid cell digital elevation data. Drumlins were grouped into three zones between 0 and 18 km, 18 and 48 km, and 48 and 88 km down a flowline from Lake Ontario. Each zone has a central area with drumlin elongation ratios >10 bounded by areas to either side with elongation ratios <10. The width of these central areas in each zone decreases down flowline from 18.3 to 14.1 to 8.6 km. The average elongation of drumlins within the central areas increases down flowline from 8.1±3.7 to 10.5±4.9 to 12.9±5.9, whereas average elongation outside of the central areas remains roughly constant (3.9±1.3 to 4.3±2.2 to 3.6±1.2). Because drumlin elongation increases down flowline and does not seem to relate to surficial geology, elongated drumlins are best explained by fast ice flow. The swath of elongate drumlins between lakes Ontario and Oneida, which does not coincide with topography, may signify the location of a deglacial-age ice stream.