21 Formation Processes and Characteristics of Subglacial Bedforms beneath the Ice Sheets of Continental North America

Friday, 28 March 2008
8:00 AM - 10:50 AM

INVESTIGATING CONTROLS ON SUBGLACIAL BEDFORM MORPHOMETRY IN THE NEW YORK DRUMLIN FIELD – IMPLICATIONS FOR LAURENTIDE ICE SHEET PALEODYNAMICS

Paper number: 21-7
Program: THEME SESSIONS
Time: 9:50 AM – 10:10 AM

Authors

Abstract

Reconstructing the location of former ice streams has received increased attention due to their role in ice sheet response to climate change. Analysis of subglacial bedform morphometry provides crucial information regarding ice sheet behavior. However, the processes responsible for the formation of subglacial bedforms (e.g., drumlins, flutes, mega-scale lineations) have remained enigmatic over decades of research. Similar to the lack of consensus regarding formation processes, the factors that control bedform morphometry (e.g., length, width, height) remain elusive. Several previous studies have identified the velocity of overriding ice as the primary control on bedform elongation (length/width). Other studies have concluded that the time available for bedform creation and modification along with constancy in ice flow direction are critical to determining the resulting shape. In addition, recent work hypothesized that the thickness of unconsolidated sediments upon which bedforms reside is the key control on their elongation. Proper understanding of the underlying mechanism controlling bedform morphometry is required for accurate paleoglaciological reconstructions.

In this study, 6566 subglacial bedforms within the New York drumlin field were digitized from digital elevation data and their dimensions were recorded in a geodatabase. Spatial statistics were used to generate a map of bedform elongation. Depth to bedrock was determined by compiling well log data for three subregions within the New York drumlin field. The results of this study show little correlation between the thickness of deformable sediment and bedform attenuation. Our observations are best explained by differences in ice velocity across the field of study. Flow of continental ice from north to south across the Erie-Ontario lowland confronted the Appalachian upland and dissected its northern edge over multiple glaciations. The most significant clustering of elongate bedforms is generally proximal to the most deeply incised troughs. Elongate bedforms are located north of Seneca and Cayuga Lakes, the largest and deepest Finger Lakes. These observations are supporting evidence that ice velocity is the primary control on bedform attenuation thereby validating the use of bedform morphometry as a proxy for paleo-ice sheet dynamics.