DEVELOPING A CHRONOLOGY FOR THINNING OF THE LAURENTIDE ICE SHEET IN NEW HAMPSHIRE DURING THE LAST DEGLACIATION

Well constrained ages for the retreat of the Laurentide Ice Sheet have been documented at key sites throughout New England, providing a framework for the deglacial history of the region. Previous work has focused primarily on retreat of the ice sheet margin, but few studies have attempted to reconstruct changes in ice sheet geometry during its recession. This study provides the first direct age constraints on the thinning of the Laurentide Ice Sheet in central and southern New Hampshire during the last deglaciation. In situ cosmogenic ¹⁰Be exposure ages are being developed from five glaciated peaks distributed widely across the study region, in order to determine when each mountain top emerged from the ice as it thinned. A suite of samples has been collected from the summits of Mt. Major, Kearsarge, Cardigan, Dickey, and Monadnock. These peaks were selected based on their exposed bedrock, preservation of striated landforms, rock type, and position within the region. The exposure ages will be paired with striation orientations measured from each dated surface and adjacent summit areas. These data will then be coupled with previously mapped ice flow indicators throughout the region to observe how ice flow patterns evolved in this part of New England as the ice thinned and became topographically confined. This study will provide valuable new insight on potential links between past changes in ice sheet geometry and regional paleoclimate forcings and events.