Developing a Chronology for Thinning of the Laurentide Ice Sheet in New Hampshire During the Last Deglaciation

• Main Author: Hodgdon, Taylor
• Format: Text
• Language: unknown
• Published: University of New Hampshire Scholars' Repository 2016
• Subjects: 10Be; Dating; Exposure; Ice; Laurentide; Thinning; Geology; Ice Sheet
• Online Access: https://scholars.unh.edu/thesis/873; https://scholars.unh.edu/cgi/viewcontent.cgi?article=1872&context=thesis

Well-constrained ages for the retreat of the Laurentide Ice Sheet (LIS) have been developed at key sites throughout New England, providing a framework for the deglacial history of the region. Previous work has focused primarily on documenting retreat of the ice sheet margin, but few studies have attempted to reconstruct changes in ice sheet geometry and flow patterns during its recession. This study provides the first direct age control on the thinning of the LIS in central and southern New Hampshire during the last deglaciation. In situ cosmogenic 10Be exposure ages were developed from four glaciated summits, in order to determine when each mountain top emerged from the ice as it thinned. Exposure ages indicate the southernmost summit in the study (Mt. Monadnock) was exposed at 15.4 ± 0.2 ka, and the northernmost peak (Mt. Dickey) was exposed at 13.1 ± 0.2 ka. This age range supports a period of rapid ice surface lowering in New England. Striation measurements collected both from this study and previously published literature were analyzed to observe how ice flow patterns evolved in this region. The striations at the lowest elevations display a wider azimuthal range than those found at the highest elevations, indicating the development of strong topographic control on ice flow as thinning occurred. Three-dimensional ice sheet surfaces were modeled to display changes in ice sheet geometry, and suggest an increased rate of thinning from 1 m/yr to 2 m/yr at ~15 ka coinciding with the start of the Bølling Allerød warm period. This study provides valuable new insight on LIS thinning and flow patterns in New Hampshire and suggests potential links between changes in ice sheet geometry and regional paleoclimate forcings.