THE DEGLACIATION SEQUENCE AND CORRELATION OF MORAINE COMPLEXES IN THE NORTHERN WHITE MOUNTAINS, NEW HAMPSHIRE, USING LIDAR IMAGERY

A belt of prominent moraines in the northern White Mountains includes, from west to east, the Littleton-Bethlehem, Beech Hill, Randolph, Berlin, and Androscoggin moraine complexes. Recent studies support an Older Dryas age (ca. 14 cal ka) for the Littleton-Bethlehem and Beech Hill moraines. Moraine orientations and the sequence of associated ice-dammed lakes show that the Randolph moraines are the same age or slightly older, but the deglaciation chronology farther east remains uncertain. Thompson et al. (2007) proposed correlation of the Randolph complex with the Berlin moraines in the Upper Ammonoosuc River basin. However, Bromley et al. (2013) obtained ¹⁰Be cosmogenic ages of 12.9-14.1 ka with a mean of 13.5 ± 0.5 ka from boulders on the Androscoggin Moraine complex, located southeast of Berlin on the Maine-Hampshire border. These ages mostly postdate the Older Dryas and suggest a younger age for the more proximal Berlin moraines. Our study points to a different conclusion. Lidar imagery from the northern part of the White Mountain National Forest reveals additional moraines in the Berlin complex and other features that clarify the deglaciation history of this densely forested area. The landforms described here were further verified by field-checking lidar targets. The earliest and highest part of the Randolph complex is a large moraine just west of Pond of Safety in Randolph, deposited by a SE-flowing ice tongue occupying the Israel River valley. A network of meltwater channels draining northeast from this ice-margin position carried water and sediment into the Upper Ammonoosuc basin, where a composite delta built northward into a glacial lake. The terraced and locally kettled delta top records a water level that dropped in elevation from ~ 582 m to 564 m, corresponding to successive closely-spaced spillways for this multi-stage lake known as glacial Lake Crescent (Thompson and Svendsen, in prep.). Lake Crescent was dammed by the SW-flowing ice tongue that deposited the Berlin moraines and formed contemporaneously with the latter moraines. We conclude from these relationships that the Randolph and Berlin moraines are coeval. They were deposited in Older Dryas time or even earlier. Moreover we expect the Androscoggin Moraine complex, given its position in the context of regional ice retreat, to be older still.