POST-LATE WISCONSINAN GLACIAL CIRQUE ACTIVITY, PRESIDENTIAL RANGE, NEW HAMPSHIRE

It’s been long assumed that local climate in this region warmed very rapidly after the last glacial maximum, promoting rapid rise of cirque equilibrium line altitudes (ELA) and eliminating residual ice masses. However, emerging climate proxy studies suggest the initial rate of this of warming was less dramatic and that near-glacial conditions and lower ELA’s persisted, permitting favorably located residual ice masses to linger and possibly reactivate.

Recent mapping suggests such ice masses existed in the Tuckerman, Huntington, King, Castle, and Great Gulf cirques. Clast provenance and deposits below the first four suggest massive episodic debris flows resulted from rapid melting of such masses, while deposits below the Great Gulf suggest possible reactivation of a very large residual mass within its enormous, northerly-oriented catchment.

Two features in and below this cirque display distinct cross-valley morphology and hummocky surfaces strewn with very large unweathered boulders of lithologies typical of the cirque walls. Their locations, topography, and aprons of abandoned down-cirque distributary drainage suggest they may be post-Late Wisconsinan morainal features. Their gravelly deposits could not have survived overriding erosion, and the local provenance, angularity, and lack of striations on their boulders suggest only short-term entrainment in moving ice. The provenance of clasts near their limits suggest they have been superimposed on deposits from earlier glaciation.

Proposals these features were emplaced by readvance or local wasting of Late Wisconsinan ice are not well-supported. Mapping below them and to the north has failed to detect evidence of local readvance, and clast provenance study has failed to detect elevated percentages of rock types from the valley to the north over which readvancing ice would have passed. Mapping has also failed to locate randomly positioned drainage patterns typical of stranded masses of wasting ice. More work is needed to firmly establish the genesis and climatic significance of these interesting features.