TOPOGRAPHIC EXPRESSION AND SHALLOW SUBSURFACE ARCHITECTURE OF THE GREAT ESKER, WEYMOUTH, MASSACHUSETTS

Great Esker of Weymouth, Massachusetts, is situated by the southerly border of the Boston Basin and was formed during the retreat of continental ice sheets between 16,000 and 23,000 ybp. The easterly side of the esker is flanked by the Weymouth Back River, a coastal estuary; the westerly side is bounded by anthropogenic development. Currently the esker is preserved as a Town of Weymouth recreation area and hosts over 9 kilometers of recreation trails that cap the localized braided system of eskers.

The esker, and its previous incarnations, are relatively well preserved making it ideal for a study of glacio-depositional frameworks. The study determines episodes of esker building via interpretation of the resultant shallow sub-surface stratigraphy, the linear chronology of such episodes, and the subsequent reworking of the relict features by modern processes.

The team deployed ground penetrating radar (GPR) to determine the subsurface architecture of Great Esker and its contact with surrounding features. The GPR was coupled with realtime kinetic global positioning system (RTK-GPS) equipment for horizontal and vertical control. The data was post-processed and imported into a GIS framework for spatial analysis and integration of LIDAR data, aerial photogrammetry, and surface topography.

The general orientation of the esker suggests a glacial equipotential plane that orients to the southwest and is in contradiction with the southeasterly alignment suggested by other glacial features, such as the Boston Harbor drumlin field, in the immediate area. The contradiction in direction suggests a major change in the position and progression of the Southeastern Massachusetts, the Cape Cod, and the Narragansett Ice Lobes during the down-wasting associated with glacial retreat approximately 18,000 ybp. Analysis of chatter marks, striae, and erratica fields localized to the esker demonstrate a chronological change in local ice control from continental ice dome to localized topography which corresponds well with the equipotential planes suggested by Great Esker. Spatial analysis reflects multiple periods of esker activity and contemporaneous surrounding structures coupled with erosion by adjacent coastal processes. Analysis of GPR data are in progress and interpretations are pending.