THE POSTGLACIAL RIVERTON STAGE OF GLACIAL LAKE ISRAEL: AN IMPORTANT FEATURE FOR THE OCCUPANTS OF THE ISRAEL RIVER COMPLEX?

This study focuses on the relationship of the proposed postglacial Riverton Stage of glacial Lake Israel in the Israel River Valley of New Hampshire to the Israel River Complex (IRC) archaeological sites on/among till hummocks overlooking the valley (Boisvert et al., 2017). Maps were made in GIS of the Riverton stage and the three previously mapped stages, called Bowman, Pine Knob, and Bailey’s (Thompson et al., 2017), using LiDAR (from the Lancaster E and Jefferson 7.5’ quadrangles) obtained through NH Granit. A wave-cut bench found in the field further confirms the elevation of the Bailey’s Stage spillway and its respective shoreline (Thompson et al., 2017).

Mapping of geomorphologic landscape units in the study area showed three classes: hummocky till (stagnation moraine), smooth till, and what is referred to as lake bottom (even topography in the floor of the Israel River Valley, overlain by alluvium). Spatial patterning of the units was compared to models of Bailey’s and Riverton Stage shorelines made using LiDAR in GIS. Good correlation was found between boundaries of hummocky till and smooth lake bottom and the Riverton shoreline model, while the correlation with the modeled Bailey’s stage shoreline is weaker.

Riverton Stage shorelines were modeled using elevations from a spillway at Riverton, NH, (Thompson, pers comm) after digital extraction of overlying postglacial and anthropogenic gravels from the DEM. Lower and upper spillway elevations bracket the minimum and maximum areal extent of this stage. Radiocarbon dates were obtained from organic material at the top of a layer of postglacial lake sediment and from wood at the bottom of an unknown layer, either postglacial pond deposits or glacial lake clays, (Thompson, pers comm) as well as from cervid bone fragments excavated by Dr. Richard Boisvert from the Jefferson VI site in 2013. These dates help constrain timing of the disappearance of Glacial Lake Israel and determine the relationship of the postglacial Riverton Stage to the occupation of the IRC sites. Riverton Stage models made from the upper spillway elevation show the lake as proximal to the IRC. The existence of this feature in the Israel River Valley had impacts on caribou migration routes, hunting patterns/strategies, and on site usage and material culture at IRC sites (Boisvert, 2012; Boisvert et al., 2017).