REGIONAL ICE FLOW DIRECTIONS ACROSS NEW HAMPSHIRE AND WESTERN MAINE

LiDAR based DEMs provide an extraordinary view of the landscape that enable the identification of a suite of linear ice flow features. These range from small scale flutes and grooves to larger drumlinoid forms. In this study approximately 4000 features were mapped in New Hampshire and western Maine. This data was then processed to yield both regional ice flow directions as well as relative feature density.

The landform data was processed within a Geographic Information System (GIS) to create both a regional ice flow map and a map showing how those features are clustered across the region. A tessellation grid of 25 km²hexagons was overlain on the line data depicting the long axis of individual features. Linear directional means were calculated for all the features within each tessellation cell and marked by flow arrows. Cluster analysis was performed by linear density analysis within the tessellation cells and is reported in units of meters per unit area (km²).

Cluster analysis shows that the features tend to form in “fields” just like drumlins, while they are lacking in both mountainous terrains and areas affected by the marine transgression. There are many linear ice flow features in the valleys of the western Maine mountains and they indicate that ice flowed undeflected from NW to SE through the mountains, but on emerging from the mountains flow turned to the south. In contrast, the higher peaks of the White Mountains caused approaching ice to diverge around the Presidential Range especially as the iced thinned. Downstream the ice converged in the lee of the Sandwich Range and in the late stages, it pushed northeastward up the backside of Whiteface Mountain. There is evidence here that the ice direction shifted from an earlier NW to SE direction to a late SW to NE direction. This suggests that as the ice thinned and the mountains dammed the ice, the glacier was still able to maintain active flow as it flowed around the sides and filled the area behind the mountains. Alternatively, it may be that this late-stage push to the NE was driven by a readvance that pushed ice into the area from the west, perhaps associated with the Charlestown Readvance (14.7 kyr BP) in the Connecticut Valley. In any case it is clear that these linear features do not all form at the same time and therefore we should exercise some caution in interpreting the results.