EFFECT OF HIGH-RELIEF TOPOGRAPHY ON DEGLACIATION ICE-FLOW PATTERNS, PHILLIPS 7.5’ QUADRANGLE, WEST-CENTRAL MAINE

The Phillips 7.5’ Quadrangle, west-central Maine, is underlain by Devonian intrusive and phyllitic rocks of the Appalachian Mountain belt and is located above the Wisconsinan marine limit. The Sandy River flows approximately east-west through the Phillips Quad. Mt. Abraham, a topographic high with 960 m of relief, is directly north of the Phillips Quad. Spruce Mtn. and Day Mtn. are NE-SW-trending ridges that rise 370 m above surrounding areas in the southern part of the quad.

Striae in the highest parts of the area indicate that Late Wisconsinan ice covered the entire landscape. We measured 81 groove, striae, and crag and tail sets in the Phillips Quad region during summer 2002 to study topographic effects on ice-flow directions during deglaciation. Striae data were sorted into four size categories, ranging from large grooves to small, inconspicuous striae, and also separated into two geographical categories (either north or south of the Sandy River). In the northern section, rose diagrams show an ESE trend (116° azimuth vector mean) for the largest grooves/striae that formed during ice-flow maximum. Smaller striae show a more easterly flow direction of 102°. In the southern area, grooves and the largest striae have a mean orientation of 133°, more typical of the regional ice-flow direction in this part of Maine. Smaller, less distinct striae indicate ice flow more toward the east (vector mean of 108°, and some striae indicate flow to the ENE). From this data we infer that during the Late Wisconsinan glacial maximum, some ice flowed SE directly over Spruce and Day Mountains. However, Mt. Abraham to the north and Mt. Blue, Spruce Mtn., and Day Mtn. to the south also funneled ice eastward down the east-west-trending Sandy River valley during the glacial maximum. As ice thinned and wasted back, flow was deflected around the mountains. Cross-cutting striae indicate a 47° change in flow direction from SE to ENE on the northeastern flank of Spruce Mtn. Thus, flow indicators record the increasing impact of land-surface topography on ice-flow directions as deglaciation progressed. The smallest striae would have formed beneath active ice that was moving slowly (perhaps at rates of a few meters per year) near the end of the deglaciation sequence.

This study was funded by the Maine Geological Survey and the USGS STATEMAP program.