Meltwater channel scars and the extent of Mid-Pleistocene glaciation in central Pennsylvania

- Pre-Wisconsin glacial erosion cut high scars into mountains in central Pennsylvania.
- Erosional features record pre-Wisconsin ice positions.
- Scars provide more consistent levels than depositional materials.
- Geospatial modeling of ice-front is compared to published maps.
- Later meltwater carved semicircular scars into bedrock above current drainage.

High-resolution digital topographic data permit morphological analyses of glacial processes in detail that was previously infeasible. High-level glaciofluvial erosional scars in central Pennsylvania, identified and delimited using LiDAR data, define the approximate ice depth during a pre-Wisconsin advance, > 770,000 BP, on a landscape unaffected by Wisconsin glaciation. Distinctive scars on the prows of anticlinal ridges at 175-350 m above the valley floor locate the levels of subice meltwater channels. A two-component planar GIS model of the ice surface is derived using these features and intersected with a digital model of contemporary topography to create a glacial limit map. The map is compared to published maps, demonstrating the limits of conventional sediment-based mapping. Additional distinctive meltwater features that were cut during deglaciation are modeled in a similar fashion.