Revised glacial margins and Wisconsin meltwater paleoflood hydrology in Slippery Rock Creek Basin, central western Pennsylvania

Glacial margins mapped in Slippery Rock Creek basin during the 1950s are problematic. The number of sedimentological, mineralogical, petrological, and textural analyses used to distinguish glacial drifts in the southern portion of the basin were inadequate to resolve the margins. Furthermore, misidentification of man-made deposits as glacial drift led to erroneous interpretations regarding the extent and character of pre-Wisconsin glacial deposits, and appears to have influenced subsequent soil mapping.;Canadian Shield erratic weathering was the primary tool used in this study to re-investigate the glacial margins. Erratics display one of three distinctive weathering rinds, so glacial deposits can be differentiated into three relative age classes, with rind thickness clusters of <2mm, 3--5 mm, and >6 mm. Similar weathering rinds have been reported in soils associated with Wisconsin, Illinoian, and pre-Illinoian stream terraces.;More than 500 locations were examined in order to remap the glacial margins. Prior to this study, Frank Leverett published the most accurate margins in 1934. The glacial maximum is Wisconsin in age southwest of West Liberty, but Illinoian in age northeast of West Liberty. No surface pre-Illinoian glacial deposits occur in Slippery Rock Creek basin.;HEC-RAS paleoflood models were developed to investigate the role of proglacial lake outburst flooding in the glacial history of the basin. This study suggests the proglacial lakes drained slowly rather than by catastrophic dam bursts. In fact, meltwater discharges may not have exceeded rainfall floods of record.;This research developed a flow competence approach for reconstructing realistic flow discharges that are more consistent with fluvial deposits. This approach reduced the magnitude of the maximum potential meltwater flood in Slippery Rock Creek from 38,000 m3/s (1,300,000 ft 3/s) to 380 m3/s (13,000 ft3/s). Restricting the HEC-RAS flow models by flow competence data should be considered for any paleoflood that deposited coarse-grained sediments. Another technique of restricting the HEC-RAS models, using non-inundation surfaces as proxies for the water surface elevation, reduced modeled discharges in three other streams by approximately one order of magnitude.