DRAINAGE DERANGEMENTS FROM GLACIAL DEPOSITION ON THE APPALACHIAN PLATEAU IN NORTHEASTERN PENNSYLVANIA

On the glaciated Appalachian Plateau of Northeast Pennsylvania, thick glacial deposits often cause drainage derangements. Near the late Wisconsinian terminus in Sullivan County, Pennsylvania there are two abnormalities in the drainage pattern that were examined to see if they are related to glacial deposition. At one site, the head of west-draining Falls Run begins with a gentle gradient, and then makes a near 90 degree turn southward just before plunging down 60 ft. Angel Falls. Where Falls Run turns south is the head of a west draining stream that continues the trend of the Falls Run. A second drainage anomaly is where the broad valley of west-draining Rock Run turns abruptly southward and becomes a narrow, deep valley with a series of waterfalls. At that location a deep saddle continues the west trend of Rock Run and is the head of west-draining Brunerdale Run.

First the glacial deposits in the area around the drainage abnormalities were mapped. A preliminary glacial deposit map of the area was created from an interpretation of the existing soil map. Then the preliminary map was revised by field mapping. The glacial deposit map confirmed that till of considerable but unknown thickness was present at both sites where the streams made abrupt turns.

To determine till thickness at the Angel Falls site, two seismic refraction profiles were shot. One profile was done immediately north of the abrupt turn and the other 300m to the west of that. Both seismic profiles indicate that approximately 50m of till buried a west trending valley, the pre-glacial Falls Run course. The till mass is higher than a saddle in the ridge on the south side of Falls Run and thus diverted the stream southward over the saddle, forming Angel Falls.

To determine the thickness of the till present at the Rock Run anomaly, a single seismic profile was done. This array stretched across the saddle between Rock Run and Ogdonia Creek and revealed a minimum till thickness of 55m. This thick mass of till partly filled the previous west trending course of Rock Run and diverted the stream over a saddle in the ridge to the south. This caused the incision of a new deep, narrow valley to the south by Rock Run.