Environmental Geology
Report 9

Landslide Susceptibility in the Williamsport 1- by 2-Degree Quadrangle, Pennsylvania eg9cover


Landslides are a widely recognized engineering hazard in southwestern Pennsylvania, but the threat they pose elsewhere in the state is generally underestimated. Landslide Susceptibility in the Williamsport 1- by 2-Degree Quadrangle, Pennsylvania, released by the Pennsylvania Geological Survey in 1999, is a comprehensive study of the physiographic, geologic, and topographic aspects of natural and man-induced slope movements in an approximately 7,150-square-mile area of highly varied geologic structure, topographic relief, and population density in north-central Pennsylvania. Particularly common landslide types in the report area are debris slides and flows, slumps, rockfalls, rockslides, and a combination of various types. Many of the large slumps and debris flows occur in the glaciated, northern part of the quadrangle, particularly where roads and streams cut into slopes containing glacial-lake clays.

Though landslides in the Williamsport quadrangle (in contrast to those in the vicinity of Pittsburgh) have not caused any known fatalities and usually damage highways rather than homes, the fact that more than 1,300 recent and older landslides were recognized in an aerial-photograph inventory of about 63 percent of the report area shows that the hazard is certainly enough to warrant attention. This inventory and detailed analysis of 13 slides representative of slide types and geology across the area are the basis for determination of three zones of landslide susceptibility—high, moderate, and low—shown on a 1:250,000-scale map.

Environmental Geology Report 9 is authored by Helen L. Delano (staff geologist) and J. Peter Wilshusen (deceased; former chief of the Bureau’s Environmental Geology Division). The report is comprehensive in its geologic descriptions, and yet written for a lay audience. The text is heavily illustrated with 81 maps, photographs, and line drawings, and there is an appendix containing 98 page-sized quadrangle maps on which all the landslides noted and describe in the inventory are located. A short glossary of pertinent geologic terms is included to assist nongeologists in understanding the text.

Environmental Geology Report 9 was selected to receive the John C. Frye Environmental Geology Award for 2000. This award is given annually to the best paper on environmental geology published by either the Geological Society of America or one of the state geological surveys.

This report is available from the State Bookstore website. The price is $16.00 plus a shipping fee and sales tax as noted. Please use the link below for further information on ordering.

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