Landslides in Pennsylvania through time and space

Delano, Helen L., DCNR, Pennsylvania Geological Survey, 3240 Schoolhouse Road, Middletown, PA 17057

Slope failures have shaped Pennsylvania's landscape at least since the Pennsylvanian Period, and Pleistocene-age landslides are at the roots of many modern slide problems within the Commonwealth. Ancient rock slumps and debris flows, believed to have been triggered by both Pleistocene climate conditions and river erosion, are known across much of the state. The presence of extensive deposits of colluvium throughout Pennsylvania demonstrates the effectiveness of mass-wasting processes.

The most active area for modern landslides is in the Appalachian Plateau in southwestern Pennsylvania. Here, Pennsylvanian and Permian cyclothemic sedimentary rocks, slopes steepened by Pleistocene downcutting of major rivers, and human activity in the Greater Pittsburgh urban area combine to provide root causes and triggers for landslides both large and small.

Other conditions producing significant areas of recent slide activity are: valleys across northern Pennsylvania that are floored with glacial lake clays; thick colluvial deposits near the Wisconsinan glacial border; weathered rock and colluvium of the Devonian Catskill and Mississippian-Devonian Huntley Mountain Formations across north-central Pennsylvania; and glacial and lacustrine sediments in the Lake Erie bluffs. Rockfalls and rockslides can occur in any steep-slope setting, especially in artificial cuts. Debris avalanches are known to have occurred on steep slopes across many geologic units, but historic occurrences are less common than in the Appalachians south of Pennsylvania.

As human activity and development increase in rural and mountain areas, landslides will become a more serious social and economic issue in parts of Pennsylvania where they have previously received little attention.

Poster paper presented at the Annual Meeting of the Geological Society of America, Reno, NV, November 2000.

Reference:

Helen L. Delano, 2000, Landslides in Pennsylvania through time and space, Abstracts with Programs - Geological Society of America. V 32; No 7, p. A-57.