Areas of Pennsylvania Susceptible to Landslides
Southwestern Pennsylvania has by far the highest concentration of landslides, but much of the state has susceptible areas. Landslides occur primarily in colluvial (loose) soil and old landslide debris on steep slopes. Most major and minor highways have sections cut in rock or soil that can fail. Steep mountain slopes across the state have experienced debris avalanches associated with extreme rainfall or rain-on-snow events. Glacial and glacial-lake sediments underlie stream bank and lake bluff slumps and other failure areas across the much of the northern part of the state. Outside the southwest, high susceptibility areas are smaller and have more varied geology and topography.
Urban and rural land development is increasing both the number of landslides and the economic effects of natural slides. Major highway construction with large excavations and fills located in mountainous areas creates potential for many landslides.