LANDSLIDE RISK ASSESSMENT IN THE MOUNTAIN STATE OF WEST VIRGINIA: BROAD-SCALE GEOLOGIC AND PHYSIOGRAPHIC INFLUENCES ON LANDSLIDE SUSCEPTIBILITY AND SLOPE FAILURE TYPES

The West Virginia Landslide Risk Assessment has been supported by the FEMA Hazard Mitigation Grant Program and the West Virginia Division of Emergency Management since 2018. A landslide inventory component was created by mapping landslide head scarps using 1 or 2 m LiDAR-based DEMs that exist for >60 % of the state. This mapping methodology yields results that differ from other inventory approaches.

Comparison of 41,730 LiDAR-mapped landslide initiation points to >463,000 randomly selected non-landslide points indicates geologic map units have strong relationships with both landslide susceptibility and prevailing types of slope failure. NRCS Major Land Resource Areas (MLRA), used as proxies for physiographic divisions, show >10-fold variability in landslide susceptibility and even more variability in the abundance of debris flows and lateral spreads. The role of geologic units may differ from one MLRA to another, reflecting lithologic changes within a unit, a unit’s position on the landscape, or anthropogenic land use.

With few exceptions, overall landslide susceptibility is highest in units comprised of shale interbedded with sandstone, commonly located in steep topography held up by adjacent sandstone units less prone to failure. The most susceptible units appear to be the Conemaugh, Monongahela, and Dunkard groups in the Central Allegheny Plateau, where an average of 3.2 landslides/km² were mapped. In the Cumberland (Logan) Plateau, where mapping identified 1.8 landslides/km², the Kanawha Formation is the most slide-prone and most debris-flow-prone unit, because of widespread mining regolith developed on the coal-bearing unit. Southern Allegheny Mountain (1.1 landslides/km²) slides and debris flows are most abundant in the Hinton, Bluestone, and Princeton formations at the top of the Mauch Chunk Group and the Pocahontas Formation. Of a statewide total of 312 mapped lateral spreads, 247 were in sandstone-dominated members of the New River or Bluefield formations in the Southern Alleghenies. Northern Allegheny Mountain (0.5 landslides/km²) slides are most abundant in the Chemung and Mauch Chunk groups. Although the Ridges and Valleys MLRA includes many large landslides and long-runout debris flows, mapping revealed only 0.19 landslides/km², concentrated in shaley units adjacent to ridge-forming units like the Tuscarora, Oriskany, and Pocono sandstones.