DISSIMILAR SURFICIAL GEOLOGY MAPS FROM DISSIMILAR APPROACHES TO MAPPING LANDSLIDES ALONG RAIL TRAILS IN NORTH-CENTRAL WEST VIRGINIA

Surficial geology mapping based on LiDAR-derived DEMs provides remarkable insight into Appalachian geomorphology but these maps may be quite dissimilar from those created using conventional tools such as field work, air-photo interpretation, or other forms of remote sensing. The ongoing West Virginia Landslide Inventory is comprised of a variety of mapped landslide polygons and points, including nearly 97,000 landslide initiation points discerned from 1 m or 2 m resolution DEMs covering most of the Mountain State. Although statewide and regional patterns are similar, specific landslide initiation points identified from DEMs seldom match specific landslides polygons shown on maps published between 1975 and 1985 by the West Virginia and U.S. geological surveys (projects that relied heavily on series of air-photos taken over nearly two decades). A six-decade time span from the earliest air photos to the latest LiDAR explains some of the spatial disconnection, but inherent disparities in how well different landscape components are shown by different media appear profoundly important. For example, shallow landslide tracks across vegetated slopes may have obvious air-photo signatures but be indiscernible on a 1 m DEM, whereas forest-canopied high-relief scarps or landslide deposits that are obvious on a DEM may have no clear air-photo signature.

A field mapping and bicycling project covering 100 km along four Monongahela River basin rail trails provides some insight into how to reconcile disparate landslide map data, while adding a bit more disparity. Broad patterns from field work are consistent with other map approaches, but many of the rail trail slides are relatively small, shallow and promptly mitigated: unlikely to be apparent on either DEMs or air-photos. The best evidence for many landslides is not their head scarp or slide path, but linear debris piles or local trail-bed widening created when the recreational trail or old railroad grade was mitigated after slope failure. Collectively, the rail trail project and the West Virginia Landslide Inventory indicate multifaceted approaches are crucial to comprehensive surficial geology mapping in landscapes dominated by slope processes.