LANDSLIDE HAZARD MAPPING IN PAGE COUNTY, VIRGINIA: GIS PROCESSES AND PRELIMINARY FINDINGS (Invited Presentation)

The Virginia Division of Geology and Mineral Resources is currently implementing a yearlong pilot project to map landslide hazards in Page County, Virginia. The county is located in the Shenandoah Valley of northwestern Virginia and is dominated by the Blue Ridge Mountains to the east and the Valley and Ridge Appalachians to the west. In this area, high-intensity rainfall (5-in/day or greater) has been known to produce destructive slope movements in the recent past (e.g., 1949, 1969, 1985, 1995).

Landslide hazard mapping at the county-wide scale was completed by the North Carolina Geological Survey from 2005-2011 and similar mapping techniques are being applied in Page County. This project will include a comprehensive inventory of modern landslides as well as ancient landslide deposits, debris fans and talus areas in ArcGIS geodatabase format. Landslide susceptibility modeling will be completed to help delineate potential hazard areas. Landslide hazard maps will be provided to county and local governments and emergency management officials to help guide informed decisions for development and emergency access in critical areas (i.e. roads, emergency facilities, water supply areas, etc.). Completion of the pilot study is scheduled for May 2013.

High-resolution topographic data, derived from a digital terrain model (DTM), is an important aspect of the mapping and is used to remotely identify areas of past landslide activity, usually in the form of debris fans and other composite colluvial deposits. Digital techniques developed for identifying similar features in North Carolina have proven to be fairly successful in the Blue Ridge portions of Page County that are dominated by debris-flow depositional processes. Remote interpretation has been less successful in the Valley and Ridge portions of the county. This appears to be due to differences in lithologic resistance of the geologic units in the Valley and Ridge (primarily sedimentary to low-grade metamorphic rock) as compared to the study areas in western North Carolina (highly-deformed, high-grade metamorphic rock). The geomorphologic features that developed on these different lithologies will require significant field verification to confirm the interpretation of the features identified remotely using the DTM data.