SPATIAL DISTRIBUTION OF ROCK BLOCK SLIDES IN THE VALLEY AND RIDGE OF VIRGINIA: A GIS APPROACH

Some of the largest known slope failures in the world exist in the Valley and Ridge of Virginia. These rock block slides were first recognized in the late 1980s and remain poorly understood. Using a dataset of unpublished geologic data from the Virginia Division of Mineral Resources, a compilation of USGS DEMs, and maps of known rock block slides, geologic and topographic parameters favoring rock block slide development were determined. These parameters were then applied in a search for previously unknown rock block slides, which yielded several new slides. The distribution of rock block slides in the Valley and Ridge was then examined to determine implications for rock block slide formation. The rock block slide distribution appears to be controlled by the distribution of a suitably thick massive sandstone (typically the Keefer Sandstone) underlain by a significantly thick shale (often those of the Rose Hill Formation). An exceptionally large earthquake in the Giles County Seismic Zone is a potential triggering mechanism for the slides.