INVESTIGATING RECENT SURFACE MINING-RELATED LANDSLIDES IN THE APPALACHIAN COALFIELDS OF SOUTHWESTERN VIRGINIA

Between March and May 2015, numerous landslide complaints were received by the Virginia Department of Mines, Minerals and Energy (VA DMME) – Abandoned Mine Land (AML) Program in southwestern Virginia. While most of these complaints were related to stream sedimentation and water quality, one debris slide completely destroyed a trailer and others posed risks to roads, buildings, and public safety. These landslides (mostly debris slides and flows) initiated from mine spoil on outslopes associated with pre-1981 abandoned coal mines. A combination of oversteepened and unconsolidated spoil material discarded into natural colluvial hollows, rapid snowmelt, and heavy rainfall from mid-to-late March 2015, appears to be the primary trigger for these landslides. At the request of AML, the VA DMME – Division of Geology and Mineral Resources (DGMR) is presently developing an inventory of these 2015 landslide locations, providing slope stability analysis, and making recommendations for the remediation of some of these landslide areas, especially where there is a risk to public health and safety. Of special concern is an active rotational debris slide-flow that occurred along a first-order tributary of Elkins Branch in Buchanan County near the town of Grundy, VA. The total length of the slide, from the headscarp to the toe where it intersects the main stream channel of Elkins Branch, is ~490 m. This landslide has inundated an area of approximately 8100 m². As of 23 July 2015, a large secondary scarp (45 m long) had developed below the main headscarp (120 m long) and was actively shedding mud and fine debris into the first-order tributary, converting the main body of the debris slide into a debris flow. Debris from the slide was contributing to turbid water and obstructing stream flow downstream along the main tributary of Elkins Branch. Site visits by DGMR in June and July 2015 found that scarps and tension cracks continue to widen and deepen over time, indicating that the slide is actively moving and may be at risk of catastrophic failure. Continued monitoring, a volumetric analysis of the main body of the slide, and debris flow inundation modeling will help further characterize the risk to property and a state road at the base of the slope.