SELECTED GEOLOGIC HAZARDS IN NORTH CAROLINA - AN OVERVIEW

Geologic hazards occur in all geologic provinces in North Carolina, and include slope movements, subsidence above abandoned mines, limestone sinkholes, arsenic and uranium in ground water, acidic rock, earthquakes, and indirectly, high hazard dams. These hazards threaten public safety and sustainable development statewide. Damaging slope movements occur annually in the mountainous Blue Ridge Province and slope stabilization costs millions of dollars annually. Scores lost their lives from major flooding and debris flow events triggered by hurricanes that tracked across western NC in 1916 and 1940. A debris slide-flow related to residential development on steep slopes destroyed a home and killed one occupant on December 11, 2003. High hazard dams throughout NC receive increased attention as a result of recent hurricane flooding. Subsidence and collapse above abandoned underground mines occurs mainly in the rapidly urbanizing, old gold mining districts of the Piedmont. Accurately locating the mine workings is difficult as most underground mining took place during the 18th and 19th centuries, and reliable mine maps are rare. Arsenic in residual soil and groundwater is associated with gold and sulfide mineralization (acidic rock) in these areas. Uranium concentrations in groundwater >0.1 ppb occur mainly in igneous and metaigneous granitoids, and Triassic sedimentary rocks in the Piedmont. Sinkholes originate mainly in Tertiary carbonate deposits in the Coastal Plain affecting rapidly developing coastal areas. Damaging earthquakes are rare in NC; but major earthquakes in the New Madrid, Charleston, SC, and Eastern Tennessee seismic zones would cause damage in NC. The NCGS has initiated a geologic hazards program funded through the NC Division of Emergency Management, with the long-term goal to develop a GIS-based geologic hazards atlas. The initial phase includes mapping slope movements, abandoned mines and sinkholes, and compiling maps of high hazard dams and earthquake epicenters in the region. The NCGS also assists other local, state, and federal agencies to help mitigate the impact of geologic hazards. Recent and ongoing studies include detailed mapping of slope movements, and GIS-based modeling of debris flow susceptibility, compiling countywide mine location maps and underground mine maps.