OBSERVATIONS ON DEBRIS DEPOSITS IN THE BLUE RIDGE OF WESTERN NORTH CAROLINA: FERTILE GROUND FOR BASIC AND APPLIED RESEARCH

Piedmont cove and foot-slope deposits, debris fields and debris fans, collectively referred to here as debris deposits, are widespread surficial features of significant areal extent within the Blue Ridge of Western North Carolina. These chiefly composite deposits establish a geologic record of past mass wasting events of various mechanisms, magnitudes, and ages. They are evidence of the ongoing landscape evolution of the Blue Ridge, and relevant to efforts aimed at reducing societal losses from landslides. Debris deposits hold answers to questions on the spatial and temporal aspects of uplift and erosion, linkages between climate change and the recurrence intervals of catastrophic storms, and help identify areas that could be affected by future debris flow events. Seminal research on footslope and Piedmont Cove deposits by H.H. Mills strongly influenced the approaches used by the N.C. Geological Survey (NCGS) to identify and map debris deposits, and sheds light onto many possibilities for future research.

The NCGS has used compilations of previous research, geohazards mapping along the Blue Ridge Parkway, county-wide landslide hazard mapping (2005-2011), and responses to numerous emergency landslide events to identify and map debris deposits recorded at 3,200 locations in a landslide geodatabase. As a compliment to field studies, LiDAR digital elevation models have advanced our ability to recognize and map the variety of landforms characteristic of debris deposits. The locations of past debris deposits are spatially correlated with areas affected by recent debris flow and landslide events, particularly on actively-eroding landforms such as the Nantahala Mountains Escarpment and Blue Ridge Escarpment. Debris deposits can (re)activate as debris slides, and source areas upslope of deposits can reactivate as debris flows in response to factors such as excessive rainfall, undercutting by streams, and destabilizing human activity. Understanding the nature, origin, composition and extent of debris deposits is important for constraining physically-based models of debris flow and debris slide initiation, and run-out. Spatial relationships among bedrock structures, debris deposits, and modern debris flow events are evident on hillslopes bordering regional topographic lineaments.