DEFINING HOLLOWS AND COMPARING FACTORS THAT CONTRIBUTE TO MASS WASTING IN THE SOUTHERN APPALACHIANS, WESTERN NORTH CAROLINA

Debris flows are hazardous to people, property, land, and ecosystems. Sediment accumulates in hollows and intense rainfall causes deposits to mobilize, forming a debris flow. The purpose of this study was to identify and compare morphological and soil factors at hollows in the Southern Appalachians, specifically in the debris-flow prone Blue Ridge escarpment region of North Carolina. This study explores hollows, on north and south facing slopes within Hickory Nut Gorge, to better understand and predict mechanisms of slope failure by using the geomorphic properties of the sites to understand processes.

Parameters were measured in 8 hollows, 5 at FS and 3 at CRSP, with known or apparent failures and were selected by considering variables of the infinite slope model. Measurements included slope shape, up/downslope and convergent slope angles, soil characterization, grain size analysis, bulk density, sorptivity, moisture, and visual observations. Measurements were divided between two different types of hollows, those in saprolite in concave south-facing landscapes (fire station or FS) that appeared to be largely failing in saprolite, and those in steep, highly-weathering limited north-facing slopes failing in colluvial rockfall deposits (labeled CRSP).

Parameters that were similar at both CRSP and FS include bulk density, soil moisture, up/down slope angle, and grain size. Bulk density average 0.98g/cm³ in sandy soils in both hollow types. Soil sorptivity, depth to saprolite, and width/depth ratios differed between the two areas. In CRSP hollows, average sorptivity was increased by about 3.9%, saprolite was exposed, and average width/depth ratio was 1.95. In FS hollows, saprolite was about 17-60cm below the ground surface and average width/depth ratio was 5.87. Although FS and CRSP hollows are both positioned in concave areas, CRSP hollows are positioned directly below large and dominantly impermeable outcrops. Compared to FS hollows wide contributing area, CRSP hollows contributing water is funneled from the tops of outcrop. Future work could include calculating actual and potential factors of safety and exploring the bifurcation of hollow systems to better understand if there are differential modes of debris flow creation and exploring the observed bifurcation of hollow systems.