T195 Insights into Geological Processes and Hazards Acquired through Recent Technological Advances

Tuesday, 6 November 2012
1:30 PM - 5:30 PM
211AB

LIDAR AND GIS: TOOLS TO AUGMENT LANDSLIDE AND FAULT MAPPING IN METAMORPHIC ROCKS IN THE BLUE RIDGE GEOLOGIC PROVINCE OF WESTERN NORTH CAROLINA

Paper number: T195-6
Program: Technical Sessions
Time: 2:55 PM – 3:10 PM

Authors

Abstract

We used digital elevation models (DEMs) derived from airborne Light Detecting And Ranging (LiDAR) in a Geographic Information System (GIS) to augment the mapping of landslides, landslide hazards, and faults in the Blue Ridge geologic province of western North Carolina. To make landslide hazard maps for Macon, Watauga, Buncombe and Henderson Counties we used shaded relief and slope maps, and topographic contours derived from the LiDAR DEMs to identify landforms (e.g., debris fans) to target for field confirmation. These tools also helped standardize methods to map these deposits. Recent orthophotography and archival aerial photography were used in conjunction with LiDAR DEMs to identify and map the paths of over 2,300 debris flows and debris slides that occurred in 1940, 1977 and 2004. The improved slope and landform resolution of the LiDAR DEMS (sub-meter vertical accuracy, 6m pixel resolution) aided the modeling and mapping of debris flow susceptibility and debris flow routing.

We used LiDAR DEMs to identify topographic trends and lineaments in two areas where earlier ductile faulting followed by WNW-trending brittle faulting produced deformation fabrics that influence slope stability and probably groundwater flow. As part of the landslide hazard mapping in Watauga County we evaluated a 14km x 0.5km zone of existing and potential rock slope instability. This zone includes WNW-trending topographic features and lineaments where 14 active and past-active rock slides occur along the Linville Falls fault, mainly in rocks of the Grandfather Mountain Window. These WNW-trending features are expressions of a regionally extensive zone of fractures and faults that intersect the Blue Ridge Escarpment in an area of concentrated debris flows that occurred in 1940. In Buncombe County we completed 1:6,000-scale geologic mapping of a 3.5-km2 area to establish a geologic framework to support groundwater studies. Rocks are within the Ashe Metamorphic Suite, a highly deformed, heterogeneous package of metasedimentary and mafic metaigneous rocks. A >100m-wide brittle fault zone was identified by the presence of gouge, breccia and the realignment of older ductile fabrics. Locally the fault is in contact with unconsolidated colluvial(?) deposits. The fault zone trends WNW and is aligned with lineaments identified in LiDAR imagery.