USING HIGH-RESOLUTION LIDAR IMAGERY, AIR PHOTOS, AND HISTORICAL DOCUMENTS TO EXPLORE THE SLOPE FAILURE LEGACY OF SEVERAL EXTREME PRECIPITATION EVENTS IN APPALACHIA

Despite its latitude, the southern/central Appalachian orogen is susceptible to extreme precipitation events due to orographic forcing of moist air masses originating from the Atlantic Ocean or Gulf of Mexico. Localized precipitation totals of over 25 cm can occur in under 10 hours with these extreme events, producing widespread, high-density slope failure within the affected areas. Prior to the recent availability of high-resolution (1 meter or less) lidar imagery, a detailed investigation of the effects of historic and late 20th century extreme precipitation events on the landscape was hampered by incomplete historical records, vegetation recovery, and challenging terrain. By pairing new lidar imagery with post-event air photos or historical accounts of older events, a more complete record of the slope movement behavior associated with these extreme precipitation events can be developed. Events documented by aerial photography (e.g., 1940 Watauga County, NC; 1995 Albemarle and Rockbridge Counties, VA) or post-event field mapping (1949 Augusta County, VA) are particularly useful as a means of calibrating lidar interpretation. Air photos and lidar also combine to allow determination of the extent of debris deposits associated with fluidized failures on open slopes, which may produce a subtle lidar signature compared to the size of their debris field. Combined with historical records, lidar imagery can be equally useful in locating unphotographed failures (e.g., 1916 Transylvania County, NC) which produced notable damage but whose locations were not recorded in precise detail, particularly in light of land use changes and new development. The reevaluation of these storm-related landslide events in the "lidar era" represents a meaningful contribution to the understanding of slope movement potential in an increasingly populated and developed orogen.