USING HIGH RESOLUTION LIDAR TO MAP COLLUVIAL DEPOSITS ON THE CUMBERLAND PLATEAU

Using High Resolution LIDAR to Map Colluvial Deposits on the Cumberland Plateau

On the Cumberland Plateau, sandstone and limestone lithologies have been deeply incised with rugged gorges and high relief. The steep hillsides of these gorges are typically limestone bedrock covered by colluvial soils rising to a sandstone cap rock. Along the slopes of the river gorges, one finds evidence of previous landslides. However, these old landslide features have been largely uninvestigated and unmapped. This is due in part to the difficulty in accessing the area because of rough terrain and private land ownership. Additionally, landslide maps can be tedious to compile using conventional techniques. Aerial photography also has limited use because of the dense vegetation. The use of high resolution DEMs from airborne laser altimetry (LIDAR) allows for a much better look at the morphology of the river gorges. Bare earth shaded relief maps derived from LIDAR (1.5-meter resolution) give an unobstructed view of the surficial deposits, even making it possible to pick out individual boulders. Initial inspection of a three county area identified 70 potential landslide features. By using ArcGIS tools, it is possible to measure the surface roughness of hillslopes (in this case defined as the standard deviation of slope). Areas where landslides have occurred in the past have large blocks of the sandstone cap rock that have broken away and slid down the hill. These blocks tend to rest at random, jumbled angles, although a shallow organic soil has developed on some boulders. According to the literature, landslides can be delineated by analyzing the slopes for areas where the surface roughness is significantly higher than that of its surroundings. We calculated the mean surface roughness of one identified landslide using a 3 x 3 cell window and found the roughness of the landslide to be 4.74. Meanwhile the average surface roughness of the slopes along the whole gorge is 3.24. Older landslides surfaces are likely to have lower roughness values due to the accumulation of soil and organic materials.