APPLICATION OF HIGH RESOLUTION LIDAR AND AERIAL PHOTOGRAPHY DATA TO RESOLVE STRUCTURE - RAGGED MOUNTAIN, KATALLA ALASKA USA

High resolution LiDAR and aerial photography data sets are widely used for evaluation of surface manifestations of active tectonics, but also can be used for resolving bedrock structures in areas of poor exposure. This study evaluates both surface geomorphology and underlying bedrock structure using a LiDAR DEM with high resolution aerial photography draped on the terrain model. The study area is located in southern Alaska in the western edge of the St. Elias Orogen where the Yakutat microplate is colliding into Alaska. The study area contains hundreds of geomorphic surface features indicative of active deformation such as fault scarps, sag ponds, and off set streams, but a challenge has been in separating tectonic structures from gravitational collapse features. These surface features are developed on bedrock structures, such as chevron folds that can be analyzed through three dimensional virtual mapping. The LiDAR DEM together with aerial photography was used to create an accurate geomorphologic map of the study area along the length of the east flank of Ragged Mountain, which contains the Ragged Mountain fault scarp, uphill facing fault scarps, flexural-slip fault scarps, talus deposits, landslides, an alluvial fan, and stream channel patterns. In order to determine the type of displacement on fault scarps numerous topographic profiles were constructed to distinguish thrust versus normal faulting. One working hypothesis is that uphill facing normal fault-scarps along the Ragged Mountain fault trace represent extension above a buried ramp in a thrust. This hypothesis is being evaluated with a fault-parallel flow modeling of hanging-wall folding and extension, together with geomorphic mapping of the entire fault trace. Analysis of the high resolution digital elevation model and aerial photography are providing new insight into the role of tectonics versus gravitational deformation. This improves the understanding of the tectonic history and allows for seismic hazard assessments in the region.