HIGH RESOLUTION GEOMORPHIC CHARACTERIZATION AND EVOLUTION OF THERMAL EROSION FEATURES, ARCTIC ALASKA

Terrestrial laser scanning (TLS) provides high resolution topographic detail and enhances geomorphic mapping and characterization of three types of thermal erosion features in the northern foothills of the Brooks Range, Alaska. We study the topographic character and evolution of these features using georeferenced digital terrain models derived from native point clouds collected during the summers of 2009 and 2010. Features include gully thermokarsts, active layer detachments, and retrogressive thaw slumps. Erosion in this region of continuous permafrost occurs when ice wedges and massive bodies of ice melt, mobilizing large volumes of thawed sediment. These changes result from changes in climate and hydrologic processes, and are capable of reshaping periglacial landscapes and landforms currently underlain by permafrost.

Repeat surveys enable change detection and quantification of erosion, transport, and deposition. All features are located on hillslopes sufficiently steep that the sediments produced on the headwall are mobilized, maintaining the exposure of frozen ground to thermal radiation and futher erosion. Sediment transport occurs along the length of the feature and deposition occurs along the edge of the feature and in downslope areas. Gully thermokarsts grow headward as ice wedges melt and laterally by deflation of thawing soils, while retrogressive thaw slumps and active layer detachments grow by rifting blocks of tundra at the headwall. Total headwall retreat ranges from 1 to 5 meters per year. Three different mophologic zones; erosion, transport, and deposition, characterize thermal erosion features, and can be characterized using TLS. Topographic analysis reveals self-similar geometric properties between like features including: width, length, area, slope within feature, headwall height and slope. TLS is beneficial for fine scale topographic analysis in landscapes that are actively evolving and in understanding cryospheric change due to thawing permafrost.