USING LIDAR TO REFINE GEOLOGIC MAPPING AND INTERPRETATIONS IN THE UPPER TANANA RIVER VALLEY, CENTRAL ALASKA

The Alaska Division of Geological & Geophysical Surveys is evaluating geology and geologic hazards along a 12-mile-wide corridor centered along the Alaska Highway between Delta Junction and the Canada Border. This work is being completed in preparation for possible construction of a large-diameter natural gas pipeline and is now being enhanced by recently acquired high-resolution lidar (Light Detection and Ranging) data. Our current focus is to refine 1:63,360-scale surficial-geologic mapping along an approximately 1-mile-wide corridor centered along the Alaska Highway.

Investigators used lidar during the 2011 summer field season to help refine contacts between bedrock outcrops and subcrops, relatively old and young drift sheets, eolian sand dunes and blankets, and stream deposits. We were able to more accurately delineate several known landslides, and identified other slope failures not previously recognized. Features with microrelief, such as debris-flow fans and cones with natural boulder levees and U-shaped medial channels, and alluvial fans with prominent distributary channels, are clearly identifiable using lidar. Improved geologic mapping has important implications for future infrastructure and development projects along the proposed corridor.

Lidar evaluation is also leading to a better understanding of the history of outburst flooding in the upper Tanana River basin. We have been able to confirm our mapping of several outburst-related features, including flood ripples on a longitudinal flood bar west of Dot Lake Village, and have identified additional features such as a higher flood bar associated with outburst flooding during the penultimate glaciation. Based on high-level flood boulders found near granitic outcrops discovered through examination of lidar hillshade images southwest of Berry Creek, we estimate a minimum flood elevation during the penultimate glaciation of ~ 1510 to 1540 feet. By evaluating topographic profiles constructed using bare-earth Digital Elevation Models derived from lidar we anticipate being able to improve our estimates of flood discharge.