Quaternary geologic map of the northern Healy B4 quadrangle, Alaska: Denali fault tectonic geomorphology and Nenana River incision history

This mapping project targets the superimposed late Quaternary records of displacement across the Denali fault and incision of the Nenana River in the northern Healy B4 quadrangle in south-central Alaska. Remnant landforms from fluvial incision are ideal features for also recording cumulative tectonic displacement. Prior to fieldwork, we will conduct systematic landform mapping on the available high-resolution topography and develop a model of geomorphic features that record the post-glacial incision history of the Nenana River. Along with this, we map the tectonic geomorphology along the Denali fault trace to identify markers that potentially record cumulative fault displacement. Field mapping will entail examining the surficial deposits, describing units, refining characterization of geomorphic features, and testing interpretations of offset landforms. Despite having a highway pass through the middle of the proposed mapping region, very little is known about the recent earthquake history on the Denali fault and the local uplift/incision rate. Preliminary interpretations suggest the prior occurrence of earthquake-induced landslides producing landslide-dammed lakes - presenting additional hazards beyond simple fault displacement and resultant strong ground motions. Furthermore, as one of the major continental strike-slip faults in the world, expanding the paleoearthquake and slip rate data for this fault will inform both local hazard assessment and contribute an example of earthquake recurrence behavior. We expect to establish a sequence of geomorphic controls on former floodplain elevations for the Nenana River for where it crosses the Denali fault from which we can infer an incision rate. This will also establish the geologic context for surficial sediments along the Denali fault trace to inform targeting of future paleoseismic studies and identify young offset geomorphic markers to examine the recent slip history.