SHIFTING MORPHOLOGY AND HAZARD MAPPING OF THE MOUNT BALDY DUNE, INDIANA DUNES NATIONAL PARK

Mount Baldy is an active and rapidly migrating dune along the southeastern coast of Lake Michigan that gained notoriety in 2013 when a young boy was interred in a cavity produced by the decay of buried oak trees. An investigation of the internal stratigraphy produced a structure map of the surface below the active dune that determined where buried trees were likely to be present in close enough proximity to the surface to produce potentially hazardous collapse features. Ground penetrating radar successfully mapped/defined the modern dune’s predepostional surface, which is defined by a paleosol that underlies the entire active portion of the dune and produced a strong reflection. Two-foot contours from a 1970 topographic map were combined with paleosol elevations from 12 km of radar lines and 24 geoprobe cores to build a 3D structure of the dune’s underlying surface. A hazards map was created where the predepositional surface lies within 20 ft (~5.5 m) of the active dune’s stoss surface and decomposition of vertical tree trunk’s is most likely to produce cavities that reach the dune’s surface. Lidar from 2013 and 2018 permitted two additional generations of hazard maps to be created as the dune continues to migrate inward. The changing morphology of the dune and exposure of recently buried trees is also evident. Collectively, the maps show that the hazard zone is becoming wider as the dune extends landward, maximum elevation decreases, and the parabolic shape shifts to that of a dunefield.