INVESTIGATING THE ORIGIN OF HOLES APPEARING IN THE MOUNT BALDY DUNE AT THE INDIANA DUNES NATIONAL LAKESHORE

The recent appearance of temporarily stable holes on the stoss slope of an actively migrating coastal parabolic dune provided an opportunity to study a previously unreported geologic hazard. Mount Baldy is the largest parabolic dune along the southern coast of Lake Michigan and is rapidly migrating onshore over a previously stabilized late Holocene landscape. Since 2013 multiple holes have been observed to appear in sands that directly overly a stabilized relict parabolic dune that supported oak (Quercus spp.) trees visible on the 1939 aerial photo. This study focused on the analyses of fungi collected from trees uneartherd from the dune and SEM analyses of sediment collected in contact with organic material. Data indicate that saprotrophic wood decay fungi continue to actively decompose trees after burial and facilitate the biomineralization of a calcium carbonate-rich cement at the contact between the organic material and sands. Scanning electron microscopy of the cement showed neoformed authigenic minerals and organic structures consistent in morphology with fungal hyphae. We propose that within the dune, portions of the decayed trees progressively collapse and infill, producing voids that are temporarily stabilized by the calcium carbonate-rich cement. Photographic evidence suggests that similar holes have occurred in migrating dune systems in Oregon and Michigan. Ongoing work must address the dynamics of fungal communities operating within trees pre and post burial and evaluate environmental conditions within the dune's interior to better understand the processes of biomineralization and decomposition that lead to the final collapse of buried trees.