ADVERSE IMPACT OF BIOTURBATION ON STORM-INDUCED SLOPE FAILURE IN TROPICAL AND TEMPERATE SETTINGS

Bioturbation by vertebrates or mega-invertebrates in coastal and riverine bluffs has the potential to compromise slope stability, especially with respect to intense storms ands floods. However, this effect may be difficult to assess due to removal of bioturbated material. Along the aeolianite bluffs in the Bahamas, in addition to a variety of cavities produced by dissolution and plant growth, slope retreat intercepts modern or subfossil burrow networks of the blackback land crab (Gecarcinus lateralis). The extent and distribution of 5-10-cm-wide gently inclined tunnels can be partially imaged with georadar, but investigations near cliff tops may require application of drone-aided imaging. In temperate riparian settings, regolith reworking by the groundhog (Marmota monax), whereas localized, exerts a major impact on densely vegetated stream margins (high zoogeomorphic yield). Along the Pennsylvania margin of the lower Delaware River, multiple burrow complexes with entrance diameters exceeding 20 cm reduce slope stability by: 1) removal of ground vegetation; 2) creation and expansion of permeability pathways (non-linear piping dynamics), and 3) downslope transfer of sediment. Geomorphic cascades may involve treefall in areas of root-based dens, further exacerbating the potential for slope failure. In contrast to siliciclastic settings, coastal carbonates that undergo incipient lithification may have drastically different properties based on the presence and cementation state of the fill. Our findings indicate that bluff-top bioturbation increased geohazard risk during the recent storms of record – Hurricanes Sandy (2012) and Joaquin (2015) – along temperate and tropical coastal regions, respectively.