Impact of Hurricanes Katrina and Lili on the Inner Shelf of the Mississippi-Atchafalaya Delta

Box cores collected on the Louisiana continental shelf immediately following Hurricanes Lili and Katrina allow comparison of sediment event layer formation on the actively accreting Mississippi delta adjacent to Southwest Pass (Katrina) and the Atchafalaya delta (Lili). Post-Katrina box core sites in water depths of <40 m show evidence of an erosional surface at the sediment-water interface, indicating the water depth that critical erosion stresses are found in these large storms. Erosional deflations from Katrina and Lili ranged from 2–15 cm, controlled by water depth (shallower caused greater incision) and degree of consolidation of the pre-existing seabed sediments. In water depths of >25 m, post-Katrina cores display event layer deposition 1–25 cm thick above the incision surface: post-Lili cores from the Atchafalaya show similar thicknesses dependent on proximity to the storm path, but also extending into shallower water (shallowest station sampled was 4 m).