Response and Recovery of Horn and Petit Bois Islands, Mississippi, USA to Tropical Cyclone Impacts: 2004-2016

Horn and Petit Bois islands are two of five Mississippi (MS) barrier islands that provide physical protection from tropical cyclones threatening the MS Gulf Coast, in addition to critical habitat for the northern Gulf of Mexico (GOM). In September 2004, Hurricane Ivan removed a large volume of sediment from the eastern ends of Horn and Petit Bois islands with its 1 to 2 m storm surge and ~194 kph wind speeds. Then, in August 2005 Hurricane Katrina severely impacted the two islands again with its 3.5 to 5.5 m storm surge on Horn and Petit Bois islands, and estimated maximum sustained wind speeds of 204 kph at landfall in southeast Louisiana. Using topographic light detection and ranging (LIDAR) datasets from 2004 to 2016, spatial and temporal changes of the islands\u27 area, sediment volumes, and shorelines were measured to ascertain their geomorphic responses and recovery rates following the impacts of these devastating tropical cyclones. During the 2004–05 hurricane seasons, Horn Island lost ~13.3% of its pre-hurricane Ivan land area, lost ~35.9% sediment volume, and had a total average shoreline change rate of −10 m/yr. Petit Bois Island also lost ~13.3% of its pre-Ivan land area, lost ~27% sediment volume, and had a shoreline change rate of −33 m/yr. Between 2005 (post-Katrina) and 2016, Horn Island recouped ~6.6% of its pre-Ivan land area and ~4.3% sediment volume, whereas Petit Bois Island recovered ~4% of its pre-Ivan land area and ~22.9% sediment volume. The overall averaged shoreline change rates between 2004 and 2016 were −2 m/yr for Horn Island and −3 m/yr for Petit Bois Island. These changes reflect that Horn Island is no longer stable, as its sediment supply cannot keep pace with the current rate of sediment loss, and that because Petit Bois Island\u27s narrow central shoreline is retreating at a rate of 10 m/yr, the island is at risk of breaching during the next storm. Highlighting complex island response, the relationship between area and shoreline changes to that of volume changes was inconsistent