Stratigraphic Record of Hurricanes Audrey, Rita and Ike in the Chenier Plain of Southwest Louisiana

Hurricanes Audrey (1957), Rita (2005) and Ike (2008) generated storm surges of 3-5 m that flooded coastal marshes on the Chenier Plain of Southwest Louisiana and transported sandy and muddy washover sediments hundreds of meters inland. Trenching and coring of these marshes reveals that characteristics of the storm surge deposits, including texture, thickness, inland penetration and preservation, reflect the intensity and proximity of the landfalling hurricanes. Hurricanes Audrey (Category 4 at landfall) and Rita (Category 3 at landfall) were both powerful storms that made landfall in close proximity to the study area (within 10 km). Both storms left relatively thick, sandy storm surge deposits that extend up to 887 m inland and are well-preserved in the subsurface of the marsh. Hurricane Ike was a strong Category 2 storm at landfall, but struck the coast approximately 106 km southwest of the study area. It left a thinner, muddier storm surge deposit that extended 476 m inland. Although Hurricane Ike’s storm surge deposit was visually identifiable eight months after landfall, by 20 months after landfall it was no longer recognizable probably because of sediment redistribution by wind and rain wash and disturbance by bioturbation. Sedimentation rates since 1957 (the base of the Hurricane Audrey deposit) are in the range of 0.2–0.7 cm per year and generally decrease with distance inland. A significant finding of the study is that much of the sedimentation in these marshes since 1957 was derived from storm surge deposition, suggesting that large episodic sediment input from hurricanes is the dominant source of sediment input for these nearshore environments.