Wave-induced mudslides during recent hurricanes in the Mississippi Delta Region of the Gulf of Mexico

This study involves the examination of wave-induced submarine mudslides caused by recent major hurricanes in the Mississippi Delta region of the Gulf of Mexico, including the development of a model that can be used to analyze and predict these mudslides. Reports of mudslides caused by Hurricane Ivan in 2004 and Hurricane Katrina in 2005 were collected and studied to determine locations of mudslide activity. A simple limit equilibrium model was developed to calculate a factor of safety against mudslide occurrence given the soil shear strength, the water depth, the slope angle, and the wave height and period at a site. The limit equilibrium model was verified using a more rigorous deformation model, and parametric analyses were performed to determine the sensitivity of the model to changes in input parameters. Results of the limit equilibrium model generally agreed well with reports of mudslides, though due to the difficulty in obtaining site-specific shear strength data and the variability in shear strength over the area of study, the most successful analyses were those that took variation in soil shear strength into account. The limit equilibrium model was used to formulate conclusions regarding the characteristics of ocean wave-induced mudslides. Mudslides were generally found to be rare events, occurring only in instances of major hurricanes over most of the Mississippi Delta region, but more frequently in water depths less than about 100 feet. The slope angle was found to be a relatively insignificant factor in mudslide vulnerability when compared to other parameters. Analyses suggested that mudslides are small in areal extent - on the order of a few thousand feet in length and width - and that mudslides are unlikely to result in movement of soil over long distances. Risk analyses were performed in order to determine the return periods of mudslides, both on a site-specific scale and on a regional scale.