Mass wasting on the Mississippi River subaqueous delta

The Mississippi River delta front (MRDF) is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to seafloor failures. The occurrence of seafloor landslides on the MRDF has been recognized since the 1950s, but the bulk of research on the topic was conducted in the 1970s-80s after seafloor landslides triggered by Hurricane Camille damaged offshore infrastructure. Through these efforts, it was recognized that seafloor instability features are present across the entire delta front, that rapid sediment delivery from the Mississippi River is a primary preconditioning factor for failures, and that cyclic loading from hurricane waves is the main triggering mechanism for deep-seated catastrophic events. However, mounting evidence shows that MRDF seafloor motion occurs even during periods of no hurricane activity, which could be attributed to creep-like motion of underconsolidated sediment, or smaller episodic flows triggered by winter storms or Mississippi River floods. Given the extensive spatial distribution of instabilities on the MRDF, the multiple mechanisms of failure and variety of resulting morphology, and the range of potential triggering mechanisms with short recurrence, the MRDF is an exceptional location to assess the complex problem of seafloor landslides. An improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling, as they can evacuate large volumes of sediment into deep water over short time periods. Additionally, seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation, and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments. This paper presents a review and synthesis of geological and geotechnical research on the MRDF, particularly with respect to seafloor landslides: their occurrence, geological and geotechnical controls, triggering mechanisms, and knowledge gaps related thereto. This synthesis is conducted at times of rapidly developing technologies for studying seafloor instability, and as the MRDF enters a stage of degradation characterized by reduced sediment delivery and accumulation.