As part of our pilot project to delineate mudflow failures, sediments susceptible to future slope failure, and areas of relative stability in the Mississippi Delta, we have developed and tested a geomorphology-based approach to map mudflow susceptibility on the sea floor bottom. Our research is designed to provide regionally-consistent hazard information for the siting and design of pipelines and structures using readily available datasets.
Based on interpretation of available datasets for the Mississippi Delta region, and our results for a test area using post-Hurricane Ivan (pre-Hurricane Katrina) bathymetric data, mudflow transport within the Delta generally occurs within well-defined submarine channels or gullies, spreading out onto the seafloor in deeper water to form overlapping lobes of thick, viscous silty clay. We have used available bathymetric data to delineate areas of relative sea floor stability over the past century, areas of active mudflow transport, and areas of active mudlobe deposition.
Our mapping delineates the region of mudflow gullies, as mapped by Coleman et al1, as the mudflow transport zone. Local accumulation of sediment coupled with scour during mudflow transport results in highly variable and unstable conditions within the gullies. Semi-stable areas between the mudflow channels locally provide the least hazardous locations for siting of future production facilities and pipeline routing. The zone of overlapping mudlobes located downslope of the gullies is an area of recent deposition vulnerable to mudflow overruns from upslope mudflows.
As first recognized during evaluation of the extensive damage caused to offshore oil production in the Gulf of Mexico by Hurricane Camille in 1969, hurricanes have the potential to move massive amounts of sediment on the shallow sea floor. Large-scale wave-induced, cyclic bottom pressures created by major hurricanes (such as Camille, Ivan, and Katrina) directly impact the sea floor, causing seafloor failures and mudflow overruns of deepwater regions from upslope sources (Bea et al2; Hooper3; Hooper and Suhayda4).
Our pilot project tests the applicability of developing regionally consistent hazard maps that delineate the relative susceptibility of the Mississippi Delta in the Gulf of Mexico to future submarine mudslides. We have developed and applied GIS-based techniques for delineating the relative susceptibility of underwater slopes to mudflows for the offshore Mississippi Delta area impacted by Hurricanes Katrina and Ivan (Figure 1).
Fig. 1. Regional mudfloor susceptibility map produced for the Mississippi Delta area for this study, showing extent of available historic bathymetry datasets (1874 through 1977-79). (available in fullpaper)
Similar to landslide and liquefaction mapping on land, mudflow susceptibility mapping identifies areas vulnerable to submarine failure that may be mitigated by avoidance and/or further investigation and design. Our susceptibility maps are designed, in conjunction with information on hazard opportunity (e.g. recurrence of major hurricanes), to form the regional map framework required to evaluate likely locations of future submarine failures.
Mudflows along the submerged Mississippi Delta apron are part of a complex, dynamic system of sediment transport and deposition developed on the sea floor bottom (e.g. Coleman et al1). Mudflow transport within the Delta generally occurs within well-defined submarine channels or gullies, spreading out onto the seafloor in deeper water to form overlapping lobes of thick, viscous silty clay (Shepard5; Ho