DECLINE OF THE SUBAQUEOUS MISSISSIPPI RIVER DELTA FRONT: IMPLICATIONS FOR MUDFLOW HAZARD
Analyses of these datasets show significant changes to delta front growth during the last century. Progradation of Southwest Pass (measured at 10 m depth contour) has slowed from ~67 m/yr between 1764 and 1940 to ~26 m/yr between 1940 and 1979, with evidence of further deceleration from 1979-2009. The 10 m contour at both South Pass and Pass A Loutre has begun retreating at rates >20 m/yr between 1979-2009. The data reveal that advancement of the delta also decelerated in deeper water across many areas of the delta front. Furthermore, over the area offshore from Southwest Pass, the sediment accumulation rate decreased by ~82% between 1940-1979 and 1979-2005. The subaqueous delta front appears to be entering a phase of decline, and we expect these sedimentation trends to impact the spatial and temporal patterns of subaqueous mudflows. Nevertheless, despite the decreased sediment input and accumulation, we still observe advancement of some mudflow lobes during the past ~30 years, and mudflows have recently been documented associated with Hurricanes Ivan (2004) and Katrina (2005). New geophysical and sedimentological data will be required to assess potential mudflow hazards associated with changing sedimentation rates and patterns.