HR: 1340h
AN: OS53A-0977    [Abstracts]
TI: Mudflows in the Southwest Pass Region of the Mississippi River Delta: Results From Multibeam, Sidescan Sonar, and Subbottom Profiler Data
AU: * Henning, A T
EM: ahenning@rice.edu
AF: AOA Geophysics, 2500 Tanglewilde Suite 120, Houston, TX 77063, United States
AU: Garcia-Garcia, A
EM: agarcia@pmc.ucsc.edu
AF: AOA Geophysics, 7532 Sandholt Road Suite 6, Moss Landing, CA 95039, United States
AU: Garcia-Garcia, A
EM: agarcia@pmc.ucsc.edu
AF: University of California, 1156 High Street Dept. of Earth and Planetary Sciences, Santa Cruz, CA 95064, United States
AU: Orange, A
EM: aorange1@compuserve.com
AF: AOA Geophysics, 7532 Sandholt Road Suite 6, Moss Landing, CA 95039, United States
AU: Orange, D
EM: dorange@blackgoldenergy.com
AF: University of California, 1156 High Street Dept. of Earth and Planetary Sciences, Santa Cruz, CA 95064, United States
AU: Orange, D
EM: dorange@blackgoldenergy.com
AF: Black Gold Energy, Plaza City View 5th floor Jl. Kemang Timur 22, Jakarta, 12510, Indonesia
AB: The offshore portion of the active Mississippi delta is characterized by frequent submarine mudflows, which have caused extensive damage to offshore infrastructure in the area. The slopes in this area are very gentle (typically < 1.5°) and the mudflows are thought to be triggered by deep waves during storms. The 2005 hurricane season in particular caused unprecedented levels of damage in the Gulf of Mexico. Post-hurricane surveys carried out by the industry determined that much of the damage was caused by mudflows that originated on the upper portions of the Mississippi birdsfoot delta, just outboard of Southwest Pass. Mudflows generally consist of a source area, a chute (or gully), and a downslope depositional lobe. Large erratic blocks are characteristic of the mudflow gully floor, and recently emplaced mudflow lobes show a more irregular and blocky surface topography. Gullies often form natural levees, which can give the gully a perched topographic expression. A June 2007 survey aboard the UNOLS vessel R/V Pelican focused on the upslope portion of the mudflow area with the goal of imaging the source of the mudflows. Multibeam echosounder, sidescan sonar, and subbottom profiler data were acquired over an 8 km by 2 km grid at a 100 m line spacing in order to study the possible sources of the mudflows. Multibeam and sidescan sonar data imaged the upslope portions of eight separate mudflows, including the origin of one of the flows. The five westernmost flows originate at a known dredge dump site and appear significantly wider than the three flows to the east. The eastern flows are more clearly delineated on the seafloor data and follow more tortuous downslope paths. This suggests a possible anthropogenic component to mudflow sourcing in this area. The subbottom profiler data show large blocks of material containing intact stratigraphy located within the mudflow gullies. High dips were observed in numerous blocks in both the strike and dip directions. The base of these blocks was imaged in places, suggesting that the blocks move downslope by sliding on top of more rigid material. No high relief mudflows were observed in these data.
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3070 Submarine landslides
DE: 4558 Sediment transport (1862)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting