APPLICATION OF INFINITE SLOPE ANALYSIS TO SUBAQUEOUS SEDIMENT INSTABILITY, MISSISSIPPI DELTA

Submarine landslides are described on very low angle slopes (0.5°-1.7°) in the Mississippi prodelta area and are evaluated using infinite slope analysis. For instability to occur, pore water pressure ratios in excess of hydrostatic (u/γwz) and approaching geostatic (u/γ′z) are needed. These calculated values, based on three sets of effective strength parameters and for two sediment depths to failure, are in close agreement with measured pore water pressure data from in situ piezometers. Ratios of (u/γ′z) as large as 0.986 have been monitored. Mud vents are also indicative of large internal pressures within the sediments, generated by rapid sedimentation, wave perturbation, and biogenic methane. The analysis suggests that the reduction in effective stress may be sufficient to cause failure by gravitational stresses alone. © 1979.