# Pore Pressure Response to Sedimentation, Erosion and Sea Level Change and
their Influence on Submarine Slope Stability

(AGU)
*Lincoln F. Pratson (1) and Ulisses T. Mello (2)*

(1) Lamont-Doherty Earth Observatory, Palisades, NY 10964

(2) IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598

## Abstract

For saturated submarine slopes, excess pore pressures induce a seepage
force that decreases the frictional resistance of the slope to failure
while also potentially enhancing the downslope shear stress due to gravity.
Delinger and Iverson (1992) and Orange and Breen (1992) have examined the
influence of seepage forces on the stability of submarine slopes assuming a
2-D, infinite slope and steady-state fluid flow. Here, we also assume a 2-D
infinite slope, but examine pore pressures and seepage forces resulting
from transient pore fluid flow in response to sedimentation, erosion and
sea level change. Initial results indicate that for sedimentation rates in
which accumulation occurs faster than dewatering during compaction, pore
pressures increase while the effective stress on the slope sediments (i.e.,
the total stress minus the pore pressure) decreases, promoting frictional
slope failure, and in the limiting case liquefaction. The model predicts
that rapid erosion fosters the opposite response, reducing the pore
pressure and increasing the effective stress, thereby lowering the
possibility frictional slope failure and liquefaction on an infinite slope.
Changes in sea level, on the other hand, have no effect on slope stability,
regardless of rate of sea level fall/rise or the hydraulic conductivity of
the slope sediments. This is because while changing water depth does cause
a corresponding change in pore pressure, the effective stress on the slope
sediments remains unchanged.