Abstract
Abstract Submarine slope failures pose risks to coastlines because they can damage infrastructure and generate tsunamis. Passive margin slope failures represent the largest mass failures on Earth, yet we know little about their dynamics. While numerous studies characterize the lithology, structure, seismic attributes and geometry of failure deposits, we lack direct observations of failure evolution. Thus, we lack insight into the relationships between initial conditions, slope failure initiation and evolution, and final deposits. To investigate submarine slope failure dynamics in relation to initial conditions and to observe failure processes we performed physical experiments in a benchtop flume and produced numerical models. Submarine slope failures were induced under controlled pore pressure within sand–clay mixtures (0–5 wt% clay). Increased clay content corresponded to increased cohesion and pore pressure required for failure. Subsurface fractures and tensile cracks were only generated in experiments containing clay. Falling head tests showed a log-linear relation between hydraulic conductivity and clay content, which we used in our numerical models. Models of our experiments effectively simulate overpressure (pressure in excess of hydrostatic) and failure potential for (non)cohesive sediment mixtures. Overall our work shows the importance of clay in reducing permeability and increasing cohesion to create different failure modes due to overpressure.
Highlights
Despite the risks associated with submarine slope failures on passive margins, little is known about their initiation and dynamics
This experimental and modelling approach builds upon previous experiments that looked at the role of yield strength to assess failure morphology (Sawyer et al 2012) by investigating how pre-failure geometry, clay content and pore pressure affect slope failure dynamics, including sediment remobilization
Slope failures initiated after sufficient water pressure was supplied through Reservoir 2 (R2) and the pressure front migrated into the sediment above the pebbles
Summary
Despite the risks associated with submarine slope failures on passive margins, little is known about their initiation and dynamics. We investigated failure mechanics and dynamics as influenced by pore pressure, cohesion and clay content in a benchtop flume in the Geomechanics Laboratory at the Colorado School of Mines and developed numerical models that quantify the observed processes. We focused on a mechanistic understanding of dynamic processes rather than a specific geological study area. This experimental and modelling approach builds upon previous experiments that looked at the role of yield strength to assess failure morphology (Sawyer et al 2012) by investigating how pre-failure geometry, clay content and pore pressure affect slope failure dynamics, including sediment remobilization
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