Investigating Feedbacks Between Deformation and Groundwater Flow in a Slow Moving Landslide

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In the U.S., landslides annually claim 25-50 lives and cause $1.6-3.2 billion in damage. While some landslides fail catastrophically, others exhibit slow seasonal slip, often amounting to only centimeters to meters per year. What determines which of these two differing modes of behavior dominates remains a key problem in landslide mechanics and natural hazard prediction. This project will investigate the physical processes that are thought to govern slow slip in landslides.Specifically, this project will test two hypotheses for feedbacks between landslide deformation and groundwater flow at a large, active, slow-moving landslide (Oak Ridge earthflow) near San Jose, CA. The first hypothesis argues that sliding along a landslide's margins causes changes in permeability that will lead both to retention of water and to patterns of groundwater flow that will encourage future failure in one location. The second hypothesis argues that sliding induces expansion of soil pore spaces in slow moving landslides, which reduces water pressure inside the slide and hence stabilizes basal sliding. Both of these hypotheses suggest feedbacks on sliding that are fundamental to the process of landslide failure. Although each hypothesis rests on a sound physical and experimental basis, only very limited field data exist to test each.