Numerical Modeling of the 2014 Oso, Washington, Landslide.

2014 Fall Meeting

Section: Natural Hazards

Session: The Oso Disaster and Other New Perspectives on High-Mobility Landslides and Debris Flows II

Title: Numerical Modeling of the 2014 Oso, Washington, Landslide.

Authors:
Iverson, R M, USGS, Vancouver, WA, United States
George, D L, USGS, Vancouver, WA, United States

Abstract:

Numerical simulations of alternative scenarios that could have transpiredduring the Oso, Washington, landslide of 22 March 2014 provide insightinto factors responsible for the landslide's devastating high-speed runout.We performed these simulations using D-Claw, a numerical model werecently developed to simulate landslide and debris-flow motion frominitiation to deposition. D-Claw solves a hyperbolic system of fi
ve partialdiff
erential equations that describe simultaneous evolution of the thickness,solid volume fraction, basal pore-fluid pressure, and two components ofmomentum of the moving mass. D-Claw embodies the concept ofstate-dependent dilatancy, which causes the solid volume fraction m toevolve toward a value that is equilibrated to the ambient stress state andshear rate. As the value of m evolves, basal pore-fluid pressure coevolves,and thereby causes an evolution in frictional resistance to motion. Our Ososimulations considered alternative scenarios in which values of all modelparameters except the initial solid volume fraction m0 were held constant.These values were: basal friction angle = 36 ; static critical-state solidvolume fraction = 0.64; initial sediment permeability = 10-8 m2; pore-fluiddensity = 1100 kg/m3; sediment grain density = 2700 kg/m3; pore-fluidviscosity = 0.005 Pa-s; and dimensionless sediment compressibilitycoe fficient = 0.03. Simulations performed using these values and m0 = 0.62produced widespread landslide liquefaction, runaway acceleration, andlandslide runout distances, patterns and speeds similar to those observed orinferred for the devastating Oso event. Alternative simulations that usedm0 = 0.64 produced a much slower landslide that did not liquefy and thattraveled only about 100 m before stopping. This relatively benign behavioris similar to that of several landslides at the Oso site prior to 2014. Our
findings illustrate a behavioral bifurcation that is highly sensitive to theinitial solid volume fraction. They suggest that the destructiveness of the2014 Oso event may have resulted in part from prior slope deformation thatproduced a dilated sediment state that made the sediment susceptible tocontraction and liquefaction as it began to fail on March 22.

Cite as: Author(s) (2014), Title, Abstract NH53C-02 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec.

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