A GIS-based numerical simulation of the March 2014 Oso landslide fluidized motion

Thursday, 18 December 2014
Igwe Ogbonnaya1, Chunxiang Wang2 and Hiroshi Fukuoka2, (1)University of Nigeria, Nsukka, Nigeria, (2)Niigata University, Research Institute for Natural Hazards and Disaster Recovery, Niigata, Japan
Sliding and flowing are the major movement type after slope failures. Landslides occur when slope-froming material moves downhill after failing along a sliding surface. Most debris flows originally occur in the form of rainfall-induced landslides before they move into valley channel. Landslides that mobilize into debris flows usually are characterized by high-speed movement and long run-out distance and may present the greatest risk to human life. The 22 March 2014 Oso landslide is a typical case of landside transformint to debris flow. The landslide was triggered on the edge of a plateau about 200 m high composed of glacial sediments after excessive prolonged rainfall of 348 in March 2014. After its initiation, portions of the landslide materials transitioned into a rapidly moving debris flow which traveled long distances across the downslope floodplain. U.S. Geological Survey estimated the volume of the slide to be about 7 million m3, and it traveled about 1 km from the toe of the slope. The apparent friction angle measured by the energy line drawn from the crown of the head scarp to the toe of the deposits which reached largest distance, was only 5~6 degrees. we performed two numerical modeling to predicting the runout distance and to get insight into the behaviour of the landslide movement. One is GIS-based revised Hovland’s 3D limit equilibrium model which is used to simulate the movement and stoppage of a landslide. In this research, sliding is defined by a slip surface which cuts through the slope, causing the mass of earth to move above it. The factor of safety will be calculated step by step during the sliding process simulation. Stoppage is defined by the factor of safety much greater than one and the velocity equal zero. The other is GIS-based depth-averaged 2D numerical model using a coupled viscous and Coulomb type law to simulate a debris flow from initiation to deposition. We compared our simulaiton results with the results of preliminary computer simulation of the Oso landslide movement which was produced by David L. George and Richard M. Iverson on April 10, 2014.