Document Type

Thesis

Date of Degree Completion

Spring 2019

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Dr. Lisa Ely

Second Committee Member

Dr. Breanyn MacInnes

Third Committee Member

Dr. Karl Lillquist

Abstract

Washington has one of the fastest growth rates in the nation, and unfortunately also is among the most landslide-prone states. With increased population density and urban sprawl, the need for landslide hazard assessment grows. On the Columbia Plateau in central Washington, the smooth rigid, inclined surfaces of the Columbia River Basalts (CRBs) with loose sediment layers between them induces landslides of large blocks of bedrock. These hazards remain poorly understood, but their significance was heightened by the 2017 Rattlesnake Hills Landslide that currently threatens a community and an interstate highway south of Yakima, Washington. I propose that the strongest influences on translational landslides within the folded CRBs and sediment layers are dip slope angle, sediment composition and hillslope base removal. Using ArcGIS 10.5 mapping software, my research combines previous mapping efforts, the Washington State Landslide Inventory, and the Washington DNR Lidar Portal to evaluate landslide factors. Having conducted field work and sampled material from two sedimentary members in the area with the highest frequency of translational landslides in my study area, I compare grain size, hydraulic conductivity, dip slope angle, and the apparent dissection and debuttressing of overlying basalt members to identify relative significance of these factors. I aim to better understand where and why translational landslides are likely to develop to asses associated risk and avoid hazardous conditions of area prone to translational landslides.

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