Landslide

gettyimages-Landslide-612x612Landslides in Wasco County generally range in size from thin masses of soil a few yards wide to deep-seated bedrock slides. Travel rate may range in velocity from a few inches per month to many feet per second, depending largely on the slope, material, and water content.

The recognition of ancient dormant landslide masses is important as they can be reactivated by earthquakes, unusually wet winters, or following wildfire events. Also, because they consist of broken earth materials and disrupted groundwater, they are more susceptible to construction-triggered sliding than adjacent undisturbed material. Landslides in the County tend to occur in isolated, sparsely developed areas threatening individual structures and remote sections of the transportation, energy, and communications infrastructure. However, there is a risk that a major landslide could cause the partial closure of segments of Interstate 84 or impact developed regions along with the I-84 corridor, for example, residential developments between The Dalles and Mosier. In the spring of 2017, a rockfall affected the Historic Columbia River Highway just below the Rowena Plateau at mile marker 64.7, blocking this transportation route for several weeks.

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