Washington state Department of Ecology
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bench slides
houses perched on a mid-slope bench
Mid-slope benches can be hazardous slide areas.

Relatively level benches on an otherwise steep slope may indicate past slope movement. Mid-slope benches, though not a specific type of landslide, are a common setting for slides for a variety of landslide types and are often vulnerable. These features occur along many Puget Sound shorelines.
 
how bench slides work
 
more about bench slides

Long term erosion or deep slide
Benches may occur along layers of resistant geologic materials, where long term erosion or landsliding of the overlying units has produced a stepped slope. Alternatively, a bench may indicate the dropped-down portion of an ancient, deep-seated landslide.

Obscured by development
Benches present attractive sites for development, since they offer level ground near the water on otherwise steep terrain. In many places, roads have been built down the steep upper slope to serve home sites along the bench itself. Benches can be obscured by heavy vegetation in undeveloped areas or by grading and construction activities in built up areas.

A variety of hazards
A variety of landslide hazards affect benches. Shallow landslides off of the upper bluff can damage structures built on the bench. Much of the material on the bench may consist of older landslide debris and may be subject to further movement. Slides can also occur on the lower bluff above the shore itself. In the worst case, the entire bench may be part of a deep-seated landslide.


Examples of benches
Examples of benches can be seen along the shoreline north of Kingston, above the railroad grade north of Carkeek Park and on Magnolia Bluff in Seattle, and along portions of the south shore of Hammersley Inlet.
Magnolia Bluff
Magnolia Bluff
 
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