While Saturday’s deadly mudslide could not be predicted, many are wondering whether their home is at risk.
The state Department of Ecology has stability maps that shed light on coastal slopes around Western Washington. All the data is based on aeriel photographs, geological mapping, topography, and field observations.
For example, the cliffs along Magnolia Blvd, inside Discovery Park, and areas of West Seattle are considered unstable “because of geology, groundwater, slope and/or erosional factors. They include areas of landslides and talus too small or obscure to be individually mapped. ”
Many pockets along Vashon Island are unstable from a recent slide, but “investigations were carried out in the late 1970s; subsequent landsliding is not reflected.”
There are large areas of unstable pockets along the Everett waterfront and in Tacoma.
Maps extend to the first 2000 feet inland from the shoreline.
The department makes it very clear that the mapping represents conditions as they were in the mid-1970s and human activities may have altered the stability since then.
Also, the department says the maps are for educational purposes and should not be a substitute for site-specific studies done by geologists and engineers.