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Lands are sliding around the Sound, again

Gravel plus rainwater plus clay mean slides

By Tom Trimbath
Tom Trimbath

Look around the news, or maybe just your neighborhood, and notice that landslides are happening around the Sound. Homes, roads, and tracks have all been hit because of our recent rains. The threat is not over, yet.

Our region has a particular mix of geology and meteorology that mix to make the ground move. Because we sit near the end of the glaciers’ advance, much of our ground is gravel layered over silts and clay. That may be stable enough for a while, but it is like a pile of sand that will eventually collapse. Add water and the process speeds up as the internal friction drops letting the gravel roll down the clay layer. The combination is worst in the winter, which is when it is messiest to clean it up.

If you already own property, are considering buying some, or just happen to live or commute by steep slopes, there are a few things to watch for. Here’s a list from the Washington State Department of Natural Resources:

  • Cracks forming in your yard, driveway, sidewalk, foundation or in other structures.
  • Trees on slopes, especially evergreens, start tilting.
  • Doors and windows suddenly become more difficult to open or close.
  • Water begins seeping from hillsides, even during dry weather.

They also produce and update a map (in beta) of the regions under the greatest threat. That doesn’t mean slides won’t happen elsewhere, but the map shows the target zones.

WA DNR

Because the weather has an effect, the National Weather Service also adds alerts, such as today’s “Special Weather Statement.“

“...Heavy rainfall today will lead to an increase threat of landslides in western washington...“ - National Weather Service

To quote from our previous article, which includes photos of previous, larger slides;

“You can hire people to analyze and assess specific properties. Find out if your backyard is going to end up in someone else's, or vice versa. Maybe you can do something about it, and then you can truly enjoy the view.“

Take a look around, and be careful out there.