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Worried About Landslides? Seattle Has A Map For That

In the wake of the deadly disaster in Oso, many people may be worrying about the potential for mudslides in their neighborhoods.

Seattle’s city council is hosting a briefing on landslide hazards. It turns out the city has extensive maps to help landowners and developers mitigate the risks. All you have to do is go to the city's website and type in your address.

"So it’ll go to your parcel. And then you can click," said Susan Chang, geotechnical engineering supervisor with Seattle’s Department of Planning and Development. 

You can find out where the known landslides are on or near your property, says Chang, and where the steep slope layers are. And you can look at detailed contours, "so you can see how steep an area is," she said.

Chang says it’s true that Seattle is very prone to landslides. But the city is also pretty advanced when it comes to prevention policies. She traces that back to the winter of 1996 to 1997, when heavy rains caused slides all over the region. Seattle saw hundreds of them, including the legendary Perkins Lane incident in which several houses went tumbling down a bluff in Magnolia.

But Chang says that also led authorities to conduct an extensive study, using data going all the way back to 1890.

“So we know areas where we've historically had landslides. And they went out and did some mapping and field checking and helped come up with these areas of the city where landslides are more likely to happen," she said.

They're now designated as environmentally critical areas for landslide hazard in the city of Seattle. And if someone wants to build there, they have to sign a covenant, indicating awareness of the risks and agreeing to mitigate and inform future owners.

“They’re not perfect, but they’re far better than most of the cities that I interact with,” said Richard Hagar, an appraiser and teacher of real estate law.

He says Seattle sets a pretty good example of how cities ought to handle landslide risk. He says it starts with the maps, but they have also set out some very good guidelines for developers.

“If you’re going to build in one of these sites you can, they’re not going to stop you for the most part," Hagar said. "But you have to have a reinforced concrete foundations, or things that can handle whether a slide is coming at you, or sliding away from you."

That covers new developments. But other experts say there’s less protection for older properties, where landslides could hit seemingly out of the blue.

The city has response plans in place for that possibility. They’ll be part of Monday's briefing before the Seattle City Council.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to