ENVIRONMENT

Landslides are part of the geologic heritage of the Pacific Northwest, where a deadly mudslide claimed eight lives. But it’s almost impossible to tell when a slope is primed to fail. (Seattle Times)

Use our resources to learn more about landslides.

Discussion Ideas

• Read through our short encyclopedic entry on landslides. It lists three major causes of landslides: geology, morphology, and human activity. What contributed to the mudslide along the Stillaguamish River?
  • Geology and morphology. The Seattle Times article cites “a nightmare scenario.”
    • The geology of the hillside, like much of the Pacific Northwest, is prone to landslides. “The glaciers that sculpted our landscape and created high bluffs also left behind the sandy, crumbly soils that make slopes prone to collapse,” the article says.
    • The morphology of the slope also contributed to the slide. The article describes how heavy rains loosened the soil on the slope, and led the gushing Stillaguamish River to undercut it.

• Read through our short section on “landslide movement” in our encyclopedic entry on landslides. Then take a look at the Seattle Times‘ interactive photograph of the massive mudslide. How do you think geologists and geomorphologists would describe the movement of the Stillaguamish River mudslide?
  • It looks like a translational slide, where surface material is separated from the most stable underlying layer of a slope. In the case of the Washington mudslide, surface material includes vegetation such as pine trees as well as loose soil and rocks.

• Read through our activity “Extreme Natural Events.” Adapt and work through the questions.
  • Besides landslides, what are some other extreme natural events that might be common in western Washington? Take a look at our MapMaker Interactive and try turning on layers in the “Physical Systems” theme for some help.
    • avalanches
    • earthquakes (the article mentions several faults that cut through western Washington, including the nearby Darrington-Devil’s Mountain Fault)
    • wildfires (the area is heavily forested)
    • flooding (both rivers and coastal)
    • volcanoes (the region is part of the so-called Ring of Fire, and Mount St. Helens, in southwestern Washington, is among the most active volcanoes in the U.S.)
    • snowstorms
    • thunderstorms (Seattle’s rainy weather is a symbol of the city)