Wednesday, February 04, 2009

Deer Creek

Early in the morning of January 15th, 1997, during a very wet winter, a huge chunk of the hillside just south of Deer Creek let go, collapsing on the railroad tracks and spreading across the beach (Woodway Landslide). The point of land created by the resulting dirt pile has been gradually eroding ever since, leaving this 2-meter high retreating scarp and an assortment of broken trees, large chunks of the bluff, and train parts. And yards and yards of green and purple fabric, something probably related to the Catholic center at the top of the slope.

Slides this big are pretty unusual on Puget Sound, which is probably a good thing, since if they happened more often the human cost would be high. Figuring out where they are going to happen next is a challenge. You can predict that a shallow landslide or debris avalanche will occur on just about any steep bluff on Puget Sound sometime in the next few decades, but we only know of a few slides this big that have occurred in the last 30-40 years. They leave their marks - hillslopes covered with single-aged stands of alder, trees and big blocks of clay sticking out of the lower beach, strange promontories on otherwise steep shorelines.

This stretch of shoreline is notorious for landslides. In the 1950s, the railroad actually relocated the grade away from the base of the bluff to reduce slide damages. The result is a series of linear wetlands between the new causeway and the bluff - on top of the original beachface. But since then slides, including some very large ones in the early 1970s, have begun to fill the trough in.

Too bad we never systematically monitored the erosion of this dirt pile - or figured out how to track the resulting sediment offshore or downdrift. People did report lots of accretion and scattered debris showing up at the park up in Edmonds in the years following the slide.

No comments: