Our continuing series on the science that informs DNR’s stewardship of natural resources had a well-timed posting yesterday (Science behind the choices: Mapping landslides helps protect people and saves money). It was no coincidence that reports have also been in the news about landslides. This is the time of year when heavy rains start moving across Western Washington. And, given our topography and soils, that can mean landslides, or mudslides to be more accurate.
The Tacoma News Tribune yesterday (Oct. 11, 2010) reported that downed trees and other debris blocked Vashon Highway between Southwest Burton Drive and 115th Avenue SW following a mudslide early Monday morning. Two other small slides occurred; one, a rockfall that briefly blocked lanes of I-90 near Hyak and the other which closed a road in north Tacoma, blocking nearby railroad tracks.
All of these landslides came in areas hit by a belt of heavy rain — from the Tacoma/Lakewood area to Everett and into the Olympics and to northern Cascades. Rainfall in this area exceeded 1 inch in a 24-hour period. These short-term, intense rains provide clues to how landslides are triggered and how better to predict where they might occur. The slides were most likely driven by intense rainfall and prime conditions for failure (thin soils over an impenetrable substrate and weak rock joints).
We’ve already heard that we could be in for a harsher, colder winter than normal because of La Nina conditions in the central Pacific, as this story on Seattle’s King-5 TV describes. Maybe it’s time to get serious about putting together a home emergency kit and other precautions recommended by the Washington Emergency Management Division.
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