Report: Washington state mudslide area had 60-year history of instability
The area in Washington state hit with a devastating mudslide over the weekend has been the subject of concern over its instability dating back to the 1950s, the Seattle Times reported on Tuesday.
“We’ve known it would happen at some point,” geomorphologist Daniel Miller told the Times on Monday. “We just didn’t know when.”
Miller and his wife, Lynne Rodgers Miller, wrote a 1999 report for the Army Corps of Engineers saying that the affected area in Snohomish County, where the mudslide took place, had “the potential for a large catastrophic failure.”
However, the head of the county’s department of emergency management, John Pennington, was quoted as saying on Monday that the area “was considered very safe” and that “This was a completely unforeseen slide. This came out of nowhere.”
Daniel Miller also told the Times that construction was allowed to continue in the area less than a week after a mudslide in 2006 that plugged part of the Stillaguamish River and posed a risk to prospective homeowners in the area, which has been known to some residents as “Slide Hill.”
“Frankly, I was shocked that the county permitted any building across from the river,” Miller was quoted as saying. “We’ve known that it’s been failing. It’s not unknown that this hazard exists.”
A report commissioned in 1951 to assess potential mudslide damage to the local salmon-fishing industry found that while building terraces on the border of the river or permanently diverting it could help stem future slides, it would not do so permanently.
“It is almost impossible from a practical standpoint to stabilize this slide in its present position. The slope will continue to slide and the area will increase,” an addendum to the report concluded. “Drainage ditches, dikes, walls, etc., would give at best only temporary relief. The structures would need constant repair and replacement.”
Records also indicate that no actions were taken to reinforce the area until 1960. More recently, officials installed a 1,300-foot “crib wall” of boom logs, using 9,000-pound concrete blocks to serve as anchors at 50-feet intervals, but the measures proved to be ineffective against last weekend’s mudslide.
Reuters reported on Tuesday that the number of people presumed dead as a result of the slide had increased to 24.
Watch a video on the history of instability in the area, as posted by the Times on Tuesday, below.
[Image: Workers dig through debris using heavy equipment in the mudslide near Oso, Washington March 25, 2014. By Ted S. Warren for Reuters/Pool.]