Road to Darrington Washed out in Mud Slide, 3 Dead

[genepires]

on a much smaller scale, this illustration looks like the slide into the river right by the pilchuck turnoff. the one that took out the original turnoff.

 

Are these kinds of slides usually caused by rivers eating at the base? I thought that the Oso slide was not started by the river erosion.

 

[num1mc]

Many causes

[G-spotter]

So Dave says we've got the motions backwards. The first slide was the lower one, it removed support for the upper block, which then rotated.

 

http://blogs.agu.org/landslideblog/2014/03/28/oso-mechanisms-1/

[JasonG]

Well if it was a one, two event, the "lower" block was still quite high on the slope. the remains of the 2006 failure were low angle and extended 700' from the river to the head scarp. I will need to go back and look at the imagery post 2006 slide, but I'm not sure if there was a stair step above the 2006 scarp. Very interesting, thanks for the link.

[G-spotter]

Here's the first paper o the slide:

 

http://pubs.usgs.gov/of/2014/1065/pdf/ofr2014-1065.pdf

 

That big orange B slide on the last page makes me cringe.

[olyclimber]

that was a large slide. how recent was "B" I wonder?

[JasonG]

Impressive LiDAR isn't it? That "Large B" slide in particular was something that all of us in the office keyed in on when we first got the imagery in 2003. At the time, it was really sobering to see what the geology in this area is capable of. It sounds like many of the residents in this area weren't familiar with the data, unfortunately. SnoCo does have the LiDAR though, I'm just not sure if it is available to the public. I suspect that will change.

Edited March 30, 2014 by JasonG

[JasonG]

that was a large slide. how recent was "B" I wonder?

 

That's a good question. Probably more than 200 but less than 1000. I don't think anyone knows for sure.

[JasonG]

I thought that the Oso slide was not started by the river erosion.

 

This will come out in the months and years ahead as qualified folks puzzle through this. My take is that the river was well away from the failure plane and the failure rode over and entrained the old debris before barreling across the river. Dave Montgomery needs to stick to sites he's familiar with and hold off on suggesting causes.

[num1mc]

And you know that he isn't familiar with this site? Bold claim that.

[JasonG]

http://www.king5.com/news/local/Expert-Erosion-on-satellite-photo-not-a-factor-in-slide-252985581.html

 

I've worked on the Stillaguamish for more than 14 years and I do know that he isn't very familiar with the site. I don't make that statement lightly. Dave's a good guy though, and my boss had a productive talk with him today about the project we did in response to the 2006 slide.

[num1mc]

The seismic data sure makes sense, but you'd have to wonder if the lower debri pile was steep enough while in-situ to fail, let alone fail with such a strong seismic signature.

[JasonG]

I know, the two seismic signatures are certainly puzzling (at least to me, based on my recollection of the site this winter). I will be interested in what the geomorphs come up with in the final reports.

[Off_White]

Interesting article in today's NYT by Tim Eagan: A Mudslide, Foretold

 

 

[JasonG]

Thanks for that, I'll forward it to Pat. Sounds like Tim's time researching "The Good Rain" stuck with him. He's a fine writer.