Washington landslide.

yes, and also a warning to those who would build in environmentally susceptible area's, don't become a statistic.

 

I used to have a client up in that beautiful area. I hope all are safe. I didn't see anything in the articles I've read, but was there recent wildfire damage in the area that made it unstable in the rain?

 

As I recall reading, it was simply too much water over too short a period of time.
We need to plan for fewer rainfall occurances, but when they do happen it will be more of a deluge.

 

Frankly would like to see more photos of the surrounding slopes. Pix on CNN showed no fire damage on nearby slope that did not fail. Have to say that all visible factors seem similar to large areas in the vicinity. Youngish even-aged mixed forests on Andisols derived from very thick volcanic ash. The slope that failed was probably not unusually steep, nor undercut (need better pictures preferably 'before' for that).

For now, going with 'heavy intense rainfall' and bad luck for the people below the slope that failed. I should think this would happen in lots of places in the vicinity. Have there been other reports of (smaller) landslides?

If replacing old-growth forests with 'young' on such soils and slopes makes them much more susceptible to slope failure, then it is a general problem of long standing. Those old trees are long gone from the PNW.

 

Latest report mentioned the same region had another landslide in 2006.
Pour enough water over any slope and it will eventually fail.

 

This area has had many many slides over far more than a few years. Check out Deer Creek near this area, for example. What has exacerbated this more than nearly all variables is they have clearcut nearly 100% of this area. Nothing remains to hold the soil together, erosion accelerates overall watershed degradation, etc. Then we act surprised or confused when slides happen.

I have gotten in hundreds of disputes over this subject over the years, and the world record response I got from this one timber industry guy: "We have too much oxygen in the air in this valley and need to get rid of some of the trees." Delivered with a straight face, I must add.

 

Thanks, appreciate the information from the local area.
That response from the timber company is just too damn funny, and sad.

 

Landslides are a fact of life in many parts of this region, both natural and induced by human activity. But they are far more linked to slope stability and rainfall and earthquakes and surface water management and development than to fires. This location had something like three previous major slides in the past century.

It appears the slope may have been undercut by a shifting river channel. I believe there was no development below the slide on that side of the river, all the human damage was on the other side of the Stillaguamish River.

PS: some Seattle Times news stories --
River probably undercut, destabilized soggy slope

Site has long history of slide problems

 

I found a newspaper's list of missing people (not the complete law enforcement list), and it confirmed my fears. The man I worked with to replace my roof last year, just before installing my home PV system, is missing. So is his wife, and a technician who was working at their new retirement home.

Larry was an extremely helpful roofing advisor. He was excited about my solar PV plans, and did a very good job of making our roofing plan accommodate the planned PV. I saw him again at this year's Seattle Home Show, met his wife Sandy there, and even saw the photos of their not-yet-finished house, at the booth of the PV installer that did their new system. My PV excitement spilled over to them, so they had also hopped on to the solar bandwagon.

My fingers are crossed, but it doesn't look good.

 

Local info is key to understanding this and I thank our folks nearby for responding. Have not been in that area for >10 years and at that time I was not looking for slopes ready to fail.

All I offer is a very general idea that volcanic ash is not 'structurally stable' and the only thing that holds it in place is tree roots. In the PNW a lot of mid- and steep slopes are just waiting for a reason to follow gravity's bidding. In this particular place, I saw photos on CNN that the remaining upslope forest was intact (but young). If the (now absent) mid-slope forest had been removed, that would be important and really why I'd hope that earlier photos exist.

Rivers change course to find a better 'gravity solution', constrained by the stuff they might cut down through. Aldo and Luna Leopold explain it better than I ever could. Great reading there.

 

Jamesh8251 welcome to PC! Hope you find many ways to participate here.

Anybody who thinks 21% oxygen is too much should try a couple of minutes without it Now, 30% is troubling because at that level just about everything burns and is hard to extinguish. But at present we are not heading in that direction. Fossil-fuel burning is very slightly lowering atmospheric O2. Search Scripps O2 for the graph.

 

Besides fuzzy1 link to the Seattle Times, see this

Landslide in Washington State: USGS is working with partners to provide up-to-date information -- ScienceDaily

One would sure like to see LIDAR images over a wider area, they seem pretty clear about what locations have slid before. Some boots on the ground are required to determine when, though.

Building your house in the flat 'runout' area downhill of a crescent arc does not seem entirely wise. For that matter, not on the land above an arc either. This may leave one with few choices however. Seattle Times coverage gives the impression that building permits have not considered this. Perhaps they will in future. I am highly sympathetic towards landowners who are not technical in this way, getting the go-ahead from some (responsible) government agency, and then getting smooshed.

OTOH, if the agency says you can't build, it will draw negative comments about lost freedoms and nefarious UN Agenda 21 and so forth. Can't win I guess.

If the sliding has been going on for 1000s of years (as USGS says) and if the recurrence rates have not quickened (not clear from the research), then an hypothesis that young trees are not so good at preventing landslides would need to be withdrawn.

 

Larry has been confirmed dead. His wife, and the contractor at their house that morning, are still among the seven remaining missing.

A full victims list, with profiles of most, is posted on the Seattle Times: Remembering the victims of the Oso mudslide

 

My condolences fuzzy ;(

 

+1

 

While earth movement is not new to this area... the devistation to the local community is.

Washington will have a much much bigger landslide when one of the northwest slopes gives way towards the Sound... the folks living there now will be under much much more material when Rainier gives way again.

Volcanic Landslides at Mount Rainier volcano, Washington

 

Yes, several valleys in this region has experienced very many lahars (volcanic mud or debris flows), not just the single Mt. St. Helens disaster of white man's memory. A number of them have reached all the way to Puget Sound. Many more will come. Most will not be linked to any recent volcanic activity, but will instead be triggered by glacial outbursts or slope failures of the high rock formations weakened by millennia of leaching sulfuric acid in the groundwater. Mt. Rainier was originally several thousand feet higher, and much of the missing rock came down this way.

So the areas most at risk have the Mount Rainier Volcano Lahar Warning System - Wikipedia, the free encyclopedia, which should detect most of these events far upstream and warn local residents to flee to higher ground before the flows reach the primary towns. This is much like the coastal tsunami warning systems, complete with warning sirens, reverse 911 notifications, signed evacuation routes, and periodic practice drills in the schools in the primary flow paths.

As an example, here is information for the city of Orting, and its siren test schedule:
Lahar Information - City of Orting | City of Orting
Lahar Siren Test - City of Orting | City of Orting

This region is geologically young, so it is not particularly stable. Volcanoes build and collapse. Other mountains are tectonically pushed up, then rapidly erode. Glacial till gets built up or rearranged each ice age, then later collapses as new or shifting river channels erode the sides of the deposits, as happened last month at Oso. Coastlines keep shifting. Earthquakes or extended heavy rains trigger weak slopes to slide, dumping whole forests into Puget Sound or Lake Washington or the Columbia River.