This morning there were only a few reported landslides, one that occurred near Port Angeles that unfortunately resulted in the death of Neal Richards of WSDOT, who was struck by a branch while working on clearing the landslide. The only other reported landslides so far was by Jefferson County, who said they have received reports of mudslides. As the morning goes on, we should be able to gather more information on these landslides.

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Two bigs storms are hitting Washington State, one blowing in last night, another blowing in this afternoon. So far, no landslides have been reported over major roadways or have made it into the media (although where we had rainfall so far isn’t well covered by the media). However, this last storm added water into already soaked hillsides, setting up the stage for the potential for sliding this evening and into tomorrow.
We don’t have a forecasting system up yet (so far I have been swamped by other projects and haven’t been able to spend enough time getting it going). But, we can try and make some estimation of areas that will have a higher chance of sliding. I would put this akin to a back of the napkin calculation.

Landslide Risk Map Nov 19-20

Landslide Risk Map Nov 19-20

This is our forecasted rainfall for the next day or so (including some of the precipitation from yesterday). The things to note in all of this, much of the higher elevations where higher rainfall is shown is mostly snow, I never parsed that out in the file. Next, I just used forecasted inches of rainfall to determine where the difference between low and high should be. It is a little arbitrary, but I did look back at the other smaller storms with somewhat similar soil saturations to help determine when we started seeing landslides initiating. This is more of an experiment at this time to see if we can make a really simplified forecasting system that tries and predicts which counties will be at risk of landslides during a storm. A note of caution, even in the low areas we can expect landslides, especially in urban areas. In less urban areas, water usually knows where it wants to go, has been going there for a long time. In urban areas, we have a lot more control over that water, we channel it on roadways and usually discharge it into sewers or into creeks. The problem, if a road channeling water is blocked (either by leaves, debris or some other thing), that water can be diverted, saturating a nearby hillside and causing a landslide, even though rainfall was low. This can also occur with property owners concentrating water on their property. There are a lot of other factors involved of course, but you get the idea.

I talked with Gus Melonas of Burlington Northern Santa Fe. He said that the reported landslides are not quite landslides (well, one probably is a small slump or something). A landslide occurred 4 miles north of Carkeek Park on November 17th, around 6-7am. The landslide was about 30 feet in length, 4-6 feet deep (mostly brambles and blackberry bushes) and composed of mud (no rock). He said it didn’t flow across the track, but any landslide can close the Amtrak Service in that area, so sorry train folks, you have 48 hours to wait. The ‘landslide’ in Skykomish was only a tree that was blown over onto the tracks.
There is one other landslide, one reported up on the Hoko Drainage (Olympic Peninsula), reported by one of our Forest Practice Geologists who helps evaluate that area. That brings our total to 5 landslides from this last storm.

Here was the original post (now defunct):
Two landslides were reported on Burlington Northern Santa Fe railroad lines during this storm, but the news is slow to get out. A landslide in the Carkeek Park area north of Seattle closed Amtrak passenger service for the mandated 48 hours. Another landslide was reported to be on BNSF tracks near Skykomish (I suspected there were a couple of landslides up there). I am attempting to contact BNSF to get some more information on these landslides.

November 16-17, 2009 Storm

November 17, 2009

Here is a precipitation map of this last storm (with reported landslides):

I suspect we have a landslide or two up in the area north of Highway 90, but so far, nothing has been reported.

A small landslide occurred in Gig Harbor today (Nov. 16), damaging a garage and two vehicles. The landslide occurred at 29th Street Court Northwest near Shawnee Drive around 1:30am.

Landslides in urban areas, especially during these first storm events, could be caused by misdirected water or water inadvertently being directed into an unstable area. Something like a drain blocked by leaves causing water to flow onto the hillside. Unfortunately, I have been dealing with my computer dieing this morning, so I haven’t been able to investigate this landslide on the scene. Hopefully I will make it out there tomorrow.

This ground is starting to get to a good saturation level. The chance is probably low to moderate for at least one or two more landslides around the Puget Sound Area from this storm.

Each week we will feature a new landslide in Washington State. Washington State is covered with dynamic and sometimes quirky landslides.

Pe Ell Landslide, Pe Ell, Lewis County

The Pe Ell Landslide failed during the December 3rd Storm of 2007, closing State Route 6 just west of Pe Ell.

Pe Ell Landslide - Photo by WSDOT

Pe Ell Landslide - Photo by WSDOT

The debris avalanche/slide flowed across the highway and pushed a truck into the living room of the house across the way. Remarkably, most of this was caught on tape by the residences of the house.

Pe Ell landslide impact of house - WSDOT Photo

Pe Ell landslide impact of house - WSDOT Photo

On December 11, Kelsay and I arrived at the landslide. The drive through the Chehalis valley was spooky to me, a lingering stench filled the air and misery could be seen all around. Home after home, farm after farm all showed damage from the floods. By time we arrived, WSDOT had already arranged for an emergency contract with Scarsella (on December 9th) to begin work on clearing State Route 6. Unfortunately, with all of the heavy equipment working on the site, we decided to stay on the periphery of the landslide and investigate the damage to the structures.

The damage was localized to the western lobe of the landslide. It impacted the houses at a low speed, warping and pushing them.

Pe Ell landslide impact to a house - DNR/DGER Photo

Pe Ell landslide impact to a house - DNR/DGER Photo

Pe Ell Landslide impact to second house - DNR/DGER Photo

Pe Ell Landslide impact to second house - DNR/DGER Photo

Meanwhile, WSDOT was working hard on figuring out the landslide. The WSDOT Geotechnical Division has access to many really neat tools to help with their investigations. Here is a 3-D representation of the landslide mass created by their division:

Pe Ell Landslide 3D Model - WSDOT Geotechnical Division

Pe Ell Landslide 3D Model - WSDOT Geotechnical Division

They also compiled a small scale geologic map of the landslide mass (with an amazing aerial photo of the landslide):

Pe Ell Landslide Geologic Map - WSDOT Geotechnical Division

Pe Ell Landslide Geologic Map - WSDOT Geotechnical Division

In the end, WSDOT removed over 47,000 cubic yards of material to stabilize the landslide mass at a cost of around $4 million dollars. The project was completed on March 13th, 2008, over three months after the storm.

The landslide prompted a debate on logging, landslides, and highway safety. The landslide itself was logged weeks before the storm. The interesting part, this landslide wasn’t caused by root strength loss, it was probably too deep anyway to have much impact. The lack of canopy, however, might have played a roll in the landslide initiation. Canopy plays a role in reducing the rate rainfall from reaching the ground (to a certain point) or slow melting of snow on the ground by reducing rain rates and buffering changing temperature. It is difficult to say in an intense storm how much it might have slowed the rainfall, or reduced snow melt (by reducing the warm rain and temperature from reaching the snow), but the lack of trees, even with this intense rainfall, probably did increase the likelihood for its initiation.

Cause aside, the cost of repairing these landslides is expensive. This is just one of probably hundreds of landslides to fall on our highway systems each year. Figuring out why these landslides fail and if we can either mitigate or possibly find better management practices to help reduce landslides would help save millions of dollars and reduce injury and death.

Each week we will feature a new landslide in Washington State. Washington State is covered with dynamic and sometimes quirky landslides.

Racehorse Creek Landslide, Whatcom County

On January 6th, 2009, a Pineapple Express (actually to have formed off of Hawai’i) flowed into Washington State, hitting the northern counties first and moving into the southern counties. Whatcom and Skagit Counties were first to report landslides late on January 6th as warm rains melted away snow and thawed the ground. As the rain continued, a small rain on snow type event occurred, spawning over 1,500 landslides. Debris flows and debris avalanches were the most common landslide to have formed from the storm event and the majority of the landslides occurred on the flanks of the Cascade Mountain Range.

January 2009 storm map with an incomplete landslide inventory

January 2009 storm map with an incomplete landslide inventory

This map shows the storm intensity overlain with landslide initiation points, primarily from DNR/DGER aerial surveys after the storm and reported landslides from public and private folks.

One of the largest landslides during the January 7-9th storm occurred along Racehorse Creek in Whatcom County.

Racehorse Creek Landslide; DNR/DGER Photo

Racehorse Creek Landslide; DNR/DGER Photo

The landslide occurred in two major components, the main debris avalanche and near lateral debris flows. The main debris avalanche is over 160,000 square yards and moved a significant amount of trees into Racehorse Creek. The debris flows scoured into the ground, removing timber in its way, also reaching Racehorse Creek. Once in the swollen waters of Racehorse Creek, the moved debris moved downstream, forming a massive logjam.

Logjam formed by the Racehorse Landslide, looking towards Kendall Creek; DNR/DGER Photo

Logjam formed by the Racehorse Landslide, looking towards Kendall Creek; DNR/DGER Photo

Logjam formed by the Racehorse Landslide, looking towards Racehorse Creek; DNR/DGER Photo

Logjam formed by the Racehorse Landslide, looking towards Racehorse Creek; DNR/DGER Photo

The size of the landslide has caused many to scratch their heads as to what possibly might have triggered this landslide. Some point to an earthquake as a possible trigger (one did occur on January 6th, 2009), others, natural factors of erosion and saturation. Or, as is common, a combination of saturated ground, erosion of the toe and a bit of shaking from an earthquake.

Whatcom County Earthquake Map; DNR/DGER

Whatcom County Earthquake Map; DNR/DGER

Each week we will feature a new landslide in Washington State. Washington State is covered with dynamic and sometimes quirky landslides.

Hornby Landslide, Glenoma Area, Lewis County

This is one of the more fascinating landslides that occurred during the January 2009 storm. Numerous debris flows and avalanches dotted the slopes above Mark and Jon Hornby’s farm.

Map of landslide in Glenoma Area, Lewis County

Map of landslide in Glenoma Area, Lewis County

Hornby Landslides

Hornby Landslides

Series of Events

At about 9:00 am on January 8, a large debris flow moved into Mark Hornby’s farm pasture, plugging a culvert and covering it with mud and debris. About a half an hour later, another landslide came off the slope, nearly striking Mark and his brother, Jon. I think this landslide also struck a bull and carried it a ways across the pasture. There full story can be found here.

View of debris flow deposit near house; DGER/DNR Photo

View of debris flow deposit near house; DGER/DNR Photo

The debris avalanche/flow in the middle of the clear cut slope is very shallow, less than 2 feet of incision in many places. The landslide incised down to bedrock in most places, which was probably why the landslide was so shallow. When it reached the pasture, the landslide turned into a short debris flow and then transformed into a hyperconcentrated flow and made its way across the Hornby’s Farm pasture. The landslide ponded against Highway 12, flowing to the Hornby’s driveway and then onto Highway 12. One of the oddities discovered in Glenoma was that many of the hyperconcentrated flows that reached the valley floor were entrapped into roads by snow berms from plowed snow.

Hornby Landslides; DGER/DNR Photo

Hornby Landslides; DGER/DNR Photo

January 7-8 Storm Summary

In December of 2008 and into January of 2009, cold air from British Columbia created an ideal condition for snowfall across Washington State. Snow accumulations preceding the storm were low in the Puget Lowland, with at only inches on the ground in most places. On January 7, a stream of moisture originating from around Kauai (Hawaiian Islands) flowed into Washington State, bringing warm temperatures and high amounts of rain, rapidly melting what snow remained in the lowlands and eating away at the snowpacks in the mountains. By January 8, the largest evacuation in the state’s history was under way, forcing more than 30,000 people living in the Puyallup River area to flee. The town of Orting, with a population of more than 26,000, was almost completely flooded. For the second year in a row, flood waters closed Interstate 5 in Centralia/Chehalis. In the rest of the state, rivers were also flooding—the Stillaguamish, Snohomish, Chehalis, Naselle, Hoko, Cedar, and Cowlitz were the most significant, peaking above the 100-year flood level.

King and Snohomish County were least affected, as a rain shadow from the Olympic Mountains shielded their low-lying areas. In the Puget Lowland, rainfall totals ranged from 1.5 inches in Seattle to 5 to 7 inches in southwest Washington and 3 to 6 inches in the northwestern counties. As the storm progressed into the Cascades, the higher elevation forced the clouds to release water as they moved over the mountains, leaving more than 20 inches of rain in two days. The rainfall saturated slopes, many already wet from melting snow, triggering debris flows and debris avalanches throughout most of western Washington. Areas sensitive to high-intensity storms, such as Glenoma, Concrete, and Van Zandt, were the site of numerous large debris flows, blocking roads, limiting emergency response, and destroying homes. In the end, more than 1,500 landslides were reported or recorded from Washington Division of Geology and Earth Resources (DGER) field and aerial surveys.

Logging and Landslides

DGER and AEG hosted a field trip in the Glenoma Area (field trip guild). The purpose of this stop was to discuss logging and landslides. Unfortunately, the conversation never got going very well. It certainly caught my attention when I was looking over the photos coming in. One of the first things that caught my attention was the prominent deep-seated landslide on the west side of the clearcut. It is difficult to see if it is active from a photo, but when I first saw it from the aerial photo I thought it probably had some recent movement (within the last 100 years, maybe?). In the subsurface, there are places of thick, mostly unconsolidated pumice. So, is this logging related? It is possible. Was it illegal? Probably not. I didn’t do any detailed ground survey of this area, but just at a general glance, I cannot think of any forest practice rules that they might have broke. Maybe we need to look at if the FP rules are protecting our slopes, especially in Lewis County.

One of the more interesting landslides I have ran across was a debris flow triggered during the December 3rd, 2007 storm west of Pe Ell, Lewis County. Kelsay and I were conducting a reconnaissance of SW Washington to try and find out just how bad the landslides were. We pulled up through Pe Ell to find two debris flows that had come across State Route 7 and surrounded a house.

Pe Ell Debris Flow - Impact to House

Pe Ell Debris Flow - Impact to House

We parked and I decided to hike up the western debris flow as Kelsay went to look at the eastern debris flow. Unfortunately, I didn’t see the ditch that was covered in mud and quickly went up to my hips in mud (and since I do all my field work in a skirt, that was about as awful as it got!).

Western Pe Ell Debris Flow

Western Pe Ell Debris Flow

Past falling in the mud, the hike up was fairly easy and the scarp was amazing. A thin layer of soil and dirt has slid off of a hollow area (not to be confused with the DNR Forest Practices definition of a bedrock hollow), that is a volcanic tuff.

Western Pe Ell Debris Flow Scarp

Western Pe Ell Debris Flow Scarp

The soil is between 6 inches and two feet, depending on which side of the scarp you are at. The convergent topography with intense precipitation probably greatly contributed to the landslide moving. The rainfall in this area was probably between 16-20 inches during the storm (the majority falling on December 3rd). Intense rain + shallow soils + impermeable substrate = landslide. Actually, that is the formula we saw again and again for almost all landslides during the December 3rd storm.

The other interesting thing to point out, the area was recently harvested. The lack of canopy coverage can increase the rate that rainfall will reach the ground (from a timed delay to no delay). On weak storms and wet winters, this could increase landslide activity, but we haven’t seen it very many compelling cases around Washington State (but there is a nice study from Canada). However, during the December 3rd storm, the intense precipitation and lack of canopy might (and I will go out on a limb and say almost certainly) have increased landslide activity. To what extent and what increase, that remains to be seen.

We tried getting into the Pilchuck headwaters yesterday to no avail. Roads were washed out and gates were locked. We did see a number of landslides on the Sultan Basin Road heading up to Olney Pass. These landslides bare the mark of a large rainstorm event and almost certainly moved during the January 7-8th, 2009 storm event

Sultan Basin Road Landslides

Sultan Basin Road Landslides

The picture has a backdrop of 2003(? I think it was later than that) Snohomish County LiDAR.

The most interesting of these landslides is a debris avalanche at the bridge crossing at Olney Creek. It was probably dealt a one-two punch, the swollen Olney Creek was probably eating away at the bank (and probably has been for years) and the saturated ground allowed enough driving forces to overcome the resistive forces. It also moved a good amount of timber into the creek, which might cause a problem down the road by creating a debris dam behind the bridge.

Sultan Basin Rd Debris Avalanche.  Photo by Carol Serdar

Sultan Basin Rd Debris Avalanche. Photo by Carol Serdar