Nile Landslide LiDAR

December 10, 2009

Sometimes you get a Christmas gift you weren’t expected. I guess in this case, it was more of a birthday gift. LiDAR for the Nile Landslide has finally preliminarily been released to various people to help in analysis on the landslide, but has not yet been released to the general public until the proper QA/QC has been established on the data. If you are working on the Nile Landslide (and I have talked with many of you already) and would like a copy of the LiDAR, contact me and I’ll see what we can arrange.

That being said…

I am going to analyze the lidar a bit more, but some interesting things. You can clearly see some of the uplifted areas, although it might not be as extensive as we previously thought. There are a few secondary landslides within the landslide mass, one major one by the quarry. Near the center of the landslide, there are some odd peaks (near the toe), not sure what those are, but I’ll try and find out today. Anyway, stay tuned, this is a key piece of data to help us understand the Nile Landslide. The Lidar also covers the Sanford Pasture Landslide as well and this will give us clues to the activity and morphology of this landslide as well.

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.

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.

I should have given the chance of landslides a bit higher than low to moderate, but at the time, the rainfall might not have been intense enough.

We have a couple of landslides across Washington State this morning, most notably, a landslide out near Hoodsport on US 101 at milepost 324. The road was closed at 11/16/2009 9:39 PM, so the landslide occurred somewhere in the 9:00 PM hour. This is very near the same spot that a handful of landslides occurred on the December 3rd Storm in 2007 and this area is quite susceptible to intense precipitation (storm) events.

Another landslide occurred on the Olympic Peninsula on State Route 112 at milepost 2.00. Apparently this occurred on 11/16/2009 at 1:00 PM, but I didn’t catch wind of it until this morning.

If you see a landslide, please report it to us. You can contact me at: 260.902.1425 or by email: isabelle.sarikhan@dnr.wa.gov

It has been awhile since I completed a Landslide of the Week. I think the Sanford Pasture Landslide is a good candidate since it has gotten so much press lately and what we know about it is fairly limited (at least, in publications).

The formation of the Sanford Pasture Landslide started back in the late Miocene and early Pliocene epochs, where the eruptions covered much of Eastern Washington with basalt, known as the Columbia River Basalts. Between the eruptive cycles, sandstones, generally fluvial in origin, deposited on top of the flows, only to be covered by the next pulse of magma. These are known as interbeds and are suspected to be Ellensburg Formation. At the Sanford Pasture Landslide, the dominant flows of the Columbia River Basalts are the N2 and R2 flows of the Grand Ronde Basalts, some of the last recorded flows of the eruptive cycle. Much of the deposits were lain horizontally, but as we know them today, the geologic units are folded and faulted. This is accomplished by stress from the subductive oceanic plate pushing its way underneath the continental crust that we live on here in Washington State. The force of the collision compresses Washington State, forming wrinkles and faults as the stress is dissipated through the plate. In the Naches area, this folding resulted in the formation of Cleman Mountain as a steeply dipping anticline. The area was not able to just fold to reduce the stress on it, it faulted as well, forming the Nile Thrust Fault. The failure mechanism is something that we probably do understand. The oversteepened anticline combined with the weak interbed layers of sandstone created a perfect weak plane for the above rock to slide on. An earthquake, probably on the Nile Thrust, or perhaps something larger like a Cascadia Subduction Earthquake, probably reduced the restraining forces enough to start the material moving downhill, depositing where we see it today (more on that below). These events occurred after the Columbia River Basalts and interbeds were lain in place, giving us a limiting age on the landslide. Given the flow age, coupled with the folding and faulting of the area, the general estimation of the landslide is 2 million years old.

Determining the age of a landslide is often difficult. Dates can be acquired through a couple of different methods, most often coring into sag ponds, or lake bed deposits (on older landslides that have dammed rivers), or by coring old tree snags that have been drowned. The goal is to find datable material or stratigraphic reasoning to determine a specific of general age. For the Sanford Pasture, there are no found lake bed deposits up valley of the landslide initiation and the landslide is too old to support sag ponds that formed during its initial movement. The general thought is that the landslide occurred prior to glacial times.

The Sanford Pasture landslide moved across what is today the Naches Valley and deposited material almost a mile inward from the valley’s edge. During this time, the Naches Valley was less incised and contained much less water (remember, no lake beds deposits), so whatever damming of the paleo-fluvial system here, it was minor. During the age of glaciation in the Quaternary Period (predominantly alpine glaciation influences at the Sanford Pasture). Advances and retreating of the glaciers, combined with their constant run-off carved much of the valleys and fluvial systems we see today in the area. I should point out, I don’t think any glaciers have reached the Sanford Pasture Landslide area. The melt water flowing through what is now the Naches Valley would have eroded out the landslide and continued to incise into the valley, exposing in-place Columbia River Basalt Flows on the western side and eastern side of the valley. Unfortunately, all of this erosion created yet another unstable element into the system. The eroding river removed much of the lateral strength that the landslide had when its mass continued for another mile. It literally shortened the landslide by half. In response, the Sanford Pasture landslide didn’t fail as one large piece, but as smaller failures within the older landslide material.

This image of the Sanford Pasture Landslide is a quick drawing of the possible major landslide events. There are dozens of smaller events throughout the landslide. The most difficult part to figure out is the northwest section of the landslide, that appears to have gone through a series of deformations, probably more than I have drawn here. That is something we are going to try and unravel down the road. It is difficult to determine if the last major movement was on the eastern or western section of the landslide. The only sag pond that exists on the landslide is on the eastern side, known as Dog or Mud Lake. This makes me suspect that the last major movement has been on the eastern side. Other evidence also suggests that the morphology is younger, less stream development and incision on the eastern side. Regardless, the western side is the side where the Nile Landslide initiated off of and probably has a much more active, smaller landslide activity.

The area where the Nile Landslide has occurred has experienced several large landslide events. Looking at the history, the Nile Landslide is probably the 4th in a series of movements in the area (Sanford Pasture, Largest block in purple, smaller block in green, then Nile Landslide). That is the larger movements. Further evidence looks like smaller landslides have been recent in the same area as the Nile, maybe being able to form and move every couple of hundred years (not sure how far back this might go, but maybe a thousand or two years, depending on when the major movement of the largest block in purple and smaller green block occurred). Granted, that is a bit of speculation. In the 1940’s photo, there is clearly areas without vegetation that look hummocky that might indicate recent movement, like within the last 50 years. Comparing that 1940’s photo to today, areas that were once void of vegetation now are supporting sparse tall trees, indicating a possible regrowth period. Maybe we are looking at something that is geologically common here.

The last work, Sanford Pasture Reactivation. This has been pushed around in the media about State Geologists concerned about future movement of the Sanford Pasture Landslide. They are right, we are concerned, I being on of them. The removal of lateral support by the Nile Landslide could reactivate something larger uphill. Remember, this is really torn up landslide material, it has its strength reduced and it looks like it is sliding on something that is fine grained. Reactivation of the Sanford Pasture Landslide, worst case scenario, would completely block the Nile Valley, forming a massive lake (Lake Naches?) behind the debris. The threat would then continue into the competency of the material to hold the water, a race to safely dewater the lake and the possible major dam-burst flood into the Yakima Valley. The destruction of that last one would be unlikely, but something we have not seen the likes of in modern society.

Orthophoto and Fissures

November 9, 2009

WSDOT released an orthophoto of the landslide last Friday (at least, this is when I got it). The image is spectacular and helps give us some much needed data. This weekend I worked on mapping out all of the fissures in the “Woodshed Restraint”, as well as other places (that was much quicker, since the cracking was predominantly localized there).

A note of caution on this map, these fissures haven’t been field verified, so they could change, move, or disappear. Especially some of the cracks outside of the Woodshed Restraint area. We have some data on these as well as for the types of movement (uplift, down dropped or translational movement) and that will help us map the stresses and block movement within this mass of earth.

Last week DNR issued an order to suspend mining at the Simmons Quarry. There is a long story within that, but also one that may lead to some legal issues. The continued potential for danger and instability in the area gave us concern for public safety in the area, especially since we have residences living in houses right on the landslide. More on that later.

This landslide has brought together an surprising amount of scientists from various agencies around Washington State. One that certainly deserves mention is John Vidale, Director of the Pacific Northwest Seismic Network, and his crew, who has been of invaluable help to us in helping to unravel the timeline of this landslide. Here is an excerpt and some data that John had given us:

These are spectrograms, which plot frequency content of the seismogram the vertical axis against time on the horizontal axis. The number on the horizontal axis is hours after the start of Saturday, for example, 34 is 10am Sunday. I think you can see more detail on them by looking at them in a graphics program. This 1st plot runs from 25 to 35 hrs, the bright red spot is the landslide noise at 10am Sunday. The vertical axis is frequency – 0 at the top grading to 10Hz at the bottom. The 5Hz sound of the landslide grows from imperceptible on the left until the racket at 34, then fades slowly.The industrial source at 9Hz is visible as the pulsation on the bottom, and the pops are too short to see in this plot. The 5-10Hz smears in the lower right are probably unrelated cultural noise that starts at daybreak after a quiet night.


Close-up of the noisy part, spanning about 1.3 hrs or 80 minutes.

This is the noisiest part of Saturday, hours 5-21, on the same color scale. More cultural noise 5-10Hz starts about 7am, as appeared above for Sunday. There is not a signal similar to the 5Hz band above, which is apparently how the landslide appears on this station. Also, the patches of signals present do not match the timing of energy on the other nearby station ELL. So maybe some Saturday landslide noise could be invisible on this plot, but it would be less than the noise on Sunday.

Here is an example of the pops at their most frequent, 2 hours before the big noise. The plot spans about 15 minutes, and the pops appear on the upper half of the plot, 1-5Hz, and agree in timing with pops seen on station ELL.


This is the burst at 7:38 Sunday in a 15 minute window. Note the strong 1-2Hz energy, more so than during the rest of the landslide-related signals, and most of the action takes place within 1 minute.

This is the 4:55am Sunday burst in a 15-minute window, weak but with the same frequency range and gradual onset as the other slide related shaking.

This sort of data allows us for form a timeline to the landslide movement. Combined with eye witness reports, we can reconstruct the various parts of the landslides and when they moved. With that data, we can look at the places of initial movement and evaluate the pre-failure conditions to see if there is any likely event that might have triggered this landslide. Vary preliminary data, however, has been suggesting that landslide movement might have been prior to 2002 (we are still working on this), but this movement was quite slow, just about creeping. I am currently working on tying together a series of aerial photos to determine the amount of movement and hopefully to constrain the first start of movement.

slide3

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

Koontzville Landslide, Okanogan County
This landslide is part of the 1961 USGS publication Landslides along the Columbia River valley, northeastern Washington.

Location Map for the Koontzville Landslide

Location Map for the Koontzville Landslide

Koontzville Landslide Map

Koontzville Landslide Map

An excerpt from USGS Professional Paper 367 on the Koontzville Landslide:

“The Koontzville landslide involved the entire village of about 35 houses, one store, and a section of State Highway lOA [replaced by State Highway 155]. The village was built in 1934 and 1935. … Old landslide materials extend from river level almost to the top of the terrace, or to an altitude of about 1,600 feet. Little or no landslide activity was noticed before the 1948 flood. There may have been some slight highway settlements or minor movements owing to irrigation and river-bank erosion below the highway, but no property damage from landslides was reported. In the fall of 1948 (about the time of the Seatons landslide movement) one resident of the area had trouble with water pipes parting and resorted to flexible hose connections to keep his water system operating. So far as is known, this marked the beginning of reactivation of the ancient slide. The slide has moved many times since. Movements are recorded on the following dates:

December 23, 1951;
November 10 or 11, 1952;
November 27, 1952;
and January 10, 1953.

In contrast to the diminishing rate of movement observed in the Seaton slide since 1948, the Koontzville slide seemed to move more and at more frequent intervals in successive years to and including the spring of 1953. Local residents have noticed that their houses cracked and moved each weekend during low stages of the Columbia River, which corresponded to drops in river level due to power operations at Grand Coulee Dam. Many houses and the store have been severely damaged, the springs have changed their courses, large fissures have crossed the village area, and each year the slide has worked farther back into the hillside. In 1952, a fissure connected the Koontzville slide with the Seaton slide along the silt-granite contact (fig. 20). The displacement in 1955 extended all along the bedrock outcrops between Seatons Grove and Koontzville. Vertical movement along this bedrock scarp ranges from a few inches to 5 feet. Before the 1948 movement there was a light-colored zone on the granite immediately above the contact with the surficial deposits which ranged in width from 0 to 15 feet. Above this zone, all the granite wall is much darker due to weathering and organic growths. This light-colored zone may represent the amount these slides moved down following an earlier Columbia River flood such as the one in 1896. Geologically, Koontzville is in a setting where the sequence of Pleistocene deposits is the most favorable for landsliding. A preglacial channel of Peter Dan Creek underlies Koontzville and because of this geologic setting ground-water conditions are very high.

Figure 20 from USGS Professional Paper 367

Figure 20 from USGS Professional Paper 367

Conditions similar to this have been described in the Reed terrace area, and they can be anticipated, almost without exception, where deposits of silt and clay now occupy the area of confluence of preglacial valleys with the main valley. The causes of the initial reactivation of this ancient landslide seem to parallel those outlined for the Seatons landslide. The causes of the periodic movements, however, are not well understood. In 1953, the Corps of Engineers drilled three test holes in the slide to obtain undisturbed samples of the soil and to install gauges to record pore-water pressures throughout the year.”

The factors pertaining to the Seatons Landslide movement were:

“Many factors influenced the renewed landslide action in this area, of which the following seem the most important:
1. The unusually heavy rainfall during the spring and summer of 1948.
2. The high water in the Columbia River during the flood of May and June, 1948, undoubtedly resulted in a higher water table throughout the entire slide area.
3. The flood eroded and unloaded the toe of the slide, which is on the outside of a bend in the river where erosion would be greatest.
4. Melt water from the heavy snowfall in the winter of 1948 and 1949 kept the slide lubricated and moving after sliding began.
5. Very deep freezing in the winter of 1948 and 1949 may have had some effect in extending old slide cracks and in damming ground water.
6. Seatons Lake was created in a key position at the head of the ancient slide so that it kept much of the lower part of the ground saturated. Springs on the lower slopes of the hill produced more water when the level of Seatons Lake was higher, and the lake surface was raised purposely at times to make the springs at lower altitudes flow at a greater rate for irrigation.
7. The material at the toe of the slide consisted of silt J and clay thinly mantled with sand, gravel, and boulders. Silt and clay could be observed pushing through the gravels at several places along the toe of the slide. Since the construction of Grand Coulee Dam, a replacement supply of sand and gravel to cover and protect the silt and clay from erosion had been largely cut off.
8. The extensive use of this area for homes, gardens, irrigated tracts, and roads had undoubtedly been a factor in encouraging the renewed activity of the slide. Renewed activity might have been postponed if the natural cover of grass and sagebrush had not been removed and if the streams had been kept in their natural channels. The principal spring, which flowed a full stream through a 2%-inch pipe, supplied the entire area with domestic water. The other two springs in the drainage above were about the same size. The small stream, which was seasonally diverted into Seatons Lake, flowed between 0.5 and 0.6 cfs, even in dry years. The stream probably flowed about 1 cfs in the early spring and during unusually wet seasons. The supply of water to the main spring was cut off during the slide of November 1948, but the flow of water was restored to about normal by driving a pipe into a small seep which broke out near the spring. The spring water was milky for several days before it cleared.”

Looking at the 10m DEM, it looks like they missed a rather large earthflow that came down.

Earthflow on the Koontzville Landslide

Earthflow on the Koontzville Landslide

Although this probably didn’t play much of a role in the Koontzville movement in the 1950’s, except for the overall instability in the area. Finding information on this landslide has been difficult. I would only assume it has mostly stabilized out, as houses still dot the landscape.

Reference:
Jones, Fred Oscar; Embody, Daniel R.; Peterson, Warren Lee, 1961, Landslides along the Columbia River valley, northeastern Washington: U.S. Geological Survey Professional Paper 367, 98 p., 6 plates.

Hyak Landslide

June 3, 2009

One of the more talked about landslides from the January 7-8th storm was the landslide that occurred at Hyak. The landslide started at the Summit at Snoqualmie ski area and moved into the Hyak community.
This landslide got a lot of press and originally, it was thought that is might be an avalanche. I remember having a discussion about this at a NOAA/NWS video conference meeting. Although, looking at the photos, it seemed that instead of the snow scraping up the soil beneath it, the slope gave way and moved the snow along. Something like a debris/snow avalanche.

Hyak Landslide Location Map

Hyak Landslide Location Map

The landslide occurred at approximately 11:40 a.m. Wednesday, January 7, 2009. Heavy rains (probably at about its elevation limit before turning into snow) from the storm had reached the summit earlier, warming the hillside and inundating it with rain.

Here at DNR – Division of Geology and Earth Resources (Washington Geological Survey), we were in emergency mode. We mobilized all of our geologist and sent them into the field to document landslides, but more importantly, sent them to check on residences that were impacted from landslides and to make sure they were safe from future landslide movement. Unfortunately, I was in the office, directing geologists to specific areas and creating updated maps of where we had located landslides or had damaged houses or blocked roads. I sent one of our geologists on the east side to get to Hyak and investigate what had happened and determine if it was an landslide or a snow avalanche. Plus, it did damage a handful of houses and the hillside had the potential to continue moving.

Aerial photo of the Hyak Landslide - DGER Photo

Aerial photo fo the Hyak Landslide - DGER Photo

Oblique aerial view of the Hyak Landslide - DGER Photo

Oblique aerial view of the Hyak Landslide - DGER Photo

Our geologist arrived I think late on January 7th and found numerous other crews investigating the landslide. Talking to them and doing some investigation herself, it was determined that it was most certainly a landslide and further, the slope was completely saturated. The scarp and material had woody debris within it and within the scarp, casts of old logs could clearly be seen, most with water gushing out the casts. It turns out that the slope had been modified about 40 or so years earlier and it appears they incorporated woody debris into the material. Over 40 years, the wood deteriorated and probably allowed water to more easily infiltrate into the subsurface, probably to the contact between the fill and rock/soil.

According to Matt Cowan, Fire Chief of the Snoqualmie Pass Fire and Rescue, the landslide impacted eight houses, one which was pushed off its foundation, the other lightly damaged. Two people were injured.

(Photo from Hyak Flickr site)

May 27 photo of Hyak Landslide

May 27 photo of Hyak Landslide

The hillside might still pose a threat to future failures. If woody debris exists in the subsurface then continued weakness still exists. I am not sure if the ski resort is planning on regrading the hillside to make the slope usable to skiing, although I cannot imagine that they will abandon the ski area. Unfortunately, we have inherited a lot of legacy problems from early land-use modifications (from the early 1900’s to 1970’s) that still plague us today. They are rarely recognized as a hazard, but their results can be deadly.