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.

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

Bonneville Landslide, Skamania County

The Bonneville landslide is perhaps the second most well known landslide in Washington State, following the 1980 Debris Avalanche of Mt. St. Helens. The landslide was probably first recognized by the Klickitat Nation (also known as the Qwû’lh-hwai-pûm, or loosely translated as prairie people). The landslide is known as the Bridge of the Gods and served as a water crossing for trade routes across the Columbia River. The Bridge of the Gods has many stories of its origin, perhaps the most well known is the story by the Klickitat people.

From Wikipedia:
“Native American lore contains numerous legends to explain the eruptions of Mount St. Helens and other volcanoes in the Cascade Volcanic Arc. The most famous of these is the Bridge of the Gods legend told by the Klickitats. In their tale, the chief of all the gods, Tyhee Saghalie and his two sons, Pahto (also called Klickitat) and Wy’east, traveled down the Columbia River from the Far North in search for a suitable area to settle.

They came upon an area that is now called The Dalles and thought they had never seen a land so beautiful. The sons quarreled over the land and to solve the dispute their father shot two arrows from his mighty bow; one to the north and the other to the south. Pahto followed the arrow to the north and settled there while Wy’east did the same for the arrow to the south. Saghalie then built Tanmahawis, the Bridge of the Gods, so his family could meet periodically.

When the two sons of the Saghalie fell in love with a beautiful maiden named Loowit, she could not choose between them. The two young chiefs fought over her, burying villages and forests in the process. The area was devastated and the earth shook so violently that the huge bridge fell into the river, creating the Cascades Rapids of the Columbia River Gorge.

For punishment, Saghalie struck down each of the lovers and transformed them into great mountains where they fell. Wy’east, with his head lifted in pride, became the volcano known today as Mount Hood and Pahto, with his head bent toward his fallen love, was turned into Mount Adams. The fair Loowit became Mount St. Helens, known to the Klickitats as Louwala-Clough which means “smoking or fire mountain” in their language (the Sahaptin called the mountain Loowit).”

The story captures two important keys to the landslide. A strong shaking and burying of forests and villages. Early research into the Bonneville Landslide places the landslide movement around 1,100AD. However, a recent find of a buried douglas fir log about 150 feet deep in the landslide mass places the landslide failure somewhere between 250 and 400 years ago. This conceivably places the Bonneville Landslide at the 1700 Cascadia Earthquake. This would follow the story of the Klickitat People or great shaking and landslide movement. When the landslide moved, it completely blocked the Columbia River, creating a temporary dammed lake. The waters would have slowly cut through the material, reestablishing the channel.

Cascade Landslide Complex

The Bonneville Landslide is part of a larger complex of landslides. The ages are not well constrained and may have occurred with episodic movement through time. The two landslides that are most recent are the Bonneville Landslide (probably failed around 1700) and the Carpenters Lake Landslide (Age Unknown).

Cascade Landslide Complex

Cascade Landslide Complex

The two smaller landslides, the Greenleaf Basin and the Piper Road Landslides are more recent, smaller landslides.

Geology
The Cascade Landslide is composed mostly of debris of the Yakima Basalt, Eagle Creek Formation, and a platy olivine basalt flow (Wise, 1961). The landslide is suggested to have a depth of about 300 to 400 feet and slides on a clay layer at the base of the Eagles Creek Formation. The units are gently dipping southward, which probably adds to the instability of the area.

Current Hazards
The Cascade Landslide Complex is perhaps one of the more dangerous landslides in Washington State. The Bonneville Dam sits on the landslide debris of the Bonneville Landslide. Major pipelines, powerlines, and transportation routes cross the landslide. Future movements (potentially during a Cascadia Subduction Earthquake) would result in major disruptions in utilities and the potential for the redamming of the Columbia River. The other problem, it might not occur in the Cascade Landslide Complex at all, large landslides dot the area surrounding this area and some might have the potential to also partially or completely block the Columbia River. A damming of the Columbia River would be devastating. The waters would form into a lake, flooding low lying communities, further impacting transportation routes and utilities. The potential exists for the Columbia to then rupture the dam, creating a massive damburst flood. That flood has one major target in its way, Portland. Although this is a very extreme example (and the odds for the events to occur this way are very slim), a large debris flood through the Columbia River would cause unprecedented damage, especially for a landslide. However, chances are future landslide movements would be less extreme, although the likely major disruption of utilities and transportation would be felt throughout western Washington and Oregon.

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

Aldercrest Banyon Landslide, Cowlitz County

The Aldercrest Banyon Landslide is one of Washington’s famous landslides. It was the second worst landslide disaster (in cost) in the United States, following the Portuguese Bend Landslide on Palos Verdes Hills in Southern California, 1956, where 130 out of 160 homes on a ancient landslide were damaged or destroyed destroyed when the landslide reactivated.

Location map for the Aldercrest Banyon Landslide

Location map for the Aldercrest Banyon Landslide

Aldercrest Banyon Landslide Map

Aldercrest Banyon Landslide Map

The Aldercrest-Banyon Landslide started moving in February of 1998, many years after a housing development was established on the landslide mass. A description of the events by Dr. J David Rogers of the University of Missouri-Rolla Department of Engineering Geology follows:

“The Aldercrest-Banyon neighborhood in eastern Kelso, Washington began experiencing gross ground movements in February 1998, following 3-1/2 years of above-average rainfall. The initial signs of distress were the breakage of underground utilities. In March 1998 some framing distress was noted on a few homes. On April 10, 1998 a noticeable crack, 2.5 to 6 feet high, developed above the natural crest of slope west of Banyon Drive and north of Cedar Glen Court. Two homes on Cedar Glen Court were evacuated. The City made a valiant effort to patch streets, fill cracks and provide above-temporary above-ground utilities to the affected neighborhoods so that people could remain in their homes as long as possible.”

In October of 1998, a federal disaster declaration was issued by President Clinton for 138 homes affected by the landslide (Wegmann, 2006). The destruction exceeded $70 million, but the buyout for the houses was 30 cents on the dollar and totaled around $30-$40 million.

Map of houses affected by the Aldercrest Banyon Landslide

Map of houses affected by the Aldercrest Banyon Landslide, Map from Dr. J David Rogers

Photo of landslide damage

Photo of landslide damage, Photo from Dr. J David Rogers

Triggers

Deep-seated landslides are difficult to determine the cause of movement. This landslide was a relict landslide that could have been many thousand years old. The original triggers for movement are gone, perhaps an earthquake, a series of storms or prolonged (for years) rain, or maybe perhaps some sort of removal of lateral strength, by a stream or river. In modern day, the causes can be just as difficult to determine and each scientist has their theory, sometimes in agreement with one another, more often, not. For the Aldercrest Banyon landslide, the only theory most people seem to agree on is years of higher than average above rain probably played a big role.

Rainfall Rates for the Cowlitz County Area, from DGER RI35

Rainfall Rates for the Cowlitz County Area, from DGER RI35

Karl Wegmann (who was a landslide geologist here at the Washington Geological Survey) states in his publication that 6 years of increased rainfall correlates to a period of increasing landslide activity (Wegmann, 2006). Others reduce this somewhere between 2-4 years of increased precipitation. As a friend of mine would ask about now, but there are many areas of above normal rainfall on the graph, why this time, why this event? We might want to look at when the housing district first was established in this area. The housing development was in full swing in the area in 1975-76 with what I suspect is a septic system, although it could be sewer. With an increase in houses comes an increase in house related activities, watering the lawn, roofs pouring out water in the downspouts, concentrating water, etc. All things bad for landslide stability. Increased in rainfall would rates could have contributed to the reactivation of the landslide as well.

Geology

The subsurface in any landslide is an important characteristic to study. The area surrounding the landslide was mapped by Walsh et al., 1987. The deposits that the landslide sits on is known as the Troutdale Formation, which is appoximately 2 to 14 million year old Columbia River deposited gravels, sands, silts, and clays. Under the Troutdale is the Cowlitz Formation(roughly 38 million years old), depositing silt, sand, and mud in a near-shore marine deposition environment.

Geologic formations associated with the Aldercrest Banyon Landslide, image from Dr. J David Rogers

Geologic formations associated with the Aldercrest Banyon Landslide, image from Dr. J David Rogers

The formation creates areas of weaknesses at the contact between the Troutdale and Cowlitz Formation (and probably somewhat between the upper and lower Troutdale Formation).The increase in water over time probably contributed to increasing pore water pressure between the contact. This combination is present in many areas around the Kelso area and is probably responsible for much of the instability in the area.

The Aldercrest Banyon Landslide got the attention of many people. Its destruction caught the attention of the legislature, who initiated a landslide mapping project within the Washington Geological Survey. The landslide also propelled counties to look closer at landslide hazards to prevent another Aldercrest Banyon Landslide.

Reference

Walsh, T.J., Korosec, M.A., Phillips, W.M., Logan, R.L., and Schasse, H.W., 1987, Geologic Map of Washington Southwest Quadrant. Washington Division of Geology and Earth Resources Geologic Map GM-34.

Wegmann, Karl W., 2006, Digital landslide inventory for the Cowlitz County urban corridor, Washington; version 1.0: Washington Division of Geology and Earth Resources Report of Investigations 35, 24 p. text, 14 maps, scale 1:24,000. [accessed Mar. 6, 2008 at http://www.dnr.wa.gov/ResearchScience/Topics/GeologyPublicationsLibrary/Pages/pub_ri35.aspx]

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

Ribbon Cliff Landslide, Chelan County

The Ribbon Cliff landslide moved on December 14th, 1872, during (or shortly following) the 1872 earthquake. The landslide moved into the Columbia River and blocked it for several hours.
The earthquake location has been sort of a mystery until recently, as paleoseismic scientists have tracked down an approximate location for the landslide. The landslide was centered somewhere near Lake Chelan and caused some fairly interesting stories. Excerpted from the USGS website:

“Most of the ground fissures occurred at the east end of Lake Chelan in the area of the Indian camp; in the Chelan Landing-Chelan Falls area; on a mountain about 19 kilimeters west of the Indian camp area; on the east side of the Columbia River (where three springs formed); and near the top of a ridge on a hogback on the east side of the Columbia River. These fissures formed in several localities of differing physiographic environments. Slope failure or settlements or slumping in water-saturated unconsolidated sediments may have produced the fissures in areas on steep slopes or near bodies of water. Sulfurous water was emitted from the large fissures that formed in the Indian camp area. At Chelan Falls, “a great hole opened in the earth” from which water spouted as much as 9 meters in the air. The geyser activity continued for several days, and, after diminishing, left permanent springs.”

It would take some time, but it would be interesting to try and find the locations of slope failures from this landslide.

Ribbon Cliffs Landslide Location Map

Ribbon Cliffs Landslide Location Map

Ribbon Cliff Landslide

Ribbon Cliff Landslide

The landslide toe is a bit difficult to determine. The Rocky Reach Dam, built in 1962, formed Lake Entiat, which inundated the toe of the Ribbon Cliff Landslide. Older topographic maps indicate a probable toe (which is the loosely drawn toe on the map above). The landslide was drawn to the area mapped out in Madole et al, 1995.

The landslide location is along the Columbia River and was probably subjected to undercutting and oversteepening from erosion. Evidence of landslides (one just north of the Ribbon Cliff Landslide) is evident when looking at aerial photos of DEMs. The landslide itself was probably not a rock fall/topple event, but more of a translational landslide, that carried the mass relatively intact.

One of the more interesting summaries of the landslide can be found on this website. It gives a general summary of the landslide (plus some amazing oblique pictures of the landslide).

Controversy
It turns out (like most things in science) that not everyone agrees the Ribbon Cliffs Landslide is from the 1872 earthquake. The 1872 date, beyond the account of the 15-year old youth living in a cabin 3 km up stream, is also based on the presence of Mt. St. Helens Volcanic ash (set W) near the top of the undisturbed talus deposit (absolute maximum date). However, a dendrochronology study by Kienle et al (1978) reported that two of the oldest trees examined and three younger trees examined pointed to a failure date prior to 1872. No evidence was found within the tree rings of disturbance. This could be explained by the mass of the landslide did considerably disturb the trees (if the landslide mass moved as a whole).

Reference

Kienle, Clive F., Jr.; Farooqui, Saleem M.; Strazer, Robert J.; Hamill, Molly L., 1978, Investigation of the Ribbon Cliff landslide, Entiat, Washington: Shannon & Wilson, Inc., 26 p., 23 figs., 2 plates.

Madole, Richard F.; Schuster, Robert L.; Sarna-Wojcicki, Andrei M., 1995, Ribbon Cliff landslide, Washington, and the earthquake of 14 December 1872: Seismological Society of America Bulletin, v. 85, no. 4, p. 986-1002.

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.

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.

Hazel Landslide, Snohomish County

The Hazel Landslide is a persistent deep-seated landslide that is probably driven by groundwater and erosion by the North Fork of the Stillaguamish River.

Hazel Landslide Location Map

Hazel Landslide Location Map

The landslide has caused some headaches for DNR, as a catastrophic failure and partial blockage of the Stillaguamish River around 1988 spurred many to consider logging as the culprit.

Hazel Landslide

Hazel Landslide

Logging in the northwest area above the landslide came into question as a area that was a groundwater recharge area. The addition of water from the removal of trees was considered to be at least a partial catalyst for the failure of the Hazel Landslide and it is seen as a poster child of what groundwater recharge in sensitive areas can do.

Since 1988 the forest land has recovered and groundwater recharge should have been diminished, but in January of 2006, following a period of prolonged precipitation, the Hazel Landslide once again moved, diverting the river into a small community of houses. This landslide was another large landslide and has been called the Steelhead Haven Landslide. During that month, about 8 inches of rain fell, well above the average 4.5 inches that typically falls during the month of January (in 93 months of record). This would overwhelm any recovery that may have occurred with the maturing forest.

Hazel Landslide 2009 - DNR/DGER Photo

Hazel Landslide 2009 - DNR/DGER Photo

Hazel Landslide 2009 - DNR/DGER Photo

Hazel Landslide 2009 - DNR/DGER Photo

The landslide produced a lot of sediment, which I hear from some of my sport fisherman up there, caused quite a poor year of fishing. The long term effects might not have been devastating, but with a weakening population of fish, it certainly hasn’t helped any.

In the landslide world, the Hazel Landslide is certainly one of the more well known landslides. The unstable nature of the glacial lakebed lithology it sits in has caused countless landslides throughout Western Washington and is a legacy of our glacial history. However, it has taught us some valuable lessons in how groundwater affects lacustrine beds and its potential sensitivity to water.

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

Sultan River Debris Avalanche, Snohomish County

When I first started at DNR, I lived in Seattle (commuting to Olympia), but most of my field work was in or near the Sultan Basin. The Sultan River watershed was the first watershed I worked on for the LHZ Project. My first year working was almost comical, every day I was in the field, it rained. In the summer, we would have long stretches of dry weather and one day of rain every couple of week and those were the days I ended up in the field.

On December 10th, Pat Pringle and I were in the field investigating the Sultan River basin. We didn’t hike or really get out of the car much due to a torrent of rain coming down. We never quite got over to the area of the Sultan River debris avalanche, but we were just about across the way from it. I did end up heading out there after it failed.

Sultan River Hydrology

Sultan River Hydrology

On December 11th, a group of Kayakers decided to ride the Sultan, mostly because of the elevated water levels from the storm. During their ride down, they ran into more than they bargained for.

Sultan River Debris Avalanche Location Map

Sultan River Debris Avalanche Location Map

Sultan River Debris Avalanche

Sultan River Debris Avalanche

A large debris avalanche/fall came down right after the kayakers passed by. As you can see in the video, the landslide dammed the Sultan River for a short time, but eventually over topped/breached the dam. The kayakers, a bit shaken up by the landslide decided to leave the river and hike out and head back to civilization. Unfortunately, they didn’t know the area and headed east of the the Sultan Basin, eventually reaching a small nudist community. They all make it out safely.

To make matters worst, the City of Sultan received a report of a large landslide damming the Sultan River. Their main concern was a dam burst flood that would damage the city. The Snohomish County sheriffs office had a helicopter in the air trying to find the landslide and see how bad the blockage was. This was a real thing to worry about. The Sultan River is entrenched and a dam could potentially block a large amount of water. Strangely enough, many of the rapids (that the kayakers seem to enjoy so much) came from old landslides that probably partially or fully dammed the Sultan River and slowly eroded out, just like this landslide.

Landslides are rarely caught on video and when caught, they are a valuable source of scientific information. In this video, you can see how the landslide overcomes what almost looks like a small rock that is holding back the mass of material break apart shortly before movement. You can almost calculate the acceleration as it heads towards the river and what happens as a mass of material impacts into the water, the size of the waves and so forth. We can also see how the river responds to the debris dam and how it returns to normal flow without breaching the dam.

This video also caught the attention of others and it was part of a Discovery Channel series called Raging Nature. I was interviewed by the show, but I didn’t appear on camera for the show (probably the background river sound, which was really loud). The narrator during the show did say much of the exact words that I said (which was kinda creepy for me).


Geology

Bedrock Units

Regional bedrock that includes the Sultan River watershed belongs to the Western Mélange Belt, part of the Western and Eastern Mélange Belts (WEMB) terrain. The WEMB includes Mesozoic (late Jurassic to early Cretaceous) marine sedimentary rocks, along with lenses of Paleozoic limestones, Mesozoic intrusives, and other rich types in fault-bounded bodies that were tectonically juxtaposed (Tabor et al, 1993). The WEMB rocks underwent high pressure, low temperature metamorphism in the late Cretaceous orogeny at about the time they were juxtaposed against the Northwest Cascade System terrain to the North.

Bedrock in the Sultan River watershed is mainly composed of the Western Mélange Belt (Phipps et al., 2003; Dragovich et al., 2002). These rocks were deposited during the late Jurassic to early Cretaceous (170 to 100 million years ago) periods (Carithers and Guard, 1945). Sediment was thickly deposited in a marine setting, comprising mostly of silt and mud. Hydrothermal systems and submarine eruptions (similar to black smokers) formed from intruding magma, creating large pyritic deposits (such as the Lockwood Pyrite deposit) and overlaid the marine sediment with volcaniclastic and mafic flows (for example, basalt) material (Olson, 1995; Snohomish County, 1979). This magma chamber underwent differentiation, where the heavier mafic material (rich in iron and other metallic minerals) filtered to the bottom of the chamber and lighter felsic material (rich in silica, such as quartz and feldspar) rose to the top (Stewart, 2005). These rocks were then metamorphosed (exposed to heat and pressure), folded, uplifted and eroded. The metamorphism changed the marine sedimentary and volcaniclastic rocks into argillite (metamorphosed siltstone) and phyllite (metamorphosed mudstone). The granitic magma chamber also experienced metamorphism, altering the granitic rocks into meta-tonalites (light colored granitic rock), meta-gabbros and meta-peridotites (dark colored granitic rock).

As the rocks experienced pressure from the west (most likely from the oceanic plate colliding with the North American continental plate), they tilted the stratigraphic section to the northeast. This tilting, along with erosion of the overlying rock, exposed the relict magma chamber (gabbro and peridotite in the west, grading east to tonalite) in the western part of the Sultan River watershed. The metamorphic marine rock, which overlies the relict magma chamber, can be found primarily in the southern and eastern parts of the watershed. The metamorphic volcaniclastic rock, which overlies the marine rock, is located primarily on Blue Mountain, in the northeast part of the watershed.

The meta-tonalite rocks, where not overlain by glacial drift, is very stable, even with slopes steeper than 60% (A prime example of this is the large hill, located in T. 28N R. 8E, section 2 and 11). The meta-marine rocks can be unstable, especially when the beds are tilted to near vertical. The north flank of Blue Mountain is an excellent example, where the meta-sedimentary rocks are tilted to near vertical and failures are frequent within the section. The meta-volcanic rocks can be very unstable and appear to be very susceptible to slope failures when the rock is exposed to water. A prime example of this is the water run-off from the radio tower located at the highest peak on Blue Mountain; many debris flows initiated from this deposit, independent from harvest or road construction.

Poorly-Consolidated Surficial Units

Surficial units in the study area consist of continental glacial drift. Other surficial deposits are composed of alpine glacial drift, colluvium, and alluvium. About 14,000 years ago, the Puget Lobe of the Cordilleran ice sheet, which represents the most recent advance of continental ice sheet, flowed into surrounding valleys. This advanced was named the ‘Vashon Glaciation’ locally. Tongues of the Vashon glacier dammed valleys that were tributaries to the Puget Lowlands, creating large ice dammed lakes. Glaciers advanced up the Pilchuck River system and the Sultan valley, covering the northwestern portion of the watershed (Tabor et al., 1993). This blocked the paleo-Pilchuck River, creating a large ice-dammed lake and depositing deltas and lake deposits on the north flanks of Blue Mountain to Bald Mountain. This rising lake eventually overflowed, washed over Olney Pass, and deposited fluvial outwash across the plains in the west and south parts of the Sultan River watershed.

Ice margins near Lake Chaplain and Echo Lake also produced significant outwash towards the town of Startup (Booth, 1990). As the glaciers retreated, the terminal moraine (called the Pilchuck plug) blocked the upper drainage of the Pilchuck River, creating the new Sultan River watershed (Coombs, 1969; Bliton, 1989). The Sultan River established a channel, rapidly incised into the glacial material, cut into the bedrock, and became entrenched. This incision is probably due to easily eroding glacial material and isostatic rebound of the bedrock in the area. Old meander bends and channels can be seen near the main channel of the present Sultan River.

Near the confluence of the Sultan and Skykomish River, glacial lakes formed by the advancement of the Cordilleran ice sheet, creating thick lake deposits in the southern extent of the watershed (Booth, 1990). These lake deposits formed low-permeability clay and silt layers that perch water and spawn large landslides during high precipitation. The silt and clay layers are commonly overlain by permeable glacial outwash from the paleo-Spada Lake and ice-margin flows. This combination of silt, clay and sand makes much of the hillsides in the southern part of the watershed susceptible to shallow and deep-seated landslides.

Reference

Booth, Derek B., 1990, Surficial geologic map of the Skykomish and Snoqualmie Rivers area, Snohomish and King Counties, Washington: U.S. Geological Survey Miscellaneous Investigations Series Map I-1745, 2 sheets, scale 1:50,000, with 22 p. text.

Bliton, William S., 1989, Sultan River project. IN Galster, R. W., chairman, Engineering geology in Washington: Washington Division of Geology and Earth Resources Bulletin 78, v. I, p. 209-216.

Carithers, Ward; Guard, A. K., 1945, Geology and ore deposits of the Sultan Basin, Snohomish County, Washington: Washington Division of Mines and Geology Bulletin 36, 90 p., 1 plate.

Coombs, H. A., 1969, Leakage through buried channels: Association of Engineering Geologists Bulletin, v. 6, no. 1, p. 45-52.

Olson, Duane F., 1995, Geology and Geochemistry of the Lockwood Volcanogenic Massive Sulfide Deposit, Snohomish County, Washington: Western Washington University Master of Science thesis, 118 p., 8 plates.

Phipps, Richard W.; McKay, Donald T., Jr.; Norman, David K.; Wolff, Fritz E., 2003, Inactive and abandoned mine lands–Spada Lake and Cecile Creek watershed analysis units, Snohomish and Okanogan Counties, Washington: Washington Division of Geology and Earth Resources Open File Report 2003-3, 36 p.

Snohomish County Public Utility District No. 1; Washington Department of Ecology, 1979, Sultan River project, Stage II; Application for amended license, FERC project no. 2157–State of Washington final SEPA EIS and FERC environmental report (exhibit W): Snohomish County Public Utility District No. 1, 2 v.

Stewart, Richard, May 27th, 2005, Personal Communication

Tabor, R. W.; Frizzell, V. A., Jr.; Booth, D. B.; Waitt, R. B.; Whetten, J. T.; Zartman, R. E., 1993, Geologic map of the Skykomish River 30- by 60-minute quadrangle, Washington: U.S. Geological Survey Miscellaneous Investigations Series Map I-1963, 1 sheet, scale 1:100,000, with 42 p. text.

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

Piper Road Landslide

The Rock Creek Landslide (also known as the Skamania, Stevenson, or Piper Road Landslide) started in 2007 probably after heavy rains hit the area in November of 2006. Movement started to accelerate in February of 2007 and continues to today.

Piper Road Landslide Location Map

Piper Road Landslide Location Map

The Piper Road landslide is located north of the town of Stevenson, located in Skamania County. The landslide is situated on the eastern side of Rock Creek near a waterfalls.

Febuary 2007 Photo of Piper Road Landslide; Photo by DGER/DNR

Febuary 2007 Photo of Piper Road Landslide; Photo by DGER/DNR

This photo was taken shortly after the landslide started to become more active. The landslide itself has started to cut back into the bluff. DNR Division of Geology and Earth Resources Geologists investigated the landslide at this time to determine clues to the landslide and possibly mitigation to help reduce or stop the landslide movement.
By November of 2007, the landslide had progressed significantly upslope:

Piper Road Landslide November 2007; Photo by DGER/DNR

Piper Road Landslide November 2007; Photo by DGER/DNR

At this point, the landslide had destroyed one house (in July of 2007) and the town of Stevenson was desperate for aid and help to mitigate the landslide. The landslide was no longer threatening only houses, but now threatened to destroy a road (with utilities below) and inundate a sewage treatment plant. If left unchecked, sediment would continue to aggregate and threaten to take out the bridge of State Route 14, which is one of the few points that connect major utility lines between eastern and western Washington (such as a natural gas pipeline). Unfortunately, no aid was forthcoming and Stevenson was left to deal with the landslide on its own. I think the quote was (in a conference call regarding the landslide) something akin to “larger towns have been destroyed or abandoned by landslides”. It is, perhaps, the unfortunate result of building in unstable areas.
The long term problems might be bigger than losing a couple of bridges and a sewage plant. The Bonneville Dam is located just downstream of Stevenson and Rock Creek drains into Lake Bonneville. Sediment from the landslide is flowing into Lake Bonneville, which can impact fish populations and slowly inundate the lake and create a sediment headache down the road (of course, this could be dredged out). If the sewage plant is impacted, raw sewage could flow into Lake Bonneville (as far as I know, it isn’t used for drinking water), which could lead to things like an algae bloom or dead zones, anoxia, or just misery and destruction. Granted, probably not enough sewage to do that in such a big lake, but worst case scenario.

The landslide is located on the Bonneville/Cascade Landslide complex and is probably the result of continued movement and activity of the landslide.

Piper Road Landslide in the Bonneville Landslide Complex

Piper Road Landslide in the Bonneville Landslide Complex

As in the Greenleaf Basin Landslide, a combination of higher rainfall and geologic setting probably resulted in the landslide movement. Erosion of the toe of the landslide by Rock Creek, overtime, probably reduced the lateral strength of the landslide and eventually resulted in a breakdown in resistive forces.

The geology of the landslide is well covered in this report by Mark Yinger Associates.
The Rock Creek Landslide Website has been established for the Piper Road landslide (with webcams fixed on the landslide) and additional images.