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.
November 10, 2009
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.
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.
October 28, 2009
Precipitation is an important component into landslide movement. During the investigation into the Alderwood-Banyon and the Carlyon Beach-Hunters Point Landslides, long-term precipitation (over five years) had been above the mean average. This is thought to be the main driver of these landslides. In the same thought, maybe the Nile Landslide has experienced above average rainfall over a period of time, similar to the other two landslides. We asked Cliff Mass (click here for his Blog) at the University of Washington Atmospheric Sciences to help us figure out the the precipitation history of this area. The data, emailed from Mark, an colleague of Cliff Mass, isn’t a smoking gun. The email below:
I have looked at water year annual precipitation for 2 snotel sites situated on the east slope of the Cascades but somewhat north of the Niles Landslide. They are Blewett Pass and Grouse Camp snotel sites.
There are no snotel sites in the immediate vicinity of the Niles Landslide.
Over the past water year (Oct 2008-Sept2009) precipitation totalled 10% above the long term average (1983-2008) at a composite of the two snotel sites.
Over the past 2 years ==> 2% above the long term average (1983-2008).
Over the past 3 years ==> 6% above the long term average (1983-2008).
Over the past 4 years ==> 7% above the long term average (1983-2008).
Over the past 5 years ==> 0% above the long term average (1983-2008).
The 2005 water year was unusually dry bringing the 2005-2009 5-year average back to nearly the same as the long term average.
Hmm, well, looks like we are back to the drawing board.
October 28, 2009
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.
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 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.
October 22, 2009
October 22, 2009
I just got back from GSA, so I apologize for the delay in the posts. We have had a lot of talks about this landslide at the conference and have a lot of heads thinking and working on it. Particularly, the ice. It actually might play a big part in the landslide failure. If the landslide formed deep cracks through previous slower movement, it could have allowed warm air into the area where the ice was. This could have resulting in melting of the ice, which would have added in water to the system or just made the perfect slide for a block of ice to flow on. The low angle of the landslide would suggest something like this could have occurred. Once we gain a sample of the ice, we will run some tests on it, try and determine its age and so forth. Hopefully it will shed some further clues on this landslide.
As I thought might have occurred, the places where we first found the ice had collapsed and it was impossible to safely gather a sample of ice (ever try digging on an unstable talus slope?). So, that clue looks like it might be lost unless we can recover something from drilling.
October 14, 2009
One of the odd things that we discovered during our investigation on Sunday was chunks of ice in the Nile Landslide. Ice. I guess I should qualify this a bit better. The ice is between the coarse rocks and it doesn’t look much like ice when you are next to it. Here is what I mean:
To get it out of the way, the ice probably didn’t play much, if any role in the landslide failure. It is probably a product of the talus, which in Eastern Washington can sometimes form ice cores. These are well known to many in Eastern Washington and even were mined early on as natural cold storage. This isn’t something I know a whole lot about, but my geologist friend Jack from Eastern Washington explained it to me. Cold air from the surface is able to permeate into the talus, forming a barrier from the hot air. As water infiltrates down into the talus, either through precipitation, snow melt, or shallow groundwater (or other ways), the water hits that cold air and starts to freeze (as long as the air is colder than freezing). The cycle continues as cold air can continue to permeate down, keeping the ground cool and protecting it from the hot air above.
I will be heading into the field on Thursday, either with WSDOT on a helicopter flight or by vehicle. Either way I will be hiking on the west side of the Sanford Pasture Landslide, checking for stability. I’ll keep you posted.
October 14, 2009
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It is a strange thing to see how TV works from the production side. The interview I had was maybe 15 minutes or so, but it all boiled down to about 10 seconds of film on air. I am glad to see that this landslide is getting the attention it deserves. This is a major event in Washington’s history, at least, landslide history.
October 14, 2009
The Nile Landslide is part of a much bigger landslide system. The Sanford Pasture Landslide is perhaps the second largest landslide in Washington State, it is about 6 miles long an over 2 miles wide. The Malaga (aka Stemilt) landslide is the largest landslide in Washington State.
That little red blob at the bottom left of the map, that is the Nile Landslide that just occurred. The Nile Landslide is actually on a secondary failure (probably resulting some point after the initial movement of the bigger landslide), probably on the toe of that landslide. The worry is that the removal of mass on the toe might weaken the upper material by the removal of lateral material. There is a lot of rock up there and if the landslide propagated up or actually triggered a larger block up slope, the result could be the entire valley filling up with sediment. Bare in mind that there is a very low chance of this occurring, but it is something we need to checking out.
The age of the Sanford Pasture Landslide is unknown, but probably Holocene. The landslide, when it moved, crossed the valley and flowed up onto the other valley wall. This might have been done is a rapid, catastrophic failure. The landslide probably formed lakebed deposits upstream and sometime in the near future, we might be able to date this landslide.
I will heading out into the field again soon. I will try and keep you all updated. Most of our photos will be posted on our DNR flickr site located here:
I am going to try and post some new photos either tonight or early tomorrow morning.