Catching up - recent landslide events

The next few posts will be an attempt to catch up on the things that I missed whilst on vacation in Switzerland last week.  Thanks to the many people who have tipped me off about landslide events.  I will cover Pakistan in another post.


1. A large flow in Austria
Thanks to Martin Springer for highlighting this one.  On Saturday 21st August a severe storm triggered a 100,000 cubic metre flow in the Karwendel Nature Reserve.  Fortunately no-one was killed, but a dozen cars are trapped in a car park.  It will take two months to clear the debris.  There is a short video of the deposit and further details about the landslide (in German) here.

Read more by clicking below:



2. The power of a mudflow illustrated by an articulated truck in California
Thanks to Lisa Denke for this one.  A large storm in eastern California on Thursday last week triggered a mudflow in the Owens Valley in eastern California.  An articulated truck (known as a tractor trailer in the US) was caught in the path.  There is a short but useful video of the event in this news report:



3.An excavator in Gilgit-Baltistan
Accompanying the video above is an extraordinary image of the aftermath of the rains in Pakistan, courtesy of the Pamir Times:

I am reminded of the old "how does the driver of a snowplough get to work?" line.


4. Devastating landslides in Turkey
Also on Thursday last week, heavy rainfall triggered landslides in the town of Gundogdu, in Rize Province in Turkey, killing 12 people.  The image below is taken from this news report:

5. The typhoon season has now got started
Finally, the very slow start to the Pacific typhoon season has now come to an end, with a series of storms developing at the moment.  The three storms currently active all have the potential to cause landslides (image from Tropical Storm Risk):

Lionrock and Namthuen could both bring very heavy rainfall to southern China as they track inland over the next couple of days.  Meanwhile, the forecast track of Typhoon Kompasu suggests that this very intense typhoon could bring substantial amounts of rainfall to the Korean peninsular.  North Korean in particular is very vulnerable to the effects of heavy rainfall due to the extensive deforestation endemic in that country.  The potential impacts of this storm are serious, although note that there is considerable uncertainty in track forecasts.

Amazing new rockfall video from Yosemite

Thanks to Greg Stock for bringing this one to my attention.  Yosemite National Park have produced a video providing information for visitors about the hazards associated with rockfalls.  It includes an extraordinary piece of footage - captured by a visitor to the park - of a rockfall detaching from the cliff, fragmenting on impact on the the slope, and then travelling down the talus slope.  The video of the detachment event is fantastic - I have never seen anything as good.  However, the rest of the video is great as well, and will be very valuable to those trying to provide improved awareness rockfalls in many environments.  The video should be viewable below (click on read more to see the rest of the post):






Or you can view it here: http://www.youtube.com/watch?v=H0YhlqP1BgE

OK, so who put that there?

Easy to miss? Good Lord indeed...

New rockslide video: Highway 96 at Klamath River near the Siskiyou-Humboldt county line

Thanks to Kyle House of the Nevada Bureau of Mines and Geology for bringing this one to my attention.

A great new video was posted yesterday showing a rockslide onto Highway 96 at Klamath River near the Siskiyou-Humboldt county line in California. The video should be embedded below:

Rock slide on Hwy 96 in Northern California near the Humboldt/Siskiyou County line. from Paul Hailey on Vimeo.

Well worth a look! More details of the slide here:

http://www.redding.com/news/2010/mar/03/staggering-rock-slide-closes-highway-96-near-humbo/

Impressive roadside landslide in Pomona, California

Thanks to reader CConkle for the heads-up on this one. An impressive slide happened this morning by the side of Freeway 10 near to Pamona in California. The slide has completely blocked the road (pictures from the LA Times):




It is uite interesting that the weather does not indicate an obvious trigger for what appears to be a failure on a reprofiled slope. However, California has suffered recent exceptional rainfall in the last few weeks, so it may be progressive failure is the key factor here.

Most recent reports suggest that the slope is still moving and the road is likely to be closed for a week.

Mudslides occur in the areas affected by the 2009 Station Fire in Los Angeles

The Station Fire was a huge forest fire that occurred on the northern edge of Los Angeles in late 2009:It was finally brought under control on 16th October 2009, by which time it had burnt a huge area, thought to be over 160,000 acres (image from NASA):


In the aftermath of the fire considerable concern has been expressed about the potential for damaging mudflows in the burnt area, magnified by the current El Nino conditions, which typically bring very heavy rainfall to California at this time of the year.

Early on Saturday, unexpected heavy rainfall triggered a series of mudflows from the burnt area that affected the northern part of Oceanview Boulevard in La Canada Flintridge, causing extensive damage to properties but fortunately no fatalities. The most seriously affected area appears to be Manistree Drive, which is shown on this Google Earth image:

This is apparently the location of this image, from the LA Times:

At least 43 houses were damaged, together with 25 cars (see image below from AP). A dozen houses have reportedly suffered major structural damage.

The Rivermist subdivision in San Antonio, Texas is on the move again - and it is a rotational retaining wall failure

The woes of the families displaced by the slope failure at the Rivermist Subdivision in San Antonio, Texas have been exacerbated by a new phase of movement. AP Texas News reports that heavy rain has triggered additional cracking of the wall, and the movement of some debris. However, the houses at the top of the slope are apparently not moving.

I have been wondering why they are so confident that the wall won't fail. In an earlier post I suggested that this is not a simple retaining wall failure, given the toe scarp - a couple of subsequent commenters agreed. These aerial images, from My SA news show that this is the case:

The key part of the image is actually at the bottom of the first image above, although once you have your eye in you can see these features in the other image too. This is an annotated version of that first image:


This landslide is clearly not a simple retaining wall failure. It is a rotational slip in the slope that has caused the retaining wall to fail. It is not surprising that they do not expect the wall to collapse during these rains as the wall is being rotated to lean backwards by the failure.

Of course, as per the comment below, ensuring that the retaining wall would not be affected by this type of rotational failure should always be a key part of the design process for such structures. I suspect that this will become a textbook example of the problems that can affect retaining walls.

The San Antonio retaining wall collapse - did the developer have a permit?

Reports suggest that ground movement has ceased in the Rivermist subdivision, which suffered a fairly spectacular retaining wall failure over the last few days. Attention is now focussing upon that retaining wall - and in particular on why it failed. This is a pretty key issue given the potential liabilities and its magnitude - the wall is 1000 feet (>300 m long).

Press reports note two interesting aspects of this accident:

1. The City of San Antonio has released a statement that says "The hillside collapse yesterday within the River Mist subdivision that damaged several homes was a result of an improperly constructed retaining wall, as well as improper compaction of fill on which homes were constructed by the developer, Pulte Homes. The developer did not obtain the required City construction permits for the retaining wall that collapsed."
2. Some reports suggest that this is the second time a retaining wall has failed at this site: "One neighbor who was among the first homebuyers in the subdivision set among rolling hills on the outskirts of San Antonio said he was initially told no homes would be built on the crumbling ridge because it was too steep. Romeo Peart, 32, said one retaining wall failed several years ago before the current one was built and homes were constructed above it" (Washington Post).

I should also add that I am not sure that this is a particularly simple retaining wall failure, based upon the image below (from here):

In particular, it appears that the slope / small retaining wall below where the man in the green jacket and hat is located has also failed. I wonder why?

Finally, I thought I'd embed this video, at least in part for the picture shown before the video starts, which is a somewhat surprising image in my opinion:



The video itself provides an interesting overview and a verification that a section of the wall had needed rebuilding on a previous occasion.

Ongoing massive retaining wall failure in San Antonio, Texas, USA

Updated here

In the United States there is an interesting developing story about a large-scale retaining wall failure that is causing the collapse of a housing estate in San Antonio, Texas. The housing development, called the Rivermist subdivision, is the one shown in the Google Earth image below. It is still under construction. The marker shows the approximate location of the slide, as far as I can tell:


According to the media reports the slide started moving on about Friday is now sliding at about 4 inches (10 cm) per hour. There is a pretty clear video of the slide here (but note that this is definitely not a sinkhole as the report suggests).

The slide is far from trivial. These images, from this site, appear to have been taken a day or so ago:



More recent reports and images suggest that the slide has moved a great deal since these pictures were taken. More than 80 houses have been evacuated.

The area of the failure is, as far as I can tell, shown on this Google Earth image. This is two years old and was taken before the houses in this area were built. I have highlighted a rather peculiar feature that runs across the road on this image:

Interesting! The worst-affected houses in this area already look beyond recovery. I wonder how many more will be affected. Personally, I would not allow people to stand or to wander around anywhere near the toe of that wall, but maybe I am overly-cautious. This is clearly a tragedy for the families involved.

Updated here

Potential landslides in California and the ongoing crisis in Hunza, Pakistan

Amongst the (appropriate) focus upon Haiti at the moment, we must of course remember that landslides do not stop elsewhere. So, here are two important ongoing stories:

1. Potential landslides in California this week:
The US National Weather Service has issued a series of warnings for very heavy rainfall in California this week, with the pontential for landslides, flash flood and debris flows. For example: ...Flash flooding and debris flows possible for recent burn areas In southwestern california late monday morning through monday night... .the first in a series of powerful pacific storms is expected to Move into southern california tonight into monday. Initially...rainfall Is expected to be fairly light...with rainfall coverage and intensities Expected to increase significantly by late monday morning through Monday evening. Rainfall rates between one half inch and three Quarters of an inch per hour will be possible monday afternoon Into monday evening. Local rates over one inch per hour will be possible Near thunderstorms and across favored south facing slopes...including The station and morris burn areas. Rainfall totals with this first Storm system through monday night are generally expected to range Between one and three inches across coastal and valley Areas...with three to five inches in the foothills and Mountains...except local amounts up to 6 inches possible across Favored south facing slopes. For the station burn area...rainfall Totals of 3 to 6 inches can be expected through monday night. Additional periods of heavy rain will be possible later in the Week as future storm systems move into the area...which may Require additional flash flood watches to be issued.

And:
...Wet weather to continue through much of the week... A series of storms...no fewer than six...are lined up across the Pacific all the way to asia. The first of these systems was moving Through the central california interior this afternoon...and will Spread light to moderate rain to the central and southern san Joaquin valley and the adjacent sierra foothills through tonight. Rain also will spread into the high deserts of kern county by late Afternoon and tonight. A second system is developing west of the California coast...and will move into california monday. It is This system that will spread occasional rain...heavy at Times...into the region. For the rest of the week...it is still too early to say when and How much each individual system will impact central california. But there will be periods of rain...heavy at times. Preliminary Indications are for another strong surge of moisture during the Day tuesday...again wednesday...and yet another thursday. Some Decrease in activity is now seen by the weekend...or at least Becoming more showery at times.

There is particular concern about the potential for debris flows in the Station Fire burn zone in the San Gabriel Mountains, as shown in this NASA satellite image:


However, as the La Conchita landslide showed five years ago, many areas in California have the potential for a landslides during very heavy periods of rainfall. It will be an interesting week.


2. The Attabad landslide in Hunza
The blockage of the Karakoram Highway by the Attabad landslide in northern Pakistan continues to cause major problems to that area. Meanwhile, the lake is continuing to fill. The Pamir Times continues to provide excellent coverage of this serious event. Over the weekend they posted a series of images of the slide. First, the lake:


Second the contact between the water and the dam sediment:


And finally the flow path once over-topping is achieved:

In some places the materials look worryingly fine grained and even muddy, but it is impossible to get a proper idea from these images. The report says that the water level is currently 10-15 m from the dam crest, which is of increasing concern. Various reports suggest that there is little government action to date in terms of creating a channel, although clearly this is unverified. It would be unwise to allow the water to flow over the top of the dam without being controlled. However, a report from the ICRC in Pakistan, dated 14th Jan, states that "According to the local government, a dam burst is very highly unlikely to occur."

Landslides in Oregon

The Oregon Geological Survey has a quarterly magazine called Cascadia highlighting some aspect of the geology of that state. Their Fall 2006 edition focuses on landslides, with a series of articles on different aspects of landslides in that state. Some of the articles have a broader interest, such as the use of LIDAR for landslide mapping.

The magazine is here: Cascadia

A follow up to the Tennessee landslide video

A couple of weeks ago I highlighted a new landslide video from Highway 64 in Tennessee, USA. Thanks to the excellent GeoPracNet for highlighting that some aerial imagery is now available from News Channel 9 of the slide:

Photo by Dennis Hutcheson

The sliding plane was clearly an existing discontinuity sub-parallel to the slope, with movement perhaps being allowed by the cutting of the slope to create the road bench.

One of the best landslide videos so far!

Many of the landslide videos that I have featured on here have been quite low quality. The one featured below is unusually good. I have updated this to provide the (better) Youtube version:



The slide apparently occurred at Polk County in Tennessee, USA, on 10th November 2009. The slide appears to be a rockslide on a discontinuity dipping parallel to the slope. An interesting element of this is the clear signs of precursory activity - note the blocks on the road and the small slide that happens just before the main slide.

The basic physics of landslides is the same everywhere

Whilst landslides come in all sorts of shapes and sizes, the fundamental physics that controls material deformation on slopes is the same everywhere. I was reminded of this truism this week when Andrew Giles pointed out a large rockslide that occurred a few days ago, blocking Interstate 40 at Pigeon Gorge in North Carolina, USA. The Citizen-times.com website has a nice report and images of the slide:



The images reminded me very strongly of the 2003 Bukit Lanjan landslide, thousands of kilometres away in Malaysia (image from CKC Malaysia):

Animation of Seattle harbour liquefaction failures

Youtube has a rather cool video of an animation of the effects of a large earthquake on the harbour side area of Seattle. The main point is I think to show the effects of the earthquake on the elevated roadway, but it also shows liquefaction failures of the fill behind the sea wall:



Pretty neat - certainly a useful teaching tool.

Updates on the Nile River (Naches) landslide

Clearly the Nile River (Naches) landslide has effectively dropped off the media radar now. However, there are some excellent ongoing posts on this slide on the Sliding Though blog, which the is the Washington State landslide blogsite. You can access these posts here:

http://slidingthought.wordpress.com/

The Naches / Nile River landslide and the role of the quarry

Spectacular image of the Naches / Nile River landslide, from the Washington State DNR Flickr site

Hat tip to Andrew Giles for pointing this out to me.

The Seattle Times have run an article today about the role of the quarry in the triggering of the Naches landslide. They quite rightly point out that there is no firm evidence either way as to whether the quarry played a role or not, but the do make some interesting comments about the possible role:

"Washington's Department of Natural Resources warned a Naches, Yakima County, gravel pit four years ago that its operations might be destabilizing a portion of the slope that collapsed onto Highway 410 this week. Records from 2005 show a department geologist noticed a 10-foot-wide fissure between the towering basalt cliffs and a broad talus slope below. The gravel mine appeared to have removed deposits that were buttressing the slope, documents say. "Your surface mining activity may be exacerbating slope instability and, therefore, may be creating a potential hazard to adjacent property and danger to the public health, safety (and) welfare," says a notice issued to the mine owners in September 2005."

The article quotes Prof. David Montgomery from the University of Washington, who is undeniably a world class academic geologist:

"It's definitely premature to rule out the gravel pit as a contributing factor...They were definitely digging at the toe of an active landslide, and that's a recipe for a slide."

The article then goes on to note that the Department of Natural Resources (DNR) wrote a letter dated July 2008 that noted that the agency still had not received a monitoring plan.

The image above clearly shows that this is primarily a slump/rotational failure as outlined in my previous post. This is rather beautifully illustrated by the image below, also from Washington State DNR Flickr site. The back-tilting of the trees are a sure-fire sign that the slope has rotated:

There is undoubtedly some translational movement too, as would be expected in such a large failure.

So what caused the Naches landslide?

The Naches landslide, as I reported in my post yesterday, is a somewhat intriguing failure. The weather conditions were dry, the rivers are in low flow conditions, and there has not been an earthquake that could have caused the failure. So what happened?

A clue may be in the landslide type. Several reports have suggested that the initial failure was a rotational slide. I am struggling slightly to get a proper appreciation of the slide (does anyone know where there is a decent set of images taken from an aircraft or a helicopter?), but a quick inspection of the images from the galleries that Heidi posted in the comments from yesterday's post is helpful. These three images, from this Washington State DoT gallery, are particularly helpful:

First, this one appears to show the highway uplifted well above the previous position (compare this with the Google Earth image here):


The second one appears to show the uplifted road and the gravels and cobbles from the river bed also uplifted well above the previous position:


Finally, this one also seems to show greatly uplifted river bed material:

Some of the other images even show dead fish amongst this material, so there is not much doubt what this is.

So how can the river bed be uplifted in this way by a landslide coming off the hillside. One possible explanation (lets call it a working hypothesis - I must stress that this is very tentative on the basis of the images) is that this is indeed a rotational slide. A typical rotational landslide looks like this (image from Geoscape Calgary):

Notice how the movement has occurred on a curved surface - this is what makes the slide rotational. Notice also how material at the toe (foot) of the slide is lifted up due to the movement on the curved surface. Sometimes fragmentation of the blocks in this area causes flows to develop, but often this takes some time as the block starts to break up and weather. So, the uplifted road and riverbed is consistent with a rotational slide, although this is still only a hypothesis. In reality the images suggest that the slide is probably rather more complex than that shown above, but the essence may be a rotational failure.

If that is the case, why did it fail. Well, for most rotational failures movement is the result one or more of three causes:

1. The strength of the materials on the shear surface reduces. This is most likely to be the effect of rainfall causing high water pressures, although in this case that appears unlikely (although a leaking pipe or similar can sometimes be a factor). Materials sometimes degrade with time as well, causing a so-called progressive failure that usually has no trigger, so this is a possibility. If that is that is the case, and such failures are quite rare but definitely do occur, the slope should have shown lots of signs of problems for some time prior to failure;
2. Mass is added to the slope at the top of the block that fails, which adds to the driving force, triggering failure. Sometimes dumping of spoil or garbage on the slope can trigger failures of this type. No such process is evident here, but it is possible.
3. Mass was taken away from the toe of the slope. Much of the resistance to movement in a rotational slip comes from the material at the toe. Indeed, a common way to stabilise a rotational slide is to add mass the toe (often called a toe weight). A good example is the rotational landslide at Folkstone Warren in the UK (image from here):

The huge structure at the bottom of the slope is a toe weight designed to buttress the slope to prevent a rotational failure, and thus to protect the railway line.

So, removal of the material at the toe (or low on the slope) could be enough to cause failure.

Therefore, if I was asked to look at this slide I would do the following:

1. Work out what type of failure this is - i.e. is it a rotational slide?
2. Find out whether there were any water pipes or suchlike on the slope that might have been leaking, or anything that might have been feeding water into the slope from above;
3. See whether anyone had dumped a substantial amount of material high up on the slope;
4. See whether anyone had removed material from low on the slope.

I know where my immediate suspicions would lie, but a proper investigation is needed. It may well be the case that the failure occurred because of a chain of events involving two or more of the possible causes outlines above.

Updated and corrected: Large rockslide in Naches, Yakima County, Washington State

Updated: correct landslide location - thanks to various readers (especially Andrew Giles and Steve in ATL) for helping me to get this right - and apologies for the earlier error.

I have posted an update to this post here.

Various media agencies (e.g. here, here and here) are reporting a large landslide at Naches in Yakima County, Washington State, USA, which has blocked state highway. The Seattle Times has a spectacular photograph:


There is also a rather nice (if a little dramatic) video here.

As can be seen from the above video and picture the slide is large (the news reports suggest half a mile (about 750 m) and large. The slide appears to have come down in good weather.

The landslide appears to have come off this slope (from Google Earth) (this is now the corrected location):


A couple of very quick observations about this:
1. As a couple of commenters have noted, there appears to be a quarry on the right side of the area that has failed.
2. Above the road there appears to be what could be a smaller slump with a large scarp, although the quality of the image is not good enough to tell properly:


See the update to this post here.

Interesting landslide footage from La Jolla, California

Image from here

The La Jolla landslide in San Diego California occurred in October 2007, destroying three houses and a road, and leaving many more damaged. The landslide is currently the subject of a lawsuit that was filed by the householders. I am not going to comment further on the slide whilst this is going on, but as part of the evidence in the case some mobile phone footage has emerged of the slide as it occurred. This footage is unusual in that it covers a progressive, non-catastrophic slide, essentially showing the tension cracks opening as the slide occurred. The footage can be viewed here. The complete (8 minute) footage, available on that page, is worth viewing.