16 December 2014
Oso: The SR 530 Landslide Commission report
Yesterday, the Oso / SR 530 Landslide Commission released its final report – it is available online as a PDF. It its a very interesting document, carefully crafted and sensible in its recommendations. I would recommend that anyone interested in landslide, or indeed other geophysical, disasters reads the report as its findings are almost universally applicable. It is notable that the commission notes that there were many successes in the response, but that inevitably not everything went as smoothly as it could have done. Some aspects are almost bizarre – for example, the commission notes that:
On March 23, 2014, the second day following the landslide, Chief Willy Harper, District 25 (Oso), made a request to Chief Eric Andrews, Northwest Regional Coordinator for the Washington State Fire Defense Board, for a mobilization of state resources. Chief Andrews assessed the situation per state mobilization guidelines and made a formal request to the Washington State Patrol (WSP) for state fire service mobilization (all-hazards or state mobilization) under RCW 43.43.960 – -.964. This request was denied by WSP due to their legal counsel’s interpretation that state fire service mobilization resources and funding is available only for fire disasters.
Not surprisingly the commission recommends that this strange anomaly is put right.
However, in the context of this blog the most interesting aspects pertain to the landslide hazard and risk elements. Here the Commission makes a three key recommendations (amongst many others):
1. Support a Statewide Landslide Hazard and Risk Mapping Program
The Commission recommends the Legislature significantly expand data collection and landslide mapping efforts, which will provide the foundation for sound public and private land-use planning and decision-making.
The report provides more detail about how this should be undertaken, in particular with the use of lidar data. It is also suggests prioritization of transportation corridors, residential areas, urban growth areas, emergency evacuation routes and some forest lands. The work should be undertaken by the State Geological Survey, be subject to peer review and be overseen by a technical advisory group. The Commission illustrates the structure of this programme with the following diagram:
It is hard to disagree with this recommendation, and indeed it is reported that the Governor has requested a budget of $36 million for “improved mapping and other landslide mitigation measures”. Whether this budget is granted is a different matter of course. My only criticism of this recommendation is in terms of the use of the information. Hazard maps are only useful if there is clarity in how and when they are to be used, and by whom. In particular it is perhaps slightly surprising that there is no mention of risk assessment or mapping, but perhaps this is considered to be a step too far at this point.
2. Establish a Geologic Hazards Resilience Institute
The Commission recommends the Governor explore the creation of a geologic hazards resilience institute to address education, outreach, and research needs, professional practice guidelines, and other geologic issues impacting Washington communities.
In my view this is the most interesting recommendation, and the one that could have the greatest long term impact. The vision is for an institute that provides support by:
Assisting tribal, state, and local governments to establish programs and staffing to address local geologic hazards.
Providing accurate information on geologic hazards and risks relevant to land use planners as well as to the general public.
Identifying needs and providing training for geohazard specialists; for example, ICS training, and other training that assures successful emergency response.
Establishing public information response protocol for emergencies.Enhancing public education and awareness programs and partners.
Identifying long-term research and education/outreach funding partners.Conducting educational, outreach, and research activities.
If such an institute were to be established then Washington State could become a world leader in hazard management, a very exciting prospect.
3. Conduct Landslide Investigations
The Commission recommends the Department of Natural Resources (DNR) Division of Geology and Earth Sciences, Washington State Department of Transportation (WSDOT), Snohomish County, and the US Geological Survey (USGS) conduct landslide investigations to characterize the mechanisms that activated the landslide and to understand the stability of the landslide mass.
I cannot over-emphasize just how important this is. Undertaking a proper, detailed assessment of this landslide, and others as they occur, using a combination of detailed mapping, drilling, monitoring, lab testing and modelling is vital if we are to understand where such hazards will occur in the future. Opinion remains divided as to whether the incredibly destructive, fast and long runout of the landslide could have been foreseen (I remain convinced that it could have been), but we still need to understand properly the mechanisms that allowed this behaviour to occur. Proper forensic investigations are the key. Interestingly, this will be discussed in detail at the AGU Fall Meeting on Friday – I wish I could be there for both the poster session and presentations).
So overall, I think that this is an excellent report that deserves to be both read widely and to be implemented properly. It will be interesting to see what happens to the budget requests over the next few months.
15 December 2014
The Banjarnegara landslide
Late on Friday night a large and apparently very rapid landslide was triggered by heavy rainfall at Banjarnegara in Central Java, Indonesia. Latest reports suggest that 32 bodies have been recovered to date, with a further 76 people thought to be missing. The likelihood of their having survived the landslide is low; one can only hope that, as is often the case, it turns out that at least some of those reported missing were elsewhere at the time of the landslide. A further 15 people were injured, 11 of those seriously.
This image, from the Straits Times, shows the landslide site from close to the toe:
As well as being a tragedy, this is an interesting landslide for two reasons. First, the slide appears to have been a very mobile earthflow – in fact there appears to be two lobes with an untouched area between. Second, the landslide appears to be surprisingly deep-seated in the source area judging by the size of the lateral scarp on the left side of the lower part of the source area. It seems that this deep-seated nature created a very large mobile mass that overran the village.
The source area of the landslide is quite well illustrated in this AP image via CTV:
As far as I can see the slide has occurred in deeply weathered residual soil, with no evidence of bedrock, or a bedrock – regolith contact, in any of the images that I’ve seen. I wonder if this was a static liquefaction type process to generate the exceptional mobility. An alternative might be an undrained loading process generated by an initial failure near to the crown of the landslide, which would also explain the mobility, although the depth of the failure surface might be harder to explain.
Whatever the cause, this is a landslide that deserves detailed analysis. Java is a global hotspot for landslide deaths because of the toxic combination of steep slopes, volcanic soils, heavy rainfall and lots of people. There is an urgent need to understand better the mechanics of these large and immensely damaging landslides there.
4 December 2014
Yesterday I highlighted the very large Domkar Monastery landslide in Tibet, which failed in a somewhat spectacular manner last month. I have managed to track down a good image of the slope that failed, from the Tibetan Trekking website:
It is not clear to me whether this mass is loess or an old landslide body – I am still tending towards the former, but it could be the latter. The failed body has deeply incised drainage lines on each side, but little sign of erosion or excavation at the toe.
It is quite interesting to look at the Google Earth archive imagery of the site, taken from a perspective view. This is November 2007:
This is May 2009 (in black and white):
This is November 2010, which post-dates the April 2010 Yushu earthquake that affected this area and damaged the monastery:
The most obvious change is the development of works beside the road in the bottom right hand corner of the image – I wonder what this is? But the remarkable thing is that there is really no sign in these three images of the development of the landslide except perhaps that the rear scarp formed along the line of the track at the rear of the settlement. Even after the 2010 earthquake the landslide does not seem to have progressed, although it would be interesting to see an image from earlier this year. But from these images there is little sign that an incipient collapse was developing. I suspect that this supports the notion that this is a loess failure – loess can be a collapsible material, which means that it can be subject to rather spectacular landslides.
3 December 2014
The Domkar Monastery landslide
In mid November the ever impressive Tibet Earthquake twitter feed (@aam868) posted a number of reports about a landslide at the Domkar Monastery in Qinghai, eastern Tibet. This landslide, appears to have occurred on 2nd November 2014, is both spectacular and catastrophic. The Domkar Monastery is located at 33.01N, 97.14E:
The site appears to have undergone a massive rotational slip with an enormous displacement across the back scar: From the Tibet Express, these are the before and after shots:
Note the damage to the access road. Interestingly, this site was severely damaged by the Yushu earthquake in 2010; rebuilding had only been completed this year. In fact, if you look carefully at the before image it is clear that the back scar of the landslide had already formed, with substantial displacement have already occurred. The lateral scarp of the landslide has cut through the main temple, with major part of the building having been completely destroyed. China News has this image of the landslide, showing some detail of the damage. A translation of the text confirms that there were no injuries:
The material forming the landslide appears to be loess, which is prone to large-scale landslides. It would be interesting to know if there had been any construction works at the toe of the slope – often rotational landslides of this type are triggered by unloading of the foot of the slope.
1 December 2014
The Railway Children – Landslides in the Movies Part 2
This is Part 2 in my new series on Landslides in the Movies. Part 1 is here. The 1970 movie The Railway Children, which was based on a novel of the same name by Edith Nesbit, stars a very young Jenny Agutter. Probably the most famous scene in this film occurs when a landslide blocks the railway line at a time when a train is approaching. The three children run up the line to flag down the approaching train, thus preventing a disaster. This scenario is far from impossible – indeed I have featured landslide-induced derailings of trains on many occasions on this blog, and some of them do indeed have catastrophic consequences.
The landslide scene in the film is shown in this sequence on Youtube:
If nothing else it makes you realise how far special effects have come in the last 45 years. The movement starts as a translational slide – note how the trees remain perfectly upright as they displace – although the movement of the trees whilst the grass around them remains static is quite amusing in some ways. A really nice element is that the landslide occurs on a cut slope that clearly has an inadequate retaining structure at the toe – it looks like poor engineering by the construction crew to me. The should never have expected to retain a slope of this size with old railway sleepers. In addition, the way that the wooden posts topple onto the line suggests that they had very shallow foundations – surely a recipe for disaster:
It is this poor engineering that probably accounts for the collapse on a beautiful sunny day and in a dry condition (note the dust that is kicked up by the collapse at various points). The boulders on the line at this point is a nice touch, suggesting some precursory deformation.. Of course the sequencing of the failure is a little odd, in that the upslope section moves before there is much deformation in the retaining structure – there is clearly a complex process at work here.
I’m not sure that the film crew managed to depict the post-failure landslide scar particularly well – the deformation at the start suggests that the scar should extend right up the slope.
Finally, I think that the children need to study natural hazards at school, given that they diagnose the event as an earthquake.
30 November 2014
It has been a long time since I posted in my Landslides in Art series, so this one is well overdue. The last posting in this series was made almost a year ago. I really don’t know very much about this artist, except that she is based in Taipei in Taiwan, and uses the pseudonym Harlequin or Harlequipan. The painting in question appeared on her blog, which new seems to be defunct, four years ago. It is simply titled Landslide:
To me this appears to depict the type of channelised flow failures that are common on the steep slopes in the Central Mountains of Taiwan, triggered both by heavy rainfall and by earthquakes, such as this one from the 1999 earthquake:
I would welcome suggestions for future posts in this series.
18 November 2014
Rabenstein, South Tirol
A large landslide occurred at Rabenstein in the South Tyrol northern Italy (this is the German-speaking area of northern Italy). Fortunately it was caught on video and is now available on both Liveleak and Youtube – I have embedded the Youtube version below because it is easier:
The reported volume of this latest landslide is 20,000 cubic metres. The very large amount of precursory deformation is notable, as is the very rapid fragmentation of the rock mass as the collapse developed:
This is not the first landslide event at this site – Liveleak also has a smaller, earlier landslide event, which I think occurred on 30th September:
This second video is worth watching for the movement of the enormous boulder at the foot of the slope, which was safely captured by an engineered runout zone.
An update on the Mannen Landslide in Norway
Meanwhile the Mannen landslide in Norway has now clearly entered a steady secondary creep phase of movement. The Rauma Kommune website posted an update in Norwegian two days ago, which includes this movement graph:
The commentary suggests that continued low temperatures and dry conditions suggest that little change in the rate of movement is expected in the days ahead.
17 November 2014
The Markagunt gravity slide
In the current edition of the journal Geology, a paper by David Hacker, Robert Biek and Peter Rowley (Hacker et al. 2014) describes the Markagunt gravity slide in southwest Utah. This is a very exciting piece of work as it identifies for the first time a truly gigantic landslide. Whilst I like to avoid superlatives, the scale of the Markagunt landslide is remarkable:
- 90 km long
- 1700 – 2000 cubic kilometres in volume
- Surface area of over 3400 square kilometres
- Up to 200 m thick.
This is part of the area that it covers:
The landslide deposit is located in the Marysvale volcanic field in Southwest Utah in the USA. This is not the first time that these landslide deposits have been identified, but previous studies have suggested that they were formed in multiple landslide events, and have termed the deposit the Markagunt volcanic breccia. The change in Hacker et al. (2014) is that the deposit is now recognised as having originated in a single landslide that occurred about 22 million years ago. The paper demonstrates that the landslide consists of a large sheet of volcanic rock broken up by faults. The authors divide the landslide deposit into three distinct sections:
- A 58 x 42 km bedding plane segment;
- A 1-2 km wide ramp segment;
- And a 32 km long land surface segment.
The question of course is how such an enormous landslide can form. The base of the Markagunt gravity slide consists of of a clear shear surface with brecciated (i.e. intensely shattered) rocks. However movement has occurred on a shear surface that has an inclination of only a small number of degrees. The authors suggest that as the Maryvale volcanic field developed, it uplifted the Turshar Mountains, generating a slope in the surrounding rocks. At the base of what was to become the landslide is a very weak volcanic deposits known as the Brian Head formation, allowing sliding to develop.
There is only one other known landslide on this scale – the infamous and equally enormous Heart Mountain Gravity Slide. These two deposits are now the largest subaerial landslides on Earth. Both are of course in the USA; I wonder how many more there are around the world that have yet to be identified?
David B. Hacker, Robert F. Biek and Peter D. Rowley 2014. Catastrophic emplacement of the gigantic Markagunt gravity slide, southwest Utah (USA): Implications for hazards associated with sector collapse of volcanic fields. Geology 42, 943-946. DOI: 10.1130/G35896.1
12 November 2014
Over in Norway, the Mannen landslide continues to creep slowly – about 2 mm per day now, as the graph below shows:
- The risk level has been downgraded red to yellow, but this still requires continuous evaluation of monitoring data.;
- The monitoring system has been upgraded to provide better radar systems, the installation of a geophone (that might generate some very interesting scientific data), a LIDAR (laser) monitoring system and enhanced use of weather stations to determine the water inflow to the landslide;
- The railway has reopened to freight traffic only;
- Those evacuated from the site remain out of their houses;
- A decision has been taken (wisely in my view) not to use water-bombing due to the uncertainties
The latest update report from Aknes is also online (PDF again in Norwegian). The most interesting aspect of this report is a map showing the deformation across the hillside, with the monitoring positions marked as well. The map shows deformation over the period 6th to 29th October; I’d think this is slope radar data:
The very high level of deformation at the top of the slope is clearly visible, as are the smaller deformations downslope. This map helps gain an understanding of just what a large block makes up this active landslide. Given the onset of winter conditions the monitoring of the landslide and forecasting its future behaviour are becoming increasingly difficult. whilst the next obvious danger point will be the spring snow melt and thaw season, a period of warmer weather might also pose risks. Of course there is also a chance that the ongoing secondary creep will tip the landslide into a tertiary creep phase, leading to failure, so it is not possible to make any assumptions.
11 November 2014
The Donghekou landslide
One of the largest landslides triggered in the remarkable 2008 Wenchuan earthquake in China occurred at Donghekou in Qingchuan County. This was a large slide – it has a volume of about 100 million cubic metres and it traveled over a distance of about 2 km. Four villages were buried, resulting in about 780 deaths. This landslide has been examined in detail in a paper, Wang et al. (2014) just published in Engineering Geology. This pair of images, whose provenance is somewhat unclear but which was reproduced in another paper on this landslide (Zhou et al. 2013) provides a before and after view of the landslide site:
The paper is interesting in a number of ways. First, it notes that the slope was known to be unstable and indeed that during heavy rainfall events the local population was frequently evacuated. Of course this was not possible when the earthquake struck. Second, the paper notes that the landslide had a very long runout distance over a near horizontal surface, which suggests very high rates of movement. Using experimental data, the authors conclude that the landslide had such a long runout because of liquefaction of the valley fill deposits during the earthquake, which provided a very low friction surface. The landslide itself was retrogressive in nature, which is unsurprising for such a large slide.
Perhaps the most interesting aspect of the landslide though is that about six months after the earthquake fumaroles appeared on the landslide mass, generating high temperature gas and a sulfurous odour. These fumaroles are still active, although less so now than in the early phases. Unsurprisingly there has been considerable speculation as to what these fumaroles represent. The authors both sampled the gases emanating from the fumaroles and measured the temperatures a metre into the vent. They found that the ground temperatures were in the range of 50 to 60 degrees Centigrade and that the gases were primarily carbon dioxide and methane, with fluid emissions being rich in potassium, sodium, magnesium and some other trace elements, From this they concluded that the cause of the fumaroles was oxidation of carbonaceous siliceous shale that had been exposed to the air and oxygen-rich water as a result of the movement of the landslide.
This is of course not without precedent – indeed back in 2008 I wrote a blog post about the strange phenomenon of burning landslides, using an example from Dorset in the UK.
Zhou,J-W., Cui, P. and Yang, Y.G. (2013). Dynamic process analysis for the initiation and movement of the Donghekou landslide-debris flow triggered by the Wenchuan earthquake. Journal of Asian Earth Sciences. 76, 70-84. DOI: 10.1016/j.jseaes.2013.08.007
Wang,G., Huang, R., Lourenço, S.D.N. and Kamai, T. 2014. . A large landslide triggered by the 2008 Wenchuan (M8.0) earthquake in Donghekou area: Phenomena and mechanisms. Engineering Geology. DOI: 10.1016/j.enggeo.2014.07.013