26 April 2015
Landslides from the Nepal Earthquake
Whilst the Nepal Earthquake is now the centre of global attention, the true pattern of loss is not yet apparent. As usual, the focus in the first 24 hours is on the locations that have both media presence and easy telecommunications – in this case Kathmandu. The impacts there are undoubtedly serious, especially for historic masonry buildings, and the city will never be the same again. But the true impacts of this event are going to have been felt in the rural areas to the north of the city. At present there is little information from those districts, but expect the picture to be tragic as it emerges over the next two days.
Landslides are going to be a very real problem in those areas affected by the Nepal earthquake, and by its aftershocks. Indeed, just 15 minutes ago there was a very shallow M=6.8 aftershock that is likely to have caused substantial damage in its own right, albeit in a more limited area. There has been some confusion about the area affected by the earthquake, and in particular the area of most intense shaking. This is because there is a perception that the epicentre is the centre of the earthquake, and thus that the damage should radiate away from this point. This is not the case. The earthquake energy is derived from movement on a fault (or sometimes more than one fault) – a complex three-dimensional structure that extends over a large distance. The epicentre is just where the rupture initiates – i.e. the location at which the fault starts to move. The rupture then propagates along the fault, releasing energy as it goes. Often the rupture propagates quite evenly away from the epicentre, in which case the epicentre is close to the centre of the earthquake-affected area. But at other times the rupture propagates preferentially in one direction or another.
In the case of the Nepal Earthquake the rupture appears to have propagated mostly towards the east of the epicentre, not to the west. So the epicentre itself is at the west end of the earthquake affected zone. This is clear from the USGS shakemap, which shows the epicentre as a star:
This was good for Pokhara, but bad for Kathmandu. It also explains why the impacts at Everest were so serious.
Possible landslides from the Nepal earthquake
The most seriously affected area from the earthquake is mountainous and remote, but there are substantial numbers of people living in the valleys and on the hillsides. This is a typical landscape:-
Further to the north the mountains become higher and the slopes longer. Note the terracing in the fields, the steep slopes and the large numbers of houses. There are many substantial villages, often located high on the slopes. This is highly landslide-prone territory, and the impact of the earthquake in these regions is going to be dreadful. Some effort is already being made to analyse the likely landslide effects, although at this stage such efforts are tentative. Over on the EWF blog, Alex Densmore has posted an initially analysis by Tom Robinson from the University of Canterbury of the likely areas affected by landslides:
There are a few things to note here. First, the analysis is dependent on the data quality, and you can see that there are some issues there (this is why there appears to be straight line boundaries in landslide hazard in places) – that is an important caveat. But the analysis is really interesting and helpful. It shows that to the north of Kathmandu, the very remote areas are likely to have been severely affected by landslides – but as yet there is no information from up there of course. And interestingly the hills to the south of Kathmandu are also badly impacted by landslides triggered by the Nepal earthquake – indeed the landslide picture might be as bad there as to the north. This is significant for two reasons – first, there are lots of people living in this area; and second, the roads that link Kathmandu to the outside world have to cross these hills.
Tom has run a quick analysis of the main roads affected by these landslides – the impacts look to be very serious:
Kathmandu is entirely dependent on goods being brought into the city on these roads. If they are badly affected by landslides then the impacts will be severe.
There is a real urgency about the need to assess the actual landslide impacts, especially to the north – we need satellite imagery quickly. There must be a strong possibility of large valley-blocking landslides triggered by the Nepal Earthquake in the high mountains to the north- if so these will need to addressed without delay. The monsoon is going to be a real problem this year.
25 April 2015
The M=7.9 earthquake in Nepal this morning
NB updated to reflect the fact that this is now thought to be M=7.9 rather than M=7.6.
It appears that there was a large, shallow earthquake in Nepal this morning. The initial data suggests that this was a comparatively shallow event in the Central part of the country. Current data suggest:
This will become clearer as the day wears on, but either way this is going to be serious. In terms of depth and magnitude this is generally comparable with the 2005 earthquake in Kashmir (updated: M=7.9 means that it is significantly larger), which killed over 70,000 in Pakistan and Nepal. Nepal has similar levels of vulnerability, but a lower capacity to cope (there is just a single runway at Kathmandu for example, and the armed forces are not well-equipped). The only thing that might help in this case is that the epicentral region does not contain a major city, but both Pokhara to the west and Kathmandu to the east are close enough to have been damaged. Kathmandu in particular is vulnerable, with poor quality buildings and soils that are prone to liquefaction, although in this case the distance should help. The Lamjung area itself is less densely population, which should reduce losses, but this is such a large earthquake that the effects will be severe.
This is the location as defined by the USGS:
So, we should expect extensive building damage with many thousands buried (there are already some images appearing on Twitter); serious damage to infrastructure, especially roads, telecommunications and electricity grids; and many landslides. This is likely to be a humanitarian crisis in the epicentral area, and with the monsoon just two months away the situation is going to be acute. The initial focus will be on Kathmandu, but the situation to the northwest of the city will be far worse. Expect to see little news from there for at least two days though.
Landslides are going to be a very serious problem. They will have caused losses; will have destroyed roads and other infrastructure, which will make the rescue and recovery operations very challenging; and they will continue to threaten the population. It is also likely that there are valley-blocking landslides in the mountains, which will be particularly problematic as the monsoon approaches. We need to find these very quickly.
20 April 2015
The Bolshaya Talda earthflow
Many thanks to those who have helped to uncover the facts behind the amazing Bolshaya Talda earthflow in Russia, which was filmed in the amazing video about which I blogged late last week:
A couple of people emailed to suggest, and Brett Gilley noted in comments, that this might be a mine waste landslide, based on the materials involved, the appearance of the hills in the background and the presence of heavy equipment. In comments on the original post, Michal cracked it though:
Whilst it is difficult to be certain, the most likely location appears to me to be at about 54.144, 87.098. This site has all of the correct characteristics, including the appearance of the topography, the presence of the high voltage cables and the structure of the road:
The image above is dated 8th September 2014. There is also an image from 9th September 2013 of the same site:
A comparison between the two images suggests that there has been recent active storage of waste at this site. The video suggests that it was this waste that collapsed to generate the landslide. It was fortunate that the failure occurred in the daytime and in an area with no houses. Of course, landslides like this should be avoidable – the mining industry is still associated with far too many landslides. Recent examples include:
- The Shawa landslide in China
- The Jiana/Gyama landslide in Tibet
- The Bingham Canyon landslide in Utah
- The Hatfield Colliery landslide in England
- The Collolar landslide in Turkey
- And of course the Aberfan landslide in Wales
And there are many more.
Thanks to everyone who helped to unpick the riddle of this landslide.
17 April 2015
An absolutely stunning new video has appeared on Youtube overnight showing footage shot from a road of the movement of a very large and very spectacular earthflow in Russia. It has to be said that the videographer was as cool as the weather in his or her slow retreat from the path of the landslide:-
There is no information about the landslide, except that it occurred on 1st April 2015 at Zarechnyi. Liveleak also has the video of the Russian earthflow, with a label that says Penzenskaya Oblast. If this is correct then it is in an area on the western side of Russia. Given that this would be the thawing season, the conditions would be right for this type of landslide. But there is also a volcano called Zarechnyi on Kamchatka, although I assume that this is not the location of this landslide.
Does anyone have any more information?
16 April 2015
The 2005 Leuwigajah dumpsite landslide
For many people the thought of being buried alive is a true horror, and for good reason. However, the thought of being buried alive in a surge of garbage – filthy, rotting, stinking and even on fire – takes the terror to a new level. For those unfortunate people that make their living picking rubbish from garbage sites this is a very real fear. It is impossible to know how many people die this way – many in all probability, but few fatalities are ever recorded. Occasionally though a catastrophic slide occurs on a waste site, with multiple deaths. The worst known case occurred at the Payatas waste site near Manila in the Philippines in 2000, killing 278 people. The second worst example occurred more recently at 2 am on 21st February 2005 at the Leuwigajah dumpsite, near to Bandung city in Java, Indonesia. The landslide killed 143 people, having buried 71 houses. In a paper published recently, available via open access (hurrah!), Lavigne et al. (2014) have undertaken a detailed investigation of this landslide. I think that this is a really important piece of work that deserves attention.
The paper includes images of the landslide, both from aerial photography and on the ground. The extraordinary nature of the Leuwigajah dumpsite landslide is clear:
The landslide volume was 2.7 million cubic metres of waste, traveling over a distance of about 1000 m and leaving a deposit that was on average 10 m thick. The team investigated the movement of the landslide, and explored its internal structure. They found that the landslide moved as a flow, and that the rate of movement was rapid. Examination of the distance that the landslide moved compared with its height change suggest that the Leuwigajah dumpsite landslide showed unusually high mobility (i.e. the apparent friction was lower than would be expected), a really interesting observation. The authors suggest that this may have been because the waste contained very large numbers of plastic bags, which facilitated internal deformation of (i.e shear within) the landslide mass. This extraordinary image, included in the paper, shows the essentially uniform horizontal orientations of the plastic bags in the landslide mass after the slide:
The details of the fate of the victims are pretty horrifying To quote the paper:
“In the months preceding the 2005 disaster, fires have been reported at the Leuwigajah dump site. Eyewitnesses reported that the waste mass was on fire while moving. Fires may have spread quickly because the landfill contained highly flammable combustible material. All the bodies of the victims were burnt, and the studied material was rather deeply charred.”
So why did the Leuwigajah dumpsite landslide occur? The authors suggest that the normal combination of processes were present – i.e. weak material forming a slope that was too steep; etc. But in this case, the release of methane, possibly explosively, from the waste may have rapidly reduced the shear strength of the waste, initiating movement. Secondly, prior to the landslide event the area suffered three days of heavy rainfall (exceeding 80 mm per day), which drive up pore water pressures. And finally, the authors suggest that the ongoing fires within the debris may have progressively weakened the waster materials, creating the conditions for the landslide.
Of course, these types of landslides are avoidable with proper management of the dumpsite. And, as Lavigne et al, (2014) make clear, the easily forgotten factor is the extreme vulnerability of the populations at risk. Sadly there remain many people making a living on these highly dangerous sites. It is now a decade since the Leuwigajah dumpsite landslide. It can only be a matter of time before a repeat of the Leuwigajah dumpsite landslide occurs.
Lavigne, F., Wassmer, P., Gomez, C., Davies, T., Sri Hadmoko, D., Iskandarsyah, T., Gaillard, J., Fort, M., Texier, P., Boun Heng, M., and Pratomo, I. (2014). “The 21 February 2005, catastrophic waste avalanche at Leuwigajah dumpsite, Bandung, Indonesia.” Geoenvironmental Disasters, 1, 10. doi:10.1186/s40677-014-0010-5
15 April 2015
Himara Viaduct landslide
A landslide beneath one of the pillars supporting the Himara viaduct in Sicily, southern Italy has generated a huge furore. The landslide itself occurred last Friday, displacing at least two of the pillars supporting the key A19 highway that links the cities of Catania and Palermo. There is not a huge amount of detail about the landslide in the English language media, although the English version of Gazzetta del Sud has a nice report. There is an excellent gallery of images on the Corriere Del Mezzogiorno website, which includes this one showing the displaced pillars:-
This one showing the landslide (note the highly displaced and damaged ground in the foreground):
And this one showing the road damage:
The landslide appears to have pushed the pillars forwards, which suggests that it is probably translational and possibly not very deep. Nonetheless the damage in undoubtedly terminal for the viaduct. Indeed, the infrastructure minister has now confirmed that this section of the Himara viaduct will need to be demolished. The estimated rebuild time is two years.
The row, which has led to the resignation of the head of the highways agency ANAS, is over both the state of the road and the failure to mitigate the landslide. In particular, it appears that at least some funds were set aside to stabilise the A19, but this money has not been spent. However, it is also likely that the level of funding was inadequate.
Of course the summer season is about to start, so the loss of this road will have a big impact on the tourism business.
14 April 2015
Yeager airport landslide
News reports yesterday indicated that the Yeager Airport landslide had another significant movement event at the end of the weekend (for reference my original post is here, this is my post with videos of the site, this post looks like the landslide history of the site, and this one examines reports that the fill slope was moving two years before the landslide occurred) . In many ways I don’t think that this should be considered to be a major surprise – the back scarp of the landslide was (and still is) composed of fill that has inadequate support. The Charleston Gazette has some nice images of the landslide taken yesterday, including this one of the main slide mass and the back scarp:-
This is an image from (a similar though not identical) perspective taken at the time of the main failure:
And this is the two side by side for comparison:
On first inspection it appears that a large block has detached from the left side of the landslide scar (as viewed from the foot of the slope), as indicated above. The darker material on the more recent image appears to indicate the location of this block prior to collapse. Bob Aaron has this view on his Twitter feed, taken from a different perspective, which gives a clear view of the detached block:
It appears that the weight of this new material on the debris pile caused further movement on the debris pile below, as shown by these two images, also from the Charleston Gazette:
This rolling up of the asphalt road is consistent with deeper movement in the landslide mass, which in turn is consistent with loading from a failed block at the crown of the landslide. It appears to me that these is still a steep slope at the rear of the landslide formed from very weak materials, so further failures seem likely. These failures will probably load the debris pile further, so further movement of the toe of the Yeager Airport landslide slide seems possible.
Further rain is forecast for the next few days in this area.
13 April 2015
Progressive failure leading to the 3 December 2013 rockfall at Puigcercós scarp (Catalonia, Spain)
Progressive failure – the idea that landslides progress to failure over a period of time – has been a topic of considerable discussion for the last 50 years, and has been a focus of considerable attention for the last decade or so. As well as being fundamental to our understand of landslide mechanics, being able to identify patterns of movement prior to collapse potentially provides the basis for early warning systems, which can (in principle at least) be used to protect vulnerable populations. Probably the most important observation in this respect is that of the so-called Saito Effect, which is that some (but certainly not all) landslides display a hyperbolic increase in velocity through time in the period leading up to failure. This is an interesting and useful observation, because plotting the inverse of velocity (i.e. 1/v) against time yield a straight line, which allows the time of failure to be correctly predicted (failure occurs when 1/v = 0). Of course the devil is in the detail, and correctly identifying when the linear trend has started is challenging in a noisy dataset. In addition, the Saito effect only works for some landslides (they have to be controlled by brittle mechanisms for example), and even then it appears that it can be a little hit or miss.
So, it is important to investigate further the mechanisms of slope failure. This has been greatly helped by technological developments. For example, monitoring equipment is now cheaper, more reliable and more capable. Even low cost dataloggers can collect very high temporal resolution data, and of course with mobile phone systems it is often possible to send the data back to base in real time. The upshot has been an increase in papers that examine high resolution monitoring data to explore progressive failure. Writing in the journal Landslides, Royan et al. (2015) have examined the pre-failure behaviour of a rockfall at the Puigcercós study site in Catalonia, Spain. This is a near vertical rockslope that suffered a comparatively large (1000 cubic metre) rockfall event on 2nd / 3rd December 2013. The team had been monitoring the slope using terrestrial LiDAR for six years prior to the collapse event.
The resolution of the terrastrial LiDAR is such that the movement of the rockfall prior to collapse could be calculated from successive scans, and from this the velocity could be determined, which in turn permits investigation of the nature of progressive failure at the site. This is in reality far from trivial, and required the developed development of new approaches by the project team. They divided the rock face into a series of zones and then looked at the velocity in each of them. In three of the zones, the Saito effect was clearly observed:-
The arrow in figure (b) indicates the time of the large failure event. The best fit line for areas 6 and 9 correctly predicts this time of failure remarkably well, with the linear trend developing more than a year before the collapse. The linear trend for area 7 predicts a later failure event – the authors hypothesize that this was developing into a separate failure, but that the major collapse precipitated the collapse of this section as well. Interestingly, the project team also saw an increase in the number and rate of rockfall events in these areas prior to the major rockfall. I would think that this is a sign of an increasing rate of deformation of the rock mass as failure developed, which is also an indication of progressive failure.
Finally, the project team looked at the major rockfall event in relation to potential trigger events, such as heavy rainfall. In their words:
“No clear external triggering factor was detected for this event. Therefore, the evolution over time of the precursory indicators suggests that just stability reasons seem to be the most probable cause of the final failure. The continuous increase in deformation of areas 6 and 9 created a critical situation in terms of stability, and these areas eventually fell without any external trigger. This approach is supported by the hypothesis exposed in Rosser et al. (2007) in which when the instability is in the tertiary creep phase, the environmental forces have little or no discernible influence in the evolution of the instability and therefore in the final failure.”
I think that this is an extremely interesting and important paper that makes a substantial contribution to our understanding of the development of progressive failure. That once again failure is seen to be a long term process rather than a one-off response to a single trigger is fascinating, and paves the way for improved early warning systems.
Royán, M.J., Abellán, A. and Vilaplana, J.M. 2015. Progressive failure leading to the 3 December 2013 rockfall at Puigcercós scarp (Catalonia, Spain). Landslides. http://dx.doi.org/10.1007/s10346-015-0573-6
Rosser, N.J., Lim, M., Petley, D.N., Dunning S. and Allison R.J. (2007) Patterns of precursory rockfall prior to slope failure. J Geophys Res 112, F04014. http://dx.doi.org/10.1029/2006JF000642
10 April 2015
Sumner road drone footage
One of the most seriously affected areas in the 2010-2011 Christchurch earthquake sequence was Evans Pass, a road that went over the hills at the back of the town of Sumner. This road was seriously affected by rockfalls and has remained closed since. This image, from the GNS Science reconnaissance report for the February 2011 earthquake, shows the level of damage that was suffered by the roads in the hills around Sumner:
A new video has appeared on Youtube showing the current state of Evans Pass above Sumner, collected by an amateur photographer. It is pretty interesting:
This road is expected to reopen in 2017 or 2018, but it is clear that there is a great deal of work to do first. Interestingly, the road has suffered from the effects of landslides on both the slopes above and the slopes below the road level. It is also clear that the walkers (who probably should not have been on the road) did not like being videoed by a drone!
A house collapse from a landslide in India
A belt of unseasonal weather in India and Pakistan has generated heavy rainfall, floods and landslides in recent days. In Doda, a house collapsed due to a landslide:
I’m not sure why they needed to show it so many times though!
An interesting roadside landslide in Greece
This one is quite interesting. The associated text says “It was the time my father was driving on that road to get home when the first small rock with the first dust came down in front of his car !!
He managed to pass that point unharmed and then he called to tell me what just happened me so i grabbed my camera and headed to this point where this LANDSLIDE happened!!”
The real action happens at about 3 minutes 30 seconds, although the run up to the main collapse is quite cool too:
9 April 2015
Back in January I posted about apparent ongoing slope stability issues at the remarkable Pakyong Airport site in northern India. To recap, this is a huge project to construct a large new airport on a greenfield site; to create the bench for the runway and associated infrastructure, a very substantial amounts of earthworks have been undertaken, including the construction of a range reinforced slope. This image, from an article in NCE, shows the projected works at Pakyong Airport:
The NCE article describes very well the proposed works, and is worth a read. In summary:-
“Strictly speaking the huge rising structures are not walls as such. They are gabion-basket facings for massive reinforced earth embankments, which help create a flat platform for the runway and the aircraft apron and terminal. Above the gabions, the upper parts of the steep sided slopes are less steep and are faced with a vegetated mesh. Maccaferri is supplying the gabions and mesh and has worked closely on the design details with main consultant Mott MacDonald India. Such a dramatic use of reinforced earth is not only unusual but probably unprecedented. Most such structures rise not more than perhaps 15m with a few examples in the world reaching 40m for the entire embankment.”
Maccaferri also have a nice PDF article about the project, whilst Geosynthetica has a nice article about how the slope works for Pakyong airport were awarded “International Project of the Year” in the Ground Engineering Geotechnical Awards. But the focus of these articles tends to be on the works are on the downslope side of the airport – i.e. those that were constructed to widen the bench for terminal and runway. I have seen no suggestions that these slopes are causing problems. There seems to be much less information about the slope works on the uphill side of the site – i.e. the locations in which the slope has been cut back and reinforced. The Maccaferri article states that on this side of the site the plan was:-
“Gabion toe walls (3 m high) at the uphill “cut” side to stabilize the slopes”
But there have been numerous reports in the last year or so of major slope issues at Pakyong. I described some of these in my earlier post, and there is a nice example in The Telegraph from last August. And today the Voice of Sikkim reports on the collapse of an abandoned building (possibly a school) on the slopes near to Pakyong. There are images of the site on their Facebook page:-
Interestingly, this collapse is apparently on the downslope side of the airport site. There seems to be significant questions about the upslope (“cut”) side of the Pakyong Airport site, and if this is correct it raises questions about what is happening below the site as well. Given the high profile nature of the celebration of this project over the last few years, the industry needs to know whether the design approach has started to yield problems at Pakyong Airport. It is interesting that this is a second example of a highly innovative slope design associated with an airport apparently being associated with significant issues.