5 August 2014
Valley-blocking landslides: latest from Sunkoshi and Yunnan, and a brief update on the Malin landslide in India
At present there are two sets of major valley blocking landslides threatening communities downstream simultaneously, one in Sunkoshi in Nepal and one in Yunnan Province of China:
Sunkoshi landslide dam update
After a major effort to recover bodies, the number now known to have been killed in the Sunkoshi landslide in Sindhulpalchok is now known to have reached 33, but about 120 remain missing. News reports suggest that 57 houses were lost in the landslide, whilst a further 18 have been inundated by the lake. Whilst news reports yesterday suggested that the level of the lake had fallen by as much as 4 m, this has now been corrected to about 50 cm, and there are suggestions that the level may have risen again due to recent heavy rainfall. The Nepalese army are blasting the crest of the dam to try to increase the rate of flow.
So now the situation appears to be similar to that of the Attabad landslide dam in Pakistan. The threat of an outburst has not gone away, although the immediate crisis has reduced. The great challenge now is to know how to manage the hazard. There are reports that people are starting to return to their houses in threatened areas – this is understandable – plus of course the blockage of the road to Tibet is deeply problematic for cross-border trade. The key will be the evolution of the spillway over the dam. There are some suggestions that there are now two or three channels, which in some ways may not be helpful. The ideal solution is for the floor of the channel to erode down slowly, releasing all of the water over a long period of time. The worst case scenario is very rapid erosion, causing a dramatic flood. But with three channels the amount of erosion may well be limited, which means that the dam may stay intact into the future. This will prevent the road from being rebuilt and will leave the hazard in the landscape.
But dealing with these problems is immensely difficult, and once again the Nepalese authorities deserve a great deal of credit for their proactive approach to this disaster.
Yunnan valley-blocking landslides
Usually I would expect that the Nepal government would be able to turn to the expert Chinese teams who specialise in valley-blocking landslides for help, but the timing is deeply unfortunate in that the Yunnan earthquake of two days ago also seems to have created a series of landslide dams. There is little information about them, but earthquakereport.com has provided the following:
Update 15:17 UTC on 3rd August : A very dangerous situation is currently building up for 800 people living along the riversides of the Kraal (Chinese translation) river . The normal river bed was blocked by the earthquake landslides and a lake has been forming. Earlier earthquakes had the same problems sometimes ending in disastrous events. Let’s hope people will be able to evacuate the area in due time.
Update 14:45 UTC : Kraal river landslide lake creates a dangerous situation
The water is rising 1.1 meter per hour. 56 houses have been flooded by the water. 11 houses did already collapsed. The population of the villages immediately downstream has been evacuated. But unnecessary to tell that the situation gets more dangerous by the hour. The Chinese engineers are doing whatever they can to reinforce the possible weak points. The location of the landslide is Huize, the orange circle on the map. The red numbers on the map are the number of deaths in that area :(.
Malin landslide in Pune, India
Recovery operations continue at the site of the Malin landslide in India. Latest reports suggest that the death toll has reached 134, comprising 64 women, 50 men and 20 children. It is expected that the final toll will be about 176 people. A decision has been taken to relocate the remainder of the village.
4 August 2014
Over the last few days there have been several developments in the Sunkoshi landslide crisis, some positive and some less so. The very high direct cost of the landslide is now becoming clear. Whilst only 18 bodies have been recovered to date, the number missing is thought to be about 155, making this the most costly landslide in Nepal for many years. The magnitude of the losses reflect the scale of the landslide – Kunda Dixit very kindly sent a set of images of the Sunkoshi landslide collected by the Nepal Army to me, including this overview of the site:
The landslide is reported to be about 45m high at the highest point and 25 m at the lowest. It overtopped late on Saturday, fortunately without a breach to date, and reports suggest that the level of the lake is falling slowly. This is of course the ideal outcome, but great care is needed. If the lake level is falling then water must either be seeping through the dam or the spillway is eroding, either of which can accelerate to generate a rapid release event. Thus, there continues to be a need to manage the hazard very carefully and the ensure that areas downstream are not reoccupied.
The response of the Nepali authorities does appear to have been admirably quick and decisive, from the early action to open drainage to the large-scale evacuations downstream. It is notable that according to reports they have made use of the very high level of technical skill on landslides within in the country, which has not always been the case elsewhere.
There has been some discussion in the media of the causes of the landslide. In an article today, Narendra Raj Khanal from Tribhuvan University suggested that this slope developed some instability last year. This would be consistent with the progressive development of the landslide, which is clear from the very good Google Earth imagery of the site. This is an image from 2009, as a perspective view:
And this is an image from 2012:
The deterioration in the state of the middle part of the hill (around the area with the location marker) is very clearly visible between the two images. Presumably this became much worse last year.
Finally, it is important to remember that this landslide will be having devastating impacts upstream as well. Clearly the Arniko Highway is closed, and will remain so for some days to come. This is the only road to Tibet from Nepal, and of course the time period each year in which it can be used is comparatively short anyway. Those living upstream will now be isolated from the rest of the country, and of course the lake has inundated a large area of road. Kapil Dhital is a civil engineer who was at Bharabise at the time of the landslide. He has tweeted a series of photographs of the landslide and lake, including this one showing a now submerged dwelling:
2 August 2014
Sunkoshi landslide crisis
Now updated – see additional text at the end of this post
Overnight a very large landslide occurred on the banks of the Sunkoshi River in northern Nepal. This landslide has created an instant, large-scale crisis as it has blocked the river. In Nepal the English language news media is excellent, so there is very good coverage of the event, helped also by the location of the landslide on the main road to Tibet, which facilitates access. The best gallery of images that I have seen is on the Nep Hub website. This is the landslide from the slope above:
This is the lake that is building behind it:
And, from the Only Nepal website, this is a view of the landslide from downstream:
The location of the landslide is 27.770 N, 85.870 E. The Google Earth imagery of the site is excellent:
My colleagues and I have been working in this valley on landslides for decade or so, and Katie Oven completed her PhD on landslides in this area. On field trips up the valley we would often stop at Lamusangu to look at the debris flow deposits at this location, so a major landslide in this area is not a surprise. However, it is now a crisis. In the peak of monsoon season the river flow is high, and the images show that the lake is filling quickly. The images suggest that there is no reason to be confident that the dam will not breach rapidly when overtopped – indeed, quite the opposite I think as the length of the dam is not large and the materials appear to be fine grained. A breach now could generate a very large flood; when full the effects could be very serious.
Mitigation is of course to try to drain the lake whist evacuating everyone downstream. The valley is quite densely inhabited because of the road. A secondary hazard is that a major flood might destabilise the walls of the valley triggering further landslides downstream. Whilst the population can be protected with appropriate measures, which need to be implemented very fast, a dam breach flood has the potential to cause major damage. Given that this is the only road north out of Nepal, and the major strategic link to Tibet and China, the impacts on Nepal could be serious in the medium term.
So what to do? Well of course the first measure is to evacuate people downstream, and this has started. The second is to put a warning system in place, probably at this stage consisting of an observation team with appropriate communications. The third will be to start to excavate a channel, which will require heavy machinery.
This is a very difficult problem to manage, so Nepal should seek international help. The best qualified people are the teams that dealt with the valley blocking landslide crisis after the Wenchuan earthquake in China. Given the strategic importance of this road, the Chinese may want to help. However, time is very limited.
Ekantipur has tweeted the follow image of the landslide:
This suggests that an overtopping event is probably very close, and may even have started (see comment below). The priority must be to relocate people away from the valley floor.
1 August 2014
Malin landslide in Pune
The Indian media has a large number of interesting stories about the Malin landslide in Pune two days ago. The rescue operations continue, in a much more organised way now. IBN reports that the death toll has reached 56 people, with nine people injured. The estimated number of people missing is in the order of 120, although hopefully this will reduce with time as the whereabouts of people not affected by the landslide becomes clear. The challenges posed by the rescue operation are clear from this image from the site:
There is not inconsiderable risks to the rescue teams working in such conditions. There are however some pleasing stories about rescues, not least the recovery of a family of four from beneath the debris after a crying baby attracted the attention of rescue teams. The family survived in a house that was buried by the landslide. To survive such an event is very fortunate and generally requires a structure to provide protection.
However, inevitably the main thrust of the news reporting is less positive. The Times of India has a terrible story about the level of loss suffered by some residents of the village. 40-year-old Hirabai Chandrakant Kengale lost all 25 members of her family, consisting of her three brothers and their families. Hirabai lives in an adjacent village but had returned to help with rice planting. She was staying in a house that was not destroyed by the landslide. The same report also notes that between 25 and 30 students of various ages were sheltering in the temple at the time of the landslide. Unfortunately the likelihood of further survivors being recovered from the debris is now very low.
Interestingly the same report considers the causes of death of the victims, noting that the autopsies indicate that asphyxia was the main cause of death, with head injuries and blunt trauma being other factors.
Inevitably there is a great deal of soul searching and speculation about the causes of the landslide. In particular there is a strong emphasis on the role of deforestation, hill-cutting and other human activities. The Business Standard quotes a Communist Party of India statement that:
“The government had adequate warning in the past few years when smaller landslips had occurred and the flow of the backwaters of the nearby Dimbha dam was one of the causes. But the government did not take any preventive measures…JCB machines (excavators) were being used on the hillside in the name of developing adivasi land but (they were being used) in fact to serve the interests of a network of JCP machine owners, corrupt officers and leaders…The use of these heavy machines caused damage to the hillside. In spite of the strong opposition of adivasis to the use of machines, the government did not prohibit their use”
Pune Mirror reports that the landslide will be investigated by a team from the Geology Department at the University of Pune. Hopefully this will provide clarity about the causes of the Marin landslide.
31 July 2014
Early yesterday morning a very large landslide occurred in the village of Malin in Pune, western India. The landslide struck and effectively wiped out the village of Malin, located close to Bhimashankar in the western Ghats. It is thought that about 40 houses were buried – sadly the timing of the landslide meant that most would have been fully occupied and of course the darkness would have impeded any escape. Latest reports suggest that 28 bodies have been recovered to date, together with eight survivors, but a further 150 people may still be buried. As such this is the second worst landslide of the year to date, after the Afghanistan landslide of a couple of months ago.
There is only a limited number of images of the landslide on the web, most looking like this (source):
The debris pile at the foot of the slope appears to be exceptionally wet:
The site of the landslide is quite well covered on Google Earth – the location is (19.161, 73.688) if you wish to take a look. This is a perspective view of the village and slope:
Causes of the Malin landslide
Inevitably there is huge speculation in the Indian media about the causes and triggers of the Malin landslide. The trigger is clear – this area was affected by very strong monsoon rainfall in the two days prior to the landslide. The NASA TRMM landslide warning tool highlighted this as a zone that was very susceptible to landslides in light of this rainfall:
The TRMM data can also be used to generate a time series graph for rainfall in the area of the landslide:
The data suggests that as much as 600 mm of precipitation may have affected this area prior to the landslide occurring. In the media there is a great deal of speculation that the dam at Dimbhe, a few kilometres downstream may have been a factor. But given the distance to the reservoir, the fact that the dam was completed in 2000 and the type of landslide this is not immediately obvious to me. There is also discussion about the role of development and deforestation, which may be far more important. The landslide appears to be a mudslide in deeply weathered soils (there is no evidence of involvement of large amounts of bedrock), so this slope would be highly susceptible to disturbance. The investigation will need to look at this in detail.
The Google Earth images are hard to interpret well because of the low resolution of the digital elevation model, but I have been looking at them to see if this slope could have been identified as being potentially dangerous. This is a more detailed Google Earth perspective view of the site:
The image appears to be dated from February this year. There is no obvious signs of cracking or suchlike that I can see, which is not unexpected for a soil slide. However, the feature that I have marked A above is interesting – this appears to be a large topographic hollow. Such features can have the effect of concentrating intense rainfall during overland and soil flow. If this occurs, then pore water pressures in the soil in the hollow can become very high, initiating failure. If I was investigating this landslide I would be very interested in this hollow. The location directly above the village is deeply unfortunate if this feature was a factor.
29 July 2014
Oso landslide analyses
The journal Science is reporting an interesting public argument about the mechanisms of the Oso landslide in Washington State, USA. This is between the authors of the GEER report (NB pdf), which was released last week, and Dr Richard Iverson of the USGS, and is in essence about the chronology of events that generated the very rapid debris flow event that was so costly. I wrote about the GEER report last week, and noted that they interpret the sequence as being a two-fold failure event, as indicated by the seismic data. The latter is not controversial – there is a nice (pdf) report from the Pacific Northwest Seismic Network that shows this double event very clearly:
In the GEER interpretation of the Oso landslide the lower slope failed first to generate the rapid flow event, followed by the second failure, which was in effect a retrogression of the landslide as a new block slid onto the main mass, and then stalled. This is consistent with the fact that the first event generated a much larger seismic signal; and the fact that the, second seismic signal appears to terminate quickly.
However, in the Science report, Dr Iverson disagrees with this interpretation of the Oso landslide, based on a more detailed analysis of the seismic signals The report notes that:
“But Richard Iverson, a landslide expert at USGS’s Cascades Volcano Observatory in Vancouver, Washington, says that a closer look at the seismic data tells a different story. “The USGS disagree[s] significantly with several aspects of the GEER report,” Iverson says. According to the unpublished analysis by scientists with the USGS and the University of Washington, all the important action appears to have been compressed into a rapid chain reaction in the first few minutes. The lower slope began to slide slowly, but just 50 seconds after that began, an upper part of the mountain broke loose and collapsed onto it. The violence of that impact could cause the soil to rapidly liquefy and shoot across the valley, much like a foot slamming down into a mud puddle, he said. Iverson and scientists working with him concluded the second incident recorded in the seismic data was an ‘extremely small event.’”
I have no experience of interpreting seismic signals from landslides, so struggle to comment either way on this interpretation. I think I can see the essence of this interpretation in the data from the more distant seismic stations:
To my untrained eye the initial seismic event shows a slow increase in energy release rather than an abrupt peak. Note also that the second event appears to be much smaller than the first. Thus, in this interpretation, the initial failure was, I think, a small, slow failure in the lower slope that destabilised the upper block of the Oso landslide, which slid onto the mass below. This then generated massive undrained loading, allowing the generation of very high pore water pressures, and hence the high mobility flow. The second seismic event is interpreted as being “extremely small”.
I think one can take issue with the latter statement – if it was extremely small it would not have generated a seismic signal, surely – but the point is that it is relatively small when compared with the first failure. The Science have clearly put this alternative interpretation to the GEER team, and report as follows:
Responding to Iverson’s critique, GEER co-leader Jeffrey Keaton, an engineer at AMEC Americas, a private engineering firm, says that observations in Oso helped convince them that much of the mountain collapsed a few minutes after the initial slide. Large chunks of relatively intact earth still covered with trees would probably have broken up if they had been part of the first slide, he said. And swaths of sand had flowed up onto the back end of the first slide, suggesting it happened after the first slide slowed to a halt.
The data that is available is insufficient to be able to make a definitive argument either way on this – the next key step will be publication of the UGSG analysis that supports their line of argument. In essence the issue is the chronology of events shown in this Seattle Time image of the landslide:
At the end of the day, this comes down to whether the most likely scenario is that the block that was formed from material marked B above failed (event 1), allowing block A to slide in (event 2); or whether block A failed, causing massive collapse of block B (event 1) followed by a small but at present unknown slide that generated event 2. I would guess that a very detailed analysis of the deformation at the front end of block A might help – if this block moved after Block B had failed then there should be some impressive compressional deformation features preserved in this area. Maybe the very high quality Google Earth imagery collected on 1st April would allow someone with the right skills to make an interpretation?
Personally I can see merits in both interpretations, so will watch with great interest as this is resolved.
26 July 2014
China Development Gateway has some interesting images of the aftermath of a landslide that occurred on 17th July at Gedi Village, located in Muhuang Township within Yinjiang Tu and Miao Autonomous County, in Guizhou Province, China. The landslide has reportedly damaged 152 buildings and caused the evacuation of 275 people:
Note the much more disrupted component of the landslide at the front on the left side. In the main slide, even the apparently intact buildings have been rendered uninhabitable:
My interpretation is that this is a deep-seated landslide because the lateral scarps are very well developed and show considerable vertical extent:
There can be very little prospect that this landslide could be stabilised at a reasonable cost, and sadly the village is already an almost complete loss. The causes of this landslide are not clear to me, but of course this is the rainy season in China.
Nagano debris flow
Meanwhile, an interesting video has appeared of the aftermath of the debris flow at Nagiso in Nagano Province of Japan, which killed a child on 8th July. The video should be visible below (if the embed works!) – if not you can watch it here.
The video starts with the CCTV footage of the front of the debris flow. Probably the most interesting aspect of this is the aerial view of the damaged area from the flow:
The area of devastation lies immediately downstream of a bend in the existing channel. Until that point the landslide had remained mostly within its banks, but at that point it left the channel and ran through the town. The terrible impacts on the buildings in this area are clear.
24 July 2014
A very large an interesting landslide occurred in Iceland on the night of 22nd/23rd July in the flanks of the Askja stratovolcano in Iceland. This is a very interesting event in a number of ways, not least because the volume appears to be large – estimates at present range from about 24 million cubic metres to about 60 million cubic metres.
Images are appearing of the landslide, which is impressive in its scale:
The landslide is estimate to be about a kilometre in width. There is a nice video taken from a flight over the landslide on the RUV website too. The landslide entered the lake at the foot of the slope, generating very large tsunami type waves. A credible witness, Ármann Höskuldsson, who was in the area with a group of students, estimates that the waves were 50 m high.
The cause of the landslide is not clear at present. Some of the articles suggest snow/ice melt, but there is no evidence to support the hypothesis. The slopes on the southern edge of the Askja massif are steep. This Google Earth image of what I think is the site suggests that there may have been previous large-scale landslides on this slope:
There is also evidence of large amounts of erosion, suggesting that the slope may have been steadily destabilising with time. It is entirely possible that this is a progressive landslide with no trigger event.
If the waves were 50 m high then the level of erosion around the lake should be extremely high given the weak materials. I have yet to see any good images of the scour around the lake. This must be a golden opportunity to understand better the generation of tsunami waves by rapid, large landslides.
23 July 2014
Oso landslide – the last set of remains
Two significant events occurred yesterday with respect to the Oso landslide in Washington State, First, it was announced that the last set of human remains were recovered from the site. In the tragic circumstances of the landslide it is an extraordinary achievement to have recovered all of the remains, given the size and mobility of the slide. The search and rescue teams at Oso deserve great credit for what they have achieved. In case you haven’t seen it, the leader of the rescue effort posted a comment on one of my earlier posts, providing insight into how this was achieved:
22 July 2014
Last Tuesday a landslide at Erzurum in Turkey destroyed an almost new, and extremely expensive, ski jumping facility. The ski jumps were constructed for the 2011 Winter Universiade, at a reported cost of 20 million Euros. The lower part of the Kiremitliktepe ski jumps collapsed. Three of the jumps have been completely destroyed (image from here), whilst the two larger jumps have been severely damaged:
Pleasingly, the collapse event was in part captured on video and is buried on Youtube:
Whilst this video provides a pretty good overview of the aftermath of the landslide
There is also an excellent gallery of images of the collapse in motion here.
This is a Google Earth perspective view of the site, taken in 2012:
Compare this with the image below of the slope, taken in 2009:
It is hard to read the topography from these images given the quality of the digital elevation model, but I would make a few initial observations. First, the topographic shape of the slope appears to have been modified – in particular, there may have been some excavation of the toe to create space for the landsliding and runout zones. The main part of the failure seems to follow the excavated and modified area for the smaller jumps on the right hand side. Second, there has been considerable additional material placed on the middle part of the slope for the main jumps (on the left side), which may have added weight to the unstable mass. And third, there is a new lake at the top of the slope, presumably to provide water for the snow-making machines.
An article in a Turkish newspaper yesterday also suggests that there were major construction defects at the site:
Prosecutors have initiated a fact-finding mission and launched an investigation into last week’s collapse. The team includes four construction and geology engineers from Atatürk University in Erzurum. The mission’s initial report has revealed some fatal problems in the construction of the towers that supported the ski jumps. The expert report shows how poorly the towers were built. An expert at the site in Erzurum found that the contractor used only one meter of steel piles in the towers’ foundations, Turkish media outlets reported on Sunday. The reports said that Sarıdağlar was required to sink 50-meter-long steel piles into the ground to support the towers. Taking a deadly risk, the contractor first poured concrete into the tower foundation then sank only a one-meter-long pile in it, a critical fault. Construction experts said, according to global standards, steel piles have to be at least 25 meters deep for towers this high. Even worse, the contractor incorrectly calculated the angle of the slopes on which the ski jumps were placed.
Thus, overall this is looking like this could be a major design and construction failure, although we’ll need to see what the official report states in due course. Given the above, the likelihood of being able to reinstate the facility without complete demolition and reconstruction look slim.