4 March 2021
The Char Dham Project: landslides associated with road widening in northern India
The dreadful landslide disaster last month in northern India has served to highlight, very clearly, the threat posed by poor awareness of slope issues in the Hindu Kush Himalayas. Regular readers will be bored of my repeatedly making the point that we are failing to adequately consider, or manage, these threats across a range of human activities as development continues apace.
In Uttarakhand there is another very major infrastructure project, alongside the hydroelectric schemes that we so badly damaged on 7 February, that is also leading to substantial levels of loss. This is the Char Dham project, a road widening scheme of sufficient magnitude that it has its own Wikipedia entry:
Char Dham National Highway (Hindi: चार धाम महामार्ग), is an under construction two-lane (in each direction) express National Highway with a minimum width of 10 metres in the Indian state of Uttarakhand. The under construction highway will complement the under-construction Char Dham Railway by connecting the four holy places in Uttarakhand states namely Badrinath, Kedarnath, Gangotri and Yamunotri. The project includes 900 km national highways which will connect whole of Uttarakhand state.
I am not against the development of infrastructure in high mountain areas, indeed quite the opposite, but these zones are fragile. These roads have the potential to be a vital lifeline, but they also have the potential to create untold havoc. Unfortunately, there are growing concerns about the latter, caused by poor alignment selection, engineering design and construction practise. In particular, there is clear evidence that the road widening is causing slope instability on a grand scale. Reports suggest that data from the Ministry of Road Transport and Highways has indicated that there are at least 161 major slope failures along the alignment, with more expected due to poor construction practises and the removal of trees. Bizarrely, a committee of the Supreme Court in India that has been investigating the project appears to be split, releasing two reports, one of which favours continuing with a 10 m wide road bench, the other indicating that it should be narrowed to 7 m.
There is an interesting article on the environmental costs of the Char Dham project on the First Post website, which includes this horrifying picture:
Whilst the Char Dham project is undoubtedly important both strategically and in development terms, it is undeniable that the practises shown above are deeply problematic. Their legacy is likely to last for a long time.
2 March 2021
Ebian Yi Autonomous County: a dramatic rockslide caught on video in China
On 27 February 2021 a dramatic rockslide occurred in Ebian Yi Autonomous County in Sichuan Province, killing one person and injuring a further three. Unfortunately I cannot find a video of this event that I can embed, but both Newsflare have a version on its website.
The best commentary that I have found on this event comes from Teller Report, which has a translated version of a CCTV report:-
A huge boulder fell and destroyed many houses in Ebian, Sichuan. According to a report from the Propaganda Department of the Ebian Yi Autonomous County Party Committee of Leshan City: At about 16:50 on February 27, a rock-injury incident occurred in a group of Xinsheng Village, Shaping Town, Ebian County. The incident caused serious damage to 3 houses. One person was injured and one person was buried.
After the incident, the county party committee and the county government immediately launched an emergency response, mobilizing emergency, fire, medical rescue, and township emergency militia to search and rescue the buried people to eliminate possible surrounding risks.
At present, the injured have been treated in the hospital and their lives are not in danger for the time being. The surrounding people have been evacuated and resettled, and the social order is stable.
The cause of the incident is under investigation.
The videos appear to show a large amount of dust being generated high on the slope, and then a trail of dust down the hillside to the houses. It seems that a larger event was occurring at the top of the slope that released the boulders – a simple rockfall? quarrying? construction?
The Newsflare video shows the event from another angle:-
On first inspection, the location appears to be approximately where I have placed the marker on the map below. The image provides the latitude and longitude:
1 March 2021
Staithes: an interesting place to pitch a tent for the weekend
The UK is currently in a Covid-19 lockdown. It is illegal to stay away from home without due reason; all cafes, restaurants and bars are closed, as are non-essential shops. In general the population has responded well, and the statistics are all pointing in the right direction. The vaccine roll-out is a remarkable success – over 90% of the population aged 65 and over has now been vaccinated, as have most frontline health workers and those with medical conditions that render them particularly vulnerable. As I’m over 50, I can expect to receive a first dose by the middle of next month.
This is the context for a remarkable decision by a couple who, at the weekend, decided to take their child for spot of rough camping. Presumably wanting to get away from it all, they chose to pitch their tent at the top of the highest sea cliffs on the east of England near to Staithes in North Yorkshire. The Staithes Coastguard. posted images on their Facebook feed:-
No-one can deny that the campers chose a beautiful spot, and the weather this weekend was glorious:-
But at this site there is a long way to fall:-
A Google Earth image of this area illustrates why this location was a poor choice:-
The ditch between the tent and the fields is of course a tension crack for the block that is actively deforming. The tent has been pitched on the top of the landslide block. Landslides on this section of cliff are frequent and are sometimes fatal, sadly.
Overall, this was not a good plan.
26 February 2021
Badong, China: population relocation due to landslides associated with the Three Gorges Dam
The Three Gorges Dam in China is without doubt one of the greatest feats of engineering. Lifting the level of the Yangtze River by 175 m, it created a reservoir that is 660 km long. The dam generates electricity, moderates floods and provides a navigable river for large ships, opening up central China for economic development.
Early in the project it was clear that landslides would be substantial hazard along the banks of the Three Gorges reservoir. It subsequently became clear that the magnitude of the hazard was substantially under-estimated, such that far more people would need to be relocated away from hazard zones. However, dispute the publication of case studies it has been difficult to determine the true impact of the landslides along the reservoir banks since the water level was raised over a decade ago.
A really interesting paper (Gong et al. 2021) has just been published in the journal Engineering Geology – this paper is open access – which explores this issue. It focuses on Badong, a county within the Three Gorges area, whose county seat has been relocated on three occasions due to landslides. The graphic below, from the paper, illustrates the series of events:
The original site of the county town of Bandong, Jiuxianping, was located on the northern bank of the Yangtze River. It was subject to repeated flood events, causing some relocations to occur, but in the Middle-Late Southern Song period it was moved to Xinling Town on the southern bank, probably because of a major debris flow.
However, Xinling town was close to the level of the river, and thus became unviable with the elevation of the water level associated with Three Gorges Dam. Xinling was also subject to problems with landslides. Thus, between 1982 and 2003 a plan was developed to relocate the population of Xinling to Huangtupo. The image below shows the locations of the various towns in the paper:-
Unfortunately, Huangtupo proved to be a problematic site. Shortly after construction started in 1982, evidence of slope instability instability emerged. A site investigation in 1988 identified two large ancient landslides. On 6 August 1991 large debris flows occurred in the area, triggered by an intense storm. These debris flows destroyed the southern part of Xinling, killing three people and injuring a further 171 individuals.
In 1995, two landslides further landslides occurred in Huangtupo, killing five people and causing substantial levels of economic loss. As the lake level rose further landslides were reported. In consequence, a decision was made to relocate the county town of Badong once again, this time to Xirangpo and Guandukou. Between 2007 and 2017 , over 15,000 people were relocated. Most of the buildings on the landslide complex at Huangtupo were demolished.
This paper provides a fascinating insight into both the landslides and the population relocations associated with the Three Gorges Dam programme. The underlying susceptibility of this area to landslides is well-illustrated by Gong et al. (2021). I have repeatedly noted on this blog that many landslide problems associated with hydroelectric dam projects come from a failure to identify existing ancient landslides in the landscape – a failure of the ground investigation phase of the project. This is the case here; the site of Huangtupo was underlain by a landslide complex with a volume of 69.2 million m³. It is unsurprising that this complex was reactivated when the reservoir level was raised.
Gong, W., Juang, H. and Wasowski, J. 2021. Geohazards and human settlements: Lessons learned from multiple relocation events in Badong, China – Engineering geologist’s perspective. Engineering Geology, https://doi.org/10.1016/j.enggeo.2021.106051.
25 February 2021
Landslides and sustainable development: managing the cost of landslides in less developed countries
Yesterday, I was honoured to be able to present on of the keynote lectures at the XIII International Symposium on Landslides. This event was meant to have been held last year in Colombia. Unfortunately, it had to be postponed for obvious reasons. The hope had been to hold it this week, again in Colombia, but once again this was stymied by the wretched virus. In consequence, the event has been held online this week.
I have to give my thanks to the organisers, The Colombian Geotechnical Society, who have done a fine job in arranging a good meeting. I have been able to attend all of the keynote sessions so far, and many of the other sessions. The range and quality of the work being undertaken across the world is impressive, especially by early career researchers. Our discipline is in good hands.
I was asked by the organisers to speak for about 45 minutes on the topic of Landslides and sustainable development: managing the cost of landslides in less developed countries. This is a vast topic, in many ways too large to cover in a short lecture, so I decided to focus on three key themes – hydroelectric dams, mineral extraction and rural roads. I tried to present the problem and to highlight some solutions.
I have uploaded the presentation onto slideshare. WordPress no longer seems to permit an embed, so you should be able to view them here:-
You should also be able to download the file from slideshare, and I have put them on my Google Drive.
One of the issues I have tried to highlight is the high landslide incidence associated with rural (mountain) roads. The slide below is my interpretation as to why so-called “dozer roads” cause such high levels of loss from landslides:
As noted above, I have tried to highlight principles for addressing these problems. The slide below illustrates some of my thoughts on how to manage rural roads properly:
I very much doubt that my presentation is in any way the final word on these important topics, but I really hope it is of some use. Please feel free to use it as you see fit, but I would be grateful if you would acknowledge me, and refer to the open access paper (download it for free):-
Petley, D.N. 2021. Landslides and sustainable development: managing the cost of landslides in less developed countries. Keynote paper published in the Proceedings of the SCG-XIII International Symposium on Landslides. Cartagena, Colombia. Download from: https://www.issmge.org/uploads/publications/105/106/ISL2020-172.pdf.
23 February 2021
Camogli, Italy: the unfortunate impact of a landslide in a cemetery
On 22 February 2021 a large coastal landslide occurred in the town of Camogli, near to Genoa in northwest Italy. In common with so much of Italy, Camogli is a historic town; thus, an urban landslide almost inevitably damages the historic fabric. In this case the landslide affected a large urban cemetery, which led to over 200 coffins falling into the sea. Fortunately no-one was injured.
An Italian fire brigade helicopter captured some images of the site. The image below shows the aftermath of the landslide:-
This appears to be a large rockfall on a near-vertical coastal slope, and it seems likely that there is undercutting by the sea. The image below is the Google Earth view of the site:-
The Italian Fire Brigade helicopter also captured the aftermath, with the remains of over 200 coffins floating in the sea, many having been damaged:-
Clearly this is a deeply unfortunate incident that will have been very distressing for all involved. News reports suggest that the slope at Camogli had started to suffer from instability problems after a major storm in 2018. Works to mitigate the instability on parts of the cliff were ongoing, with scaling and vegetation removal, prior to the installation of a reinforcing mesh. Works were being undertaken at the time, such that workers at the site had to escape. However, the reports suggest that the actual section of cliff that collapsed may not have been subject to these works.
Efforts are now underway to retrieve the coffins and the remains.
22 February 2021
The valley blocking landslide at Rishi Ganga created by the Chamoli landslide
The recovery operations in the Tapovan area of Chamoli continue. As of yesterday, the remains of 68 people had been recovered, with another 135 still missing. Operations continue in the tunnel, where more victims are thought to be located, but conditions are clearly extremely challenging. Meanwhile, there is some interest in a valley blocking landslide that has been formed on the Rishi Ganga river by the landslide.
In the last few days an Indian Air Force helicopter winched navy divers onto the dam so that they could check the depth of the water. This was determined to be 8 to 9 metres, giving the lake a reported volume of 50,000 cubic metres.  Note however that other reports indicate that the depth of the lake may be 60 metres. This report indicates that it is “400 metres in length, 25 metres wide and 60 metres deep”. If so this would give a much higher volume.
Planet Labs has managed to capture some high quality satellite images of this lake. The image below provides a really good, oblique view onto the landslide dam:-
The debris flow came from the right of the image, following the main channel to exit at the bottom of the image. The dam is left of centre, with the lake just visible.
Below is a more detailed view of the dam itself:-
The good news is that there is a well-developed channel draining the lake, which has a modest volume. The risk downstream should not be ignored, but this does not pose the sort of threat that we saw at, for example, Attabad.
These images tell us something about the flow. I remain a little perplexed by the ongoing discussion about the source of the water in the flow, which seems to ignore the well-known observation that granular flows can occur with little or no water present. Large, dry granular flows give the appearance of having water present,even where they are dry, but they do generate considerable volumes of dust (as was the case here). Where they sweep down the valley, the front may become saturated as water is incorporated.
I am not arguing that the events on the Rishi Ganga were completely dry – they were not – but I do not think that we need to find a source for very large quantities of water. There was enough water present in the form of ice on the block that failed, and in the valley in the form of dead ice, snow and saturated sediments to explain the flow, in my view.
By the time the landslide reached the point shown above it was well-contained within the channel, as demonstrated by the intact trees on either side. There is some evidence of super-elevation on the outside of the bend. The landslide has dumped a large volume of sediment in this valley, which has been retained. The latter part of the flow appears to have eroded the toe.
I would be interested in the views of sedimentologists as to what the presence of this dam tells us about the characteristics of the flow. Comments?
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
19 February 2021
Trends in landslides and landslide losses in Nepal over three decades
I have written frequently about landslide losses in Nepal, both on this blog and in papers. I started to work on landslide problems there 20 years ago. Subsequently, many others have picked up the baton, such that there is a host of good work being undertaken there at present. A really interesting paper has just been published in the journal Landslides, Muñoz-Torrero Manchado et al. (2021), which is open access, which looks at landslide losses there over three decades. Based on an area in western Nepal, this is significant for two reasons. First, it uses the rapid development in our ability to use time series imagery to extract landslide scars from the landscape, which provides new opportunities to understand temporal and spatial patterns of landslide occurrence. Second, it casts light in an unprecedented manner on landslide patterns themselves with time and in space.
Muñoz-Torrero Manchado et al. (2021) have extracted annual landslide maps for their study area between 1992 and 2018, mapping 8,778 landslide events during the study period (and many more that preceded the start of the study). They have then been able to link these annual events to the weather and other conditions in the study area.
Not surprisingly, the strongest correlation that they found was between total monsoon precipitation and the number of landslides – in wet years there were more slides. Interestingly, this effect was amplified when a year with high rainfall monsoon came after a year in which the monsoon that was warm and dry.
In many ways the most interesting aspect of this study is explained in this diagram from the paper:-
The four panels at the top show maps of the study area. The black dots are the landslides. The heat maps show variability in key parameters as per the labels. The graph below divides the study area in a set of smaller zones. The grey shading shows the landslide density, and the bars show the influence of various factors. In those areas with the highest landslide density there has been population growth, and associated changes to agriculture, and increases in the road density.
Thus, Muñoz-Torrero Manchado et al. (2021) conclude that the annual pattern of landslides is being heavily driven by the patterns of the monsoon in this area, but it is also strongly affected by human factors such as poor slope management and road construction.
The paper ends with a very clear message about the need for community-led landslide management:
[T]he increase in reported landslide fatalities in western Nepal relates primarily to the notable demographic expansion in this area, placing more people and assets in harm’s way. Hence, there would appear to be significant potential and need for community-focused disaster risk management strategies to reduce local exposure levels and minimize landslide losses.
I agree completely.
Muñoz-Torrero Manchado, A., Allen, S., Ballesteros-Cánovas, J.A. et al. 2021. Three decades of landslide activity in western Nepal: new insights into trends and climate drivers. Landslides (2021). https://doi.org/10.1007/s10346-021-01632-6
18 February 2021
A GIS-based map of the Chunchi landslide in Ecuador
On Twitter, Angel Valdiviezo of the Scuela Superior Politécnica Nacional (ESPOL) has highlighted a GIS based system that has been set up to compile information about the Chunchi landslide in Ecuador. Included in the data in this system is an aerial image of the landslide site, which starts to provide insight into the situation. The portal is attributed to attributed to the Servicio Nacional de Gestión de Riesgos y Emergencias / Instituto Geográfico Militar, who should be commended for getting this information online. This is the aerial image:-
I thought it would be helpful to label the major features on first inspection. I would welcome comments:-
There are two major headscarps in this landslide, which has a reported volume of about 30 million cubic metres. The one to the east appears to be retrogressive, the one to the southeast is rotational. Downslope from both there are large rafts of essentially intact land. There is a minor scarp to the north, and an areas of what appears to be very large tension cracks. I have drawn in an approximate boundary between the two flows from the major scarps. Downslope the landslide material us very heavily disrupted, which is consistent with the videos.
To the south there is small lake caused by the blockage of the valley.
The most likely mechanism is that one of the two major failure areas developed, driving the static liquefaction in the lower part of the slope. This then debutressed (unloaded the toe) of the other major failure. My hunch would be that it was the retrogressive failure that developed first, but it could be the other way around.
A third hypothesis is that a smaller failure developed lower on the slope, triggering a chain reaction upslope as the materials weakened.
This could only be resolved with fieldwork and eyewitness accounts. Sadly, Covid-19 is likely to hamper this work, but hopefully a locally-based team will be able to study it in detail. This is a landslide that justifies a detailed publication.
16 February 2021
The very large Chunchi landslide in Ecuador
Last week a very large landslide occurred near to the town of Chunchi in Ecuador. The scale of the landslide makes this a somewhat unusual event. It was captured on a couple of videos that were posted to Twitter:-
Increíble deslizamiento de gran magnitud en Chunchi, sector la Armenia, Ecuador. A su paso la enorme masa inestable destruye viviendas, tramos de carretera y obstruye el cauce del río. #Landslide #earthflow @davepetley #procesosmorfodinámicos #GestiónDelRiesgoDeDesastres pic.twitter.com/MlI6waa8H9
— Geotweets (@Yobanygf) February 13, 2021
— VideosDeEcuador (@NotiViralEc) February 12, 2021
The landslide occurred on 12 February 2021. It is not clear to me at the moment as to the trigger of this enormous landslide, news reports link it to the presence of a fault and to groundwater. The landslide has caused the evacuation of 80 families, and over 500 people, but fortunately did not cause loss of life. Given the very dramatic movements in the video, that is very fortunate.
The scale of the landslide is such that getting a decent image of it is challenging with a drone or satellite imagery. The best picture I have seen is this one:-
The upper part of the landslide appears to be a very large rotational failure, which can be seen in the middle right side of the image above. There are some hints that there may be a second source as well, located to the left of the main source – this is on the left side of the image. The main slide appears to have undercut the valley side, causing another substantial area of failure, on the right side of the image (this is the most obvious failure visible).
The failed debris appears to have transformed into a flow with quite high levels of mobility in places, judging by the videos. The consequence is a substantial area of inundated valley.
The biggest threat now appears to be blockage of the channel of the Picay River. Reports indicate that a lake is developing on the upstream side. Efforts are under way to create a channel to avoid an uncontrolled breach.
Many thanks to those people who pointed this one out to me – much appreciated.