11 June 2021
Chamoli, Indian Himalaya: A massive rock and ice avalanche caused the 2021 disaster
Back in February I blogged on a number of occasions about the terrible 7 February 2021 disaster in Chamoli, India, when a huge debris flow swept down a valley, with no warming, killing 200 people. Dan Shugar of the University of Calgary was the quickest off the blocks that day, using Planet Labs imagery to determine that the event was triggered by a rockslope failure. Sadly there was a great deal of disinformation at the time, with even reputable scientists claiming that the event was a glacier collapse when the evidence was clear that this was not the case.
In the aftermath of the event a truly interdisciplinary team of researchers, from around the world but including scientists from India, self-organised to try to understand the event. This team drew on skills from a diverse range of fields, including earth science, social science, seismology, remote sensing and modelling, to try to piece together what happened. Over time the story became clear, with evidence to back up the interpretations.
The group was marshalled with great skill by Dan Shugar to produce a manuscript that documented the events. In a matter of days this came together – the result was published yesterday by the journal Science (Shugar et al. 2021), and is available open access.
I don’t need to go into the detail of the sequence of events here – the abstract captures this well:
Our analysis of satellite imagery, seismic records, numerical model results, and eyewitness videos reveals that ~27×106 m3 of rock and glacier ice collapsed from the steep north face of Ronti Peak. The rock and ice avalanche rapidly transformed into an extraordinarily large and mobile debris flow that transported boulders >20 m in diameter, and scoured the valley walls up to 220 m above the valley floor. The intersection of the hazard cascade with downvalley infrastructure resulted in a disaster, which highlights key questions about adequate monitoring and sustainable development in the Himalaya as well as other remote, high-mountain environments.
Figure 1 from the paper beautifully illustrates the initiating event at Chamoli:
As I’m an author on the paper, it is not my place to comment on its quality. I would like to highlight three key elements though:
The first is that Shugar et al. (2021) provides a very detailed explanation for the sequence of events at Chamoli. It should lay to rest any suggest that this was anything other than a landslide. There may be details that will be refined over time, but the main sequence of events is clear.
Second, the paper demonstrates the amazing ability of a huge team to collaborate to bring forward an understanding of the sequence, even though this event occurred in a high mountain area in winter in the middle of a pandemic when travel is impossible. The keys were enthusiasm, ability, cooperation and extremely able leadership by Dan.
And thirdly the event highlights the perils of building infrastructure at great cost in areas subject to these events with understanding them properly. Things must change is this event is not to be repeated.
D. H. Shugar, M. Jacquemart, D. Shean, S. Bhushan, K. Upadhyay, A. Sattar, W. Schwanghart, S. Mcbride, M. Van Wyk De Vries, M. Mergili, A. Emmer, C. Deschamps-Berger, M. Mcdonnell, R. Bhambri, S. Allen, E. Berthier, J. L. Carrivick, J. J. Clague, M. Dokukin, S. A. Dunning, H. Frey, S. Gascoin, U. K. Haritashya, C. Huggel, A. Kääb, J. S. Kargel, J. L. Kavanaugh, P. Lacroix, D. Petley, S. Rupper, M. F. Azam, S. J. Cook, A. P. Dimri, M. Eriksson, D. Farinotti, J. Fiddes, K. R. Gnyawali, S. Harrison, M. Jha, M. Koppes, A. Kumar, S. Leinss, U. Majeed, S. Mal, A. Muhuri, J. Noetzli, F. Paul, I. Rashid, K. Sain, J. Steiner, F. Ugalde, C. S. Watson, M. J. Westoby. 2021. A massive rock and ice avalanche caused the 2021 disaster at Chamoli, Indian Himalaya. Science. DOI: 10.1126/science.abh4455
10 June 2021
Legal proposals to improve safety on Welsh and English coal tips
Yesterday, the Law Commission in England and Wales launched a consultation on proposals to change the legal framework on the management of coal tip safety. The proposals come in the aftermath of the recent stability problems on tips in South Wales, most notably at Tylorstown in February 2020, which have highlighted deficiencies in the current political systems and the legal framework.
The Law Commission has identified the following key issues with the existing law, which dates from 1969 when many tips were still active and climate change was not considered to be a major issue (the text below is directly from the Law Commission):
- The powers created by the Act are fragmented across local authorities, leading to inconsistent safety standards and risk classifications.
- There is no mechanism to prioritise the highest risk coal tips to ensure they are managed as a matter of urgency.
- There is no general duty to ensure the safety of coal tips and local authorities have no power to intervene until there are concerns that a tip is unstable.
- There is no power to undertake preventive maintenance before a tip becomes a danger.
The proposed legislation would create a single body with responsibility for the supervision of all disused tips. It would have the power to monitor tips to ensure compliance the regulatory requirements. A register of coal tips would be established, which would record information including potential risks at each site.
The new body would set up a regime of inspections of coal tips to ensure that risks are being managed appropriately. The inspection would include tip stability, but could also cover risks associated with flooding, pollution and suchlike. And finally, for high risk coal tips, an enhanced safety regime would be established, with the supervisory authority having involvement in the management of the tip to ensure that the risk of incidents in minimised.
I think for many it will be a surprise that such a management body and regime is not already in place. There can be little doubt that this is an important step towards improving coal tip safety.
The consultation is open until 10 September 2021, with the final report being due next year. I hope that legislation will follow quickly.
7 June 2021
The South Asian monsoon in the time of a pandemic
The start of June marks the onset of the South Asian summer monsoon. As I have noted previously, this is by far the most important annual global process in terms of landslides. The monsoon typically strengthens reasonably quickly through June, peaking in mid-July, and then slowly declining through to the autumn. In landslide terms, the events mostly occur when the monsoon reaches the hills of Sri Lanka, Kerala in W India and the Himalayan Arc across the north of South Asia. The monsoon advances from the southeast, so Bangladesh and Sri Lanka are often affected first.
Over the weekend, heavy rainfall in Bangladesh caused landslides and extensive flooding and landslides killed a number of people in Sri Lanka. Thus, the impacts of the monsoon are starting to be felt.
The monsoon this year is going to be different. There is nothing unusual meteorologically as far as I’m aware, but in South Asia civil society is under severe stress. The two most affected countries in South Asia in terms of landslides are India and Nepal, both of which are being desperately impacted by Covid-19, with hospitals operating beyond capacity. The population will be especially vulnerable this year, and supply chains are very stretched. Thus, it is reasonable to expect that the impacts of the monsoon may be more severe than normal.
In Bangladesh, vulnerability has been increased by the continued presence of the large displaced Rohingya population, living in camps that are affected by landslides. It is salient to note that two people were killed in landslides in these camps over the weekend. And in Myanmar / Burma, the massive civil unrest following the coup earlier this year is also likely to have raised vulnerability. Mining-induced landslides are particular problem there, a result of both poor regulation and scavenging driven by economic disadvantage. The coup is unlikely to have reduced the impact of either of these two issues, but reliable reporting of landslides may have become more difficult.
In summary we are heading into the unknown in terms of South Asian summer monsoon this year, but I fear that it could well be a bad one.
4 June 2021
The 31 May 2021 landslide at the Bingham Canyon mine
At 9 am local time on 31 May 2021 a large landslide occurred at the Rio Tinto Kennecott mine at Bingham Canyon in Utah, USA. This site is famous for one of the largest mining induced landslides ever recorded, and indeed one of the largest recent landslides in North America, in April 2013. Fortunately this landslide is on a far smaller scale.
Once again, geotechnical monitoring at the site identified the instability prior to the failure, allowing the operators to ensure that no-one was at risk.
Fox 13 has posted a pair of images of the landslide:-
I also managed to download a pair of Planet Labs images of the site, before and after the failure – these should be visible used the slider below:
The image on the left was collected on 28 May 2021 and the one on the right on 31 May 2021. South is towards the top of the images.
The images suggest that the main part of the landslide, on the right side in the slide in the pictures, was a wedge failure that appears to be quite deep-seated. There is a smaller wedge on the left side too.
In its statement to the NASDAQ, the operator of the Bingham Canyon mine has confirmed that operations continue to be unaffected by the landslide.
The mining industry is the most advanced industry in terms of geotechnical monitoring of slope deformation and failure prediction. Once again this event appears to have been a successful application of those technologies.
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
3 June 2021
Not all slope failures are large
Inevitably, on this blog I tend to cover larger landslides most of the time. Large landslides have a greater propensity to cause loss and to disrupt, and of course they are also more newsworthy and they are frequently photogenic. However, this gives a very misleading impression of slope failures, the vast majority of which are small. Nonetheless, even these less impressive landslides can have substantial impacts.
Whilst walking around my home city of Sheffield in the current spell of warm, sunny early summer weather, I have spotted a series of smaller but interesting slope failures. I thought it would be interesting to highlight two of them.
The Sheffield and Tinsley Canal is a 6 km long waterway constructed in 1819 to link the city of Sheffield with the navigable parts of the River Don, allowing goods and people to be transported into and out of the city. Its greatest claim to fame is that the it is the location of part of the opening scenes of the film The Full Monty (although it looks considerably better than that now!).
Today the canal is navigable by pleasure craft, and the towpath forms a walking and cycle route. The image below shows a small slope failure that has occurred in a section of the canal:
As the image shows, about a 15 m section of the canal bank has collapsed. In the foreground a further section is failing. In other sections of the canal, failures are developing but have not collapsed:-
The stone blocks have moved towards the canal by about 50 cm, and the fill has subsided by about 30 cm. In this case failure, when it occurs, will substantially disrupt the towpath. There are other sections in a similar state.
None of these slope failures are large or dramatic, but they have the potential to close the towpath.
The second case lies on my walk to work. Here, at the top of a steep bank, a retaining wall has recently been constructed to create a pathway for pedestrians. It appears that this wall, which is about 50 cm high, has also started to fail and to move downslope. The owners of the site have employed a novel method to provide short term increased stability:
Securing a slope using cargo straps tied to the trees is not an approach that I have seen before. Again, this is small incipient slope failure, but one that is causing disruption.
2 June 2021
The 1918 Getå landslide disaster in Sweden
A recent post on Reddit has highlighted a landslide disaster that occurred close to the village of Getå in Sweden on 1 October 1918. The event is also well-described in a Wikipedia page.
Early in that evening a landslide removed a section of a railway track. A few minutes later a train, consisting of a locomotive and ten carriages, reached the landslide and derailed spectacularly. The post on Reddit has a fascinating aerial image of the aftermath of the landslide:
The landslide scar and its very large deposit are clearly visible. Interestingly, the crown of the landslide seems to almost perfectly coincide with the upslope boundary of the railway line. The crashed locomotive is visible in the scar, as is one of the carriages. There us a huge pile of debris, which is the aftermath of the fire that destroyed most of the carriages. Other carriages remained upright on the tracks.
At least 42 people were killed in the accident, the majority of whom are thought to have been trapped in the derailed carriages when the fire engulfed them. A further 41 people were injured. There are thought to be at least five people who remained missing after the accident.
The image below shows the landslide deposit:-
A detailed investigation of the landslide was undertaken. It concluded that there was a prehistoric landslide at the site that had not been identified at the time of the construction of the railway, five years earlier. Failure was triggered by high pore water pressures. The railway line was located on a gravel embankment; sliding initiated on the interface between the embankment gravel and the underlying clay.
The railway line was rebuilt and remains in use today; the accident spurred the development of the field of geotechnics in Sweden.
1 June 2021
Corinth Canal: a video of the rockfall that has left it closed since January
According to Wikipedia, the Conrinth Canal, “connects the Gulf of Corinth in the Ionian Sea with the Saronic Gulf in the Aegean Sea. It cuts through the narrow Isthmus of Corinth and separates the Peloponnese from the Greek mainland“. Built in 1893, it was for a while an important trading route within Greece. However, it is a very narrow cut through bedrock – it is 6.4 km long but only 21.4 m wide at the base – meaning that many modern ships cannot pass through today. Nonetheless it is an important route for smaller tourist ships.
The Corinth Canal has suffered landslide problems since its construction. Again Wikipedia provides some detail:
Another persistent problem was the heavily faulted nature of the sedimentary rock, in an active seismic zone, through which the canal is cut. The canal’s high limestone walls have been persistently unstable from the start. Although it was formally opened in July 1893 it was not opened to navigation until the following November, due to landslides. It was soon found that the wake from ships passing through the canal undermined the walls, causing further landslides. This required further expense in building retaining walls along the water’s edge for more than half of the length of the canal, using 165,000 cubic metres of masonry. Between 1893 and 1940, it was closed for a total of four years for maintenance to stabilise the walls. In 1923 alone, 41,000 cubic metres of material fell into the canal, which took two years to clear out.
In January this year a further large rockfall occurred along the Corinth Canal. UP Stories has published an excellent video on Youtube that shows the aftermath of the rockfall, and the serious damage that it has caused:
The image below, from the video shows the damage that has occurred along the canal:
Greek Reporter has an article about the rockfall. It seems that the collapse was caused by damage to the stone pillars supporting the slopes. The investigation is expected to last until September, after which the remediation work will start. The implication is that the Corinth Canal will remain close for many more months.
24 May 2021
Rest and Be Thankful: an update on the landslide mitigation works
Yesterday, The Scotsman newspaper posted a long and detailed article about the ongoing attempts to manage the landslide problem on the A83 at Rest and Be Thankful. I have posted frequently in recent years about the landslide problems at this site, which is undoubtedly the most challenging landslide location in the UK at the moment.
The article describes the new engineering works that have been completed to protect the diversion route lower down the hillside, the Old Military Road, which is brought into use when the main A83 route is unusable. The latest attempt to protect this road has involved the construction of a huge bund, 6 metres high and 180 metres long, on the upslope side of the Old Military Road, to capture debris from the slope above. The article includes images of this remarkable structure:-
From the perspective of the road the structure looks like this:-
Meanwhile on the main A83 road itself, catch pits are being built on the upslope side of the road to try to retain mobilised debris, and multiple flexible barriers have been constructed. At one location a flexible barrier has been constructed along the centreline of the road itself to try to protect a part of the carriageway. I have not seen that approach previously:-
The scale of these engineering works, and the construction of increasingly large structures in an area that is protected, illustrate the enormous magnitude of the challenges on the A83 at Rest and Be Thankful. Plans are progressing for the construction of an alternative alignment, but this will take several years to bring to completion. In the meantime, protecting the roads against landslides will be a mighty battle.
21 May 2021
The Pietrafitta landslide: can traffic vibration cause a landslide to move?
Over the years I have frequently heard discussions about the triggers for landslide movement. Many of these are obvious – rainfall, seismic shaking, snowmelt, construction, for example. Sometimes people have also described vibration from traffic or trains as being a potential trigger. I have always wondered how strong the evidence is to support this assertion.
There is an interesting paper in the journal Landslides (Guerriero et al. 2021) that has investigated this for a clay landslide in Italy. The site, the Pietrafitta landslide in southern Italy, is located alongside an important road, SS87. In 2016 movement of the landslide was causing periodic closure of the road to traffic. The authors have included this image of the landslide:-
This is probably best described as a retrogressive earthflow. The scale of the landslide is indicated by the truck located on the right side of the landslide toe.
The authors installed a broadband seismic station to measure the traffic vibration and an extensometer to measure landslide movement. In the period of the study traffic flow on the road occurred for only a part of the day, giving a period of no traffic vibrations to compare with a period in which traffic was occurring.
The graph below shows the startling results:
When the road was closed (the dark grey periods) no traffic vibrations were recorded. Movement of the landslide typically slowed and stopped. In the period in which traffic was flowing (the light grey periods) the landslide commenced movement, with a period of acceleration. After the traffic ceased the landslide continued to move for some hours before slowing and eventually stopping.
Guerriero et al. (2021) hypothesise that the landslide was probably on the very margin of instability in its natural state (i.e. the factor of safety was very close to one). The traffic vibration generated higher pore water pressures on the shear surface, which were enough to lower the factor of safety below one, allowing movement to start. Once the traffic ceased the higher pore water pressures took a few hours to dissipate, such that the landslide continued to move for a while, but then stopped.
The conditions in the Pietrafitta landslide are perhaps unusual, being both fully weakened and marginally stable. I’m reminded of the Slumgullion landslide (also an earthflow), which moves in response to atmospheric tides. But Guerriero et al. (2021) have demonstrated that landslides can indeed move in response to traffic vibrations.
Guerriero, L., Ruzza, G., Maresca, R. et al. 2021. Clay landslide movement triggered by artificial vibrations: new insights from monitoring data. Landslides. https://doi.org/10.1007/s10346-021-01685-7
18 May 2021
The Kara-Bogaz-Gol megaslide: the world’s largest active landslide?
A startling paper (Aslan et al. 2021) has just been published, open access (hurrah!), in the journal Scientific Reports, describing what is thought to be the largest active landslide so far identified on Earth. This is remarkable – the scale of the Kara-Bogaz-Gol megaslide is vast but until I read this paper I had no idea of its existence, even though it is clearly visible on Google Earth.
The landslide is located on the banks of the Kara-Bogaz-Gol lagoon in Turkmenistan. The landslide complex can be seen extending along the whole of the bay (and more) in the Google Earth image below, although not all of it is currently active. I have included a Google Earth ruler in the image so that you can appreciate the size of this failure:-
The latitude and longitude of the landslide is given on the image above. The scale bar shows that the landslide is up to about 5 km from crown to toe, and the complex extends for over 40 km along the banks of the lagoon. This is a truly enormous landslide.
The Kara-Bogaz-Gol Megaslide is a rotational failure. Aslan et al. (2021) provide the following cross-section to illustrate its form:-
As the cross-section shows, the landslide consists of thick blocks of limestones and marls failing of a gently dipping layer of weak Eocene marls, clays, silts and sandstones. At the top of the cross-section are two graphs showing the movement rate. In form this is broadly similar to the Ventnor landslide on the Isle of Wight, but on a much larger scale.
Aslan et al. (2021) have used 354 Sentinel IW SAR that span the period from 2014 to 2020 to extract movement data. They have shown that a mass that extends about 25 km along the lake shore and that extends up to 5 km inland is moving at up to 3 cm per year. This means that the volume of rock that is involved in the active part of the the Kara-Bogaz-Gol megaslide is about 10 cubic kil0metres! The movement rate is not constant, but responds to the level of the lake. Thus, when the lake level is high, and the soil moisture level is also high, more movement occurs.
The authors point out that this area is seismically active I would be fascinated to see how the Kara-Bogaz-Gol megaslide responds to a major earthquake.
Aslan, G., De Michele, M., Raucoules, D. et al. 2021. Transient motion of the largest landslide on earth, modulated by hydrological forces. Scientific Reports 11, 10407 (2021). https://doi.org/10.1038/s41598-021-89899-6