20 January 2022
A large rock slab topple from India
The location is reportedly the Ban Toll Plaza in Jammu and Kashmir in India, which is situated on the NH-44 road between Samba and Kunjwani. The location is 32.838, 74.940. It appears clearly on Google Earth.
There is little further information about this landslide, but it was associated with heavy rainfall. The slab topple appears to be a single, surprisingly coherent, slab of rock:-
It is likely that the release plane was a pre-existing, near vertical joint. It is extremely fortunate there was empty space in the impact zone.
The presence of this joint should have been picked up in the geotechnical investigations when the road was constructed. However, sub-vertical rock joints can be difficult to detect in rock joint surveys as they do not appear on the vertical face of the outcrop.
18 January 2022
Arhavi, Turkey: the appalling landslide impacts of new roads
Over the last two decades the appalling impact of poor quality road construction on landslides in upland areas has become increasingly clear. I have written about this issue in Nepal and India, but it is a global issue.
A really interesting open access paper has just been published in the journal Natural Hazards (Tanyaş et al. 2022) that highlights this issue in relation to a road constructed as part of the development of a hydroelectric scheme in Arhavi, Turkey. The paper comes to this stunning conclusion:-
“Our findings show that the damage generated by the road construction in terms of sediment loads to river channels is compatible with the possible effect of a theoretical earthquake with a magnitude greater than Mw = 6.0.”
The location of the study is in the area of 41.195, 41.364, from which the Google Earth image below is taken:
In this area a number of road projects have been undertaken since 2016, with the most notable providing the access routes to an under construction hydroelectric scheme. Tanyaş et al. (2022) have mapped the generation of landslides using imagery and ground truthing from 2010 to 2020. In the paper they provide some images of the impact of road-related landslides:-
As the images above show, the construction of these roads has had a shocking impact on the slopes in an area of ecological importance. The released debris has migrated into the river channels, dramatically changing the sediment loads. In total Tanyaş et al. (2022) have mapped 557 landslides along 267.2 km of roads, 33.9% of which have been constructed over the last 11 years. The authors include this fascinating graph, which shows the increase in road length and the increase in road related and non-road related landslide area over the study period:-
The authors note the change in landslide area responds to periods of heavy rainfall – in other words, the roads establish the instability and rainfall then triggers the landslides.
Tanyaş et al. (2022) draw a very interesting comparison between their findings and the landslides associated with the 2013 Ms = 6.6 Minxian earthquake in China, which occurred in broadly similar terrain over a broadly similar area. They conclude that the landslide impacts of the earthquake and the road construction in terms of sediment supply into the river system are of a similar scale, although clearly operating in a different timescale.
The sad element of this is that these landslides almost entirely avoidable – such road related landslide impacts are down to poor engineering practice. Roads do not need to be built in this way, and there are plenty of examples of good practice from around the world.
Tanyaş, H., Görüm, T., Kirschbaum, D. et al. 2022. Could road constructions be more hazardous than an earthquake in terms of mass movement? Natural Hazards. https://doi.org/10.1007/s11069-021-05199-2.
14 January 2022
Ouro Preto: a Brazilian landslide destroys historic houses
I have been writing about landslides in Brazil all week. To cap it off, videos emerged yesterday of another landslide there, this time in the city of Ouro Preto in Minas Gerais. In fact, there are two remarkable drone videos, and some additional mobile phone videos, of this event.
The landslide occurred at 9 am (local time) on 13 January 2022 at Morro da Forca. Instability in the slope had been noted by local residents, and the site had been cordoned off. As a consequence there were no casualties, but two buildings dating from the 19th Century were destroyed. Reports indicate that the failure has followed heavy rainfall, although conditions were dry at the time of the landslide.
Hoje Emdia has this image of the aftermath of the landslide:-
The second video posted above is interesting. It shows a series of collapses at the toe of the slope as the main mass destabilises and moves. The power of even a comparatively small landslide is clearly illustrated by the rapid and complete destruction of presumably well-constructed historic buildings,
Reports indicate that there (rightly) continues to be concern about the potential for a further failure at this site. The area remains cordoned off. There are concerns about the historic buildings on the other side of the street, which include a hotel, a restaurant and the Arts and Convention Center of the Federal University of Ouro Preto (UFOP).
Given the age of the buildings, this slope had presumably been stable for many decades after the initial building works. It would be interesting to know if any modifications to the slope had been conducted in recent years.
Finally, the image above suggests to me that in the upper part of the scarp the landslide might have mobilised existing planes of weakness, but this remains to be confirmed.
Brazil often receives heavy rainfall at this time of the year, and landslides are common. This year appears to have been quite bad again.
13 January 2022
The Pau Branco landslide – video of the overtopping of the dam
A video has now emerged online that shows the overtopping of the dam immediately downstream of the Pau Branco landslide in Brazil on 8 January 2022. This video was apparently collected by CCTV at the site:-
At the start of the video it is clear that the rainfall was heavy, and the dam was full with water cascading down the spillway on the far side. As the landslide becomes visible on the left side of the footage a displacement wave races across the lagoon and causes an initial overtopping event. This quickly develops as the volume of the lagoon is filled with landslide debris.
Initially most of the overtopping is water from within the lagoon, and this is reflected by the videos from the road below the dam. Later in the video solid material overtops the structure – this may be a combination of landslide debris and silt from within the pond.
The video demonstrates the power of such an event – the speed and relentless nature of the overtopping are stark. It is fortunate that the structure was in place – it has retained a large proportion of the mine waste, probably preventing a much more powerful and destructive flow from reaching the road and from a greater volume of mine waste being unretained now.
And of course it is fortunate that the retaining structure was able to stand up to the flow. If it had collapsed rapidly then the impact would have been much more serious.
Meanwhile the fallout from the Pau Branco landslide continues. Inevitably, further questions are being asked about the stability of the huge numbers of mine waste piles in Brazil (this should not be confined to Brazil of course). Reports also indicate that a licence was granted in January 2021 for an expansion of the
dry stack mine waste pile that failed. It will be interesting to know how much of this expansion had occurred at the time of the collapse.
Finally, of course, there are many similar slopes associated with this mine waste pile. Urgent work is needed to determine the stability of these slopes.
12 January 2022
Flow from the mining landslide at Pau Branco
The mining landslide at Pau Branco caused a significant release of mine waste, which appears to have flowed into the water retention structure below. This image, from the Observatório da Mineração, shows the flow path:-
As the image shows, the landslide overtopped the retaining structure, which remained essentially intact (note the superficial erosion on either side of the dam abutments). The debris, presumably now more fluid having entrained water and saturated sediment from the lagoon, flowed across a major road, the BR-040. This is captured rather nicely in the video below, posted onto Youtube:
On Youtube, videos have been posted of the situation on the road as the flow arrived. The best of these was taken from the cab of a lorry on the road at the key moment:-
Another video recorded the event from a different angle:
Meanwhile heavy rainfall continues in Brazil. As a consequence a number of mining operations have been temporarily suspended, including those by Vale and Samarco, both of whom have had major tailings failures in recent years. Vallourec, who operate the mine at Pau Branco, have been served an order for the environmental damage caused by the slope failure on Saturday, totalling over R$289 million (about $52 million).
Sadly, some newspapers are suggesting that the landslide was associated with the death of a family of five people. The situation is a little unclear – Forum reports (in Portuguese) that:-
The family dodged the landslide and took an alternate route, but ended up being buried. The bodies of the victims were found on Monday (10).
The suggestion appears to be that the family took a detour as a result of the road closure, but was then buried by a separate landslide.
11 January 2022
Pau Branco: another significant mining-related landslide in Brazil
On Saturday 8 January 2022 another significant mining-related landslide occurred in Brazil. On this occasion the site was the Pau Branco iron ore mine, which is located on the western side of Quadrilátero Ferrífero region. The mine is reportedly owned by the French company Vallourec. Mining operations at the site have been suspended by the regulator.
The location appears to be -20.145, -43.968. This is Google Earth image of the location, from a similar perspective as above:-
It appears that a benched slope has failed. The mechanism is unclear but a rotational landslide looks likely. It appears that the mass has fluidised to become a flow. The image below suggests that this then overtopped a water retention lagoon, but fortunately the dam did not fail. The landslide then impacted the major road at the foot of the slope.
A report on the Observatório da Mineração website indicates that the retention structure, which is not a tailings dam, was upgraded last year. The failure itself has occurred in a benched slope above the lagoon. It appears to me that this slope consisted of mine waste dumped onto the natural slope – Google Earth images suggest that the slope was created between 2006 and 2010 – but this needs confirmation. I would imagine that this slope was created to increase the volume of mine waste that could be dumped upslope in the main waste storage site. The Google Earth image below shows the configuration:-
So overall I this that this was probably a rotational landslide that fluidised into a flow, with the failure occurring in benched mine waste. But I would welcome views from others via the comments.
Once again, this event will ask questions about the stability of mine waste in Brazil (and beyond). It also continues to drive concerns about the capability of mining companies to ensure that slopes are stable and that regulators are able to ensure that appropriate methods are being used. It feels likely that we will see another major mine waste failure this year, despite some efforts to improve mine waste management practices.
10 January 2022
The fatal flexural topple at Cânyon de Furnas in Brazil
Many thanks to the various people who have contacted me over the weekend about the fatal flexural topple at Canyon de Furnas in Brazil on Saturday morning (8 January 2022), as shown in the image above. This event, which was caught on a dramatic video, has received considerable attention in part because of the spectacular nature of the event and in part because of the human cost.
The recording of the event can be seen at the start of the video below (I advise discretion in watching this video, the latter stages are quite harrowing):-
The failure itself is a classic flexural topple, in which failure is dominated by vertical or near-vertical structures in the rock mass. The second part of the video also captures the minute or so leading up to the main failure, in which the rock mass is (with hindsight) progressively deforming, generating a succession of rockfalls. This precursory activity is common. Once again the message needs to be that if a rock slope is generating a succession of rockfalls then a large failure event might be developing.
The video below shows the event from a more distant angle:
This video captures the fragmentation of the rock mass after impact with the water, which meant that there was fly rock affecting the boats located at a greater distance from the topple itself.
The toll from the tragic event was ten people killed and 27 people injured. Reports indicate that all ten fatalities occurred on a single boat, which appeared to be struck directly by the rock pillar. Three other boats were affected.
The location of the event is -20.646, -46.265. The site is a part of a reservoir created by the large Furnas Dam on the Rio Grande just downstream of Canyon de Furnas. The event occurred after heavy rainfall and at a time when the water level behind the dam was high.
It was the timing of the event that, in part, led to the tragedy. That the failure occurred on a Saturday morning meant that there were far more people in the path of the failure than would be case on many other occasions.
24 December 2021
Spruce Tree House – extreme rockfall management
The Spruce Tree House alcove complex is a truly remarkable cliff dwelling located in Mesa Verde National Park in Colorado. It was constructed by the Ancestral Pueblo people over 700 years ago beneath a beautiful natural arch. In total the Spruce Tree House complex includes 114 rooms:-
Unfortunately natural rock arches are, in a geological sense, transient features, meaning that in the long term the safety of this complex is inevitably compromised. Back in 1908 a large crack was documented in the arch and downward deformation of the rock mass was also observed.
The history of subsequent works to try to stabilise the arch is documented in an NPS report (Mason 2016) that analyses the stability of the arch. This notes that in the 1920s the site suffered a significant rockfall, and by the 1940s major problems were apparent, most notably a very large crack at the crest of the arch, as the image below shows:-
To manage the risk, a drainage ditch had been constructed. Mason (2016) notes the full range of works undertaken in the 1940s:
“…the arch crack was cleaned … of debris and plants and subsequently filled at the ends with emulsified asphalt and a roof structure was built over the wider center sections. Lancaster cleaned the crack along the full length and installed a “water-proofing” system to prevent surface water from seeping into the alcove. It appears that the technique was ineffective because of numerous attempts at resealing.”
In 1960 the problems became serious once again after another rockfall. A further round of works were undertaken in 1962, including the installation of 46 rock bolts and further efforts to seal the crack.
Whilst the site remains intact, a further round of inspections and analyses were initiated after a rockfall in 2015. These have found that there are problems with the rock bolt method that was adopted, and it is likely that the seal in the crack has caused a rerouting of groundwater flow paths, which is probably degrading other parts of the rock mass. And of course the whole rock mass is undergoing natural degradation.
Since then there has been an extensive set of investigations and analyses to determine a solution for the problems at the site that will protect it for the next century. The Durango Herald has a good article that provides some detail:
“It appears the fix is going to be multi-pronged. The park will likely use rock bolts again, but this time, installed at offset angles, which would increase strength (think of the root structure of a tree). And, new material, likely a type of metal, will be used to fill the crack to stop water from entering.”
It will be fascinating to see the detailed design for the Spruce Tree House site – this is rock slope engineering at its most challenging given the importance of the location; the rock conditions; the vulnerability of the arch and the archaeology; and the importance of the site to the National Park.
Mason, J.A. 2016. Condition assessment report, Spruce Tree House alcove sandstone arch, Mesa Verde National Park, Mesa Verde, Colorado. NOS Report, available online.
22 December 2021
Another fatal jade mine landslide in Myanmar
It is reported that yet another landslide affected the Hpakant area of Myanmar this morning. Whilst the picture is a little sketchy at the moment, the indications are that a jade mine landslide occurred at about 4 am. Indications are that between 70 and 100 people were swept into a lake. One body has been recovered and 25 people have been injured.
WION/AFP has the only image of the aftermath that I can find at the moment – unfortunately it doesn’t tell us a great deal:
Over the years I have repeatedly written about the terrible history of jade mine landslides in the Hpkant area of Kachin State. In 2018 I produced a timeline of reported events, whilst last year another landslide killed at least 175 miners at Wai Khar mine at Sate Mu. At the weekend there was yet another landslide, with at least six people, and possibly as many as ten people, killed.
Much has been written about the causes of these dreadful events, but this is an area in which the landscape is being pillaged by large scale mining activities. The level of regulation is negligible, and the area is riven with dangerous slopes of both mine waste and bedrock. On top of this, the dire economic conditions in Myanmar have meant that a large number of people scavenge on the waste piles, trying to find jade to sell. They often mine at night, increasing the danger. Very often the collapse of the waste piles bury these people, or sweep them into the flooded pit bottom. Sometimes displacement waves from collapsing waste piles catch the miners by surprise.
All of this is avoidable with proper regulation, but there is little or no prospect of change in Myanmar.
It is estimated that 70-90% of the jade produced in the world comes from Myanmar. Jade is a beautiful rock, but please don’t ever buy jade from Myanmar.
21 December 2021
The movement of the San Isidro landslide in Peru, and a possible relationship with the 28 November 2021 Northern Peru earthquake?
The movement of the San Isidro landslide in Peru, and a possible relationship with the 28 November 2021 Northern Peru earthquake?
Yesterday I wrote about the failure of the San Isidro Landslide in La Peca, Peru on 12 December 2021, which has led to the relocation of about 250 people. Later in the day, Sotiris Valkaniotis tweeted satellite images of the site, derived from the European Space Agency Sentinel instruments, that both confirmed the location of the landslide and provided an indication of the movement of the slope. The Tweet should be visible below:
Copernicus #Sentinel2 satellite imagery captures the motion from an activated #landslide of 800+ meters length in San Isidro, Peru (Dec 12 2021). Left; total horizontal displacement as measured by optical image correlation (before & after imagery). 1/2 https://t.co/691BgrfwE2 pic.twitter.com/4NrHKpL6hW
— Sotiris Valkaniotis (@SotisValkan) December 20, 2021
This provisional analysis indicates that the landslide was about 800 m in length, with displacements exceeding 20 metres in places. The devastating impact on the village is clear, despite the low resolution of the imagery.
There is an interesting other dimension to this landslide. On 28 November 2021 the Amazonas region suffered an M=7.5 earthquake. The epicentre was about 215 km from the San Isidro landslide. Images posted to the La Peca Facebook page indicate that significant landsliding was triggered in the area by the earthquake.
Thus, it seems quite possible that the slope at San Isidro was weakened by the earthquake, and then failed in the first heavy rainfall event after the seismic event. This is a pattern that we have seen elsewhere.
Of course this is only speculation at this point, but it is an interesting angle to explore.
As an aside, the images in the Facebook page indicate that in at least one location the valley is blocked by a landslide, possibly in the area of Bagua Grande. I hope that this has been (or is being) addressed.