4 August 2021
A rockfall video from the Couloir du Gypaète in France
With thanks to those who spotted this on Youtube, a very surprising rockfall video was posted online last week by Rémi Bourdelle, who was flying above the Couloir du Gypaète in France when a rockfall developed. The video provides an utterly unique perspective on rockfall processes. Take a look:-
My first reaction to this is of course wow! The video shows boulders bouncing down the gulley and then through the trees below. As noted previously the force of these rocks is extraordinary.
But the most surprising element of this video is the trajectory of the rock seen at the start of the video. Fortunately, this boulder (which appears to have been fragmenting) left a trail of dust that marks its path through the air:
This is the sort of trajectory that is normally associated with fly rock from blasting rather than a rockfall. It is quite extraordinary; I have not seen this previously (have any readers?).
Presumably, the boulder struck an inclined surface, whilst travelling at a very high velocity, causing a ricochet that created this ballistic trajectory.
The other obviously possibility would be ejection during fracturing, but this seems less likely to me.
I’m not sure if this is a freak, or something that is quite common. Any views?
2 August 2021
Melamchi – satellite images and helicopter videos start to explain the catastrophic floods in Nepal
On 14 June 2021 a huge debris flow and flood destroyed Melamchi in Nepal. The event was triggered by heavy rainfall, and as I noted a few days after the event, there is a very large landslide upstream of the village that might explain the surge that came down the valley. However, the event has been slightly mysterious, partly because satellite images have not been available of most of the area upstream of Melamchi. It is now clear that the event was more complex, and more concerning, than was initially obvious.
Satellite imagery is slowly becoming available – this is slow as the area is still covered in monsoon cloud most of the time. To understand this event we have to go right up to the headwater area in the high mountains. This is the site:-
This is a very steep, very rugged terrain. Note in the centre of the image the large volume of sediment, partially vegetated, in the valley floor, trapped against some sort of barrier (very possibly an old landslide deposit).
Planet Labs captured an image of the same area on 29 July 2021. This is not the best image, but the change is startling:
Upstream of this area there are some landslides, most notably from the valley to the northwest. But there appears to be huge mobilisation of the sediment trapped behind the barrier.
भीमथाङको यो विशाल पहिराेले मेलम्ची क्षेत्रमा लामाे समय दु:ख दिन्छ जस्तो छ ( भिडियो बाबू लामा) pic.twitter.com/0oEqWFnTu1
— ShIvA DaHaL (@dahalshivaji) August 1, 2021
The lower left image shows this area of sediment, clearly dramatically mobilised by the flood. The helicopter video captures this even more clearly:-
The view looking downstream is, if anything, even most dramatic:-
My interpretation is that this is effect the breach of an ancient landslide dam, which is now collapsing under successive rainstorm events. The sediment pile extends from about 2 km, and only a small proportion has mobilised to date.
The sediment pile is collapsing rapidly – the video even captures small collapses occurring – with big slumps developing, as seen in the second video. Downstream, a huge amount of erosion has developed, and the walls of the channel have collapsed extensively:
Further downstream, as I noted in a previous post, there is a large landslide near to the village of Melamchigaon, but it appears that this was not the cause of the disaster:-
These images are grim in terms of the safety of Melamchi. There appears to be a huge, unstable mass of sediment, undergoing collapse, upstream of the town. Heavy rainfall is likely to bring further major floods and debris flows, and indeed on Saturday a further dozen houses were lost to floods in the area.
My analysis is not definitive – indeed it is only provisional – a much more detailed examination of this site is needed (and is hopefully underway), led by local teams.
There is a much larger consequence of this event though. Melamchi is source of a major drinking water project for the capital city of Kathmandu – the Melamchi Drinking Water Project (MDWP). The works, which started to supply water to the city on 28 March 2021 after 23 years of construction, were substantially damaged in the June event. The excellent Himalayan Times has a good article about the impacts:
The head works of MDWP has been covered 10 metres high with flood debris according to officials. Worst of all, the flood has swept away around 10 kilometres road from Melamchi Bazaar up to the headworks, including two major concrete bridges.
The estimated costs to the project are 2 billion rupees (about £12 million), but the full extent of the damage is unclear.
However, there is a real but unquantified risk that the problems are much more serious, with continued large-scale mobilisation of sediment in future rainstorms. Once again, this needs very urgent attention.
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
30 July 2021
Tapovan Vishnugad – another landslide at the hydroelectric scheme in northern India
The Tapovan Vishnugad run of the river hydroelectric scheme in Uttarakhand in northern India was devastated by the disastrous debris flow that resulted from the Chamoli rock slope failure in February of this year. Many of those killed lost their lives in tunnels under construction as part of the project.
Inevitably the news has shifted to other priorities, but for those living in the area the turmoil continues. One of the villages most heavily affected by the debris flow was Raini, which is famous as the birthplace of the Chipko Movement in 1973, which according to Britannica was a “nonviolent social and ecological movement by rural villagers, particularly women, in India in the 1970s, aimed at protecting trees and forests slated for government-backed logging”.
On 17 and 18 June 2021 Raini was affected by devastating floods, which destroyed the lower part of the village.
And then on 24 July 2021 a further substantial landslide occurred at the Tapovan Vishnugad hydroelectric scheme. Science the Wire has an article that highlights this event, which includes the following image:-
The news reports suggest that this was a collapse at the site of the tunnel portal near to Selang village. The image would seem to support that interpretation – note the tracks leading into the slope. The failure appears to be a rockslide; the tabular form of the blocks and the inclination of the beds in the scar suggest that this is likely to be a discontinuity controlled planar failure.
Whilst this is unlikely to be terminal for the Tapovan Vishnugad project, it will be expensive to repair and it undoubtedly raises further questions about the ability of the project team to understand and manage the geotechnical hazards.
Ironically, this week five individuals, three of whom are from Raini, petitioned the Uttarakhand high court, seeking (in the words of the Science the Wire article) “revocation of the projects’ forest and environmental clearances, and eventual cancellation of the two hydropower projects.
“In their public interest litigation (PIL), the petitioners claimed that the use of explosives during project construction had weakened the already fragile hills, thereby increasing the frequency and intensity of landslips in the region. The current situation is such that for safety, the villagers from Raini sometimes take shelter in nearby forests. Considering this, the need for rehabilitation of the villagers was raised in the PIL.”
On the first day of the hearing, the court dismissed the petition and, outrageously, fined each of the petitioners 10,000 rupees (about £96).
28 July 2021
Drone footage of the 31 May 2021 landslide at Bingham Canyon mine in Utah
On 31 May 2021 a large landslide occurred at the Bingham Canyon mine in Utah. Bingham Canyon is famous for the enormous 2013 landslide; fortunately this event was on a smaller scale, although it was far from trivial.
In the last week drone footage of the landslide has been posted to Youtube:-
The video starts with the rear scarps of the slide block clearly defined. At Bingham Canyon there is a sophisticated monitoring programme for the slopes, so the failure was anticipated and all of the key assets had been removed from danger. It is interesting to note the drilling that had been undertaken through the area that failed, possibly in anticipation of blasting? I am not an expert by any means of open pit mining operations.
The failure appears to initiate as a translational slide:
Note how the surface of the main block remains approximately horizontal. At the rear a smaller block starts to fail slightly later than the main block. This slice rapidly fragments as it loses support from the main block. Thereafter the entire landslide slowly fragments and, eventually, becomes engulfed in dust. Small secondary failures develop across the scar of the landslide.
This is one of the most impressive failures caught on video to date. That the drone team were in place suggests that the mine had correctly predicted not just the location of the landslide but also its timing. The result is an excellent case study.
Incidentally, there is a book about the 2013 landslide, entitled Rise to the Occasion by Brad Ross. It is, unfortunately, very expensive. Has anyone here read it? Is it worth a read?
27 July 2021
The disastrous Taliye village landslide in Maharashtra, India
In amongst the other news associated with the current range of extreme weather events, a disastrous landslide at the village of Taliye in Raigad, Maharashtra in India on 22 July 2021 barely got a mention. This is deeply unfortunate as this landslide, one of several that occurred in India last week, was catastrophic. The search operations in the aftermath of the landslide were stopped yesterday leaving a death toll of 84 people, only 53 of whom have been recovered, with a further five injured. Mid-day has a good report about the event, including this image of the aftermath:-
The location of this landslide appears to be 18.110, 73.584, although this needs confirmation. This is the location on Google Earth – it looks to be correct:-
I believe that the geology here is likely to be the multiple layers of the Deccan Volcanic Province, meaning that the bedrock is basalt, with a high level of erosion. The landslide itself is mostly planar in nature – the Google Earth image suggests to me that this is likely to have occurred in a deposit of weathered basalt and colluvium, with the trigger being unusually heavy rainfall.
Interestingly Ajit Pawar, the Deputy Chief Minister of Maharashtra, is quoted as saying that the Taliye had not been identified as being landslide prone. This may reflect a longer than anticipated runout distance for the landslide perhaps, although we will need to wait for good satellite imagery (which is difficult to acquire in the monsoon) to be sure.
The Taliye village landslide was the largest event in the Raigad area of Maharastra last week, In total 124 people were left dead or missing, the majority of whom lost their lives in landslides.
26 July 2021
The rockslide at Batseri in India
It has been a busy weekend for landslide stories to the degree that it’s been difficult to know where to start this morning. However, I have decided it is worth writing about the rockslide at Batseri in the Kinnaur district of Himachal Prrdesh in northern India, the videos of which circulated yesterday.
There are several videos of this event, taken from different perspectives. I think it is worth starting with this one as it shows, right at the start, the source of the rockslide:-
Nine seconds into the video it also shows traffic passing along the road that traverses the slope, of which more later.
These show the dramatic movement of the boulders down the partially forested slope.
And then there is the viral video (which is also in the compilation above), which is best shown in this version:-
The rockslide appears to have started as a result of a collapse on a very steep, rocky outcrop above the bridge at Batseri. The image below shows the terrain using Google Earth. The rock slope has numerous rockslide scars:-
It appears that a mass collapsed, maybe about 700 m vertically above the bridge, and fragmented to generate the “evil dancing boulders”. I have noted previously that the situation in which the boulders start to rotate about a short axis and to bounce is very dangerous. This is the case for numerous boulders here, generating extremely high velocities. Before the bridge is hit one boulder (visible at about 19 seconds into the final video above) takes an enormous bounce due to the terrain:-
The boulder that destroys the bridge also bounced very high, meaning that it impacted the structure in close to freefall. The bridge was unable to withstand the impact.
Unfortunately there is a tragic footnote to this event. A tourist bus was traversing the road at the time of the landslide, and was hit directly by at least one boulder. Nine people were killed and three were injured. Included in those tragically killed was Dr Deepa Sharma, a well known nutritionist with a large following on Twitter. Earlier in the day she had tweeted a selfie of herself standing at the start of the militarised zone along the border with Tibet.
This stands testament to the tragedy of the event.
Many thanks to the various people who brought this to my attention. It is much appreciated.
23 July 2021
Benbrack: another peat landslide in Ireland
Over the last few years I have blogged about peat landslides in Ireland on a number of occasions. Peat landslides are particularly interesting as they tend to have a long run out and they are extremely environmentally destructive, both in the source area (where the peat can take decades or more to regenerate) and downstream, where the peat can be a terrible pollutant. And of course peat is a key (and often degrading) carbon store; losing more is bad.
The newspaper The Anglo-Celt has a story about yet another peat landslide, this time at Benbrack in West Cavan, Republic of Ireland. The location is about 54.152, -7.852. This is the topography from Google Earth:-
The landslide apparently occurred on 4 July 2021 during heavy rainfall. The landslide was photographed by a trekking enthusiast called Kevin Dockery:-
The landslide is also visible on the Planet Labs imagery of the area:-
Based on this image the landslide is about 600 m long. The newspaper article includes a description of the landslide:
…[T]he landslide started on the Benbrack summit plateau at a height of 470 metres above sea level, about 400m south west of Derrynananta.
“About six feet [2 m] deep of peat slipped away down the mountainside,” explained Kevin of the largest of three landslides in the area – two in Benbrack a smaller one on Cuilcagh.
“It was as if a big Hi-Mac scooped away all the peat down to the level where there were gravel and stones.
“There were massive chunks of peat gouged up – they wouldn’t fit into a car trailer they were that big. It just cascaded down the mountainside, it was extraordinary.”
This landslide does not appear to be associated with either forestry or wind farm development, as far as I can see.
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
21 July 2021
The extraordinary, almost unbelievable, rainfall in Henan Province yesterday
There are widespread reports today of the terrible floods that affected Henan Province in China yesterday, triggering floods and landslides. There are some dreadful videos and images of the result of this rainfall, some of which are deeply harrowing, focusing mainly on the city of Zhengzhou. Xinhua is reporting that 25 people have been killed, but rescue operations continue and more heavy rainfall is forecast.
What has not been widely reported is the extraordinary nature of this rainfall event. The long term average annual rainfall in Zhengzhou is 640.8 mm. These are the stats for the current rainfall as at the end of the day yesterday:
- Max. 24 hour rainfall: 552.5 mm (from 20:00 on 19 July to 20:00 20 July);
- Max. 72 hour rainfall: 617.1 mm (from 20:00 on 17 July to 20:00 20 July);
- Max one hour rainfall: 201.9 mm (from 16:00 to 17:00 on 20 July).
This is extraordinary rainfall. To put this in context, there is a yellow weather warning for the UK for this coming weekend because there are fears of localised convective storms that might lead to locations receiving 100 mm of rainfall over the course of a 24 hour period.
As such, statistically, this rainfall in Henan was one in one thousand year event.
The highest one hour rainfall ever recorded is (I believe) 214.8mm in Penghu, Taiwan, but this was associated with a typhoon. To have >200 mm without the local presence of a tropical cyclone is very surprising.
The all time record one hour rainfall in China before yesterday was 168.3 mm, recorded at Maoming in Guangdong on 2 July 2002. Clearly the Henan event has soundly exceeded that value. It is worth noting that this rainfall event extended over a wide area, whereas many large one and 24 hour totals are highly concentrated. This may well also be the highest rainfall intensity ever recorded within a major city.
The cause of the heavy rainfall in Henan was a typhoon located to the east of Taiwan, with a high pressure system located to the north of Taiwan over the Sea of Japan. This fed an atmospheric river of water vapour into central China. This was intensified by another airstream from the south, pushed by a smaller tropical cyclone located off the south coast of China. The warm, moist air encountered the uplands of Henan, generating orographic rainfall in vast quantities.
20 July 2021
Hulunbuir: a very serious double dam failure in China on 18 July 2021
There has been surprisingly little international reporting of a very serious double earthen dam failure in the Hulunbuir area of Inner Mongolia in northern China on Sunday 18 July 2021. This looks to have been one of the most serious dam failure events in recent years, with 46 million cubic metres of water having been released, causing massive flooding. Reuters has a report of the event, but there are few other outlets providing much attention to it.
The dams in question are called Yong’an Dam and Xinfa Dam, located in Morin Dawa Daur. There is dramatic footage of the collapse of the Xinfa Dam on Youtube (apologies for the awful music):-
This dam is located at 48.609, 124.241. This is a Google Earth image in happier times:-
Note that this dam has a substantial spillway structure, so overtopping is surprising. However, the video of the collapse shows that a very substantial volume of water had already overtopped the structure:-
A good working hypothesis is therefore that this dam was affected by the collapse of the Yong’an Reservoir, which would have released a catastrophic volume of water. About 10 km upstream of the Xinfa Dam there is another dam, located at 48.675, 124.327. The Google Earth image below shows the comparative position of these two structures. Interestingly the adjacent town is called Yongfu:-
One of the videos of the dam collapses, posted to twitter, appears to show the failure of a structure that is definitely not the Xinfa Dam:-
内蒙古 呼伦贝尔市 莫旗自治州 境内二座水库 新发及永安水库决堤
2021年7月18日 一部曲 pic.twitter.com/at4FEGw9qF
— 白七 (@tw_tomy_) July 19, 2021
This is a still from this video:-
I’m reasonable confident that this is the dam located upstream of the Xinfa Dam – the configuration looks to be identical. Edit: indeed this is now the confirmed location of the Yong’an Dam – see comments below:-
Thus, my hypothesis (untested at the moment) is that the Yong’an Dam failed due to the intense rainfall, which released a huge wave of water that overtopped and failed the Xinfa Dam, releasing a far greater volume to inundate the surrounding area.
There are images and videos online showing very extensive and damaging flooding from this event, such as this:-
A report on Apollo News details the damage (I have edited lightly to improve the English):
“16,660 people were affected; 325,622 mu [21,775 hectares] of farmland was flooded; 22 bridges, 124 culverts, and 15.6 kilometres of highway were destroyed….Casualties are unknown.”
Given the sale of the disaster it would be surprising if there were no human casualties although the Reuters report claims that there were no casualties. In the past such reports from China have not been reliable, so the jury is still out.
Large-scale dam collapses such as this are rare but very serious. Interestingly, the Reuters reports includes the following:
China has more than 98,000 reservoirs used to regulate floods, generate power and facilitate shipping. More than 80% of them are four decades old or older, and some pose a safety risk, the government has acknowledged.
Given the rate of change of intense rainfall events, this must be of great concern.
19 July 2021
Mumbai: at least 29 fatalities in monsoon landslides
As the South Asian summer monsoon continues to intensify, the city of Mumbai in India has once again been affected by serious landslides in the last 24 hours. As is often that case, the current picture is quite confused, but details of two large events are emerging. The clearest picture at the time of writing is in an article in the Hindustan Times.
First, at 1 am on 19 July 2021 a retaining wall collapsed in New Bharat Nagar in the Chembur suburb of Mumbai, burying about five houses. In total it is believed that 19 people were killed, of whom at least four were children. At least five more people were injured.
A few hours later, at about 3 am, a further landslide occurred at Surya Nagar in the suburb of Vikhroli, burying at least seven houses. Reports indicated that ten people were killed, of whom three were children. The image below shows the aftermath of this landslide:-
Note that these landslides occurred in densely populated suburbs with informal houses constructed with a very high density. The vulnerability of such areas to slope failures is high.
News reports suggest that this was the second of two large rainfall events this week. On Friday 253 mm of rain fell, followed 235 mm of rainfall in four hours on Sunday. Reports also suggest that there had not been a warning for a heavy rainfall event on Sunday.
The Deccan Herald has a good article about the landslide problem in Mumbai, which notes that at least 290 people have been killed by slope failures since 1992. Many inhabited locations are prone to landslides, and action has been urged to relocate the most vulnerable and to engineer solutions in other spots. However, as usual I note that whilst relocation is often desirable and has been successful elsewhere, poorly planned displacement of people can make them vulnerable to a range of other (usually social) hazards, negating the benefits.