12 November 2021
An update on the Ministro Hales mine landslide in Chile
An update on the Ministro Hales mine landslide in Chile
A picture has now emerged of the 9 November 2021 Ministro Hales landslide in Chile:-
The 9 November 2021 landslide at the Ministro Hales mine in Chile. Image tweeted by Marcela Hernando.
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This confirms the satellite image that I published on Wednesday, showing that this is a large rockslide in a benched section of slope.
News reports indicate that the landslide was anticipated. Movement was detected in the wall in July, allowing a plan to be put in place to mitigate the threat. BNAmericas reports that Codelco have stated that:
“In July – through focused monitoring – the control and contingency plan was designed and defined based on the safety of people, which considered the total closure of all access to the identified area and preventive detention of the adjacent phase”
10 November 2021
A large landslide at the Ministro Hales mine in Chile
A large landslide at the Ministro Hales mine in Chile
Loyal reader Luis Donoso highlighted to me yesterday a tweet of a video that showed the aftermath of a very large landslide in a high wall mine:-
***NOTICIA NO CONFIRMADA***
Circula este video de un derrumbe de bancos en mina a rajo abierto. Se especula Ministro Hales.#Antofagasta pic.twitter.com/NalZIiYmdc— W.E.U.H.V.H. (@INSOLENTES) November 9, 2021
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The tweet speculated that this was at the Ministro Hales mine in Chile, which is operated by Coldelco. A second tweet suggested that the failure might have been “expected and controlled”.
Planet Labs imagery of the Ministro Hales mine suggests that a large landslide did indeed occur at this site sometime between 8 and 9 November. An image captured at 13:55 UTC on 8 November shows no new landslide (although a smaller previous event is visible):
The Ministro Hales mine in Chile on 8 November 2021. Image Copyright Planet Labs, used with permission.
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An image captured at 14:42 UTC on 9 November clearly shows a large landslide:-
The Ministro Hales mine in Chile on 9 November 2021, showing the landslide. Image Copyright Planet Labs, used with permission.
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I have tried to include this as a slider below so that the before and after images can be easily compared:-
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Based upon the imagery the landslide is about 700 m long and 450 m wide. It has encompassed the existing slide but is far larger. The mobility of the landslide does not seem to be exceptional. There are some large blocks visible in the head scarp region.
Large rock slope failures in high wall pits are not unusual, and this is not the largest event that I have described. Big pits typically use radar and other monitoring methods to detect potential failures, so it is credible to believe that this landslide was anticipated. It will be interesting to see better imagery of the aftermath of the landslide, and to learn about the transition to failure.
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Reference
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
8 November 2021
Mallama: a deadly landslide in Colombia on 2 November
Mallama: a deadly landslide in Colombia on 2 November
On 2 November 2021 heavy rainfall triggered a deadly landslide in the village of Mallama in Nariño Province of Colombia, killing 17 people and injuring a further nine.
The best image that I can find that provides a good view of this failure is on the Nariño Government website:-
The 2 November 2021 landslide at Mallama in Colombia, which killed 17 people. Image via the Gobernacion de Nariño.
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Based on this image this is a failure in deeply weathered regolith on a very steep slope. It appears to have demolished a number of houses. This is probably best characterised as a debris avalanche, although with a comparatively moderate runout distance.
RCN Radio has this very dramatic image of the aftermath of the landslide from a different perspective:-
The aftermath of the 2 November 2021 landslide at Mallama in Colombia. Image by JHR Ingeniería via RCN Radio.
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According to news reports, the site had not previously been identified as being at risk of landslides, and the reason for the failure at this time is not clear. There is however a risk of further failures that will necessitate the relocation of people whose houses are as yet undamaged.
2 November 2021
The Tonghua landslide in Sichuan Province, China
The Tonghua landslide in Sichuan Province, China
A paper just published in the journal Landslides (Cheng, Yang and Du 2021) describes the Tonghua landslide, which is located at 37.575, 103.414, in Sichuan Province, China. This landslide occurred on 8 August 2017. The authors used InSAR to extract pre-failure creep with rates in the order of 15-25 mm per year in the three years prior to the failure event.
This is a really interesting landslide – the image below shows the slope that failed before and after the event:
Google Earth images showing before and after the Tonghua landslide in China
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The image below shows the landslide itself in more detail:
Google Earth image showing the 8 August 2017 Tonghua landslide in Sichuan Province, China.
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As the image above shows, the Tonghua landslide is a 600 m long translational debris slide in moraine deposits, with a volume of about 220,000 cubic metres. The analysis of Cheng, Yang and Du (2021) suggests that three earthquake events are associated with the landslide. The epicentre of the M=8.0 2008 Wenchuan earthquake was 59 km south of the landslide, whilst the epicentre of the M=7.0 2013 Lushan earthquake was located 158 to the southwest. On the day of the landslide, the M=7.0 2017 Jiuzhaigou earthquake was located 195 km to the northeast, but as this occurred ten hours after the failure, it was not a factor. The first two earthquakes may have played a role in preparing the slope for failure.
Perhaps the most interesting aspect of the landslide is the trigger. Cheng, Yang and Du (2021) note that there was no seismic event that coincided with the failure, and that rainfall in the 30 days prior to the collapse was not exceptional. There was no heavy rainfall event in the days immediately preceding the collapse. However, 25 days before the failure event, drilling and blasting commenced for the CNH G4217 Tonghua No. 1 tunnel, close to the site. In the days leading up to the failure event, Cheng, Yang and Du (2021) record 13 blasting events, with the last occurring about one hour before the failure. They conclude that ground vibrations associated with the tunnel construction were responsible for the failure.
Since the main failure event the Tonghua landslide has continued to creep and to expand. Initially rates were high, but they have now declined to rates in the range of 0.1 – 1.0 mm per day. The image below, from Cheng, Yang and Du (2021), illustrates how the landslide has evolved since the initial failure event:
The evolution of the Tonghua landslide in China post-failure, from Cheng, Yang and Du (2021). The left image was taken on 9 September 2017, after the failure, whilst the right image was taken on 30 May 2019.
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Reference
Cheng, Q., Yang, Y. & Du, Y. Failure mechanism and kinematics of the Tonghua landslide based on multidisciplinary pre- and post-failure data. Landslides (2021). https://doi.org/10.1007/s10346-021-01770-x
1 November 2021
A large landslide or glacial lake outburst in the headwaters of the Kameng River in Northern India?
A large landslide or glacial lake outburst in the headwaters of the Kameng River in Northern India?
Loyal reader Robert Wasson has very kindly highlighted an interesting article in the Discovering Arunachal blog, posted on Saturday. This article observes that at about 10:30 am on 29 October 2021 the Kameng River in East Kameng district in Arunachal Pradesh in northern India became extremely muddy. News reports indicate that the measured dissolved solids increased by about five fold and there was a mass die off of the fish population in the river.
Chintan Sheth, the author of the Discovering Arunachal blog, has used satellite images to try to discover what caused this unexpected event. The upstream area, along the banks of the Warriyang Bung river, is almost permanently covered in cloud at this time of the year, but on 29 October 2021 Planet Labs captured an image of part of the Warriyang Bung river catchment, from which Chintan Seth has created an image of the impact of the event:-
A composite set of Planet Labs images showing the change in the visible section of channel on the Warriyang Bung river in northern India. Image compiled by Chintan Sheth and published on the Discovering Arunachal blog.
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The location of the site is 27.877, 92.702. The images appear to show that there has been heavy erosion and deposition along the river. Unfortunately the source of this event is under thick cloud.
Back on 1 October 2021 Planet Labs captured a beautiful image of the catchment:
The catchment of the Kameng River that was the source of the event of 29 October 2021. Image copyright Planet Labs, used with permission, captured on 1 October 2021.
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This is a complex catchment, with small glaciers and steep slopes. I cannot see any obvious glacial lakes, but these could be obscured by clouds. The most three obvious candidates for this event are the collapse of a glacial lake, a the collapse of a glacier or a rock slope collapse. The latter seems more likely, but we may not know until a cloud free image with low levels of snow becomes available. That might not be the case until the spring.
Imagery of the channel downstream shows erosion and deposition along the channel, suggesting that this was a significant event.
The upper catchment of the Kameng River showing changes to the channel following the event of 29 October 2021. Image copyright Planet Labs, used with permission, captured on 29 October 2021.
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Reference
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
29 October 2021
The mobility of a rolling volcanic boulder
The mobility of a rolling volcanic boulder
On this blog I have frequently written about the mobility of boulders once they start rotating on their way down slope. A very beautiful example of this was posted to Twitter yesterday by Harri Geiger. The video was shot on the flanks of the still erupting Cumbre Vieja volcano on La Palma in Spain:
Spallation lava bomb coming down from #LaPalmaVolcano on 27 Oct 2021.#CumbreVieja pic.twitter.com/mvKFKn6rme
— Harri Geiger (@harrigeiger) October 28, 2021
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The video captures a spallation lava bomb. As the video shows, this was a boulder that was roughly spherical, and it was moving on a surface essentially devoid of obstructions and that had, until late in the sequence, a steady slope. The resultant video is a remarkable record of the extreme mobility in these situations.
If the film Raiders of the Lost Ark is ever remade then this video of a high mobility, extremely hot boulder might be food for thought.
The boulder chasing Harrison Ford in the Film Raiders of the Lost Ark. Still from Screenrant.
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Meanwhile, the eruption continues with a great deal of energy. There is no reported evidence of the much-hyped catastrophic flank collapse, and thus of the resultant mega-tsunami, as far as I can see. On 25 October Sotiris Valkaniotis tweeted his latest InSAR analysis of deformation on La Palma:
Cumulative displacement & interferograms from Copernicus #Sentinel1 imagery, for the past month of volcanic activity in #LaPalmaVolcano #Canarias. Descending interferogram has quite decent quality despite of 36d interval. Processed at @Ak_Satellite DAAC HyP3 using GAMMA. 1/2 pic.twitter.com/xbHkoLXRgj
— Sotiris Valkaniotis (@SotisValkan) October 25, 2021
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As I’d expect, this shows inevitable inflation and deflation around the vents, but no indication of large scale instability in the flank. La Palma is being monitored closely by multiple groups using multiple sets of tools, so any changes would be rapidly detected.
28 October 2021
The 21 July 2020 Shaziba landslide at Mazhe Village in Enshi, China
The 21 July 2020 Mazhe Village landslide in Enshi, China
Back in July 2020 I wrote about a landslide that had just occurred on the banks of the Qingjiang River in Enshi Tujia and Miao Autonomous Prefecture in Hubei Province, China. This was a really impressive event, triggered by heavy rainfall:-
The 21 July 2021 Shaziba landslide at Mazhe Village in Enshi, China. Image from China Daily.
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As the above image shows the failure, now known as the Shaziba landslide, temporarily blocked the river. In a paper recently published in the journal Landslides, Xue et al. (2021) have investigated the precursory movement of this landslide using satellite imagery.
The results are interesting. Their InSAR data demonstrates that the landslide seen above is part of a much larger complex, as shown in the figure from the paper below:-
The full extent of the Shaziba landslide in China, from Xue et al. (2021).
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The July 2020 landslide involved a volume of 250,000 cubic metres, with a length of 1,500 m, a width of up to 580 m and an average depth of 25 m.
The InSAR data shows that the landslide was creeping in the years leading up to the major failure. The creep was seasonal, with the higher rates of movement associated with the rainy season. This is unsurprising – presumably the landslide was responding to elevated pore water pressures. Detailed analysis of the data suggests that over time the landslide was becoming more responsive to rainfall, presumably an indication of the evolution of the landslide towards failure, and a possible indicator for a warning system.
Interestingly, Xue et al. (2021) have used InSAR to look at other slopes on the banks of the Qingjiang River, and have detected three further large landslide complexes that are showing seasonal patterns of displacement. These landslides, and the unfailed portion of the Shaziba landslide, now need monitoring. Fortunately InSAR represents a technique through which this can be achieved if there is sufficient funding for the processing.
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Reference
Xue, C., Chen, K., Tang, H. et al. 2021. Heavy rainfall drives slow-moving landslide in Mazhe Village, Enshi to a catastrophic collapse on 21 July 2020. Landslides (2021). https://doi.org/10.1007/s10346-021-01782-7
27 October 2021
The cost of mitigating slope safety risk for Welsh coal waste tips
The cost of mitigating slope safety risk for Welsh coal waste tips
A small failure in a coal waste tip in South Wales. Image from Clear South Wales’ Coal Tips.
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In February 2020 Storm Dennis triggered significant instability in a coal waste tip at Tylorstown in South Wales. Whilst mitigation of that problem is now underway, at very substantial cost, it has raised the issue of stability across the large number of coal waste tips across South Wales. Inevitably the underlying concern is a repeat of a major failure, as occurred at Aberfan 55 years ago this month.
Yesterday the Welsh Government published the results of an analysis undertaken in the aftermath of Storm Dennis. This work has comprehensively documented the location of coal waste tips and has provided a first order analysis of their potential to cause risk to safety. The results, which do not make good reading, were discussed at a meeting of the Coal Tip Safety Summit yesterday.
In total 2,456 coal tips have been identified. They have been classified in terms of their safety from A to D, with A representing tips that are minor or have been restored, and D representing those posing the highest risk. The BBC has published a table presenting the results by area:-
Welsh Government data showing the classification of coal waste tips by region. Table from the BBC.
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In total 327 tips have been classified as C and D and thus need remediation. Many of these coal waste tips are on private land, so the management of the hazard is far from simple. In no case is the risk considered to represent an immediate or imminent threat, but these coal waste tips are now being subjected to increased monitoring.
The Welsh Government has estimated that the cost of mitigating the high risk coal tips is likely to be at least £500 million over the next 15 years, but experience indicates that this will probably rise once the work begins. The issue will become more severe with time unless action is taken as rainfall intensities continue to increase and the waste piles continue to weather.
Meanwhile work will continue to develop techniques to monitor the coal waste tips through the coming winter. Meanwhile, the Twitter account Clear South Wales’ Coal Tips provides interesting commentary on the evolving situation.
26 October 2021
The 5 April 2021 Tiejiangwan landslide in Sichuan Province, China
The 5 April 2021 Tiejiangwan landslide in Sichuan Province, China
The journal Landslides has just published an interesting article (Liu et al. 2021) about the 5 April 2021 Tiejiangwan landslide in Sichuan Province, China. This failure, triggered by heavy rainfall, destroyed five houses, killing three people. The article provides a brief commentary on the events.
The image below shows the aftermath of the landslide (unfortunately the image appears to be mistitled as, according to the article, the landslide occurred in 2021 not 2020. This error occurs throughout the article):-
The aftermath of the 5 April 2021 Tiejiangwan landslide in Sichuan Province, China. Image from Liu et al. (2021).
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As the image shows the landslide, which was triggered by heavy rainfall, initiated as a 30,800 cubic metre near-vertical rock slope collapse in thick-bedded sandstones with thin-bedded silty mudstones. The source area of the collapse was about 134 m long and 92 m wide. The debris initiated a debris slide that entrained colluvium on the slope. The debris ran out for a distance of about 1050 metres.
On 10 April 2021 further heavy rainfall triggered a debris flow in the landslide deposits. Further rainfall on 14 April 2021 triggered another debris flow. The debris dammed the main channel downstream, presumably requiring mitigation (although this is not described), to a height of over 3 metres.
This is an interesting example of a complex landslide involving a cascade of hazards starting with a fatal rock slope collapse. The evolution over time into debris flows that then blocked the main channel, inducing the risk of an outburst flood, illustrates very well the challenges of managing slope hazards in high mountain areas. Such landslides occur naturally (although changing patterns of rainfall mean that the frequency might be changing, and remobilised debris flows might be more likely. Such events are disasters because people are living in places that have a high level of vulnerability.
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Reference
Liu, B., Hu, X., He, K. et al. 2021. Preliminary analyses of the Tiejiangwan landslide occurred on April 5, 2021 in Hongya County, Sichuan Province, China. Landslides (2021). https://doi.org/10.1007/s10346-021-01763-w
25 October 2021
A rockslide video from Pyuthan in Nepal
A rockslide video from Pyuthan in Nepal
The heavy rainfall last week in Nepal and India caused widespread damage including many landslides. Interestingly, as I type an atmospheric river event is affecting the West Coast of the USA, also with reports of of landslides. It will be interesting to see what the effects of that event will be, especially in areas affected by recent wildfires.
Pyuthan is a hill district located to the west of Nepal. A video emerged over the weekend of a very interesting landslide in Pyuthan, apparently triggered in this event (although this remains to be verified). This video was originally posted onto Tiktok by aashishsenchury10, but it has also been posted onto Twitter:-
https://twitter.com/sanjeevdevs/status/1451906525996347395
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Unfortunately there is little information that I can find about the location of this dramatic failure. However, there are a few things to note. First it appears to be a wedge failure in bedrock. The post failure images show that the sliding was controlled by two very clear, pre-existing discontinuities in the mass. One of these is very clear in the image below, whilst the other is orientated towards the camera:-
A very clear discontinuity defining the block that slid in the Pyuthan rockslide. Still from a video posted to Tiktok by aashishsenchury10.
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Second, there is landslide debris between the houses and the rockslide, indicating that this was not the first failure in this area. The age of this debris is not clear.
Third, immediately below the slope there is a road. I can only speculate on whether the construction of the road has been a factor in destabilising the slope. That is a factor that is common in many slope failures in rural Nepal.
And finally, perhaps most worryingly, some versions of this video (for example this one on Twitter) end with a view of the setting of the houses in the foreground:
The setting of the houses in the foreground of the Phyuthan landslide. Still from a video posted to Tiktok by aashishsenchury10.
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This appears to show that the houses have been built adjacent to a very high, unsupported cut slope in colluvium. That does not appear to be a safe situation.
Dave Petley is the Pro-Vice-Chancellor (Research and Innovation) at the University of Sheffield in the United Kingdom. His blog provides a commentary on landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.