20 October 2020
Hanyuan County: an initial analysis of the 21 August 2020 landslide in China
On 21 August 2020 a significant landslide struck Hanyuan County in Sichuan Province, China, killing nine people. In a new paper published in the journal Landslides, He et al. (2020) provide an initial account of this event. It is impressive and unusual to produce a description of a landslide so quickly.
The image below, which was published by China News in the aftermath of the landslide, provides an impression of the scale of this failure:
He et al. (2020) report that the landslide, which is located at 29.341, 102.698, had a volume of about 5 million cubic metres, and dimensions of 880 m long, 280 m wide and a depth of about 20 m.
Prior to the landslide, Hanyuan County suffered two substantial rainfall events, on 16 August 2020 and 18 August 2020, which together deposited 149.5 mm of precipitation. Interestingly, He et al. (2020) report the following local observations of the development of failure:
“According to our visit to local villagers, intermittent ground deformation in the landslide area has been observed since August 17, 2020. From August 17 to 18, numerous cracks have developed on the ground, and the length and width of cracks increased slightly. On August 20, a series of new cracks appeared in the rear edge of the landslide area, and the crack depth exceeded 1 m. At 3:50 am on August 21, the sliding materials began to slip along the sliding surface, accompanied by “swoosh” sound and the sky of dust.”
Note the quite long gap between the rainfall and the final failure event.
He et al. (2020) indicate that the failure in Hanyuan County occurred in three stages, which initiated at the top of the slope. This initial failure loaded the material further down the slope, which progressively failed. Finally, the entire slope failed and underwent a fluidisation process (presumably static liquefaction) to generate a high mobility flow that was devastating to buildings in its path.
Interestingly of course, if the population had been able to understand the precursory signs of failure that they were observing then loss of life might have been prevented. Building capacity of remote communities to understand these signals continues to be one of the great challenges in landslide work.
Quickslide 1: Improved models of landslide tsunami
EurekAlert has a good article about new research to improve the modelling of landslide tsunami, being undertaken in Russia.
Quickslide 2: Learning lessons from the hazards faced by mountain railways
India and Taiwan are sharing information about how to preserve mountain railways. Landslides have been a major problem in recent years for both the Darjeeling Mountain Railway in India and Alishan Forest Railway in Taiwan. Climate change, and in particular the increasing intensity of the most significant rainfall events, is going to be a severe threat in the decades ahead.
He, K., Liu, B. & Hu, X. 2020. Preliminary reports of a catastrophic landslide occurred on August 21, 2020, in Hanyuan County, Sichuan Province, China. Landslides . https://doi.org/10.1007/s10346-020-01566-5
19 October 2020
Huong Phung: another deadly landslide in Vietnam
Early on Sunday 18 October 2020 a large landslide struck an army barracks in Huong Phung commune in Huong Hoa District of Quang Tri Province in Vietnam. This was the latest in a series of deadly landslides in Vietnam in recent weeks, triggered by heavy rainfall. It is the second event to kill a substantial number of soldiers.
The landslide, which happened at about 1 am, buried 22 soldiers in the barracks. As I write, it is reported that 17 bodies have been recovered, whilst the search continues for the other five. There seems to be little prospect of survivors at this stage.
The best image to illustrate the event that I have found is on the VnExplorer website, which seems to show a large collapse in deeply weathered soils:-
It is interesting to note that at least some of the building have not collapsed.
Quickslide 1: A landslide tragedy in Pakistan
Meanwhile in Pakistan, 15 people were buried in a minibus traveling bewteen Rawalpindi and Skardu. Reports suggest the vehicle was pushed off the road and buried. The prospects for survivors look bleak.
Quickslide 2: 20 years after the Gondo landslide in Switzerland
Swissinfo has a good article about the 20th anniversary of the Gondo landslide, which occurred on 14 October 2000. As the article notes, “the landslide swept away ten houses, the school, shops and the road. It also reduced most of the historic Stockalper Tower to rubble, leaving only the very oldest part of the building standing”. A total of 13 people were killed in the landslide, which was triggered by three days of heavy rainfall.
16 October 2020
Harrison Lake: newly discovered, large, ancient landslides in Canada
There is increasing interest in the hazards associated with large landslides into enclosed bodies of water, such as fjords and lakes. Examples include the famous Lituya Bay landslide and the ongoing concerns about the potential for a major failure at Barry Arm, both in Alaska. Clearly large landslides are a hazard in themselves, but in general the main worry is the potential for a destructive landslide-induced tsunami that can travel large distances in an enclosed water body.
An interesting open access paper has just been published in the journal Landslides (Hughes et al. 2020), which examines newly discovered deposits of three large landslides in the bed of Harrison Lake, in southwest British Columbia. The landslides were discovered during a bathymetric survey of the lake floor, and have then been investigated in more detail through seismic imaging. This is the location, as shown on Google Earth:-
The largest failure, termed the Mount Douglas landslide, which was a subaerial rock avalanche, has a volume of 2.4 million cubic metres. Of the other two, the Mount Breakenridge landslide, which was a rockslide, has a volume of 1.3 million cubic metres and the nicely named Silver Mountain landslide has a volume of 200,000 cubic metres. The landslide deposits are blocky and flow-like, suggesting that they were emplaced rapidly. Given the volumes, the two largest landslides into Harrison Lake, which both had a runout distance of over a kilometre, are likely to have been tsunamigenic.
As the Google Earth image above shows, the banks of Harrison Lake are populated, meaning that any future event could have serious consequences. Interestingly, Hughes et al. (2020) found that there is significant bulging at the base of Mount Breakenridge, “indicating that the slope continues to slowly deform and could be the site of a future landslide.” This clearly needs further investigation.
Understanding past landslides into lakes is a key to understanding future hazard. This study provides a really useful insight into the nature of previous rockslope failures into Lake Harrison. It would now be really interesting to see a model of the resultant tsunamis and also to date the landslide events.
Quickslide 1:The duel hydroelectric landslides in Vietnam
Rescuers have now recovered the 13 bodies of the soldiers killed by the second of the two landslides associated with the Rao Trang 3 hydroelectric scheme in Vietnam. That these people had been sent to rescue the vicims of the earlier landslide feels particularly poignant.
Quickslide 2: A nice landslide video from Costa Rica
With thanks to Tom Hodgson, there is a nice video of a large roadside landslide in Costa Rica on the CRHoy website. The landslide, which was triggered by heavy rainfall, occurred on the South Interamerican highway.
Hughes, K.E., Geertsema, M., Kwoll, E. et al. 2020. Previously undiscovered landslide deposits in Harrison Lake, British Columbia, Canada. Landslides . https://doi.org/10.1007/s10346-020-01514-3.
14 October 2020
A double tragedy: two landslides close to the construction site of the Rao Trang 3 hydropower plant in Vietnam
A double tragedy: two landslides close to the construction site of the Rao Trang 3 hydroelectric plant in Vietnam
Heavy rainfall has triggered landslides across a swathe of Vietnam in the last few days. The most notable event occurred on Monday at the construction site of the Rao Trang 3 hydroelectric plant, which located close to Phong uan commune in Phong Dien District, Thua Thien-Hue Province. Reports suggest that between 10 and 17 people were buried by the landslide, but information is extremely sketchy because of many other landslides in the area. Reports suggest that the alarm was raised by a local person, who climbed a mountain to make the call. That person has been out of contact since.
On Monday a rescue team of 21 people was dispatched to the site. At 11 pm they found that their progress was blocked by landslides on the road, and so they stopped at a rangers station for the night. Unfortunately, during the night a further landslide occurred, hitting accommodation for 13 of the rescue team. They have not been seen since.
Further rescue teams were dispatched on Tuesday, but at the time of writing the picture remains very unclear.
The location of this landslide is not been provided, but some Vietnam press reports seem to indicate that it is the set of hydropower schemes that can be seen on the river at (and upstream of) 16.409, 107.250:-
I have highlighted previously the unacceptable rate of fatal landslides associated with hydropower projects, especially in Asia. This is on top of a wide landslide problem in these projects, which causes extreme levels of economic loss. I have no sense that the industry is getting on top of this problem.
13 October 2020
The role of mycorrhizal fungi in preventing landslides
It is well-established that there is a strong inverse correlation between forests and landslides. In general, careless removal of woodland can increase the susceptibility to landslides, and sometimes the restoration of forest can be an effective way to stabilise slopes. I sometimes worry that we oversimplify this relationship – for example, restoration of slope stability through tree planting is far from straightforward, and in general requires professional input. And of course the ways that forests provide improvements in slope stability are far from simple too – indeed as this topic has been investigated in more detail it has proven to be more complex than had been appreciated (which of course is often the way).
There is an interesting piece on the Waldwissen.net website about the complexity of this relationship. This is not a new article – it was published in 2017 – but it points out an issue that I had not considered previously. The article comes out of a research project undertaken in Switzerland that looked at the ways in which vegetation influences slope stability. One finding was that plant diversity plays a key role:
“Forests containing a wealth of species, a diverse root structure and trees of various heights and ages are especially effective in increasing soil stability. The study also showed that slopes with ideal vegetative cover and root mass can remain stable up to 5° steeper than bare slopes.”
But the more interesting insight is that Mycorrhizal fungi can also play a key role:
“Mycorrhizal fungi, which live in a symbiotic relationship with plants and trees, can improve the stabilising effect of the vegetation.”
The term mycorrhizal does not refer to a type of fungus, but rather to the symbiotic relationship between different types of fungi and plants. The concept is that this relationship is key determinant of the ways that plants influence soil structure and texture, and thus the mechanical behaviour of the soil. The take home message is that improvements in slope stability can be optimised if both the plants and their associated fungi are carefully nurtured.
Quickslide 1: The village of Gardenstown in Scotland is being affected by a landslide
The Scotsman newspaper reports that a landslide in Aberdeenshire is threatening to close the only access road to Gardenstown.
Quickslide 2: improving the disaster warning system in Japan
The Asahi Shimbun has a good article about improvements that are needed to the disaster warning system in Japan. This focuses on a clearer set of warnings of the need to evacuate. There are lessons to be learnt here for many other locations.
12 October 2020
Landslide sessions at the AGU Fall Meeting in December 2020
The AGU Fall Meeting 2020 is almost upon us. This was the first year in several that I had been planning to attend; of course Covid-19 had put paid to that. In consequence the meeting will be virtual and will extend over a much longer period.
I will be interested to see how it works. The positives of course will be that we are all now used to online meetings; our carbon footprint is hugely reduced; and more people will potentially be able to attend as the costs are so much lower. The negatives will include the loss of face-to-face contact and those informal conversations over a coffee, lunch a drink or a beer; the impacts of time zones causing people to struggle to attend some sessions; and the challenge of blocking out other daily pressures (this will be a big problem for me, given my day job, and many others will face the same, especially in these CoronaVirus times).
Anyway, I thought I would pull out the main landslide sessions. The times are those in San Francisco:-
Monday, 7 December 2020
20:30 – 21:30: NH006 Debris Flows and Floods in Mountainous Terrain I
Tuesday, 8 December 2020
Monday, 14 December 2020
Tuesday, 15 December 2020
Quickslide 1: Mitigating the Tylorstown coal tip landslide in South Wales, but it isn’t anywhere near enough
The Welsh Government has released £2.5 million to pay for the remediation of the Tylorstown coal tip landslide, which failed in February. “However, the Welsh government has said the overall cost of the repairs and making Welsh coal tips safe is “significantly more” than £2.5M, with repair work in Rhondda Cynon Taf estimated at £82.5M in total.”
Quickslide 2: La Niña has been officially declared
9 October 2020
Rest and Be Thankful: the cause of the landslide problems
In recent years a key strategic highway in Scotland, the A83, has repeatedly been blocked by landslides at the rather beautifully named Rest and Be Thankful. This road provides the main access from north of Glasgow to a large part of western Scotland. The alternative routes involve a long detour.
I recently drove along the road, and stopped at the viewpoint to photograph the problematic slope. This is one of my images:-
This is a steep slope that is heavily dissected by drainage lines (channels). The underlying geology is the Beinn Bheula schist formation. In my experience schists are often associated with slope instability, but in this case the problem is the material that sits on top of the bedrock. At Rest and Be Thankful this is a comparatively thick layer of colluvium – deposits left from earlier phases of slope instability – and varying amounts of topsoil and peat. These materials are susceptible to failure in heavy rainfall. Unfortunately, as the intensity of rainfall increases due to climate change, and the United Kingdom is getting longer spells of rainy conditions as well, repeated failure is occurring. As the image shows (and note the bus for scale on the lift side of the image), there is a vast amount of potentially unstable material on the slope.
The image below highlights the nature of the instability:
Note the vehicles for scale again. This image shows multiple sources of instability, and at least one ongoing failure. Note also the extensive use of flexible barriers to attempt to retain the debris. The image illustrates why the capacity of these barriers is being exceeded by the regular slope failures.
As I drove through the very extensive works at this site I shot a video using a dashcam, which I have uploaded to Youtube:
An 18 year old Land Rover Defender is probably not the ideal stable camera car, and hence the video is a little wonky, but it gives a sense of the scale of the works at the site. It is hard to believe that we will not continue to see extensive disruption at this site into the future, despite the best efforts of the engineers. The road was closed yesterday (8 October 2020) as a precaution due to heavy rainfall.
Quickslide 1: 15 years after the Kashmir Earthquake
Yesterday was the 15th anniversary of the devastating 08 October 2005 Kashmir earthquake, which may have killed 100,000 people. Landslides were a very substantial cause of loss of life in that dreadful event.
Quickslide 2: Landslides on asteroid Bennu
A new paper in Science Advances describes probably the most exotic landslides to date – potential slope failures on Asteroid Bennu. The authors speculate that the asteroid has undergone rotational failure to generate longitudinal ridges. There is also some evidence of toppling failure.
8 October 2020
Post wildfire mudslide potential in the Pacific West of the United States
It is well-documented that 2020 has seen exceptional wildfire activity in California, spurred by drought, exceptional thunderstorm activity and, at least in the eyes of some, the legacy of management practices in forest areas. As I type the August Complex wildfire is being named the first gigafire, a fire that has burnt over 1 million acres (about 407,200 hectares as of 6 October 2020). This was started as 38 separate fires triggered by lightning in the middle of August. They have now morphed to form a huge, complex wildfire.
A legacy of these massive wildfires is the potential for mudslides and mudflows triggered by heavy rainfall in the forthcoming winter. There is good scientific evidence of this process, and such post wildfire mudflows have had a devastating impact in the past.
Loyal reader Ken has very kindly created a mosaic of eight recent Sentinel satellite infrared, atmospheric penetration images covering Washington, Oregon and California. The images are dated 29 September 2020, so do not capture the full impact of the August Complex wildfire. In this image, the areas burnt by the fires are rusty red-brown, healthy forest is blue, grasslands yellow, urban areas grey:-
This is of course a beautiful image, but the scale of the rusty red-brown (wildfire) areas is enormous, both in terms of the number of fire-burnt areas and in the size of many of them.
A month ago, the NOAA Climate Prediction Centre indicated that La Nina conditions are likely to prevail through winter 2020-2021:
A majority of the models in the IRI/CPC plume predict the continuation of La Nina (Niño-3.4 index less than -0.5°C) through the Northern Hemisphere winter 2020-21. The forecaster consensus supports that view, and favors a borderline moderate event (Niño-3.4 index near -1.0°C) during the peak November-January season. In summary, La Niña conditions are present and are likely to continue through the Northern Hemisphere winter (~75% chance).
La Nina conditions are quite variable, but in general they lead to drier than normal conditions in the southern part of this area, and wetter than normal in the northern part. So, in parts of this area, post wildfire mudslide potential is high.
Quickslide 1: The location of the Eyjafordur landslide in Iceland
In the comments to my post yesterday, loyal reader Fabien has successfully located the landslide at Eyjafordur. This is at 65.404°, -18.251°. I note incidentally that the problem with comments not displaying is back. I don’t know why the WordPress software does this.
Quickslide 2: A 1.2 billion years old rockfall in Western Scotland
National Geographic has a nice article, based on a paper in the journal Geology, on the geological evidence for a 250,000 tonne rockfall that occurred 1.2 billion years ago at Clachtoll in northwest Scotland.
7 October 2020
Eyjafordur (Eyjafirði): a large landslide in Iceland yesterday
With thanks to Iain Johnson (@iainjg), who posted this to Twitter, a large landslide occurred in the Eyjafordur (Eyjafirði) area of northern Iceland yesterday. This image, Tweeted by Iain, shows that this was a large and mobile slide:-
The landslide was also caught on video, which can be viewed here. The owners of the house close to the toe of the landslide appear to have had a lucky escape. The reports indicate that the landslide stopped about 100 m from the house (the camera lens has significantly foreshortened the distance in the image above).
A better impression of the scale of the landslide can be gained from this image, posted to mbl.is:-
Interestingly, the accompanying article reports that the area was not affected by heavy rainfall at the time of the landslide, but that in recent days individual rocks have rolled down the slope, perhaps suggesting precursory landslide movement.
There is a pretty good news report (in Icelandic) of the aftermath of the landslide, which includes this stunning aerial image:-
Quickslide 1: A Department of Disaster resilience in the Philippines
The Philippines is establishing a new Department of Disaster Resilience to “improve the government’s capacity for disaster risk reduction and management”. This is a very interesting and very positive move from a country that is subject to multiple hazards.
Quickslide 2: Nepal struggles to re-establish border trade with Tibet
The devastating landslides in the 2020 summer monsoon have meant that the Kodari border crossing into Tibet was closed for three months, causing serious economic harm. My Republica reports that it was reopened on Monday, but was then closed again on Tuesday due to Covid-19.
6 October 2020
Saint-Martin-Vesubie: Planet Labs images of the aftermath of the extraordinary flooding from Storm Alex
Saint-Martin-Vesubie: Planet Labs images of the aftermath of the extraordinary flooding from Storm Alex
As I noted yesterday, Storm Alex generated extreme levels of rainfall across much of Europe at the weekend, causing extensive damage. One of the locations that suffered the greatest impact was the village of Saint-Martin-Vesubie, located in the Alpes-Maritimes department to the north of Nice, and close to the border with Italy. Planet Labs have very kindly captured some high resolution SkySat imagery of the impacts of the storm, and have made the images available to me.
This is a an image of the area around the village prior to the storm – the image was collected in September 2018:
This is the same area of Saint-Martin-Vesubie, after the flood:
Note the very extensive damage along the channel to the west of the village. Comparison of the two images suggests that several structures have been lost. To me the level of change in the channel suggests more than simple flood damage, especially when compared to the channel to the east of the village. I wonder if the channel upstream became blocked and then breached to generate this level of catastrophic flooding.
It is worth taking a look at the image in more detail. This is the area in the immediate vicinity of the historic centre of Saint-Martin-Vesubie before the flood:-
This is the same area after the flood:
Quickslide 1: Imagery of the Barry Arm rockslide in Alaska
NASA has posted a very nice article, with some excellent images, of the Barry Arm rockslide in Alaska. It is easy to see from these images why this site is such a concern.
Quickslide 2: Gender and natural disasters
The ever excellent Nepali Times has a good article on why natural disasters in Nepal kill more women than men. The conclusion is that “Women bear the brunt of most disasters like floods, earthquakes and landslides in Nepal because the countryside has been ‘feminised’ by the outmigration of men. And it is the women who tend to be inside the house more often than men”. In addition, “women have less access to information and seldom participate in disaster learning skills. Socio-cultural perceptions of sexuality and traditional beliefs about gender responsibility also put women at greater risk in disasters.”
These are really important issues; addressing them needs to be a part of the ways in which communities build resilience to natural disasters.
Reference and acknowledgement
Planet Team (2020). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
Thanks to my friends at Planet Labs for collecting the images and making them available to me.