3 August 2020
Yigongxiang: a valley blocking debris flow in Tibet
On 2 August 2020 a Twitter user named Swapna (@swapna_apsrsac), a specialist in remote sensing, tweeted news of a valley-blocking debris flow high in the mountains of Tibet. The location is extremely remote, located upstream of Yigongxiang in Nyingchi, Tibet. This event is reported in the Arunachal Times in some detail. This reports that the landslide was spotted from satellite imagery – if so that was a very shrewd piece of detective work. The article is by Chintan Sheth (@blueczkfox), who suggests that it might have been triggered by recent seismic activity in this area.
This part of Tibet is very difficult to image in August due to extensive cloud cover. It is located at 30.428, 94.547 if you wish to see the location – this is close to the termination of a glacier in rugged mountain terrain. The only optical satellite to have captured it as far as I am aware is an ESA Sentinel 2 image from 27 July 2020:-
The debris flow appears to have come from the western side of the valley. It is large – the barrier appears to be about 500 m wide, and probably over a kilometre long. A lake has developed upstream (to the north). This appears to have been about 1.5 km long on 27 July.
The images are partially obscured by cloud. A better understanding can be gained from a false colour image, in which vegetation shows as red, bare rock as a light brown and water as cyan. Cloud is still white:-
For reference, this is the site on 2 July 2020:-
There is a risk here of a breach of the landslide dam and a subsequent flood downstream. It is not possible to estimate the magnitude of the risk at this site, but further investigation and monitoring is needed urgently.
Quickslide 1: Deadly landslides in South Korea
South Korea is suffering a spell of heavy rainfall that has triggered extensive flooding and landslides. The spell of poor weather is expected to extend into Tuesday.
Quickslide 2: Continued landslide losses in Nepal
The toll from fatal monsoon-induced landslides in Nepal continues to rise in a manner that is alarming. In the most recent incident, eight people appear to have been killed in a landslide at Melamchi in Sindhupalchok.
29 July 2020
The Niushou landslide in Jiangsu Province, China
The journal Landslides has an article (Li et al. 2020) in its Recent Landslides section describing the interesting Niushou landslide, located in a tourist area in the region administered by Nanjing City in Jiangsu Province, China. This is located at 31.912, 118.740. This is the site as depicted in Google Earth:-
Niushou Mountain is an important cultural area, home to over 30 Buddhist temples. To accommodate visitors, a project was initiated, as the works in the image above show, to construct a hotel for the Atila group. This was a large project, including 29 villas as well as the main hotel complex, over an area of about 24,000 m2. The image, from Li et al. (2020), below shows the site in June 2016 – the image is taken looking downslope:
Li et al. (2020) report that after construction of the hotel began, a tension crack developed upslope of the hotel in June 2015 (marked in red on the image above). I assume, although this is not explicitly described in the article, that the slope had been cut to create the platforms for the hotel complex. Movement developed during heavy rainfall.
From summer 2015 to March 2016 efforts were made to stabilise the site with piles, anchor cables and drainage. However, on 11 June 2016 the slope failed during a further period of heavy rainfall, although the rate of displacement was low. Monitoring data indicates that the landslide has continued to move in periods of heavy rainfall.
Li et al. (2020) present a detailed investigation of the landslide, which has a volume of about 4 million cubic metres. It’s about 170 metres long and 105 metres wide with a maximum depth of 26.3 metres. Movement occurs on a weathered tuff layer with a mean slip surface gradient of about 10 to 12°. The paper does not describe whether this was a pre-existing area of instability (i.e. a relict landslide), but my interpretation of the morphology of the site suggests that this could be the case.
It is clear that the excavations for the hotel project activated (or reactivated) the slope, which failed when groundwater levels were high. Li et al. (2020) note that the 2016 rainfall event was unprecedented – it is likely that we are seeing the combination of design issues and increased rainfall from global heating.
As a consequence of the Nuishou landslide the hotel project has been abandoned, with a direct economic cost of 30 million RMB (US$4.3 million) and a potential total economic cost of up to 150 million RMB (US$21.5 million).
Quickslide 1: landslide costs in Nepal continue to mount
There are various reports this morning of further fatal landslides in Nepal, including up to ten fatalities in Rukum and Kalikot.
Quickslide 2: landslides along the Istanbul Canal
The Istanbul Canal is a proposed waterway between the Black Sea and the Sea of Marmara. A recent study has identified 267 landslide zones along the alignment.
Li, Z., Zhang, F., Gu, W. et al. 2020. The Niushou landslide in Nanjing City, Jiangsu Province of China: a slow-moving landslide triggered by rainfall. Landslides (2020). https://doi-org.sheffield.idm.oclc.org/10.1007/s10346-020-01441-3
28 July 2020
Mapping landslides in Nepal
Heavy monsoon rainfall continues to drive landslide losses across Nepal. As in all disasters, a key aspect of an appropriate response is highly quality spatial data. In the summer of 2019 the National Emergency Operation Centre (NEOC), a part of the Ministry of Home Affairs, launched a new disaster management portal (bipad.gov.np) to provide high quality data. It collates and displays spatial data for a range of natural and anthropogenic hazards, including floods, landslides, GLOFs and fires. The data can be displayed in a variety of formats, including events for the last 3, 7 and 14 days, as well as having a customised date range facility.
This is the distribution of recorded landslides for the last seven days, as of 7 am (UK time) on 28 July 2020:-
Each brown dot here is a landslide event recorded in the last seven days, with the size of the dot representing the losses (see the key in the bottom left corner). The tool indicates that 16 landslide related fatalities were recorded in this period. Note the cluster of landslides in the centre of the country – it is interesting to compare this with data on precipitation over the same period, using the NASA Global Precipitation Measurement system, mapped with the GPM IMERG Global Viewer tool:-
Note the area of higher levels of rainfall in the centre of the country, which corresponds with the area of higher levels of landslides.
The map below shows the reported landslides over the last 28 days:-
In this period the tool has records for landslides that resulted in 111 deaths.
Very few countries have a publicly accessible database of disaster information of this quality. Nepal deserves great credit for setting up such a system.
Quickslide 1: An Irish peat bog landslide in 1896
The Irish Examiner has a story about a peat bog landslide at Shass Mountain that killed eight people, of whom six were children. The landslide had a runout distance of up to 8 km.
Quickslide 2: A journal article about the Brumadinho tailings dam failure
The journal Landslides has published a research article (de Lim et al. 2020) about the Brumadinho ( Córrego do Feijão) tailings dam failure in 2019. It concludes that the event can be caharcterised in four phases: “(a) a rotational slide which destroyed the complete dam structure; (b) a debris avalanche; (c) a debris flow; and (d) a mudflow, composed by a mixture between tailings material and the soil.” The article has been placed on Research Gate, so you can request a copy from the authors.
de Lima, R.E., de Lima Picanço, J., da Silva, A.F. et al. 2020. An anthropogenic flow type gravitational mass movement: the Córrego do Feijão tailings dam disaster, Brumadinho, Brazil. Landslides https://doi.org/10.1007/s10346-020-01450-2
27 July 2020
Liujing Village: a large, ongoing valley-blocking landslide in Chongqing, China
The landslide has partially blocked the the Yancang River, a tributary of Wujiang River, and a lake has developed, although at this stage the size of barrier is not large:-
In the Xinhua article the estimated volume of the landslide is 1.3 million cubic metres, which would seem to be about right to me. In the upper reaches of the landslide the recent displacement is large. In the image below, the displacement of the road appears to be in excess of 20 metres:-
Interestingly though, the blockage of the valley is being caused not this part of the landslide, but by a more active flow on the true left (i.e. the left side when facing downslope) of the landslide. This more dynamic part of the landslide is captured in the image below:-
Thus, at the moment only a small portion of this landslide is causing the valley-blockage. If a greater part were to become active then a much larger barrier could develop.
Quickslide 1: a violent landslide caught on video in India
An energetic landslide was caught on video in India this morning:
#WATCH Uttarakhand: A landslide occurred near ITBP camp in Gauchar of Chamoli district this morning, blocking Badrinath Highway. The operations to clear the highway is underway. pic.twitter.com/UHaP1AGnih
— ANI (@ANI) July 27, 2020
Quickslide 2: Continued landslide problems in Nepal
The unusually active monsoon in Nepal continues to cause substantial problems. My Republica reports that the road to the border crossing to Tibet at Rasuwagadhi has been blocked by landslides since Thursday. The price of fruit and vegetables across the country has risen 50% because of the blockages to the major transportation routes. Unfortunately, in a Tweet this morning, the National Emergency Operation Centre warned of further heavy rainfall this week.
24 July 2020
The deadly start to the monsoon season in Nepal
Loyal readers will know that I have a particular interest in landslides in Nepal, having been undertaking research on that topic since 2000. Nepal is one of my favourite places in the world, with a beautiful landscape and wonderful people. It has two vices however, both of which are a huge impediment to a thriving economy. The first is a largely dysfunctional political system, which has reeled from crisis to crisis over the last 20 years (I strongly recommend Sam Cowan’s articles on this topic). The moral of the story is that it is bad news to be the junction between the world’s two most populous countries, and the malevolent influence that they both exert with casual ease.
The second is of course a terrifying range of natural hazards, including high seismic hazard, GLOFs, flooding and landslides. The latter are triggered by occasional earthquakes (and of course their aftermath) and the annual summer (southwest) monsoon. The monsoon develops through the months of July, August and September, bringing heavy and prolonged rainfall. But, the strength of the monsoon varies a great deal from year to year, meaning that the landslide outcomes are also highly variable.
The graph below shows the number of fatal landslides, and the resultant loss of life, that I have recorded in Nepal since 2004. It includes data up to 20 July 2020:-
The data shows the extraordinary variability in landslide impacts in Nepal from year to year – compare for example the number fatal landslides (the red line) in 2018 and 2019.
Back in 2015 I wrote about the seasonality of landslides in Nepal, and in particular the variability through the monsoon. July is the peak month, but large numbers of landslides occur in August and September too. The graph above shows that by 20 July, the number of fatal landslides in 2020 (43) had already exceeded the average annual total for the period 2004-2019 (36).
This suggests that Nepal is likely to have a particularly high total number of fatal landslides this year. The level of disruption is already high. It once again strengthens the argument for the need for a national agency to manage slopes across the country.
Quickslide 1: The cost of the peat slide in Ireland
Work continues in the aftermath of the large and amazing peat bog landslide in County Leitrim in Ireland. The estimated cost is over 5 million Euros.
Quickslide 2: Another landslide warning in Japan
Heavy rainfall is forecast in western Japan over the weekend. Landslide warnings are in place once again.
22 July 2020
Qingjiang River: an unusual valley-blocking landslide in Hubei Province, China
On 20 July 2020 a very large landslide occurred in the Enshi Tujia and Miao Autonomous Prefecture in Hubei Province, China, blocking the Quinjiang River. The Xinhua report for this event indicates a volume of about 10 million cubic metres. The main valley was blocked and a barrier lake developed, although it has now breached safely.
I cannot find any images of this landslide in the English language media, which is a shame as it is an impressive event. A quick search for Hubei landslide in Chinese (湖北滑坡) yields a number of images on Chinese news sites. This is the best overview of the landslide that I have found:-
This appears to be a large, mobile earthflow type landslide, The nature of the material suggests to me that it is probably a failure in a thick loess deposit, although this needs to be confirmed. The original failure is surprisingly deep-seated and broad, butt appears that there is little or no failure in the underlying bedrock that forms the gorge.
There is a good drone video of the landslide on Youtube. You will need to excuse the corny music (I recommend that you turn the sound off), but it provides a really good sense of the nature of the failure. The blockage on the Quinjiang River had breached at the time of the video:-
Chine continues to undergo extremely heavy and prolonged rainfall, and there is another Yellow rainfall warning in place today for a large swathe of the country. These conditions are likely to set off an increasing number of landslides. The combination of saturation to a deep level (as the Qingjiang River landslide indicates) and high intensity rainfall (the current forecast includes rates of up to 70 mm per hour) is ideal for promoting slope failure.
Quickslide 1: The Skredkallen landslide in Norway
Yesterday, Louise Vick tweeted some nice images of the Skredkallen rock slope failure in Norway. I’d like to visit this one!
This summer I FINALLY have time to write up my project on the Skredkallen #rockslopefailure. The active slope overlies a large old deposit which displays remnants of marine transgressions. This work has been baptism by fire for me in terms of Arctic coastal geomorphology! pic.twitter.com/olVKzB3Did
— Louise Vick (@LandslideLouise) July 21, 2020
Quickslide 2: Continued landslide mayhem in Nepal
Nepal continues to suffer a high level of losses from landslides as abnormally heavy monsoon rainfall affects a large part of the country. Nepal News has a nice summary of the rainfall that is causing these problems. As with China, these issues will become increasing severe as the rain persists.
21 July 2020
Rio Coca: a valley-blocking landslide in Ecuador caught on video
On 18 July 2020 a substantial landslide occurred on the Rio Coca in Ecuador, blocking the river. The landslide occurred between the Montana and Marker river junctions, is located in El Chaco canton in Orellana. The image below, published in El Universo, shows the aftermath of the landslide:-
The landslide has occurred on the outside of the river bend – a classic location for undercutting of the river to create instability – in weak (possibly volcanic) deposits.
This landslide is remarkable because both the initial failure and the breach event have been caught on video. This is the video, posted on Youtube, showing the failure:-
I am not sure as to the circumstances in which this video was captured, but am impressed by the coolness of the people at the site. The video is interesting in that it captures the precursory deformation of the landslide block.
A video of the breach of the landslide dam on the Rio Coca has also been collected and has been posted to Twitter:
.#Deslizamiento – Así fue el desfogue del represamiento del río Coca la tarde de ayer.
Se represó por un deslizamiento en la confluencia con el río Marker.
— ESPECIGEST (@ESPECIGEST) July 19, 2020
Whilst a video has also been posted to Youtube that shows the breach event underway:-
Reports suggest that the landslide was triggered by heavy rainfall and that the breach occurred about four hours after the initial failure. Whilst there is considerable erosion downstream, the nearest community on the Rio Coca was located about 50 km downstream, so little damage occurred.
Quickslide 1: Another valley-blocking landslide
Xinhua reports that a landslide has blocked a valley on the Qingjiang River, a tributary of Yangtze River, in Enshi Tujia and Miao Autonomous Prefecture, Hubei, China. Evacuations are underway.
Quickslide 2: Continued landslide damage in Nepal
Heavy rainfall associated with the monsoon continues to cause loss of life and extensive damage across Nepal. Many roads are blocked by landslides and, according to the DRR portal, at least 117 lives have been lost to landslides since the beginning of June. There is increasing awareness in Nepal that poor quality road construction is a major factor behind these landslides, an issue that we highlighted in a paper (Petley et al. 2007) 13 years ago:-
It is concluded that a major component of the generally upward trend in landslide impact probably results from the rural road-building programme, and its attendant changes to physical and natural systems.
Petley, D.N., Hearn, G.J., Hart, A. et al. 2007. Trends in landslide occurrence in Nepal. Natural Hazards 43, 23–44 . https://doi.org/10.1007/s11069-006-9100-3
17 July 2020
Satellite imagery of the Myanmar jade mine landslide
Myanamar in the summer is not an easy place in which to acquire satellite imagery, because of the high incidence of cloudy conditions. This has meant that tracking down the site of the 28 June 2020 Myanmar jade mine landslide has been difficult. However, fprovost posted an article on Discuss that highlights the use of Sentinel-1 radar imagery to identify the site. Radar can see through cloud, but is hard to interpret. Change maps are the answer for large landslides, allowing the site to be pinned down to 25.477°, 96.259°.
The advantage with Planet Labs daily imagery is that it allows far more opportunities to capture an image. This is an image of the site before the landslide, collected on 18 May 2020 when the conditions for capturing imagery were better:-
The extraordinary level of environmental degradation caused by the jade mining activity in the Hpakant area is clear. Note that this does not appear to be well organised mining – look how close the houses are to the edge of the mine workings for example.
This an image after the landslide, captured on 10 July 2020:-
The slope failure is just to the north of the position marker in the image, travelling roughly towards the east into the lake. It is not a huge failure – about 400 m x 400 m. The problem of course was the number of people on the slope at the time, and the displacement waves in the flooded pit bottom. Although the site is in shadow, the landslide is clear.
The image below is from Google Earth, from December 2018, showing the mining operations at the site:-
The image above shows the extremely large-scale of the mining operation at this site.
Quickslide 1: More fatal landslides in Nepal
This morning a further fatal landslide occurred in Nepal, with a family of three being killed in Machhapuchhre Rural Municipality in Kaski. Meanwhile, up to five people have been killed by a landslide at Pulpingkatti in the Bhotekoshi rural municipality in Sindhupalchowk.
Quickslide 2: Old Fort Road reopens
Planet Team (2020). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
15 July 2020
Cromwell: helicopter sluicing to manage a landslide
An interesting landslide problem, and an unusual management approach, are under way at Cromwell on the South Island of New Zealand. The problem is a large rock slope failure that has developed at a critical road junction, between State Highway 8 and State Highway 8B, at Deadman’s Point Bridge. The image below, distributed by NZTA, shows the development of this slope failure and the obvious hazard to the road:-
This appears to be a wedge failure with substantial displacement in the rear scarp. The landslide is actively deforming. Clearly there is a high chance of a collapse event. To manage the hazard the road is closed at night.
In the aftermath of the Kaikoura earthquake, the transportation authorities had some success in using helicopter sluicing to manage slopes. This technique uses 1000 litre underslung buckets to deliver water onto the slope. This video, posted to Youtube, shows this operation underway at Cromwell:-
NZ Transport Agency (NZTA) said this morning that sluicing work, involving helicopters with monsoon buckets dropping water on the slip, would continue and traffic would be stopped for up to 30 minutes at a time.
“This sluicing work will continue for the next few days at least until we are sure the hillside is again stable.”
NZTA maintenance contract manager Mark Stewart said after dropping 150,000 litres of water to control and flush the landslip yesterday, helicopters and crew got to work again about 9.30am this morning.
I haven’t seen this approach used much outside of New Zealand – it is certainly an interesting way to manage a slope.
The Cromwell Gorge is one of the most famous landslide sites globally. Detailed monitoring of slope behaviour in the large creep landslides continues.
Thanks to John Davies and Scott Johnson for highlighting this one to me. Much appreciated.
Quickslide 1: Cape Kidnappers risk assessment
Also in New Zealand, the Department of Conservation (DOC) has released the Quantitative Risk Assessments of the Cape Kidnappers site following the landslides there, which injured two people. The documents are a very interesting exemplar of how to undertake this type of work. Scoop has published some expert analyses of this work.
Quickslide 2: Mudslides and landslides in Indonesia
Heavy rainfall in North Luwu district of South Sulawesi province in Indonesia has killed 16 people and left 23 missing. Whilst the reports blame flash floods and landslides, the images appear to show the aftermath of mudslides. Information is a little sketchy at this point.
14 July 2020
Deadly monsoon-induced landslides in Nepal in the last few days
Over the last few days intense monsoon rainfall in Nepal has triggered a wave of landslides that have caused extensive loss of life and damage. Worst affected appears to be the district of Myagdi in the central part of Nepal, one of the former Hill Districts of alpine height mountains. There, 27 people are known to have died and a further four are reported to be missing.
The most significant landslide appears to have occurred in Dhaulagiri Rural Municipality, where 18 people were killed, whilst eight people died in Malika Rural Municipality and one person was killed Raghuganga Rural Municipality.
Meanwhile, on Sunday another landslide struck Besinda, in Sankhuwasabha District at about 1 a.m. Eleven people are reported to have been killed, whilst four were rescued with injuries.
There is less clarity about a landslide that occurred on Sindhupalchowk District, which has suffered repeated landslide events since the 2015 earthquake. Three fatalities have been confirmed, but up to 20 people are reported to be missing.
In Jajarkot District, landslides in Borekot Gaunpalika-4 and elsewhere are reported to have killed ten people, whilst in Kaski there are reports of landslides at Sarangkot (five fatalities), Hemja (one fatality) and Paitedanda (one fatality).
Yesterday, a series of landslides in Tanahun District is reported to have killed another ten people and to have left two more missing.
On Twitter, @basanta58_raj has been posting and retweeting images of some of the landslides. This image shows the landslide at Barekot Gaonpalika-4 in Jajarkot, which I note above:-
This is a fascinating image showing both channelised debris flows and open hillslope failures. Meanwhile, this image from Ghartigaun, also in Jajarkot, appears to show incising flows that have initiated on a road high on this hillside:-
Interestingly, there is increasing recognition in Nepal that a part of the problem is unconstrained and unregulated road construction. The Kathmandu Post has a good article highlighting this issue:-
However, disaster management experts say many of the deadly landslides were triggered by haphazard road construction that disturbed the slopes and natural drainage, while in the plains floods have been made worse by poorly designed roads, urbanisation of floodplains, deforestation and sand extraction in the Chure, as well as embankment building across the border in India.
Quickslide 1: Further landslide fatalities in Japan
Two people are thought to have been killed in a landslide at Higashihiroshima in Hiroshima Prefecture in Japan this morning.
Quickslide 2: Eight more landslide fatalities in India
The monsoon in India continues to trigger landslides that are causing substantial levels of loss. On Friday a series of landslides were triggered by heavy rainfall, killing eight people in Arunachal Pradesh.