20 October 2021
A very late sting in the tail of the South Asian monsoon
As I have noted previously, the dominant continental scale meteorological phenomenon for landslides globally is the South Asian summer (SW) monsoon. In a normal year this develops in early June and withdraws through September. Heavy monsoon rainfall in mid October is not the norm.
But this year the summer monsoon has had a very nasty sting in the tail. Earlier this week I wrote about the serious landslides and floods in the Kerala area over the weekend. In the last couple of days it has been the high mountains of India and Nepal that have been affected.
In Nepal the rainfall has been very serious. The Department of Hydrology and Meteorology tweeted data and a map of rainfall totals across the country:-
Most parts of Sudurpachchim province received precipitation of more than 150 mm in 48 hours. A station in Dadeldhura district recorded 502.2 mm in 2 days. For real time rainfall information, pls visit https://t.co/xfWfmbmEq3#Flood #landslide #Nepal pic.twitter.com/AxJPiQp7Ya
— Climate Analysis Section_DHM (@ClimateDhm) October 19, 2021
In Dadeldhura District in the west of Nepal rainfall totals on 18-19 October exceeded 500 mm. The consequences across the country are all too predictable – the Kathmandu Post reports that at least 18 people have been killed and a further 24 people are missing, with reports still coming in. This includes a probable debris flow that killed four people in Doti and three people killed in a landslide in Baitadi. The worst event might have occurred in Dikla village of Thalara Rural Municipality, Bajhang, where 24 people are reported missing in a landslide that buried seven houses.
Dr Basanta Raj Adhikari tweeted a video of landslides on the famous Dharan-Dhankuta highway, which is the best engineered mountain road in Nepal:
A number of landslides have blocked the Dharan-Dhankuta Road. pic.twitter.com/vvFvH2tyHK
— Dr. Basanta Raj Adhikari (@basanta58_raj) October 19, 2021
Meanwhile, in Uttarakhand in India the late monsoon rainfall has also had a devastating impact. Reports indicate that at least 47 people have been killed, with more reported missing. A serious incident occurred at the Ramgarh area of Bhawali Tehsil, Nainital, where a landslide killed nine people. India Today has this image of a landslide on the Askote-Jauljibi road in Pithoragarh:–
19 October 2021
The Mira Mar landslide in Albany, Australia
In the Mira Mar suburb of the city of Albany in the southern part of Australia a landslide is slowly destroying a number of houses. I have covered such events before around the world – when this occurs it is devastating for the home owners.
The landslide, which has been moving since at least August, has been linked with heavy winter rainfall. The location is Sleeman Avenue, which can be seen in the image below:-
Three houses have been evacuated and a further three are threatened. A part of Sleeman Avenue has collapsed. This is a site that would benefit from drone footage to understand what is occurring, but GWN7 News has posted a video on Facebook with a series of images that are useful:-
This image, which I think was taken from Sleeman Avenue, shows a very large rear scarp with substantial vertical and horizontal movement. Meanwhile the image below, presumably taken from lower down the slope, shows serious deformation within the landslide mass that is causing structural damage to the houses:-
A 2013 City of Albany report noted ground movement on Sleeman Avenue, where cracks in the road surface had appeared.
The Mira Mar residents link the landslide to a water main leak on 30 July, possibly caused by movement of the ground. This scenario is not unusual – movement of the soil causes the failure of a water pipe that then feeds more water into the ground, exacerbating the problem. The role of the water pipe rupture is disputed by the operators of the water main:
Water Corporation Great Southern regional manager Adrian Stewart said initial findings from geotechnical surveys commissioned by the authority and the City of Albany suggest above-average rainfall in winter and an “extreme Albany storm event in late July” likely caused of the slip.
Mr Stewart said the burst water main released about 70,000 to 140,000 litres of water, compared to the estimated 2.7 million litres of rain in winter.
Whilst it is impossible to draw any conclusions without detailed investigations, I do not believe that the role of the water main should be discounted so simply. First, if the water main fed 70,000 litres or more of water into the slope in a short period (a day or two) then at that particular time it might have been very material to the stability of the slope. And second, when slopes are very close to a factor of safety of one comparably small amounts of water can be enough to trigger failure.
That is not to say of course that the water main was responsible, but I do not think it can be ruled out without a proper survey.
18 October 2021
Multiple fatal landslides in Kerala, India
Heavy rainfall in Kerala, SW India, since Friday has triggered landslides and floods that have killed at least 26 people. It appears that most of the deaths have occurred in landslides and debris flows.
A large failure occurred at Poovanchi, destroying five houses and killing at least seven people. The Indian Express has a good image of the landslide:
The landslide is apparently about 500 m long. The Indian Express article links the failure to unregulated local quarrying:
But was that purely an instance of natural calamity? Not necessarily. Local people suspect the landslide in Poovanchi has more to do with man’s greed than nature’s fury. Poovanchi is located in an area made fragile by unregulated quarrying. A hill in the remote village has more than two quarries. The granite quarry on the opposite side of the hill, where the landslide happened, has scooped out a portion equal to what was lost to the landslide.
Unfortunately I am unable to find an image of the source area to verify whether quarrying might have played a role.
A further significant landslide occurred at Kavali in Koottikkal in Kerala, in which six people were killed:-
Three of the people killed were children, aged 14, 12 and 10.
Kerala, located on the west side of India, frequently suffers from landslides during the monsoon. However, this event is comparatively late in the annual cycle. It appears that the heavy rainfall is now subsiding, which should allow the recovery operations to be completed. Heavy rainfall has affected other areas of South Asia in recent years. The Melamchi area of Nepal has once again suffered from serious damage, and there are warnings of rainfall across other areas of Nepal.
15 October 2021
Indications of landslides on Google Street View
Yesterday I was reading an article (Rayes-Carmona et al. 2021) in the journal Landslides that described the movement of a large landslide on the banks of the Rules Reservoir in Spain. This slide, the El Arrecife Landslide, is a 14.7 million cubic metre creeping mass movement (location = 36.872, -3.491) that was detected comparatively recently. Analysis using historic InSAR data indicates that it is moving on average at about 2 cm per year, but that sections of the slope are moving at 26 cm per year. There are no immediate causes for concern, but clearly the landslide needs careful attention.
This Google Earth image shows the slope in question:-
The slope shows few signs of classic landslide morphology such as obvious lateral scarps and a rear tension crack or scarp. There is a large spoil heap toward the toe of the slope on the centre right of the image – it is this feature that is showing the greatest movement, probably because the spoil is compacting – but the rest of the landslide is creeping.
An aspect of the paper by Rayes-Carmona et al. (2021) caught my attention:
The activity of the El Arrecife Landslide has been also evidenced by the N-323 National Road that runs across the landslide. This road has been consistently in need of repair work due to the existence of bumps, cracks, and partial collapses of the road pavement … In 2013, the Spanish Ministry of Public Works and Transport invested a total of 3.8 million Euros to repair 8 km of the N-323 National Road, which entailed the resurfacing of the pavement and the structural restoration of the northern abutment of the El Arrecife Viaduct …, located in the southern limit of the El Arrecife Landslide.
There is good coverage of this area in Google Street View. The image from June 2021 at the margin of the landslide looks like this:
The image beautifully captures the lateral margin of the landslide, with a large patch in the road where repairs have been needed. Note also the subsidence of the blocks on the downslope margin of the highway, coinciding exactly with the road repairs. These are classic indications of landslide movement.
The images also allow the history of movement to be determined. This image is from May 2011:
At this point a much larger repair to the road had been required. Note the lateral offset of the white line on the edge of the road, indicating relative motion. There is less evidence of vertical motion. Further down the road there is another large set of repairs, possible indicating an arcuate scarp defining a smaller area of more rapid motion.
In the image from May 2014 the road had been upgraded and repaired, such that the tarmac surface appeared undamaged. But by October 2018 cracks were reappearing and the curb side blocks were showing clear signs of movement. There is some evidence that this short section had been resurfaced once more:
Understanding landslides is often a fascinating piece of detective work, piecing together multiple strands of evidence to create a coherent understanding in the three dimensions and in time. That is one of the reasons why I love studying them so much. Google Street View can be a remarkably powerful tool to aid this process in the right circumstances.
Reyes-Carmona, C., Galve, J.P., Moreno-Sánchez, M. et al. 2021. Rapid characterisation of the extremely large landslide threatening the Rules Reservoir (Southern Spain). Landslides (2021). https://doi.org/10.1007/s10346-021-01728-z.
14 October 2021
Large rock slope failures on the Southern Patagonian Icefield
Loyal reader Hernán De Angelis has very kindly highlighted two very interesting large rock slope failures on the Southern Patagonian Icefield (SPI) at Glacier Amalia. He has written about these on his blog, including some excellent satellite images. I decided to take a look at them using Planet Labs imagery.
The first that he has highlighted occurred between 24 and 27 March 2018 at -50.919, -73.601. This is a Planet Labs image of the aftermath of the landslide, with a large volume of debris sitting on the glacier:-
Hernán has run the stats on this failure – it has a surface area of 1.6 square kilometres, with a runout length (on the glacier of 1.6 km – about a mile) and a width of 1050 metres. There are also some smaller failures, such as the one on the very right of the image. Interestingly, on flickr there is an image of the landslide deposit on the glacier.
Hernán has identified a second event a little to the east of this location on the Southern Patagonian Icefield, this time in 2019. This can be seen in a partially obstructed image on 28 April 2019 but the first image that captures it clearly is on 8 May 2019, when it was covered in a layer of snow:-
This is a slope failure on a similar scale – about 1.6 square kilometres surface area. It is about 1,100 metres long (on the ice) and about 1,600 metres wide. Including the source area the length is about 2.5 km.
Hernán has pointed out that an abstract for the AGU Fall Meeting in 2019 (Van Wyk de Vries et al. 2019) mentions two landslides of this scale on the flanks of Reclus volcano. This is likely to be these two events. This what they wrote:
We identified a series of large debris avalanches from the volcanoes, suggesting that previously stable slopes have been disrupted. Two large (1-5 km2) avalanches occurred on the north flank of Reclus over the last two and a half years, and one 12 km2 avalanche occurred on the north flank of Lautaro earlier this year. Here we present a detailed description of the conditions preceding each collapse, and the properties of each collapse. The Reclus collapses are inferred to have been mostly unconsolidated rock, with moderate to low cohesion. The 2019 collapse was the larger of the two and settled onto Amalia glacier, causing local speedup and slowdown, possibly due to the loading of the ice.
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
Van Wyk de Vries, M. S. ; et al. 2019. Large Volcanic Landslides on the Southern Patagonian Icefield and Linkages to Glacial Retreat. American Geophysical Union, Fall Meeting 2019, abstract #V52C-07
13 October 2021
The Chgega landslide in Tunisia
The Chgega landslide is an interesting and unusual slope failure located close to the village of Tahint in the Mateur region of northern Tunisia (36.901, 9.521 is the location – it is very clearly visible on Google Earth). Every landslide is of course unique, but this one is quite unusual. The landslide is described in an article in the journal Remote Sensing (Gaidi et al. 2021), in which the authors have used a variety of remote sensing methods to examine its movement. There is also a short summary on the Terradue website, which includes this image:-
The landslide consists of a block of limestone that is 900 metres long and 400 metres wide sliding over a lower layer of clays and marls. The hill has a peak of 553 m asl, whilst the toe of the landslide is at about 395 m asl, giving a vertical extent for the Chgega landslide of about 160 m. The landslide is characterised by a rear scarp in the form of a huge graben, which is about 800 m long and up to 120 m wide.
This area of Tunisia is subject to active tectonic deformation, and as a result has a significant level of seismic hazard. Documented earthquakes in this area of Tunisia include major events in 410 AD and 856 AD. Thus, it is possible that the landslide was initiated by, and indeed principally moves during, earthquakes.
In their research, Gaidi et al. (2021) used a combination of INSAR and photogrammetry to measure the annual movement of the Chgega landslide. They concluded that over 4.7 years it moved a total of about 1 cm. Thus, this is a landslide that in asiesmic conditions is undergoing very slow creep type movements.
The Chgega landslide is a beautiful example of a spreading type of landslide. It’s accessibility means that it is worthy of further investigation. I shall certainly be adding it to my bucket list of places to visit when I retire.
Gaidi, S., Galve, J.P, Melki, F. et al. 2021. Analysis of the Geological Controls and Kinematics of the Chgega Landslide (Mateur, Tunisia) Exploiting Photogrammetry and InSAR Technologies. Remote Sensing, 13 (20), 4048; https://doi.org/10.3390/rs13204048.
12 October 2021
A large rock slope collapse from Punta dei Ross, Croda Marcora in the Italian Dolomites
On 9 October 2021 a large rock slope collapse occurred on the Punta dei Ross, Croda Marcora in the Dolomites of northern Italy. The failure was captured on a series of videos that have been posted online.
Probably the best video of a part of the failure process has been captured by Emanele Compagno and posted to Youtube. The really interesting part of the video starts at the 38 second mark:
The videos appear to show a major collapse that initiates near to the ridge line. As is often the case for large rock slope failures, it occurs in a series of collapses rather than in a single failure event. One of the videos shows the collapse of a pinnacle, but the fresh scar and presence of dust shows that this was not the first failure:-
It appears that after collapse the debris has gone through a near freefall stage and then transitioned into a rockslide or a rock avalanche.
Jan Beutel of the University of Innsbruck has tweeted about the event:
Local news are doing a great job with coverage of the developments https://t.co/olNtZUzkYN
— Jan Beutel (@jan_beutel) October 11, 2021
At altitude, refreezing of the #permafrost active layer just started. At #Matterhorn just slightly higher have just past the days with the highest displacement rates. Red in this plot means ~3cm/month in solid bedrock!https://t.co/xzNDiqq0U4 @uniinnsbruck @SLFDavos @ETH_en pic.twitter.com/UpWKA72meH
— Jan Beutel (@jan_beutel) October 11, 2021
The timing of the collapse is interesting, occurring as the temperatures are falling after the summer.
11 October 2021
An updated landslide inventory map for Attica Region in Greece
Guest post by Nikolaos Tavoularis, Engineering Geologist at NTUA, Greece
A new web GIS platform has been recently constructed for the Attica region in Greece, whose importance is increasing after the recent mega-fires that happened in north and western Attica county in the the first days of August 2021. This platform is going to be the basis upon which hazard and risk maps will generated for the area based upon dynamic trigger factors such earthquakes and rainfall. Attica region is a territory of 3810 square kilometres, in which almost half of the Greek population and more than 60% of the industrial production in Greece and high value properties and infrastructure is concentrated (Figure 1).
The cartographic products, as well as the GIS platform, will be used by civil protection agencies, public works authorities, planners, civil engineers, and researchers in landslides for urban planning and designing mitigation measures against potential slope failures caused by fires, floods and earthquakes (Figure 2).
For the time being, the landslide inventory and the resultant susceptibility map (depicted in a 1:100.000 regional scale in Figure 3) of the Attica Region has been generated. The research project, named DIAS, which was co-financed by Greece and the European Union (European Social Fund – ESF), covers a chronological period from 1961 up to 2020.
The identified slope failures were stored in a GIS database as spatial and tabular data, including information per slope failure such as: (i) geographic details, (ii) lithological composition – active faults, (iii) mass movement date – field survey date, (iv) type of movement, (v) triggering factor, (vi) landslide causes, based on Working Party on World Landslide Inventory (1990) findings.
Given that over the next five to ten years, very important civil engineering projects will be constructed in Attica county, the existence of a regional-scale landslide susceptibility map could be a very useful tool for supporting decisions in order to prevent the location of high-value constructions in unsuitable locations.
This work has been undertaken under the auspices of Democritus University of Thrace, Civil Engineering Department and the fruitful co-operation with George Papathanasiou (Associate Professor of Democritus University), Athanasios Ganas (Researcher at National Observatory of Athens, Institute of Geodynamics) and Panagiotis Argyrakis (Researcher from Peloponnese University).
Additionally, characteristic slope failures from this research were presented at the Safe Greece 2020 on-line conference, which took place on 14-16 October 2020 in Athens.
8 October 2021
Multiple landslides in Þingeyjarsveit and in Kinnarfjöll in Iceland
In recent days heavy rainfall has triggered multiple landslides in Iceland, at Þingeyjarsveit and in Kinnarfjöll. These are two settlements within 10 km of each other in the northern part of central Iceland. Fortunately there have been no casualties, but some houses needed to be evacuated to manage the risk.
At Þingeyjarsveit, a series of large failures occurred. The best image that I have seem that illustrates these landslides was published on mbl.is:-
This is an interesting set of landslides, apparently resulting from multiple shallow slips high on the slope. These have combined to generate a large scale open hillslope flow in which there has been entrainment of material. Such landslides are usually caused by a loss of suction forces and / or high pore water pressures as a result of high intensity rainfall.
Note that this main complex is not the only landslide – there are further slips on each side of the image.
This landslide, from the video, is something of a classic:
At Kinnarfjöll there were further multiple landslides. mbl.is has a rather spectacular image of these landslides as well:
The two main landslides in this image appear to be channelised flows with a great deal of entrainment of material. The lower failure has flowed out of the channel. Note that the soil and debris is very black – this may indicate volcanic materials. There are other, different, landslides present too – for example, there is a shallow failure with a debris trail in the top left of the image and a disrupted translational slide in the middle right.
These landslides are worthy of a detailed investigation.
6 October 2021
Heishui: a rockslide at a tunnel portal in Sichuan Province, China
Loyal reader Mark Shore has kindly highlighted an interesting rockslide that was caught on video in Heishui County, in Sichuan Province in China. The landslide apparently occurred on 30 September 2021. The two tweets below capture the event:-
Whilst the video below captures the aftermath and, at the end, some further landslide activity:
Clearly this type of event is exceptionally dangerous – it is perhaps surprising that there is no apparent landslide mitigation on the slope or around the portal given the obvious potential for rockslides at this site. According to a report in NTDTV.com, in Mandarin, the landslide occurred at 9:20 am at the entrance of the Xi’er Tunnel of National Highway 347 in Heishui County, Aba Prefecture, Sichuan. There were no casualties, but a transformer and a car were damaged.
Some reports suggest that an accident was avoided because a security officer at the site raised the alarm.
Mark has identified the likely location for the landslide, which is at 32.080° N, 103.181° E:-
Clearly this is a location with a high incidence of landslides, but it seems like that the slope above the tunnel portal shown in the Google Earth image has been quarried.