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20 May 2022

The Mount Popa debris avalanche

The Mount Popa debris avalanche

Yesterday, in response to the coverage of the 42nd anniversary of the 1980 Mount St Helens flank collapse and eruption, Wang Yu (@Wangyu1979) tweeted a Google Earth image of the Mount Popa volcano in Myanmar.  This is my version of the image that he tweeted:-

Google Earth image of the aftermath of the flank collapse at Mount Popa in Myanmar.

Google Earth image of the aftermath of the flank collapse at Mount Popa in Myanmar.

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The image beautifully illustrates that Mount Popa has also undergone a flank collapse event (a flank collapse is an extremely large-scale landslide on the flanks of a volcano).  The huge gap in the side of the volcano is the scar of the landslide.

The sequence of events at Mount Popa is described in a paper published in 2018 in the The Journal of Volcanology and Geothermal Research (Belousov et al. 2018).  They demonstrated that Mount Popa underwent a catastrophic flank collapse about 8,000 years ago.  The resultant debris avalanche, which had a volume of about 1.3 cubic kilometres, travelled about 11 km from the former summit of Mount Popa.  The landslide debris is 5.5 km wide and on average 50 m thick.

By any standard this is a vast landslide.

On the Google Earth image below I have marked the approximate boundaries of the debris avalanche deposit – it is reasonably easy to see in the landscape at this scale:-

Google Earth image of the aftermath of the flank collapse at Mount Popa in Myanmar, marked with the approximate boundaries of the debris avalanche.

Google Earth image of the aftermath of the flank collapse at Mount Popa in Myanmar, marked with the approximate boundaries of the debris avalanche.

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Belousov et al. (2018) suggest that prior to the collapse, magma moved up through the volcano, whereupon the flank collapsed.  Unlike Mount St Helens, there is no evidence of a directed blast.  The landslide occurred in two stages, with an initial failure of about 1 cubic kilometre, followed by a smaller (0.3 cubic kilometre) secondary failure shortly after.  The subsequent volcanic eruption generated pyroclastic flows that are now draped over the landslide deposit.

There is no geological evidence of any volcanic eruption since this date, although some historical accounts suggest that some sort of small event occurred in the year 442 BCE.  What this represents is uncertain in the absence of any geological evidence.

There is no doubt that this site deserves more detailed investigation, but the scale of the geologically recent flank collapse at Mount Popa is truly epic.  These huge volcanic landslides are some of the most impressive landslides on Earth.

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Reference

Belousov, A., Belousova, M., Khin Zaw, Streck, M.J., Bindeman, I., Meffre, S. and Vasconcelos, P. 2018.  Holocene eruptions of Mt. Popa, Myanmar: Volcanological evidence of the ongoing subduction of Indian Plate along Arakan Trench. Journal of Volcanology and Geothermal Research, 360, 126-138.

 

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17 May 2022

The University of Hull

The University of Hull

This morning, the University of Hull has announced that it has invited me to become its next Vice-Chancellor, starting on 1 September 2022.  In the UK system, the Vice-Chancellor is the most senior academic and administrative officer of the University – a role that is not dissimilar in some ways to that of CEO in industry, but of course it is important to remember to be an academic.

The University of Hull

The University of Hull

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It will be an enormous honour and privilege to take on this role.  The University of Hull, located in the city of Kingston-upon-Hull in the East Riding of Yorkshire, was founded in 1927, and thus is the 14th oldest university in England. It is a campus based institution that provides an excellent student education.  It has a very strong research pedigree across a wide range of disciplines.  Through the appointment process I have been immensely impressed with the students and staff that I have met – they are passionate, ambitious and kind, with a real desire to make the world a better place.  The university motto is Lampada Ferens, which translates to ‘carrying the light of learning’.  The wonderful university community exemplifies that spirit.

The spirit of Hull

The spirit of Hull

I want of course to pay tribute to the current Vice-Chancellor, Professor Susan Lea, who will step down in August.  She has led the University through the challenging times of the last few years with skill and dedication.  It is the aim of all Vice-Chancellors to leave the institution in a strong position, ready to take advantage of opportunities.  There is no doubt that Susan has done so.  She has been instrumental in creating a University that provides a rich student experience, that is strong in research and that is supporting the region to flourish. She will be much missed.

Looking forward, I’m hugely enthused by the range of opportunities that lie ahead for the University of Hull.  The new strategy focuses on providing a world class education, on increasing research strength and on work with partners.  Underpinning this is a strong commitment to social justice and to sustainability. The University of Hull has committed to move to being carbon neutral for Scope 1 and Scope 2 emissions by 2027.  This typifies the ambition of the institution.

This means of course that I will leave my current institution, the University of Sheffield.  I have been here since November 2016, serving through that time as Vice-President and Professor of Geography.  I have loved being at Sheffield, and will depart at the end of August with an real sense of sadness.  It has been the happiest five years of my career.  The university community has achieved so much in that time, and it has been wonderful to play a small role in that.  I will write more about my time at Sheffield in due course, but let me say thanks to my colleagues and to the students here.  You are amazing.

Finally, I should say something about this blog.  I have been writing about landslides here for almost 15 years – I started in December 2007.  Whilst I recognise that a move to being Vice-Chancellor will mark the end (or at least a suspension?) of my research, my intention is to continue to write here regularly.  This blog links me to my original academic discipline, and I remain deeply committed to the reduction of losses from landslides.  I will of course write in my own time, before the start of my working day.  And I’ll continue to enjoy my interactions with all parts of the landslide community.

And so I will now start the process of moving to the University of Hull in a little over three months.  I do so with a sense of excitement and anticipation.  It will be a huge honour to take up the role.

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16 May 2022

Assam: damaging landslides at the start of the monsoon

Assam: damaging landslides at the start of the monsoon

Over the last few days parts of the state of Assam in NE India has suffered from serious rainfall, resulting in flood and landslides.  At least five fatalities have been reported, including three in a landslide in Dima Hasao district.  The Assam State Disaster Management Authority (ASDMA) produces a daily flood reportthe edition for 15 May 2022 indicates that seven districts have been affected – Cachar, Dhemaji, Hojai, Karbi Anglong West, Nagaon and Nalbari.  In total almost 57,000 people have been impacted by these events.  Over 4,000 people have been forced to seek refuge in relief camps.

The Central Water Commission has produced an online hydrograph for the Kopili River at Dibrugarh in Nagoan in Assam:-

Hydrograph for the Kopili River at Dibrugarh in Assam, from the Central Water Commission.

Hydrograph for the Kopili River at Dibrugarh in Assam, from the Central Water Commission.

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As the graph shows, the river is already substantially above the danger level, and is continuing to rise.

There are images of multiple landslides in Assam in the media.  A particularly dramatic example shows a suspended railway line after a very large-scale failure or washout – at present I am unsure of the location of this event:-

A large washout on a railway line in Assam, India

A large washout on a railway line in Assam, India. Image from Livemint.

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Meanwhile, the road network has also been severely impacted by the landslides.  This example is reportedly from Dima Hasao district:-

A landslide on a road in Dima Hasao district, Assam, India.

A landslide on a road in Dima Hasao district, Assam, India. Image from PTI via The Indian Express.

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Heavy rainfall is continuing in parts of Assam.  The Customized Rainfall Information System of the India Meteorological Department reports that Tangla in Assam had received 196 mm of rainfall on 16 May 2022 at the time of writing (07:00 UTC).  Thus, it is likely that damage is continuing to occur.

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12 May 2022

The Sakae village landslide in Japan

The Sakae village landslide in Japan

In the morning of 9 May 2022 a significant landslide occurred near to Sakae Village in northern part of Nagano Prefecture in Japan.  Saito Hitoshi (@GinHS) from Nagoya University has tweeted about this landslide, noting that it has partially blocked the valley:-

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A rough translation of the tweet is: “The slope collapse of Sakae Village, Nagano Prefecture. The estimated amount of collapsed sediment is about 140,000 cubic metres, and it seems that a small natural dam has also been created.”

In a further tweet he has pinpointed the location:-

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The link provides further detail of the site, which is centred on 36.813, 138.623.  The Google Earth image shows a small existing failure at this location.  The map above highlights that the Sakae Village landslide has occurred in terrain that has many existing failures, and that the topography of the site indicates that this is likely to be a reactivation.  The location on the outside of a bend in the river suggests that erosion of the toe is likely to have been a factor in the triggering of the most recent failure.

NHK has an article in Japanese that provides greater detail about the landslide.  It is about 100 m long, 200 m wide and about 7 m deep.  The estimated volume is, as noted above, 140,000 cubic metres.

The best image that I have been able to obtain is in a pdf document released by the Ministry of Land, Infrastructure, Transport and Tourism of Hokuriku Regional Development Bureau:-

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The video in the NHK article and the image above both indicate that there is water flow past the dam, indicating that the risk associated with valley blockage from the Sakae Village landslide is small.

Japan is probably the most capable country in dealing with landslides, based upon many decades of experience.

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10 May 2022

Bijie – a large rockslide, caught on video – in China

Bijie – a large rockslide, caught on video – in China

As we move through the northern hemisphere spring towards the summer we are most definitely moving into landslide season.  The latest notable event occurred on Sunday 8 May 2022 in Bijie village in Guizhou Province.  This event appears to be poorly reported in English language media at the moment, but there are better reports in the local media.  For example, 163.com reports that landslide occurred at Baiyan Community in Bijie City, Guizhou.  It is estimated that 25,000 cubic metres of rock were involved in the landslide, which appears to have detached from a steep mountain scarp.  The news reports indicate that the site remains unstable, with another 10,000 cubic metres being considered to be in a dangerous state.

The same reports indicate that there is likely to have been three fatalities from the event, although this in unconfirmed.

This image, also from 163.com, gives a very strong indication of the nature of the collapse:-

The rockslide at Baiyan community in Bijie, Guizhou on 8 May 2022.

The rockslide at Baiyan community in Bijie, Guizhou on 8 May 2022. Image from 163.com.

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There is a somewhat dramatic version of the videos from this event posted to Youtube – apologies for the music and the editing, but you get a good idea of the nature of the event:-

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You can also view it on the Accuweather site.  It’s worth a look.

In the videos, note also the fresh-looking rockfall scars on other parts of the rockface.  It is perhaps unsurprising that this area had been previously identified as having a high level of rockfall hazard. Reports indicate that the collapse followed rainfall, but the reported volumes do not seem exceptional for this area.

There are also reports of another rockslide in China, this time in Sichuan Province on Monday 9 May 2022.  The location is reportedly in Rongxian County.  Five people are reported to be missing.  At the time of writing the details of this event are sketchy.

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9 May 2022

The Lowell Point landslide in Alaska

The Lowell Point landslide in Alaska

On Saturday 7 May 2022 a substantial landslide occurred near to Lowell Point, in the Seward area of Alaska in the USA.  The landslide has blocked the only road into the community.

Must Read Alaska has a great aerial image of the landslide, taken by Chip Arnold:-

The Lowell Point landslide close to Seward in Alaska, USA.

The Lowell Point landslide close to Seward in Alaska, USA. Image by Chip Arnold, via Must Read Alaska.

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The landslide, which is located at about 60.093, -149.445, is estimated to be about 60 metres high and 90 m wide.  As of Sunday, the landslide was still considered to be potentially unstable, impeding clearance operations.

There are at least three good videos of the landslide, one from each side.  The start of this video shows the landslide from one side – note the attempts to clear the road before the main failure:-

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Whilst the other has a slightly better perspective from the other side:-

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The image below was taken by local landslide-watcher Harold Faust:-

The Lowell Point landslide close to Seward in Alaska, USA.

The Lowell Point landslide close to Seward in Alaska, USA. Image by Harold Faust.

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Note the landslide scar to the left of Sunday’s failure.  This event reportedly occurred a few years ago.

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Acknowledgement

Thanks to loyal reader Hig, who highlighted the event to me and identified the correct location.  He also passed on the image from Harold Faust.

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5 May 2022

Malvik: an interesting landslide on the E6 highway in Norway

Malvik: an interesting landslide on the E6 highway in Norway

On Wednesday 4 May 2022 an interesting landslide occurred on the E6 highway near to Malvik in Norway.  The site of the landslide appears to be 63.403, 10.804.  The best image that I have found of the landslide has been posted on the nettavisen.no site:-

The aftermath of the landslide at Malvik in Norway on 4 May 2022

The aftermath of the landslide at Malvik in Norway on 4 May 2022. Image posted on the nettavisen.no website, by NTB scanpix.

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One person was caught up in the landslide.  Fortunately he was recovered from the landslide in a conscious condition.  An image from tv2 shows the impact of the landslide on the road:-

The aftermath of the 4 May 2022 landslide at Malvik in Norway.

The aftermath of the 4 May 2022 landslide at Malvik in Norway. Image from Frank Lervik / TV 2.

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As per the comments below, there is also a Google Streetview of the site: https://goo.gl/maps/x1TmWHaaTZj6Msi98

It is probably very fortunate that there were not more casualties from this serious incident, given that it occurred at about 1 pm local time.

It is clear from the images that the landslide occurred at a site of ongoing groundworks, and indeed the injured individual worked for a subcontractor at the site.  Note the backhoe located immediately below the back scarp of the landslide, heavily tilted, suggesting a rotational failure that has transitioned into an earthflow.

In the aftermath of the landslide 100 local residents were evacuated from areas around the site, but they have now been allowed to return home.  The E6 road is now closed.

The online newspaper nrk.no reports that this stretch of road has ongoing works for the construction of a new motorway.  The most recent Google Earth image of the site, from September 2018, shows that the site was forested.

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4 May 2022

The Claxton Bay landslide in Trinidad

The Claxton Bay landslide in Trinidad

The residents of a community in Belle View in the Claxton Bay area of Trinidad in the Caribbean are having their lives destroyed by a landslide.  The failure started to damage the houses in September 2021; to date six houses have been affected.  Last week the residents received a letter from the owners of a quarry downslope from the site, informing them that their houses are likely to suffer further damage in the rainy season.

This image, from the Trinidad Guardian, shows the scale of the problem:-

Landslide damage from the landslide at Claxton Bay in Trinidad.

Landslide damage from the landslide at Claxton Bay in Trinidad. Image by Ivan Toolsie via the Trinidad Guardian.

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I believe that the location of the landslide is 10.381°, -61.445°. This is a Google Earth image of the site, dated May 2021:-

Google Earth image of the site of the Claxton Bay landslide in Trinidad

Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in May 2021, before the landslide retrogressed to affect the houses.

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The key features here are the quarry on the downslope side, the clear active landslide beneath the marker, and the houses at the top of the slope (top of the image).  This image was collected before the landslide retrogressed to affect the houses.

The historical image set for this site is really interesting and very informative.  An image from February 2015 shows active quarrying at the site, and the creation of a steep slope on the quarry face:-

Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in February 2015, before the landslide retrogressed to affect the houses.

Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in February 2015, before the landslide retrogressed to affect the houses.

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By January 2016 the situation had changed considerably.  The intensity of quarry activity appears to have been lower, but a landslide had started to develop in the wall of the quarry, immediately to the right of the marker in the image.  Two clear lobes had developed, one of which had impinged significantly into the workings.  Land was being lost from below the houses:-

Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in January 2017, before the landslide retrogressed to affect the houses.

Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in January 2017, before the landslide retrogressed to affect the houses.

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By November 2018 the landslide had developed very significantly.  The head scarp of the main failure had retrogressed by about 100 metres, the landslide had widened and the lobes had extended much further into the quarry:-

Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in November 2018, before the landslide retrogressed to affect the houses.

Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in November 2018, before the landslide retrogressed to affect the houses.

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It also appears that the remaining unfailed portion of the slope was degrading rapidly.

The image in May 2021, although partially affected by cloud, shows that a much larger failure had developed.  This is zoomed in view from that time:-

Zoomed in Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in May 2021.

Zoomed in Google Earth image of the site of the Claxton Bay landslide in Trinidad, collected in May 2021.

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It is not difficult to see how a further episode of retrogression has directly impacted the houses.

It is interesting to note that the letter from the owner of the quarry is explicit that it does not accept liability for the landslide.  Readers will be able to come to their own conclusions as to whether this is a reasonable position.

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3 May 2022

The Pilar landslide in the Philippines

The Pilar landslide in the Philippines

One of the largest landslides triggered by Tropical Storm Megi last month occurred at Pilar, a little to the southeast of the town of Abuyong in Leyte.  This location, which is also known as Dang’s Beach Resort, suffered from one of the three very large landslides during the storm.  It is located at 10.717, 125.040.  The latest NDRRMC situation report lists 53 known fatalities at this site.

Planet has succeeded in collecting a high resolution satellite image of the landslide at Pilar:-

 

The Pilar landslide in the Philippines.

The Pilar landslide in the Philippines. Image copyright Planet, used with permission. Image dated 20 April 2022.

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By way of comparison, this is a Google Earth image of the same area, collected in June 2016:-

Google Earth image from June 2016 showing the site of the Pilar landslide in the Philippines.

Google Earth image from June 2016 showing the site of the Pilar landslide in the Philippines.

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A particularly interesting aspect of this landslide is that it clearly generated destructive displacement waves when it reached the sea.  The damage to the main part of the seaside resort appears to be consistent with damage caused by these waves:-

Damage caused by the Pilar landslide in the Philippines.

Damage caused by the Pilar landslide in the Philippines. Much of this appears to be consistent with the impact of a displacement wave. Image copyright Planet, used with permission. Image dated 20 April 2022.

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There is a paper in the Annals of Tropical Research (Cabelin and Jadina 2019) that analyses of the soils in landslide areas in the Cadac-an Watershed, which includes the site of this landslide.  It notes that:

“…it was concluded that the soils are susceptible to landslide occurrence.

“It is highly recommended to conduct constant assessment and monitoring of landslide occurrences in the area. Moreover, it is encouraged to plant more trees, prohibit tree cutting, delineate danger zone , establish more rain gauge stations and provide early warning systems to somehow prepare for the consequences brought about by landslides.”

It is hard to disagree.

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References and acknowledgement

Planet Team (2022). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

Cabelin, J.P. and Jadina, B.C. 2019.  Physical characteristics of soils in landslide areas of Cadac-an Watershed in Leyte, PhilippinesAnnals of Tropical Research 41 (2) 11-129.

Thanks to Robert Simmon and Anne Pelligrino for their support in acquiring the image.

 

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22 April 2022

Understanding the deadly landslides in the Durban area of South Africa

Understanding the deadly landslides in the Durban area of South Africa

In the last week I have posted extensively about the deadly landslides on 11 April 2022 in the Philippines.  At around the same time an event of a similar scale occurred in a completely different location.  It is reasonable to ask why I have not written about that one.

The event in question occurred in the Durban area of South Africa.  Once again it was triggered by heavy rainfall.  Reliefweb posted an update on this event yesterday – the statistics are appalling:

According to national authorities, 443 people died in KwaZulu-Natal and over 40,000 are missing. More than 40,000 people have been displaced, while nearly 4,000 houses were destroyed and more than 8,000 others were damaged, mostly across Durban City and its surrounding areas. A National State of Disaster has been declared in response to the floods and landslides, and rescue teams have been deployed to the affected areas to provide humanitarian assistance to those most affected. 

Hopefully the number missing is primarily the result of challenges of documenting displaced people, but even if the death toll remains at its current level, the picture is truly grim.

The challenge that I have had with this event has been obtaining reliable information about what has actually happened.  It is not at all clear to me as to why this is the case.  However, The Conversation has now published an article by Charles MacRobert of Stellenbosch University, who provides a readily understandable explanation for the underlying causes of the landslides in this area.  It is worth a read – the underlying problems are weak geology.

In the coastal region, the problems are associated with a large, vegetated dune formation that is prone to rapid erosion:

Ground adjacent to the sea from Durban to Mtunzini (a coastal town 140km north of Durban) is almost exclusively made up of ancient red sand dunes termed the Berea formation. South of the Durban harbour these sands form a ridge called the Bluff and north of the harbour they form the Berea Ridge. In some places these sand dunes are extremely steep…The investigation showed the slopes’ stability was not significantly affected by rainfall. That makes sense as these slopes have been battered by storms over geological time. But concentrated flows from poorly controlled flood water or broken water pipes were found to be catastrophic.

This is dramatically illustrated at the town of Umdloti:-

Highly destructive gully formation at Umdloti, near to Durban in South Africa.

Highly destructive gully formation at Umdloti, near to Durban in South Africa. Image from the North Coast Courier.

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Meanwhile, inland the geology also causes problems.  Part of the area is underlain by the shales of the Pietermaritzburg formation, which consist of thin layers of clay and silt.  These shales weather easily and trap high pore water pressures, making them very susceptible to failure.  Other parts of the region are underlain by sandstones of the Natal group, which also contain layers of clay that trap high pore water pressures.

Understanding the distribution of these landslides, and the associated floods, is going to be a challenge but is urgently needed.  Meanwhile, the best pictoral record I can find has been posted to Facebook by Kierran Allen Photography.  This is an example of one of their images:-

A landslide in the Durban area of South Africa, triggered by the April 2022 rainfall event.

A landslide in the Durban area of South Africa, triggered by the April 2022 rainfall event. Image by Kierran Allen Photography.

 

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The devastating impact of such a landslide, even though it is small, is clear to see.

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