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5 July 2021

The Atami mudslides in Japan

The Atami mudslides in Japan

Over the weekend there was considerable attention paid to the remarkable videos of the mudflows in Atami, Japan.  This one in particular gained traction:-

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But there are several others, which are helpfully combined into a compilation here:

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I particularly draw your attention to the excerpt that begins at 8 minutes 16 seconds into the second video (the same sequence appears in the first video too).

The main, extremely violent, footage is a particularly nasty example of a channelised flow, common in steep terrain that is subject to extreme rainfall.  Long term readers of this blog will remember the classic examples from Lantau in Hong Kong in 2008 and South Korea in 2011 for example, but there are many, many other examples.

The Google Earth image below shows the general location of the Atami disaster.  I have placed the marker on what is, I think, the location of the prominent red building in the main video:-

Google Earth image showing the presumed location of the Atami mudslide

Google Earth image showing the presumed location of the Atami mudslide

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Some important insight into this event is provided in a tweet by Yoshi Kariya:

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A translation of the text is:

Valley of occurrence. It can be seen that the valley head, which is the forefront of slope failure, extends several times along the volcanic slope, and the past debris flow and landslide deposits that have accumulated at the bottom of the valley are formed in the shape of a terraced rice field. It seems that there was a land on the ridge in the upper part of the basin [Geographical Survey Institute 2017 photo].

Shizuoka Prefecture has released a drone video that shows the landslide at the crown of the mudslide:

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This suggests that the Atami mudflows started as a conventional landslide high up in the catchment.  This is a typical response to very heavy rainfall.  The ground will probably have undergone static liquefaction to form the highly mobile flow.  Once channelised, it will have entrained water from the channel and deposits within the channel, especially those left from previous landslides, to create this terrifying mudflow.

The destructive power of these events is much greater than that of a river flood as the density of earth materials is much higher.

There are two interesting elements to this landslide.  The first is that the initial failure appears to be quite deep-seated.  The second is the presence of the road right at the headscarp.  In other cases, most notably the Sarno landslides in Italy, roads have played a key role in the destabilisation of the slope.  Given the deep-seated nature of the landslide, that may not be the case here, but it is an interesting juxtaposition.

Japan has high quality landslide management programmes and amongst the best engineering prowess for managing these hazards.  However, the combination of the geological setting, the climate and the high population levels means that entirely preventing these events is impossible.

Sadly, but unsurprisingly perhaps, the number of people reported missing at Atami has jumped overnight.  Latest reports suggest that there are three known fatalities but as many as 80 people may be missing.  Hopefully this will reduce in the next few days as people away from home are traced, but the losses may well be high.

 

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2 July 2021

The cause of the Melamchi disaster in Nepal

The cause of the Melamchi disaster in Nepal

The 14 June 2021 disaster at Melamchi in Nepal is the most serious monsoon induced disaster to date of the South Asian summer monsoon.  It is believed that the flood that swept down the river killed 20 people.  It also caused substantial economic damage both to the riverside communities and to the Melamchi Water Supply Project.

The magnitude of the damage to the town of Melamchi is well-described in a post by Nepal Flying Labs, who have been assessing the site using drones.  Their footage of the damage is well worth a visit.  This is one of the images that they have posted after the event:-

The aftermath of the Melamchi flood in Nepal.  Image posted by Nepal Flying Labs.

The aftermath of the Melamchi flood in Nepal. Image posted by Nepal Flying Labs.

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In terms of the Melamchi Water Supply Project, the Kathmandu Post has a good article about the magnitude of the damage.  They note that:-

“The project’s headworks site at Ambathan remains buried in flood debris several metres deep.

According to Rajendra Prasad Pant, spokesperson for the Melamchi Water Supply Development Board, it remains uncertain when the debris clearance and restoration works will begin…As per the initial assessment, the project has suffered more than Rs1 billion [about £6 million] worth of damage.

Pant, who is also a senior divisional engineer with the board, said 10 to 15 metres of debris has piled up at the project site and the clean-up work could cost Rs300-Rs350 million [about £1.8 million]. Likewise, the floods have damaged the roads and bridges to the project site and washed away the campsite and construction materials.

There is also another problem. Government officials suspect that the floodwaters and debris could have entered the alternative diversion tunnel of the headworks.”

Understanding this disaster, which we know was caused by the rupture of a landslide dam, is difficult during the monsoon, when cloud cover renders satellite image collection difficult.  However, on 23 June 2021 a rare cloud-free day allowed the Planet Labs constellation to collect an image that starts to shed some light on the issue.  This is the image:-

Planet Labs image of the likely cause of the 14 June 2021 Melamchi flood.  Image copyright Planet Labs, used with permission.

Planet Labs image of the likely cause of the 14 June 2021 Melamchi flood. Image copyright Planet Labs, used with permission.

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Clearly this is a composite image, with the portion to the east being captured at a time with a much higher level degree of cloud.  But the western portion is excellent, and it shows a large landslide (about 500 metres width along the river).  It is clear that the flood deposits extend from this point down the Melamchi River.  The landslide, which is located at 29.993, 85.553, is not present on satellite images collected before 14 June.

We will need to wait for better images to become available, probably in the autumn when the monsoon withdraws (although we could be lucky sooner than this) to fully understand this disaster, but it does appear that the interpretation that a landslide dam developed during the heavy rainfall, and then breached, is correct.

Reference

Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

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28 June 2021

Kara-Keche: the September 2020 landslide in Kyrgyzstan

Kara-Keche: the September 2020 landslide in Kyrgyzstan

On 14 September 2020 a large landslide occurred in the coal mining area of Kara-Keche in Kyrgyzstan.  This landslide was captured on a remarkable video that was posted to Youtube:

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There are some not very specific news reports online about this landslide, which is located at 41.722, 74.779.  For example, for.kg has the following report:-

The landslide occurred in the evening of September 14 on the 37th km of the Dyikan-Kara-Keche road. The collapsed slope of the mountain blocked the gorge and the river. The slided mass of rocks and land is estimated at around 800,000-900,000 cbm.  This road led to the biggest coal field in Kyrgyzstan – Kara-Keche field.

There is good Planet Labs imagery of the site of the landslide.  This image was collected a few days later (NB north is at the bottom of these images):-

Planet Labs image of the aftermath of the 14 September 2020 landslide at Kara-Keche in Kyrgyzstan.

Planet Labs image of the aftermath of the 14 September 2020 landslide at Kara-Keche in Kyrgyzstan. Image copyright Planet Labs, used with permission.

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The large collapsed mass is clearly visible, covering the alignment of the road.  Note the small lake that has built up.  There is also a good image of the site a few days before the failure:-

Planet Labs image of the site of the 14 September 2020 landslide at Kara-Keche in Kyrgyzstan.

Planet Labs image of the site of the 14 September 2020 landslide at Kara-Keche in Kyrgyzstan. Image copyright Planet Labs, used with permission.

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This image, collected on 29 August 2020, shows that failure at the site was already developing, with a not insubstantial collapse being clearly evident at the toe of what became the main slide.  The debris from this collapse appears to have reached the road.

It is not clear as to the role of mining in this collapse event.  Mine workings are evident on the imagery in the upper left corner, but the slope itself does not appear to have been mined.

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Reference

Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

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21 June 2021

Melamchi: a landslide dam break flood in Nepal last week

Melamchi: a landslide dam break flood in Nepal last week

I was away on leave in London last week; as both the South Asia monsoon and the northern hemisphere mountain rockfall season are now underway, there is much to discuss.  So, to start, on 14 June 2021 a large flood struck the Melamchi area of Nepal following an early monsoon downpour.  The flooding caused high levels of damage.  Three people are confirmed to have died, whilst 17 more remain missing.  Many houses were destroyed:-

The aftermath of the Melamchi landslide dam break flood in Nepal

The aftermath of the Melamchi landslide dam break flood in Nepal. Image from the Kathmandu Post.

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It is now clear that this event resulted from the breach of a landslide dam upstream, releasing a torrential debris flow and flood that struck the settlements.  On Twitter there is a short video that has captured some of the landsliding:

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The translation of the text is:

‘Melamchi floods due to landslide’ – After inspecting the Melamchi area from a helicopter, Health Minister Sher Bahadur Tamang said that the Melamchi was flooded due to a landslide 500 meters above the Chokpu of Helambu village.

NP News has this graphic of the site:-

Graphic illustrating the landslide at Melamchi in Nepal.

Graphic illustrating the landslide at Melamchi in Nepal, created by NP News.

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If this is correct then the location is about 28.109, 85.46, but this is unconfirmed.  Unfortunately there is too much cloud to get a good satellite image.  There are better versions of the inset image on the left above, but these seem to sit on insecure sites so I am not providing a link.  They appear to show a very large, valley blocking landslide just above the area with the white circle on this image above.

There also appears to be substantial damage to the critically important Melamchi Water Supply Project.  I note once again that major infrastructure projects are being built in the Himalayas without a proper understanding of the risks from these devastating landslides, as we noted in our recent paper in Science.

Interestingly, there are also reports of another valley blocking landslide threatening communities in Nepal, this time along the banks of the Tamakoshi River – this valley blocking landslide is in Tibet.  Works are apparently underway to try to unblock the channel.  We will watch with interest to see what happens there.  Thanks to John Reynolds for highlighting this one to me.

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11 June 2021

Chamoli, Indian Himalaya: A massive rock and ice avalanche caused the 2021 disaster

Chamoli, Indian Himalaya: A massive rock and ice avalanche caused the 2021 disaster

Back in February I blogged on a number of occasions about the terrible 7 February 2021 disaster in Chamoli, India, when a huge debris flow swept down a valley, with no warming, killing 200 peopleDan Shugar of the University of Calgary was the quickest off the blocks that day, using Planet Labs imagery to determine that the event was triggered by a rockslope failure.  Sadly there was a great deal of disinformation at the time, with even reputable scientists claiming that the event was a glacier collapse when the evidence was clear that this was not the case.

In the aftermath of the event a truly interdisciplinary team of researchers, from around the world but including scientists from India, self-organised to try to understand the event.  This team drew on skills from a diverse range of fields, including earth science, social science, seismology, remote sensing and modelling, to try to piece together what happened.  Over time the story became clear, with evidence to back up the interpretations.

The group was marshalled with great skill by Dan Shugar to produce a manuscript that documented the events.  In a matter of days this came together – the result was published yesterday by the journal Science (Shugar et al. 2021), and is available open access.

I don’t need to go into the detail of the sequence of events here – the abstract captures this well:

Our analysis of satellite imagery, seismic records, numerical model results, and eyewitness videos reveals that ~27×106 m3 of rock and glacier ice collapsed from the steep north face of Ronti Peak. The rock and ice avalanche rapidly transformed into an extraordinarily large and mobile debris flow that transported boulders >20 m in diameter, and scoured the valley walls up to 220 m above the valley floor. The intersection of the hazard cascade with downvalley infrastructure resulted in a disaster, which highlights key questions about adequate monitoring and sustainable development in the Himalaya as well as other remote, high-mountain environments.

Figure 1 from the paper beautifully illustrates the initiating event at Chamoli:

Overview of the Chamoli disaster, Uttarakhand, India

Overview of the Chamoli disaster, Uttarakhand, India, from Shugar et al. (2021)

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As I’m an author on the paper, it is not my place to comment on its quality.  I would like to highlight three key elements though:

The first is that Shugar et al. (2021) provides a very detailed explanation for the sequence of events at Chamoli.  It should lay to rest any suggest that this was anything other than a landslide. There may be details that will be refined over time, but the main sequence of events is clear.

Second, the paper demonstrates the amazing ability of a huge team to collaborate to bring forward an understanding of the sequence, even though this event occurred in a high mountain area in winter  in the middle of a pandemic when travel is impossible.  The keys were enthusiasm, ability, cooperation and extremely able leadership by Dan.

And thirdly the event highlights the perils of building infrastructure at great cost in areas subject to these events without understanding them properly.  Things must change is this event is not to be repeated.

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Reference

D. H. Shugar, M. Jacquemart, D. Shean, S. Bhushan, K. Upadhyay, A. Sattar, W. Schwanghart, S. Mcbride, M. Van Wyk De Vries, M. Mergili, A. Emmer, C. Deschamps-Berger, M. Mcdonnell, R. Bhambri, S. Allen, E. Berthier, J. L. Carrivick, J. J. Clague, M. Dokukin, S. A. Dunning, H. Frey, S. Gascoin, U. K. Haritashya, C. Huggel, A. Kääb, J. S. Kargel, J. L. Kavanaugh, P. Lacroix, D. Petley, S. Rupper, M. F. Azam, S. J. Cook, A. P. Dimri, M. Eriksson, D. Farinotti, J. Fiddes, K. R. Gnyawali, S. Harrison, M. Jha, M. Koppes, A. Kumar, S. Leinss, U. Majeed, S. Mal, A. Muhuri, J. Noetzli, F. Paul, I. Rashid, K. Sain, J. Steiner, F. Ugalde, C. S. Watson, M. J. Westoby. 2021.  A massive rock and ice avalanche caused the 2021 disaster at Chamoli, Indian Himalaya. ScienceDOI: 10.1126/science.abh4455

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10 June 2021

Legal proposals to improve safety on Welsh and English coal tips

Legal proposals to improve safety on Welsh and English coal tips

Yesterday, the Law Commission in England and Wales launched a consultation on proposals to change the legal framework on the management of coal tip safety.  The proposals come in the aftermath of the recent stability problems on tips in South Wales, most notably at Tylorstown in February 2020, which have highlighted deficiencies in the current political systems and the legal framework.

The coal tip at Tylorstown in South Wales

The coal tip at Tylorstown in South Wales. Image from geograph.org.uk.

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The Law Commission has identified the following key issues with the existing law, which dates from 1969 when many tips were still active and climate change was not considered to be a major issue (the text below is directly from the Law Commission):

  • The powers created by the Act are fragmented across local authorities, leading to inconsistent safety standards and risk classifications.
  • There is no mechanism to prioritise the highest risk coal tips to ensure they are managed as a matter of urgency.
  • There is no general duty to ensure the safety of coal tips and local authorities have no power to intervene until there are concerns that a tip is unstable.
  • There is no power to undertake preventive maintenance before a tip becomes a danger.

The proposed legislation would create a single body with responsibility for the supervision of all disused tips.  It would have the power to monitor tips to ensure compliance the regulatory requirements. A register of coal tips would be established, which would record information including potential risks at each site.

The new body would set up a regime of inspections of coal tips to ensure that risks are being managed appropriately.  The inspection would include tip stability, but could also cover risks associated with flooding, pollution and suchlike.  And finally, for high risk coal tips, an enhanced safety regime would be established, with the supervisory authority having involvement in the management of the tip to ensure that the risk of incidents in minimised.

I think for many it will be a surprise that such a management body and regime is not already in place.  There can be little doubt that this is an important step towards improving coal tip safety.

The consultation is open until 10 September 2021, with the final report being due next year.  I hope that legislation will follow quickly.

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7 June 2021

The South Asian monsoon in the time of a pandemic

The South Asian monsoon in the time of a pandemic

The start of June marks the onset of the South Asian summer monsoon.  As I have noted previously, this is by far the most important annual global process in terms of landslidesThe monsoon typically strengthens reasonably quickly through June, peaking in mid-July, and then slowly declining through to the autumn.  In landslide terms, the events mostly occur when the monsoon reaches the hills of Sri Lanka, Kerala in W India and the Himalayan Arc across the north of South Asia.  The monsoon advances from the southeast, so Bangladesh and Sri Lanka are often affected first.

Over the weekend, heavy rainfall in Bangladesh caused landslides and extensive flooding and landslides killed a number of people in Sri Lanka.  Thus, the impacts of the monsoon are starting to be felt.

A 2019 monsoon landslide in a Rohingya refugee camp in Bangladesh. Image from

A 2019 monsoon landslide in a Rohingya refugee camp in Bangladesh. Image from https://en.prothomalo.com/.

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The monsoon this year is going to be different.  There is nothing unusual meteorologically as far as I’m aware, but in South Asia civil society is under severe stress.  The two most affected countries in South Asia in terms of landslides are India and Nepal, both of which are being desperately impacted by Covid-19, with hospitals operating beyond capacity.  The population will be especially vulnerable this year, and supply chains are very stretched.  Thus, it is reasonable to expect that the impacts of the monsoon may be more severe than normal.

In Bangladesh, vulnerability has been increased by the continued presence of the large displaced Rohingya population, living in camps that are affected by landslides.  It is salient to note that two people were killed in landslides in these camps over the weekend.  And in Myanmar / Burma, the massive civil unrest following the coup earlier this year is also likely to have raised vulnerability.  Mining-induced landslides are particular problem there, a result of both poor regulation and scavenging driven by economic disadvantage.  The coup is unlikely to have reduced the impact of either of these two issues, but reliable reporting of landslides may have become more difficult.

In summary we are heading into the unknown in terms of South Asian summer monsoon this year, but I fear that it could well be a bad one.

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4 June 2021

The 31 May 2021 landslide at the Bingham Canyon mine

The 31 May 2021 landslide at the Bingham Canyon mine

At 9 am local time on 31 May 2021 a large landslide occurred at the Rio Tinto Kennecott mine at Bingham Canyon in Utah, USA.  This site is famous for one of the largest mining induced landslides ever recorded, and indeed one of the largest recent landslides in North America, in April 2013.  Fortunately this landslide is on a far smaller scale.

Once again, geotechnical monitoring at the site identified the instability prior to the failure, allowing the operators to ensure that no-one was at risk.

Fox 13 has posted a pair of images of the landslide:-

The 31 May 2021 landslide at the Rio Tinto Kennecott mine at Bingham Canyon.

The 31 May 2021 landslide at the Rio Tinto Kennecott mine at Bingham Canyon. Images posted by Fox 13.

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I also managed to download a pair of Planet Labs images of the site, before and after the failure – these should be visible used the slider below:

Planet Labs satellite image of the site of the 31 May 2021 landside at Bingham Canyon in Utah.Planet Labs satellite image of the aftermath of the 31 May 2021 landside at Bingham Canyon in Utah.

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The image on the left was collected on 28 May 2021 and the one on the right on 31 May 2021.  South is towards the top of the images.

The images suggest that the main part of the landslide, on the right side in the slide in the pictures, was a wedge failure that appears to be quite deep-seated.  There is a smaller wedge on the left side too.

In its statement to the NASDAQ, the operator of the Bingham Canyon mine has confirmed that operations continue to be unaffected by the landslide.

The mining industry is the most advanced industry in terms of geotechnical monitoring of slope deformation and failure prediction.  Once again this event appears to have been a successful application of those technologies.

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Reference

Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

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3 June 2021

Not all slope failures are large

Not all slope failures are large

Inevitably, on this blog I tend to cover larger landslides most of the time.  Large landslides have a greater propensity to cause loss and to disrupt, and of course they are also more newsworthy and they are frequently photogenic.  However, this gives a very misleading impression of slope failures, the vast majority of which are small.  Nonetheless, even these less impressive landslides can have substantial impacts.

Whilst walking around my home city of Sheffield in the current spell of warm, sunny early summer weather, I have spotted a series of smaller but interesting slope failures. I thought it would be interesting to highlight two of them.

The Sheffield and Tinsley Canal is a 6 km long waterway constructed in 1819 to link the city of Sheffield with the navigable parts of the River Don, allowing goods and people to be transported into and out of the city.  Its greatest claim to fame is that the it is the location of part of the opening scenes of the film The Full Monty (although it looks considerably better than that now!).

Today the canal is navigable by pleasure craft, and the towpath forms a walking and cycle route.  The image below shows a small slope failure that has occurred in a section of the canal:

A small canal bank failure on the Sheffield and Tinsley canal

A small canal bank failure on the Sheffield and Tinsley canal

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As the  image shows, about a 15 m section of the canal bank has collapsed.  In the foreground a further section is failing.  In other sections of the canal, failures are developing but have not collapsed:-

A developing canal bank failure on the Sheffield and Tinsley canal

A developing canal bank failure on the Sheffield and Tinsley canal.

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The stone blocks have moved towards the canal by about 50 cm, and the fill has subsided by about 30 cm.  In this case failure, when it occurs, will substantially disrupt the towpath.  There are other sections in a similar state.

None of these slope failures are large or dramatic, but they have the potential to close the towpath.

The second case lies on my walk to work.  Here, at the top of a steep bank, a retaining wall has recently been constructed to create a pathway for pedestrians.  It appears that this wall, which is about 50 cm high, has also started to fail and to move downslope.  The owners of the site have employed a novel method to provide short term increased stability:

A failing retaining wall in Sheffield

A failing retaining wall in Sheffield.

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Securing a slope using cargo straps tied to the trees is not an approach that I have seen before.  Again, this is small incipient slope failure, but one that is causing disruption.

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2 June 2021

The 1918 Getå landslide disaster in Sweden

The 1918 Getå landslide disaster in Sweden

A recent post on Reddit has highlighted a landslide disaster that occurred close to the village of Getå in Sweden on 1 October 1918.  The event is also well-described in a Wikipedia page.

Early in that evening a landslide removed a section of a railway track.  A few minutes later a train, consisting of a locomotive and ten carriages, reached the landslide and derailed spectacularly.  The post on Reddit has a fascinating aerial image of the aftermath of the landslide:

A vertical aerial photograph showing the aftermath of the 1918 landslide at Getå in Sweden.

A vertical aerial photograph showing the aftermath of the 1918 landslide at Getå in Sweden. Image from Järnvägsmuseet.

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The landslide scar and its very large deposit are clearly visible.  Interestingly, the crown of the landslide seems to almost perfectly coincide with the upslope boundary of the railway line.  The crashed locomotive is visible in the scar, as is one of the carriages.  There us a huge pile of debris, which is the aftermath of the fire that destroyed most of the carriages.  Other carriages remained upright on the tracks.

At least 42 people were killed in the accident, the majority of whom are thought to have been trapped in the derailed carriages when the fire engulfed them.  A further 41 people were injured.  There are thought to be at least five people who remained missing after the accident.

The image below shows the landslide deposit:-

A photograph from the crown of the slide showing the aftermath of the 1918 landslide at Getå in Sweden.

A photograph from the crown of the slide showing the aftermath of the 1918 landslide at Getå in Sweden. Image from Järnvägsmuseet.

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A detailed investigation of the landslide was undertaken.  It concluded that there was a prehistoric landslide at the site that had not been identified at the time of the construction of the railway, five years earlier.  Failure was triggered by high pore water pressures.  The railway line was located on a gravel embankment; sliding initiated on the interface between the embankment gravel and the underlying clay.

The railway line was rebuilt and remains in use today; the accident spurred the development of the field of geotechnics in Sweden.

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