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28 September 2020

The 1920 Haiyuan earthquake in China

The 1920 Haiyuan earthquake in China

It is widely thought that in terms of landslides, one of the most deadly earthquakes was the 1920 Haiyuan earthquake in China, which had a magnitude of about 8.5.  It is generally accepted that this earthquake, which occurred on 16 December 1920, killed at least 234,000 people.  It has previously been suggested that perhaps 100,000 of these fatalities were caused by large landslides in loess deposits.  However, the amount of detailed information to substantiate this claim was limited, so there has been a great deal of uncertainty around this number.

In a paper just published in the journal Landslides (and sadly behind a paywall), Xu et al. (2020) have re-evaluated this earthquake in some detail, which is an important contribution.  Their paper goes back through the literature (including reports from the scene at the time), exracts information from field surveys, and presents the outcomes of mapping from Google Earth imagery to present a catalog of landslides triggered by the 1920 Haiyuan earthquake.  The study uses informaton from a four month tour of the area devastated by the earthquake undertaken by a team of Chinese scholars in the Spring and early Summer of 1021, who collected detailed information about the impact o the earthquake

In total Xu et al. (2020) have recorded 7151 individual coseismic landslides, noting of course that the majority of the smaller landslides triggered by the earthquake will not be visible now.  The distribution of the landslides, and the distribution of settlements, is shown in the map, from the paper, below.  The map includes the intensity zones for the earthquake:

The 1920 Haiyuan earthquake in China

A map of landslides associated with the 1920 Haiyuan earthquake in China, from Xu et al. (2020).

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The map above includes a number of clusters of landslides, but Xu et al. (2020) note other substantial earthquakes (also shown on the map) that probably account for these.

Pulling all of this information together, the authors conclude that the number of landslide deaths from the 1920 Haiyuan earthquake was in the order of 32,554.  The authors recognise that some landslide fatalities have not been recorded, but they conclude that estimates of 100,000 or more are likely to be too high.  Of course, 32,500 is still a remarkably high number.  The majority of the fatalities were likely to have been caused by the collapse of houses and of loess caves.

This is an incredibly useful contribution, providing another inventory of landslides from a large earthquake (in this case a dominantly strike-slip event) and generating a much more reasonable estimate of the landslide losses from this event.

Reference

Xu, Y., Liu-Zeng, J., Allen, M.B. et al. 2020. Landslides of the 1920 Haiyuan earthquake, northern China. Landslides. https://doi.org/10.1007/s10346-020-01512-5

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7 September 2020

The Koidern landslide: a long runout event in Canada

The Koidern landslide: a long runout event in Canada

Apologies for the lack of posts of late – due to Covid-19, and its associated secondary hazards, my day job is taking all of my time at the moment.  Anyway, on Saturday Brent Ward tweeted a fantastic set of aerial images of the Koidern landslide, in the Yukon of Canada.  This is one of the most spectacular landslides of the year to date:-

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Brent has posted a thread of images of the Koidern landslide, which includes this pair of tweets showing the structure of the landslide (mollards are cones of rock avalanche material) and the landslide dam:-

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The Koidern landslide is a very interesting rock avalanche, showing quite high mobility.  Note the very clear main track of the landslide, as well as the areas on either with lower levels of debris.  It appears to me that a part of the landslide has super-elevated on the outside of the first bend.  Some landslide debris has also spilled out on the true right side of the track.

The images show that the landslide dam has overtopped; given its size and the remote location the hazard is very low.

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Quickslide 1: A spectacular rockfall at Cima Canali at Pale di San Martino in the Dolomites

This is a pretty cool video of a recent rockfall.  Note the very large boulder that leaves the dust cloud on the right hand side and disappears down the valley:-

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Quickslide 2: Landslides from Typhoon Haishen in Japan

Typhoon Haishen swept across Japan over the weekend.  At least one substantial landslide has been reported.  The Mainichi reports:

A woman in her 60s and her son in his 30s as well as two Vietnamese male interns were reported missing and a man in his 70s broke his ribs after a mudslide struck a construction firm office, which was also used as a residence, in the village of Shiiba, Miyazaki Prefecture, local authorities said. The man, who runs the construction company, is the husband of the missing woman.

The typhoon is now headed north towards South and North Korea.

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28 August 2020

Devastating debris flows in Charikar, Afghanistan

Devastating debris flows in Charikar, Afghanistan

Whilst the world’s attention has been focused on the impacts of Hurricane Laura in the USA, a far more deadly disaster has occurred in Afghanistan.  On Tuesday 25 August 2020 deadly debris flows struck the community of Charikar in Afghanistan.  Unfortunately, as is common for such events, these events have been reported to be either floods or flash floods, but the images suggest that they were debris flows.  There is considerable uncertainty about the number of fatalities, but at least 100 died in Charikar and the total death toll in the wider area is reported to be at least 162 people.

As yet I have not been able to track down a good overview image of the site of this disaster.  This image, posted to Twitter by Salaamedia, shows the scale of the event:-

Charikar debris flow

The aftermath of the 25 August 2020 debris flows at Charikar in Afghanistan. Image posted to Twitter by Salaamedia.

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The image below, also posted to Twitter by Salaamedia, shows the nature of the deposits left by the debris flows:-

Charikar debris flow

The deposit left by the 25 August 2020 debris flows at Charikar in Afghanistan. Image posted to Twitter by Salaamedia.

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A quick look at the Google Earth imagery demonstrates clearly why Charikar is so seriously affected by debris flows:-

Charikar debris flows

Google Earth imagery of the Charikar area.

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The town is clearly built on a set of large fans emerging from steep, rugged and tectonically active mountains.  This environment is tailor-made for debris flows, especially, as is likely, rainfall intensity is increasing in response to global heating.

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Quickslide 1: The history of landslides at Rest and Be Thankful

The BBC has a very nice piece today reviewing the long history of significant landslides at the A83 at Rest and Be ThankfulThere is increasing pressure in Scotland to find a permanent solution, but this is likely to be extremely expensive.

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Quickslide 2: Thypoon Bavi

Meanwhile, on the other side of the world, Typhoon Bavi has made landfall on the Korean peninsula.  Some damage is reported in South Korea, but the main impacts will have been in North Korea.  It is of course extremely difficult to get information about the resulting impacts, but landslides are likely to have occurred.

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26 August 2020

Slieveanorra: a large peat bog landslide in Northern Ireland?

Slieveanorra: a large peat bog landslide in Northern Ireland?

Yesterday a large storm tracked across the British Isles, bringing unseasonably strong winds and intense rainfall.  Storm Francis has caused some flooding, extensive damage to trees and some landslides.  The most interesting of these has occurred at Slieveanorra, in the northern part of County Antrim in Northern Ireland.  At present there is little detail of this landslide except a report in the Ballymena Daily, which includes this image:-

Slieveanorra

The aftermath of the landslide at Slieveanorra in County Antrim, Northern Ireland. Image by KEVIN MCAULEY/MCAULEY MULTIMEDIA via the Ballymena Daily.

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There is little detail about the landslide in the report, but from the images above the slide appears to have occurred in peat.  A planar shear surface maybe apparent in the distance in the image, although it is impossible to see how far up the hillside this extends.  The report indicates that the landslide, which is on a road that links the  Ballymoney area with the Glens, will take several days to clear.

This is not the first peat landslide in the Slieveanorra area.  In January 2015 the same region suffered a large peat bog landslide:-

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Interestingly, in April this year Slieveanorra suffered from wildfires, the consequence of the exceptional period of dry weather in early 2020.  It is too early to say whether the landslide might be linked to these fires.

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Quickslide 1: a fatal landslide in Reasi, India

A mudslide killed at least three people in Reasi, India yesterday.  I am not sure as to whether the huge boulder in the image in this report moved in this event, or in a previous one.

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Quickslide 2: Network Rail launches two task forces “to help it better manage its massive earthworks (cuttings and embankments) portfolio and its understanding and response to severe weather events”

As I predicted yesterday, Storm Francis triggered landslides on the British railway network.  A failure between Buckshaw Parkway and Chorley has blocked the line, disrupting trains between Preston and Bolton.  Interestingly, Network Rail have launched two task forces to investigate the issue about which I wrote in the aftermath of the Carmont landslideThere are details in a Network Rail press release:

Dame Julia Slingo FRS, former chief scientist at the Met Office and a world-renowned expert in climatology, will lead a weather action task force with the objective of better equipping Network Rail to understand the risk of rainfall to its infrastructure, drawing on the latest scientific developments in monitoring, real-time observations and weather forecasting.

Meanwhile, Lord Robert Mair CBE FREng FRS will spearhead an earthworks management task force to see how Network Rail can improve the management of its massive earthworks portfolio, looking at past incidents, latest technologies and innovations and best practice from across the globe.

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25 August 2020

Initial information about the fatal landslide-induced train derailment at Carmont, Scotland

Initial information about the fatal landslide-induced train derailment at Carmont, Scotland

Late last week the Rail Accident Investigation Branch (RAIB) released an initial report about the train derailment at Carmont, south of Stonehaven in Scotland, which killed three people and injured a further six.  Whilst this is only a provisional report, it provides considerable factual information about the accident.  It confirms that the train struck the debris from what is described as a landslip onto the track.  At the time of the accident (9:38 am) the train was travelling at 117.1 km/h.  The impact with the debris derailed the train, which then travelled a further 70 metres before striking the parapet of the bridge.  The image below, from the provisional report, shows the situation on the ground:-

The Carmont train derailment

The aftermath of the Carmonth train derailment. Image from the initial report by the RAIB.

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The landslide that caused the derailment is just off the image.  The RAB report provides some detail about the slope that failed:-

Carmonth train derailment

The slope that caused the Carmonth train derailment. Image from the initial report by the RAIB.

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As the image above shows, to the left of the track (in the direction of travel of the train) there is a steep slope up to a field.  Water draining from the field is captured by a drain running along the top of the cutting.  The feeds a diagonal drain down to the trackside drain, consisting of a 450 millimetre (18 inch) diameter plastic pipe located in a trench backfilled with gravel.  The excessive rainfall on the day of the accident appears to have overwhelmed the capacity of the diagonal drain, leading to overland flow that eroded the gravel, and some material from the sides of the trench, which was deposited on the track.  It was this debris that derailed the train.

Clearly there is still considerable work to do to understand this accident.  An interesting aspect will be the date in which this configuration of the drainage system was installed – a plastic pipe undoubtedly post-dates the construction of the railway, but it may bot be recent.  The RAIB report will provide full detail in due course.

The UK is experiencing another spell of extremely heavy rainfall today, with yellow warnings of heavy rainfall across a swathe of the country. Further disruption to the railway is highly likely.

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Quickslide 1: Floods and landslides in Turkey

Heavy rainfall in recent days has triggered flooding and landslides in the Turkish city of Giresun. At least eight people have been killed.

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Quickslide 2: Boulder versus lorry…

The boulder won.  Fortunately the driver escaped just in time.

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14 August 2020

More information about the Pettimudi landslide in Rajmala, Kerala

More information about the Pettimudi landslide in Rajmala, Kerala

A few days ago I wrote about the large landslide at Rajmala in Kerala, India late in the evening of 6 August 2020.  In the last few days more information has become available about the disaster.

An interesting image of the landslide is the one below, which was posted on the Inquest website, although the original source appears to be Mathrubhumi.com:

The Pettimudi landslide

The Pettimudi landslide in Kerala, India. Image from Mathrubhumi.com via The Inquest

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The image shows that this was a large, long runout channelised debris flow that has followed an existing drainage line.  The landslide appears to originate high on the slope in the forest. The tweet below, which uses an image from the photographer Sebinster Francis, is a clear illustration of the length of the flow:

Loyal reader Sekhar has kindly provided some more detailed information about the landslide, which travelled about 2 km prior to striking the workers accommodation.  The location of the landslide is 10.161, 77.011:-

The Pettimudi landslide

Google Earth image of the location of the Pettimudi landslide in Kerala, India. The marker is the location of the workers accommodation. The landslide travelled down the clearly visible drainage line to the north of the accommodation.

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At the time of the landslide there were 78 people located in the workers’ accommodation.  Twelve people were rescued, suggesting an ultimate death toll from this event of 66 people.  Not all of the victims have been recovered as yet. Note the tea plantations on the lower slopes; these were tended by the workers who were killed.

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Quickslide 1: A landslide that might have caused the Stonehaven train accident

Yesterday additional drone footage emerged of the site of the Stonehaven train crash.  This clearly shows a landslide on the tracks.  It seems highly likely that this was the cause of the accixent:

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Quickslide 2: Another series of deadly landslides in Nepal

The terrible cost of landslides from the 2020 monsoon in Nepal continues.  Overnight several events have been reported, including a large slide at Lidi in Sindhupalchok district, that destroyed a number of houses.  It is unclear as to how many people are missing, but some reports suggest up to 35 people:

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13 August 2020

Stonehaven: landslides on the UK railway network

Stonehaven: landslides on the UK railway network

Yesterday a train derailed close to Stonehaven in Scotland, killing three people and injuring a further six.  Images show that the accident was extremely serious – it is fortunate that there were only 12 people on the train at the time of the accident.  A more densely occupied train would have led to a high level of loss of life.

The accident occurred in the aftermath of heavy rainfall, and there were reports of both landslides and floods on the track.  As a consequence the accident has been widely reported as being initiated when the train struck a landslide.  This may well be the case, although it is speculation at this point.  From the drone footage and images of the site, I cannot see an obvious landslide:-

Stonehaven landslide

The aftermath of the Stonehaven rail accident. Still from footage posted to Youtube by Sky News.

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The landslide could of course be obscured by the wreckage or be located off screen.  Time will tell, and the accident will be investigated in full.

The Stonehaven accident has raised questions about the safety of the UK rail system, and in particular the risk of landslides.  As usual there is a subtext that in some way the operator of the tracks, Network Rail, is failing.  I think that is unfair, but that there are reasons to be concerned.

Most of the UK rail system is old – in many cases really old.  The section of the alignment near to Stonehaven on which the accident occurred was built between 1847 and 1850.  Of course the track, the signalling, the ballast etc have all been replaced, but the earthworks were constructed at that time and in most cases remain extant today.  This is ageing infrastructure, constructed when understanding of slope stability was low, primarily through trial and error.  Huge sections of railway lines in the UK are either on embankments or below cuttings, so Network Rail has 190,000 anthropogenic slopes to manage.

In the years after construction these slopes were actively managed. Gangs would go out to remove excess vegetation, clear drains, etc., and they acted as an early warning system if slopes were deteriorating  However, in the latter years of the nationalised British Rail, and in the disastrous years of the privatised Railtrack, the earthworks were neglected and the slopes deteriorated.  In particular, drains were damaged, leading to stability problems.

Network Rail has worked hard to put this rightThey have sophisticated methods for identifying and monitoring problematic slopes, and are really good at re-engineering failing earthworks.  But the legacy of those years of neglect remains.

Of course there is an additional problem – climate change.  The slopes were designed for conditions that differ from the modern situation.  In particular, these slopes are now subject to long, very dry spells in which they desiccate and crack, followed by periods of intense rainfall that exceed their drainage capacity.  The last few days have seen record-breaking heat followed by very extreme convective rainfall.  Some slopes simply cannot cope.

This is not to say that our railways are dangerous – the Stonehaven accident is the first loss of a rail passenger in a derailment in 13 years, an exceptional record.  But we do have to recognise that we have both a legacy and a modern slope problem that will present an increasing level of risk, primarily of disruption.

This can be managed – Network Rail and their contractors know how to manage and upgrade the slopes throughout the rail network in the UK; they need to be given the resource to do so.

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Quickslide 1: A landslide in a caravan park in Fife, Scotland

Heavy rainfall in Scotland also caused a landslide that damaged a set of residential caravans.  Fortunately, so-one was injured.

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Quickslide 2: A valley-blocking landslide on the Sakunka River in Canada

In Canada, a large landslide has created a dam on the Sakunka River south of Chetwynd.

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11 August 2020

Landslides after wildfires

Landslides after wildfires

It is well established that one of the lingering affects of wildfires is increased sensitivity of the landscape to landslides.  The primary cause is considered to be the loss of vegetation, although the actual mechanisms through which this generates increased landsliding are complex.  Notable examples include the 2018 Montecito mudslides in California, but similar events can be found in many places,

In a paper just published in the journal Landslides (Rengers et al. 2020), which is open access, the occurrence of landslides following wildfires in Southern California is investigated.  The authors have looked at a 70 km² area of the San Gabriel Mountains in Southern California, which was burned in the 2009 Morris fire, the 2014 Colby fire and the two wildfires that are collectively known as the 2016 San Gabriel Complex fire.  None of the fires burned all of the study area, but some parts were burned by more than one of the fires.

The authors observed debris flows in the first year after a fire in the area that had been burnt.  The example below, the Van Tassel watershed, highlighted by Rengers et al. (2020), underwent extensive debris flow activity in early 2017 having been burnt the year before:-

Landslides after a wildfire in the USA

Google Earth imagery showing the Van Tassel watershed after a wildfire in 2016, as highlighted by Rengers et al. (2020). The area has undergone extensive debris flow activity, as evidenced by the deposits at the mouth of the canyon.

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But the pattern of landslides in time is quite complex.  Whilst debris flow activity was indeed high in the first year after a fire, triggered by heavy seasonal rainfall, debris flow activity rapidly declined with time. Three years after a fire, the primary type of landsliding had transitioned to shallow slips, with failures being triggered on both unburnt and burnt slopes.  The density of landslides was highest in areas that had been burnt three years previously, whilst areas that had been burnt five years beforehand had a low density of landslides, similar to areas had not been burnt.

Where a second fire affected a previously burnt area, the density of landslides did not increase.  A really interesting aspect of the landslides is they mostly occurred on slopes facing towards the south.  Rengers et al. (2020) suggest that this may be because slopes facing away from the sun (i.e. to the north) in this semi-arid area regenerated vegetation quickly, reducing the likelihood of landslides.  This is an important finding.

The study by Rengers et al. (2020) shows that wildfires do indeed lead to increased susceptibility to landslides triggered by rainfall.  However, the response is more complex than might have been anticipated both in terms of the types of slides triggered and their spatial patterns.  In this case the affect is quite shortlived. It is important to stress that this effect will be strongly controlled by local factors such as the topography, the geology and the climate, so responses in other locations might differ.  I hope that this study will inspire similar investigations in other environments.

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Quickslide 1: an update on the Rajmala landslide

The number of bodies recovered from the Rajmala landslide in India has increased to 49.  The Indian Express has a good article about the background to the landslide.  It is now clear that this occurred late on 6 August rather than on 7 August, as had been reported previously.

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Quickslide 2: Further problems at Rest and be Thankful

The diversion route for the A83 at Rest and Be Thankful was closed overnight due to concerns about another landslide.  The main road remains closed.

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Reference

Rengers, F.K., McGuire, L.A., Oakley, N.S. et al. 2020. Landslides after wildfire: initiation, magnitude, and mobility. Landslides (2020). https://doi.org/10.1007/s10346-020-01506-3

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10 August 2020

Rajmala: a deadly landslide in Kerala, India

Rajmala: a deadly landslide in Kerala, India

Please see an update on this landslide, now termed the Pettimudi landslide, here.

On Thursday 6 August 2020 a large landslide occurred at Rajmala near to Munnar, Kerala in western India.  The landslide, which was triggered by the same spell of intense monsoon rainfall that was a factor in the Air India Express airliner accident on the same day, struck the accommodation of workers from a tea estate.  At the time of writing, 43 bodies have been recovered from the site.  Reports suggest that a further 28 people are likely to be missing, giving a total toll of 71 people, although there is always considerable uncertainty.

So far I have found little information about the specifics of the landslide, and images that provide a decent oversight are difficult to obtain.  The best I have found to date is this one, from India Life and Times:-

The Rajmala landslide in Kerala, India

The Rajmala landslide in Kerala, India. Image from India Life and Times.

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This appears to be a large, flow type slide in highly weathered soil. although better images are needed to understand it properly.

This is the largest landslide in India so far in the 2020 monsoon, although there are several weeks of rain to come yet.  Large landslides in Kerala have happened previously.  On the same day in 2019 a large landslide occurred at Kavalaparra in Kerala, killing 59 people.

Please see an update on this landslide, now termed the Pettimudi landslide, here.

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Quickslide 1: another deadly landslide in South Korea

On Friday 7 August 2020 another large, mobile landslide struck South Korea.  On this occasion the landslide was located in Gokseong County, South Jeolla, killing five people.  Korea JooAng Daily has a good image of the landslide:-

The landslide in Gokseong County, in South Korea

The landslide in Gokseong County, in South Korea on Friday 7 August 2020, which killed five people. Image from Korea JooAng Daily.

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A tropical cyclone is expected to bring more heavy rainfall today.

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Quickslide 2: a seismically-induced rockslide in the Sawtooth Mountains in Idaho

Yahoo has news of a seismically-induced rockslide in the Sawtooth Mountains in Idaho on 7 AugustThe video is cool, although I recommend sound off (for the sake of those around you and for your own sanity):-

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5 August 2020

Recent landslides triggered by rainfall in South Korea

Recent landslides triggered by rainfall in South Korea

In the last few days South Korea has been hit by very heavy rainfall, triggering landslides that have had a substantial impact.  The recent heavy rainfall comes on the back of a 42 day long period of monsoon rainfall.  In common with other parts of Asia, most notably Nepal and China, South Korea is suffering an unusually intense monsoon this year.  Incidentally, it is likely that this rainfall will be causing substantial levels of loss in North Korea as well, but of course there is little information available about this.

Yesterday, two significant fatal landslides were reported in South Korea.  In Gapyeong three generations of the same family were killed in a holiday home.  The family were all New Zealand citizens.

South Korea landslide

The aftermath of the landslide at Gapyeong in South Korea, which killed three people. Image from AP via Internewscast.

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Elsewhere, three workers were killed when a landslide destroyed a factory.  I have not been able to track down the location of this event as yet.

News reports in Korean suggest other landslide fatalities:

  • A landslide occurred in Hwabong in Gyeonggi Province in which a man died.
  • A woman died in a landslide at Umjeong, in North Chungcheong Province.
  • In Songak in Chungnam, two men are reported to be missing.

The image below shows the aftermath of a landslide at Juksani in Gyeonggi Province:-

Juksani landslide in South Korea

The landslide at Juksani in Gyeonggi Province. Image via TBS Korea.

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Unfortunately further heavy rainfall is forecast, so further landslides are possible.

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Quickslide 1: Rest and be Thankful again…

Heavy rainfall in Scotland yesterday triggered another large landslide that has blocked the important A83 trunk road at Rest and be Thankful.  Judging by the images this might be the largest of the set of landslides in this long sequence of events.

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Quickslide 2: an urban landslide in Mumbai caught on video

Youtube has a quite exciting video of an urban landslide on a major road in Mumbai yesterday.  Fortunately no-one was killed:-

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