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15 November 2019

The Blackhawk landslide

The Blackhawk landslide

The Blackhawk landslide is without doubt one of the most impressive rock avalanches on Earth.  It is located at 34.393, -116.773 in the Lucerne Valley on the escarpment that divides the San Bernardino Mountains to the south from the Mojave Desert to the north, in California.  This is a Google Earth image of the landslide source and deposit:-

The Blackhawk landslide

A Google Earth image of the Blackhawk landslide in the Lucerne Valley of California.

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As the image shows, this is a landslide on a very grand scale.  With an estimated volume of about 300 million cubic metres, the landslide extends over a distance of about 9 km from the crown to the toe, with a deposit that is up to 2 km wide and up to 30 m thick.  The fall height is estimated to be about 1,200 m in total, making this a highly mobile landslide.

The event is not recent.  Dating of the deposit suggests that it may have occurred about 18,000 years ago, although there is huge uncertainty in that date.  However, in the dry desert environment of inland California the landslide is exceptionally well-preserved, and of course the landslide mass contrasts with the valley floor, rendering the mass highly visible.

This is a landslide that is surprisingly poorly investigated.  There is a very nice PhD thesis from 1959 by Ronald Shreeve that is online, which describes the geology and mechanics of the landslide.  This was in the days in which a PhD thesis could be just 84 pages long (there are lessons to learn from that!).   Shreeve describes the geology, and tries to explain the exceptional mobility of the landslide, hypothesizing that it may have moved on a lubricating basal air layer.  There is also a nice blog article about it on the excellent Looking for Detachment blog.  Finally, there is a book chapter from 1978 about the landslide by Brann Johnson, but even the University of Sheffield subscription to Science Direct does not provide access to that one.

This is landslide that would really benefit from a revisit using up to date techniques.  There is exquisite hummocky morphology in the landslide deposit, captured well in the this 2006 Google Earth image:-

The Blackhawk landslide

Google Earth image of the Blackhawk landslide in California

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And to me, the now dissected landslide source area suggests that this might have been quite a complex event too.  This is a Google Earth image of the landslide scar area; I have annotated the approximate boundaries of the upper part of the deposit:-

The Blackhawk landslide source

Google Earth image of the source area of the Blackhawk landslide.

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The implication appears to be a highly unusual morphology of the landslide scar.  It is not clear to me how the mechanics of this part of the landslide motion would have operated – is there a large volume of stalled material still within the scar area?

Acknowledgement and footnote

Many thanks to my friend funkenbeachin for pointing out this landslide, and for the discussions about it.  He has hypothesised that there may be other events in this area as well – take a look at the image below.    It is not hard to believe that there is more than one landslide deposit on the valley floor:-

The area around the Blackhawk landslide

Wide angle Google Earth view of the valley floor around the Blackhawk landslide

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14 November 2019

Lokeberg: an interesting quick clay slide triggered by piling in Western Sweden

Lokeberg: an interesting quick clay slide triggered by piling in Western Sweden

In Lokeburg in western Sweden a significant landslide occurred yesterday (13 November 2019).  Anton Larsson kindly highlighted this event to the community via Twitter, posting photographs of the aftermath.

Lokeburg

The aftermath of the quick clay landslide at Lokeburg in Sweden. Image by Linus Olsson via Sverige Radio.

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The large volume of displaced material under the now deformed and moved jetty is clear.  In the trees on the left side of the image is a nicely formed rear scarp of the landslide.  But note in the trees there is also clear evidence of a crane, and on the road there is a truck.  News reports in Sweden link the landslide to the construction of a house at this location.

The location of the landslide is 57.903, 11.753, and there is good Google Earth imagery of the site:-

Lokeburg landslide

A Google Earth image of the site of the quick clay landslide at Lokeburg in Sweden.

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Fortunately, no-one was killed or injured in the landslide.  Anton Larsson tweeted to provide a possible explanation:

“Based on news reports, the workers were piling the area to ensure stability ahead of a rather luxurious beach house being built.”

However, subsequent reports have confirmed that it was not piling, but ground improvement through lime/cement-stabilization (which makes more sense in terms of the equipment present at the site).  Thanks to Carolina for her helpful comment below that has clarified this point.

The most likely explanation for this landslide is that it is a quick clay slideQuick clays are materials laid down in glaciomarine conditions that are “sensitive“, meaning that their strength can abruptly reduce when subjected to rapid changes in stress.  The effect might be very local initially, but spreads through the deposit rapidly as the stress change propagates.  This can lead to large-scale failures.

In this case a good working hypothesis would be that the piling operation generated the abrupt stress change that initiated the failure.  Fortunately, the extent of the quick clay deposit was not particularly large, so the failure was contained.

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12 November 2019

The 2019 Cotabato earthquakes: the Barangay Bato landslide cluster

The 2019 Cotabato earthquakes: the Barangay Bato landslide cluster

Yesterday I highlighted a significant landslide cluster triggered by the 2019 Cotabato earthquakes, at Barangay Buhay.  I indicated that there is another cluster on the imagery, located at Barangay Bato (6.84, 125.16).

This is a Planet Labs satellite image, collected on 8 November 2019, providing an overview of this significant landslide cluster:-

2019 Catobato earthquakes landslides

The Barangay Bato landslide cluster, triggered by the2019 Cotabato earthquakes. Planet Labs PlanetScope image, captured on 8 November 2019. Copyright Planet Labs, used with permission.

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There are several hundred landslides in this cluster, located over an approximately 5 x 5 km area.  Most of the landslides appear to be shallow disrputed slides on steeper terrain.  There are two larger landslides in the cluster.  On the west side there is a large rockslide close to Barangay Bato itself:-

2019 Cotabato earthquakes

Planet Labs image of the large rockslide located close to Barangay Bato, triggered by the Cotabato earthquakes. Planet Labs PlanetScope image, captured on 8 November 2019. Copyright Planet Labs, used with permission.

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This landslide was extensively photographed in the aftermath of the earthquake:-

2019 Cotabato earthquakes

An aerial photo of a massive landslide close to Barangay Bato, triggered by the 2019 Cotabato earthquakes.Photo courtesy of Pfc. Jacil Joe Tupa 10th ID-ERC, via the Manila Bulletin.

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In the northeast of this cluster, there is another largish (approximately 300 m long) landslide, although it is difficult at present to fully understand this slide:-

2019 Cotabato earthquakes

Planet Labs image of a large rockslide located in the Barangay Bato landslide cluster, triggered by the Cotabato earthquakes. Planet Labs PlanetScope image, captured on 8 November 2019. Copyright Planet Labs, used with permission.

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The other landslides are much smaller, but there are large numbers throughout this cluster.  The next step is of course to relate these two clusters to the actual locations of the earthquakes that occurred in the sequence.  It will be interesting to see which earthquakes triggered landslides, and which did not.

Reference

Planet Team (2019). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

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11 November 2019

Planet Labs images of landslides triggered by the 2019 Cotabato earthquakes in the Philippines

Planet Labs images of landslides triggered by the 2019 Cotabato earthquakes in the Philippines

Planet Labs satellite images have now become available showing at least some of the landslides triggered by the 2019 Cotabato earthquakes sequence in the Philippines, which I highlighted last week.  Cloud is still affecting some of the area, so the picture is not yet fully clear, but there is sufficient detail to see at least two large clusters of landslides.  Below is an overview image, based on an image collected on 8 November 2019, of one of the clusters (located at 6.960, 125.200).  I’ll call this group of landslides the Barangay Buhay cluster; the other cluster I have found is at Barangay Bato (located at 6.84, 125.16).  I will endeavour to feature the other later this week.

Cotabato earthquakes landslides

Planet Labs image of the Barangay Buhay cluster of landslides triggered by the Cotabato earthquakes. Planet Labs PlanetScope image, captured on 8 November 2019. Copyright Planet Labs, used with permission.

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There are two features of note here.  One is the c. 1 km long landslide at Barangay Buhay in Makilala, North Cotabato, which is shown in a photograph in an article about survivors of the earthquake, published in Minda News.  The article details the survival of an agricultural worker, who was buried up to his neck by one of the landslides, but I think this was probably at Barangay Bato.

Landslides triggered by the Cotabato earthquakes

Planet Labs image of one of the largest landslides triggered by the Cotabato earthquakes. Planet Labs PlanetScope image, captured on 8 November 2019. Copyright Planet Labs, used with permission.

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To the east is a large cluster of landslides, the extent of which is not fully covered by the imagery.  This cluster, which extends for at least 5 km from east to west and 3 km from north to south, contains a large number of landslides triggered by the Cotabato earthquakes.:-

Landslide cluster from the Cotabato earthquakes

Planet Labs image of the Barangay Buhay cluster of landslides triggered by the Cotabato earthquakes. Planet Labs PlanetScope image, captured on 8 November 2019. Copyright Planet Labs, used with permission.

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The Barangay Bato cluster of landslides, triggered by the Cotabato earthquakes, is also large, so watch this space…

Reference

Planet Team (2019). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

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6 November 2019

Genting: a major landslide in Malaysia

Genting: a major landslide in Malaysia

Today a major landslide occurred in the Genting Highlands of Malaysia, a popular tourist area.  Fortunately, there are no reports of casualties, although this appears to have been a near miss.  The best image that I have found of the source of the landslide is this one, posted to Twitter by Bernama:-

Genting landslide

The major landslide in the Genting Highlands of Malayasia on 6 November 2019. Image posted to Twitter by Bernama.

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The landslide appears to have been quite mobile, as a channelised flow.  Some of the debris has left the channel and flowed down the road:-

Genting landslide

The aftermath of the major landslide in the Genting Highlands of Malaysia on 6 November 2019. Images courtesy of Facebook/Germit Singh and Info Roadblock JPJ/POLIS via Today Online.

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News reports suggest that the landslide was triggered three hours into a major rainstorm in the area.  The images suggest that this started as a slip in residual soil that channelised.  The volume of debris has overwhelmed the road – it is not clear to me that there was an appropriate culvert in place. Such landslides are common in tropical areas such as Malaysia, and they are of course very hazardous.  I note also though that the images suggest that the slope may have been modified in places.

Perhaps the most interesting aspect of this landslide is that one of the surge events was captured on a mobile phone video:

<a href="https://www.youtube.com/watch?v=MtBMn_sr7dM">Youtube</a>

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The extreme mobility of the landslide is clear, and it is interesting that the landslide appears to have occurred as a series of events.  This is not obvious from the morphology of the scar and the deposit.

Google Earth imagery of this site is not particularly good, but this image from 2002 suggests that this was not the first landslide at this location:-

Genting

Google Earth imagery from 2002 of the site of the major landslide in the Genting Highlands of Malaysia on 6 November 2019.

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The landslide is at 3.429, 101.787 if you would like to take a look.

 

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5 November 2019

The Tagarma rock avalanche in the Pamir-western Himalayan syntaxis of the Tibetan Plateau

The Tagarma rock avalanche in the Pamir-western Himalayan syntaxis of the Tibetan Plateau

The Tagarma rock avalanche is an ancient but beautifully-preserved landslide located on the Tibetan Plateau at 38.081, 75.185.  This large landslide has recently been described in a paper (Wang et al. 2019) published in the journal Landslides.  This is an interesting landslide in that it is located in the so-called Pamir-western Himalayan syntaxis, a major kink in the tectonic boundary that runs through the Himalayas.  As such, this is an area of high seismicity – in 1895 the area was struck by the Mw≈7.0 Tashkorgan earthquake for example.  As this is an area of low rainfall, Wang et al. (2019) conclude that this rock avalanche was probably triggered by an ancient earthquake, although the date of this is unknown.

The landslide can be seen in the Google Earth image below:-

The Tagarma rock avalanche

A Google Earth image of the Tagarma rock avalanche in Tibet.

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I have indicated the location of the crown of the landslide with a red marker, whilst the toe of the landslide, in the foreground, can be seen to have some intricate flow type structures.  According to Wang et al. (2019), the landslide is 5,430 metres from crown to toe, with a vertical elevation change of 1,510 metres.  The estimated volume is 9.6 million m³.  These statistics suggest that this was a highly mobile rock avalanche.

As mentioned above, this rock avalanche has complex structures in the landslide deposit.  In the dry Tibetan climate these are beautifully preserved:-

Tagarma rock avalanche

Google Earth image of the deposit of the Tagarma rock avalanche in Tibet

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Based on detailed analysis of the deposit, Wang et al. (2019) suggest that the Tagarma rock avalanche started as a planar slide in the source area, and then transitioned into an extensional slide, in which the front of the landslide moved more rapidly than the rear portion.  Lower on the slope, the landslide encountered increased basal resistance, and thus transitioned into a compressive phase that generated the complex structures seen in the deposit.  During this phase the landslide also went through some lateral spreading.

Reference

Wang, YF., Cheng, QG., Yuan, YQ. et al. 2019. Emplacement mechanisms of the Tagarma rock avalanche on the Pamir-western Himalayan syntaxis of the Tibetan Plateau, China. Landslides. https://doi.org/10.1007/s10346-019-01298-1

 

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4 November 2019

Cotabato, Philippines: large landslides from the series of earthquakes in October 2019

Cotabato, Philippines: large landslides from the series of earthquakes in October 2019

In the Philippines, Cotabato in Mindanao has been hit by a series of substantial earthquakes in recent weeks, including a M=6.3 event on 16 October, an M=6.6 event on 29 October and an M=6.5 earthquake on 31 October.  These earthquakes have caused substantial levels of damage, and have triggered landslides in the hilly terrain.

DOST-PHIVOLCS has published a graphic showing two of the larger landslides triggered by the 29 and 31 October earthquakes.  This appears to show two large slope failures:-

Landslides in Cotabato

Landslides triggered by the October 2019 earthquake sequence in Cotabato, Philippines, Image created by DOST-PHIVOLCS

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The image appears to show, on the left, a large, mostly planar landslide. In Hong Kong this would be considered to be an open hillslope failure,  It is mostly shallow, bar a deeper seated component at the crown of the slide.  There appears to be some flow structures in the deposit on the right side.  There are some buildings close to the toe of the landslide, just below the road that has been inundated.

On the other hand, the image on the right appears to be a large, channelised flow, starting from comparatively small slips high on the hillside.  There are some other, smaller landslides on the hillside as well.

Meanwhile, Sotiris Valkionitis tweeted some before and after Sentinel images of landslides triggered by the earthquake sequence  in Cotaboto:-

Landslides in Cotabato, Philippines

Before and after Sentinel images of the landslides in Cotabato, Philippines. Images from Sentinel 2, tweeted by Sotiris Valkaniotis.

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The Philippines National Disaster Risk Reduction and Management Council (NDRRMC) is publishing regular Situation Reports on the impact of these earthquakes.  SitRep12 (4 November 2019) indicates that the largest landslides were triggered by the 29 October earthquake.  To date they have recorded 22 fatalities in total, with five of these being directly attributed to landslides.  A further two people are reported to be missing as a result of landslides.  However, other fatalities are reported to be the result of “fallen debris”, which could also be the impact of mass movements.

News reports indicate that the impact of landslides could be more a little more substantial.  Inquirer reports four people missing in the landslide at Bato and three in Balawan.

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29 October 2019

Landslide movement mechanisms: evidence from longitudinal ridges on Mars

Landslide movement mechanisms: evidence from longitudinal ridges on Mars

It is well established that some very rapid rock avalanches develop longitudinal ridge structures.  A beautiful example is the Mount La Perouse rock avalanche in Alaska, as shown in the image below:-

Longitudinal ridges

Longitudinal ridges on the Mount La Perouse rock avalanche in Alaska. The ridge structures are clear on the lowest part of the avalanche deposit in the distance. Image by Marten Geertsema.

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These longitudinal ridges are only seen in very large landslides, and they are present on deposits from mass movements on Earth and on other planetary bodies.  Clearly the formation of these structures is indicative of the internal dynamics of the landslide, but their formation has been difficult to understand.

On Earth, such features are most frequently seen in deposits on glaciers.  This has led to the proposal that they are associated with flow over low friction surfaces, such as ice or soft (deformable) sediments.  The ridges probably  form because the avalanche behaves in a manner similar to a fluid, allowing turbulent processes to develop, generating convection cells in the flowing mass.  These observations have in turn been applied to the interpretation of large landslides on Mars, for which the presence of longitudinal ridges has been taken to infer that the landslide has flowed over an icy substrate.  The apparent presence of this ice clearly has important implications.

However, in a study just published in Nature Communications (and available open access), Magnari et al. (2019) have examined a very large rock avalanche at Coprates Labes, located in Valles Marineris on Mars.  This is beautiful landslide deposit – from source to toe it is over 50 kilometres long:-

Longitudinal ridges

Longitudinal ridges on the vast landslide on Coprates Labes, located in Valles Marineris, Mars. Image via Phys.org, by Magnarini et al. (2019).

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This landslide clearly displays spectacular longitudinal ridges.  Magnari et al. (2019) measured the size and shape of the ridges in this landslide deposit, and have analysed the more subtle morphology of the deposit, most notably en echelon structures superimposed on the ridges themselves, as shown below:-

Longitudinal ridges

En echelon structures, indicated by the orange arrowheads, superimposed onto the longitudinal ridges on the rock avalanche on Mars. Image from Magnarini et al. (2019).

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Magnari et al. (2019) note that these more subtle, but clearly evident, features have also been seen in laboratory experiments in rapid granular flows.  In the experiments, these features did not require the presence of ice to form.  Therefore, they conclude that the presence of longitudinal ridges should not be taken to infer that ice is a prerequisite for the development of these landslides on Mars.

Whilst in many ways the dynamics of landslides on Mars may seem to be a comparatively obscure topic, the analysis of these features casts a light on the mechanisms of landslides on Earth.  Most importantly, this study provides further evidence that the movement mechanisms of these giant landslides may be associated with turbulent granular processes in the flowing landslide mass.  As these very dynamic landslides become more common in response to global heating, this is an important input to our ability to assess the hazard that they may pose.

Reference

Magnarini, G., Mitchell, T.M., Grindrod, P.M., Goren, L. and Schmitt, H.H. 2019.  Longitudinal ridges imparted by high-speed granular flow mechanisms in martian landslidesNature Communications, 4711 (10). https://doi.org/10.1038/s41467-019-12734-0.

 

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28 October 2019

Gongo Soco: continued deformation of the slope of a high wall mine in Brazil

Gongo Soco: continued deformation of the slope of a high wall mine in Brazil

In the aftermath of the two disastrous tailings dam failures in Brazil, mining company Vale continues to undertake a massive programme of evaluation of the stability of its facilities.  According to Mining Magazine, this programme is costing $1.7 billion in the first instance.  In early October, the company reported on its progress to date, noting that several facilities continue to cause concern, although they are being actively managed.

One facility that continues to cause concern is at the massive Gongo Soco mine, which is located at -19.957, -43.599.  Here, a high wall rock slope on the mine side is actively deforming, raising concerns of a collapse that could displace mine waste, creating another tailings release downstream.

This is a Google Earth image of the site, taken on 1 June 2019:-

Gongo Soco

Google Earth image of the Gongo Soco mine. Image dated 1 June 2019.

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Google Earth has a further image, dated 1 August 2019, which clearly shows the development of this large slope failure:-

Google Earth image of the Gongo Soco mine. Image dated 1 August 2019.

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Three things stand out here:

  1. The large fracture that has developed on the right side of the slope, from the fork in the road down to the corner of the lake. I would provisionally interpret this as the lateral margin of the active slide;
  2. The development of tension features at the back of the deforming block, most notable in the area above the lower track on the centre left of the image;
  3. General deterioration of the terraces, presumably as the rock mass deforms.

I have take a look at the most recent Planet Labs image of the site.  The image below was collected on 18 October 2019 with the PlanetScope instrument.  The resolution is lower than the Google Earth imagery, but the continued development of the slope is clear:-

Gongo Soco

Planet Labs PlanetScope image of the Gongo Soco mine. Image dated 18 October 2019, copyright Planet Labs, used with permission.

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On the image the lateral scarp on the right side has further developed, and there is now clear evidence of one on the left too.  The rear scarp has developed significantly and there is clear evidence of further deterioration of the terraces as well.  On the lower part of the slope a set of smaller landslides have developed, with a very notable feature in the central portion.

To manage the risk, the slope is being actively monitored, and a large wall is being constructed downstream to contain any debris in the event of a major collapse.

Reference

Planet Team (2019). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

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24 October 2019

The social impact of landslides in Mexico

The social impact of landslides in Mexico

In recent years there has been an increasing number of studies examining the impact of landslides in specific countries, such as China, or in regions of the world, such as Latin America, as well as the global reviews in which I have been involved. These studies have have shone a light on the high level of losses occurring in many areas of the world.

The latest such study (Diaz et al. 2019) examines losses for Mexico over the period from 1935 to 2017. Whilst many other studies have focused directly on losses, this one places an emphasis on the social impact of landslides in Mexico, which is an interesting approach that could be replicated elsewhere. Mexico is particularly in interesting as in the study that I undertook with Sergio Sepulveda on landslides in Latin America (Sepulveda and Petley 2015 – available via open access), Mexico had the 4th largest number of fatalities.

In total, the authors have recorded 1,967 landslides across Mexico, the vast majority of which were triggered by rainfall.  The map below shows the geographical distribution of the landslides across the country – note the concentration in the central and southern part of Mexico:-

Landslides in Mexico

Spatial distribution of landslides in Mexico and altitude in the period from 1935 to 2017. Figure from Diaz et al. (2019).

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Interestingly, Diaz et al. (2019) ascribe this primarily to the population distribution:

“A higher concentration is noticed in the center of the country; in the states of Hidalgo, Mexico, Puebla, and Tlaxcala; and in the central region of Veracruz along its border with Puebla and northern Mexico City. It is likely that this concentration is related to population density since these are the states with the heaviest infrastructure development in the country.”

Whilst I’m sure this is correct, I wonder whether the climate might be a significant control as well:

Climate types in Mexico

The distrubtion of Koppen Climate types in Mexico. Image via Wikipedia.

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Diaz et al. (2019) have recorded 3,447 fatalities from landslides over the study period, with the largest event being a catastrophic landslide on 1 October 1956 that claimed 1,000 lives in La Paz, Baja California.  The study provides a detailed investigation of the municipalities with the highest number of landslide losses in terms of simple numbers of fatalities and of losses per capita.  They examine the degree to which these municipalities suffer from marginalization, defined as “the deficiencies suffered by the population as a result of the lack of access to education, housing in poor condition, low infrastructural development, and lack of material goods.”

Diaz et al. (2019) found that “the concentration of events [i.e. loss causing landslides] occurs in areas with high degrees of marginalization, which indicates that the most marginalized populations are the most prone to experience the effect of any sort of landslide.”

In many ways such a finding is not a surprise, but it is a very useful reminder that landslide losses are a social problem as much as one driven by physical processes.

Reference

Díaz, S.R., Cadena, E., Adame, S. et al. 2019.  Landslides in Mexico: their occurrence and social impact since 1935. Landslides. https://doi.org/10.1007/s10346-019-01285-6

Sepúlveda, S.A. and Petley, D.N. 2015. Regional trends and controlling factors of fatal landslides in Latin America and the Caribbean. Natural Hazards and Earth System Sciences, 15, 1821-1833, doi:10.5194/nhess-15-1821-2015. The full paper available to download as a PDF.

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