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3 September 2018

Dynamic liquefaction: a mass movement that can sink ships

Dynamic liquefaction: a mass movement that can sink ships

On 18 May 2005,  a mid-size bulk cargo ship, the Hui Long, suddenly developed a 15-degree list towards the port side whilst transiting the waters off Sumatra.  The ship, which was 158 m long and 23 m wide, was carrying fluorspar in two of its four holds.  At the time that the list started to develop, the ship was sailing in a moderate sea, with south-westerly winds blowing at force 5. The ship was rolling on the swell by about 10 degrees to each side of the vertical.

The ship reportedly started to list at approximately 15: 35 on 18 May.  The crew responded by trying to right the vessel by flooding tanks on the starboard side.  This was unsuccessful, and by 16:02 the list had worsened to 40 degrees to port, at which point the Master decided to abandon the vessel. All crew were successfully rescued, but the ship was lost the following day despite attempts to salvage it.

dynamic liquefaction

The severe list of the Hui Long following dynamic liquefaction of its bulk cargo in 1999. The ship was lost the next day.

This is one of many known examples in which bulk carriers have been lost in apparently benign conditions.  The events above are described in an article published a couple of years ago (Munro and Mohajerani 2016) that describes case studies in which bulk carriers have been lost due to dynamic liquefaction (and associated processes) of their bulk cargoes.  Last week, Susan Gourvenec of the University of Southampton published a nice article in The Conversation that explored this phenomenon of dynamic liquefaction of bulk cargoes, and the resultant loss of the ship.  As she notes at the start of her article:

“Think of a dangerous cargo and toxic waste or explosives might come to mind. But granular cargoes such as crushed ore and mineral sands are responsible for the loss of numerous ships every year. On average, ten “solid bulk cargo” carriers have been lost at sea each year for the last decade.”

This dynamic liquefaction phenomenon is the same as the behaviour that we observe in geotechnical materials during earthquakes.  Many significant landslides have been associated with this process, such as the multiple failures of loess during large seismic events in central ChinaMunro and Mohajerani (2016) describe the aftermath of another liquefaction event, on the bulk carrier Padang Hawk, in 1999.  Fortunately in this case the ship was saved.  The images taken of the cargo after liquefaction occurred nicely illustrate the problem:-

dynamic liqefaction

The aftermath of dynamic liquefaction on the Padang Hawk in 1999. Image via TMS Testing

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In each case, the motion and/or vibration of the ship has induced dynamic liquefaction, just as we see in slopes in susceptible materials when they are subjected to seismic accelerations. Once liquefaction has occurred the cargo starts to move with the rolling of the ship, potentially exacerbating the rolling motion, and creating a feedback loop that allows the situation to worsen.  The cargo can drain whilst located on one side of the ship, inducing a permanent list.  Once this has happened it is hard to correct the problem whilst at sea.

Sadly, it seems that our understanding of dynamic liquefaction is not being translated across the disciplines to improve safety in ships. Susan Gourvenec explores why ships continue to be lost through this process:-

“The International Maritime Organisation has codes governing how much moisture is allowed in solid bulk cargo in order to prevent liquefaction. So why does it still happen?

The technical answer is that the existing guidance on stowing and shipping solid bulk cargoes is too simplistic. Liquefaction potential depends not just on how much moisture is in a bulk cargo but also other material characteristics, such as the particle size distribution, the ratio of the volume of solid particles to water and the relative density of the cargo, as well as the method of loading and the motions of the vessel during the voyage.

The production and transport of new materials, such as bauxite, and increased processing of traditional ores before they are transported, means more cargo is being carried whose material behaviour is not well understood. This increases the risk of cargo liquefaction.”

It is not obvious that landslide processes can sink large ships, but this is indeed the case.

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29 August 2018

Landslides from the 16 August 2018 Mw=5.1 Molise earthquake in southern Italy

Landslides from the 16 August 2018 Mw=5.1 Molise earthquake in southern Italy

Text and photographs supplied by Salvatore Martino, University of Roma “Sapienza”

On 16 August 2018, a Mw=5.1 earthquake occurred 4 km SE of the Montecilfone village (Molise, Southern Italy); by 20 August about 200 aftershocks, of which nine with a magnitude of Mw=3 or greater associated with the Molise earthquake, (Fig.1) had been recorded by the Italian National Accelerometric Network (RAN), supported by some temporary stations installed by the Italian National Institute of Geophysics and Volcanology (INGV).

Molise earthquake

Figure 1: Aftershock distribution for the Mw=5.1 Molise earthquake in Italy. Map via INGV Terremoti.

 

The epicentral area corresponds to the hill-slope landscape between the Biferno and Trigno Rivers.  According to the official geological map of Italy, in the epicentral area outcrops a complex sedimentary succession of terrigenous deposits including scaly clays ascribable to the Argille Varicolori Formation of the Paleocene, arenaceous-pelitic flysch of the Miocene-Pliocene and silty-clays of the Pliocene (Fig.2).

Molise earthquake

Figure 2: Geology map of the area affected by the Mw=5.1 Molise earthquake in Italy.

During the days before the mainshock occurrence, intense rainfall occurred in the epicentral area, increasing the susceptibility to earthquake-induced landslides. Immediately after the earthquake the CERI “Sapienza” research center in co-operation with the local geological office Geoservizi S.r.l. carried on field surveys to create an inventory of the earthquake-induced ground effects as soon as possible, to avoid possible deletion of the ground evidence due to new rainfall and the action of local farmers.

No earthquake-induced effects had been previously documented  in this area (between Guglionesi, Larino and Montenero di Bisaccia villages) according to the available catalogues (Figs 3 and 4). Therefore, this is the first time that in this sector of the Central Apennine it is possible to inventory earthquake-induced effects and to analyze their spatial distribution.

Molise earthquake

Figure 3: Previously documented earthquake-induced ground failures in the area of the Mw=5.1 Molise earthquake in Italy.

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Molise earthquake

Figure 4: Landslides triggered by the Mw=5.1 Molise earthqauke in Italy.

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Until now some tens of earthquake-induced landslides have been identified, which are concentrated in a radius of almost 2 km from the epicenter. These landslides mainly consist in re-activations of earth slides (Fig.5); for several of them, local people testified that the movement occurred following the mainshock. The landslide reactivation caused, in some case, not negligible damage to roads and infrastructures (Figs 6, 7 and 8).

Molise earthquake

Figure 5: The landscape of the area affected by the Mw=5.1 Molise earthquake in Italy

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Molise earthquake

Figure 6: a slope failure induced by the Mw=5.1 Molise earthquake in Italy.

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Molise earthquake

Figure 7: a slope failure induced by the Mw=5.1 Molise earthquake in Italy.

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Molise earthquake

Figure 8: a slope failure induced by the Mw=5.1 Molise earthquake in Italy.

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The inventory of the ground effects will be included in the on-line CEDIT catalogue managed by the CERI “Sapienza”.

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28 August 2018

Mapping global landslides

Mapping global landslides

As I noted last week, as part of our work on deaths caused by global landslides, my colleague Melanie Froude has been establishing an online tool that allows mapping of that landslides on the database.  This tool is now online using an ESRI ARCGIS mapping tool.  It’s probably fair to say that at this stage it is a little experimental, and I warn in particular against trying to interpret too much from any individual record.  The most difficult element in compiling a database like this is in identifying the precise location of each landslide.  In the vast majority of cases the information that we have does not pin the location to a particular slope.  Thus, we map the landslide as sitting within an area, the size of which reflects the precision of the report, and from this we distill a single point to display online.  In some cases, where the uncertainty is large, we cannot map the landslide.

But the tool does provide a global and regional view of the distribution of losses from landslides.  The remarkable unevenness of the distribution of global landslides is clear:-

Global landslides

The distribution of global landslides. Data from Froude and Petley (2018).

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We have tried to provide the ability to look in more detail at the data.  So, for example, there are layers that display the distribution of landslides caused by mining, both legal and illegal (unregulated):-

Global landslides

The distribution of global landslides caused by legal and illegal mining. Data from Froude and Petley (2018).

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The data show that mining-induced fatal landslides are rare in richer countries, but are common in less developed nations, especially in tropical and subtropical environments.  These landslides are mostly avoidable.

The data should be useful at a higher resolution too.  I have frequently written on this blog about the high frequency of landslides in Nepal – examination of the data in the mapping tool explains why this is such a concern:-

Global landslides

The distribution of fatal landslides in Nepal. Data from Froude and Petley (2018).

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Reference

Froude, M. J. and Petley, D. N. 2018. Global fatal landslide occurrence from 2004 to 2016. Natural Hazards and Earth System Sciences, 18, 2161-2181, https://doi.org/10.5194/nhess-18-2161-2018.

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24 August 2018

Global fatal landslide occurrence from 2004 to 2016

Global fatal landslide occurrence from 2004 to 2016

Yesterday, Melanie Froude and I published in NHESS our paper on global fatal landslide occurrence (Froude and Petley 2018).  This paper is based upon the work that I have been undertaking since September 2002 to compile a database of events that kill people.  I published a paper six years ago (Petley 2012) that summarised the findings, and there is an accompanying blog post that provides some explanation.   The paper we have now published, which is open access, provides both an update to this dataset and some new insights into global losses from landslides.

The headline figure is that in total (excluding landslides triggered by earthquakes) about 56,000 people were killed by landslides over that period, in about 4,900 distinct landslide events.  As expected, the majority of those landslides occurred in less developed countries in Asia, with particular hotspots in for example India, Nepal, Pakistan, the Philippines and Indonesia.  We have looked carefully at the time series data as well – the graph below shows the full dataset, organised in five day blocks (pentads):-

global fatal landslide occurrence

Global fatal landslide occurrence from 2004 to 2016 inclusive. Graph from Froude and Petley (2018).

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The cumulative trend graph shows that we find no convincing evidence that overall landslide losses are increasing globally.  The strong annual cyclicity in the data is evident too, which landslides peaking each year as the Asian summer monsoons generate failures in populated areas.  But note that the shape of the annual cycle also varies hugely, presumably in response to variations in rainfall totals and locations.  We know that this needs much more investigation, and we are working on it, but we suspect that we will need 30 years of data to understand it properly.  The high quality dataset (i.e. from January 2004 onwards) is now 14 years old, and I have 17 years of my career left, so that analysis may be the one that I write as I retire!

I think the most interesting finding in this paper, and the one that goes well beyond anything we have done before, is in the patterns with time of landslides caused by humans.  The graph below, from the paper, plots a range of human-induced landslide types with time:-

Global fatal landslide occurrence

Global fatal landslide occurrence – losses from human induced mass movements. Graph from Froude and Petley (2018).

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In most cases we have recorded an increase in losses with time for landslides triggered by humans.  This is particularly the case for mining (especially illegal or unregulated mining) and hill cutting.  Our strong sense is that these patterns reflect an increase in these activities in poorer countries, especially in Asia.  These landslides are avoidable; they are in every case a tragedy.

I will post again on this early next week, but after considerable work we have been able to get the dataset online.  Melanie has set up an ESRI ARCGIS system that allows the user to access the data and to generate maps using it.  This has been an ambition for a long time, and we hope that it will be useful.

References

Froude, M. J. and Petley, D. N. 2018. Global fatal landslide occurrence from 2004 to 2016. Natural Hazards and Earth System Sciences, 18, 2161-2181, https://doi.org/10.5194/nhess-18-2161-2018.

Petley, D.N. 2012. Global patterns of loss of life from landslides. Geology 40 (10), 927-930.

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22 August 2018

High resolution imagery of the Pashgor debris flow in Afghanistan

High resolution imagery of the Pashgor debris flow in Afghanistan

A little before I took some time off to go to Australia on leave with my two teenagers, I posted about a debris flow that struck Pashgor in Afghanistan as a result of a Jökulhlaup event. In a comment on my original post, Juan Pablo Milana provided an explanation for the event:-

Dear Dave, It was a Jökulhlaup (an arid variation!): In this case the collapse of a supraglacial lake over a debris covered glacier, probably by breaking down an ice barrier due to an excess of hydrostatic pressure. It did not happened before probably because the well visible supraglacial hollow that hosted the lake (sometimes described as thermokarst) it is large and only with excessive snow melt could reach the critical depth to overcome the needed pressure to lift the mix of glacier ice and debris. In fact your last image shows that the lake exceeded the size of the hollow that in many older images showed accumulation of water, but with smaller area covered by it. I cannot send you the images that prove this, but I posted a comment in twitter with an image edited showing the glacier characteristics. It is what we locally call complex glacier system as it shows the transition form a ice-exposed part to a debris-covered ice and then into a rock.glacier, which due to its larger debris concentration cannot be floated, but there are case where ice concentration of rock glaciers in Chile reach 99%. regards.

Whilst I was away, Planet Labs kindly collected a high resolution Skysat image of the site, which I have not been able to post until now.  This is the full extent of the flow path of the debris flow:-

Pashgor

Planet Labs Skysat image of the track of the Pashgor debris flow in Afghanistan. Image collected on 20th July 2018 and used with permission.

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Most importantly, the image provides an extraordinary level of detail about the site of the glacial lake that formed and then drained to generate this disaster:-

Pashgor

Planet Labs Skysat image of the site of the glacial lake that generated the debris flow that devastated the village of Pashgor in Afghanistan in July 2018. Image collected on 20th July 2018 and used with permission.

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Whilst this is the impact on the village:-

Pashgor

Planet Labs Skysat image of the impact of the debris flow at Pashgor in Afghanistan in July 2018. Image collected by Planet Labs Skysat on 4th August 2018, and used with permission.

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This image was collected on 4th August.  At that point the lake was still in present.

Reference

Planet Team (2018). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com

 

 

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26 July 2018

Detail on the Fagraskógarfjall landslide from the Icelandic Met Office

Detail on the Fagraskógarfjall landslide from the Icelandic Met Office

The Icelandic Met Office has published two articles online about the Fagraskógarfjall landslide in Iceland.  These provide a lot more detail about the landslide and its timing, and about possible triggering mechanisms.  The first, published on 10th July, indicates that the slide happened at 05:17 am on 7th July, as measured from seismic data.  I noted at the time that seismic data might provide insight into the slide; I hope that analysis is possible on the dataset.  Interestingly, the report indicates that a smaller landslide may have been noted by a local hunter at about 23:30 the previous evening; this may have been the event that destabilised the main part of the slope.

This report also notes that the debris is up to 20 m thick, and the image below gives a better perspective on spreading mechanism of the slide:-

Fagraskógarfjall landslide

The front of the debris of the Fagraskógarfjall landslide in Iceland. Image by Tómas Jóhannesson via the Icelandic Met Office

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The way that the debris has bulldozed the turf is quite interesting, suggesting that the landslide debris may have been sliding rather than flowing, at least in the latter stages of movement.  The article also notes that the run-out angle is 12-13°, which is quite a high level of mobility for a landslide of this volume.  This probably implies quite high velocity.

The second article, published this week, provides detail from a digital elevation model (DEM) of the landslide.  This can be viewed in the following video:-

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This gives an initial volume estimate of about 7 million m³ (source volume), and about 10 million m³ for the debris volume (this allows for entrainment of debris along the route and the bulking of the sediment during motion).  Importantly, InSAR analysis of the site by Vincent Drouin at the University of Iceland and the National Land Survey of Iceland suggests that precursory deformation of the landslide mass could be detected from 2015 onwards.  This is not unexpected, but it does provide the potential for detecting these events prior to failure.  This is an exciting area, and one that needs further development.

Finally, the article notes that it is unlikely that this event was associated with permafrost degradation given the elevation of the slope.  As I noted previously, Iceland has had exceptionally wet weather this summer (this is the flip side of the drought in northern Europe).  It is likely that the heavy rainfall accelerated the creep of this large rock mass through its failure point.

Thanks to Harpa Grímsdóttir for highlighting these articles.

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24 July 2018

Fagraskogarfjall landslide – a high resolution satellite image via Planet Labs

Fagraskogarfjall landslide – a high resolution satellite image via Planet Labs

Planet Labs have succeeded in collecting a high resolution satellite image of the Fagraskogarfjall landslide, the very large mass movement that occurred in Iceland on 7th July 2018.  As a reminder, this is one of the largest known landslides in Iceland in recent history, triggered by the prolonged period of heavy rainfall from which the country has been suffering.  The image was collected on 19th July 2018 using the SkySat satellite system, providing a very high resolution (and actually rather spectacular) image:-

Fagraskogarfjall landslide

Planet Labs SkySat image of the Fagraskogarfjall landslide in Iceland. SkySat Image dated 19th July 2018, used with permission.

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The high mobility of the Fagraskogarfjall landslide is evident from the image, with the deposit traveling a substantial distance across the flat terrain at the toe of the slope.  I wonder in this case whether the likely saturated conditions in the valley floor may have increased mobility.  The image also suggests that there may have been a second, smaller event with the debris falling onto the remains of the first failure.  This would seem to be the most likely explanation for the lighter coloured debris that sits on the main landslide deposit:-

Fagraskogarfjall landslide

Detail of the Planet Labs SkySat image of the Fagraskogarfjall landslide. SkySat Image dated 19th July 2018, used with permission.

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This landslide also appears to have developed a very distinctive hummocky topography:-

Fagraskogarfjall landslide

Detail of the Planet Labs SkySat image of the Fagraskogarfjall landslide, showing the hummocky terrain. SkySat Image dated 19th July 2018, used with permission.

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This sort of hummocky terrain is common in landslides in volcanic terrain.  These hummocks are formed by extensional faulting in the early stage of landslide movement.  As the landslide ,movement develops, large blocks of mobile material develop and spread. In general, it has been noted that the largest hummocks lie at the rear of the landslide deposit, with smaller features at the front.  There is some evidence of that in this case. If you are interested in this process, it has been modelled by Paguican et al. (2014)The paper is online as a PDF.

References

Paguican, E.M.R., van Wyk de Vries, B. & Lagmay, A.M.F. 2014 Hummocks: how they form and how they evolve in rockslide-debris avalanches. Landslides (2014) 11: 67-80. https://doi.org/10.1007/s10346-012-0368-y

Planet Team (2018). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com

 

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23 July 2018

Leach XPress: a landslide caused a pipeline explosion on 7th June 2018

Leach XPress:land subsidence caused a pipeline explosion on 7th June 2018

Leach XPress is a new $1.75 billion pipeline that transports large volumes of shale gas from the Marcellus and Utica regions of Pennsylvania, West Virginia and Ohio to consumers elsewhere in the US.  The pipeline entered full service earlier this year.  On 7th June 2018 it suffered a major rupture and explosion.  Images of the aftermath are spectacular:-

Leach Xpress

The aftermath of the June 2018 explosion on the Leach Xpress natural gas pipeline in West Virginia. Image by Martin Dofka via WV Public Broadcasting

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The event has been investigated by the National Transportation Safety Board.  On 9th July they issued a safety order (NB PDF) to the operators noting that the failure was likely caused by “land subsidence”:-

“The preliminary investigation suggests that the Failure was the result of land subsidence causing stress on a girth weld.”

The operators have been ordered to inspect other sections of the pipeline that might be subject to similar geological conditions.  The location of this event on such a steep scarp would suggest that the major problem here is likely to be subsidence caused by slope movement – and indeed some news reports have stated plainly that this event was a landslide.   The NTSB letter points out that the areas of concern are related to slopes:

After evaluating the foregoing preliminary findings of fact and considering the location of the Failure Site on Nixon Ridge, the identification of six additional areas of concern based on the existence of large spoil piles, steep slopes, or indications of slips, the fact that subsidence or slippage could lead to additional failures of the pipeline in areas with similar geological conditions

Building pipelines on steep slopes is a major challenge.  Interestingly, the Nature Conservancy Council and eight energy companies have teamed up to produce a report, entitled Improving Steep-Slope Pipeline Construction to Reduce Impacts to Natural Resources, to mitigate the impacts of landslides caused by the construction of pipelines on slopes.  The report makes a number of recommendations.  As the NCC notes, the seven pre-construction best practices are identified as follows:

  • Perform a geohazard assessment
  • Develop site-specific plans
  • Accurately identify water features
  • Identify civil or geotechnical mitigation measures
  • Develop site-specific reclamation and revegetation strategies
  • Potential: optimize extent of disturbed area
  • Potential: evaluate environmental performance of contractors

The four recommendations for construction and restoration are identified as follows:

  • Optimize placement and installation of water bars
  • Optimize groundwater management
  • Utilize hydroseeding and hydromulching
  • Potential: optimize vegetative preservation

The final three recommendations pertain to operation and maintenance:

  • Effective transition from construction
  • Post-construction geohazard monitoring
  • Potential: foster a culture of environmental stewardship and shared learning

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20 July 2018

Losses from landslides in China – a new study

Losses from landslides in China – a new study

One of the great challenges of compiling my fatal landslide database has been properly capturing losses from landslides in China.  That country has a high incidence of landslides – indeed if one includes earthquake triggered landslides it probably suffers the highest annual losses of any country – but both the challenges of a character-based language and a lack of media freedom has made it difficult to collect information.  In a new study just published in the journal Landslides, Lin and Wang (2018) have compiled a fatal landslide inventory from 1950 to 2016, and they provide a detailed analysis.  This is a really important contribution to our understanding of the costs that landslides impose on society globally. The dataset specifically excludes landslides triggered by earthquakes.

The resulting stats are interesting.  Over that period they recorded 28,139 deaths in 1233 fatal landslide events.  As is usually the case with databases constructed retrospectively, the annual loss from landslides shows a substantial increase from about 2000 onwards:-

losses from landslides in China

The annual number and cumulative total of fatal losses from landslides in China. Graph from Lin and Wang (2018).

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This increasing trend is probably a consequence of a combination of better recording (most notably the availability of the digital media) plus an actual increase in landslide events.  Interestingly, there is an apparent sharp increase year on year from about 1994 through to 2007; thereafter losses have stabilised (but vary greatly from year to year).  The paper demonstrated a very strong seasonality in landslide events – as I showed in my paper a few years ago (Petley 2012).  The spatial distribution of losses from landslides is interesting too though – the study shows that landslides occur extensively in a belt that runs alongside the south-eastern coast, stretching about 500 km inland, and also in the mountainous terrain in central China.

losses from landslides in China

The distribution of losses from landslides in China. Figure from Lin and Wang 2018.

The paper analyses the potential drivers causing landslides, and concludes that the key factors are rainfall and vegetation (as measured by NDVI). But they have also undertaken a rather more sophisticated analysis, looking at the role of combination of factors.  Interestingly, the most important combination is elevation and precipitation (this is reassuring), but they also find key factors in combinations of precipitation and soil type, slope, lithology, vegetation type and population density.

Overall, this is a really interesting and important contribution.  Whilst the general pattern of landslide losses in China was already known and understood, Lin and Wang (2018) have provided a depth of understanding of losses from landslides in China that has been lacking.

Reference

Lin, Q. & Wang, Y. 2018. Spatial and temporal analysis of a fatal landslide inventory in China from 1950 to 2016. Landslides. https://doi.org/10.1007/s10346-018-1037-6

Petley, D.N. 2012. Global patterns of loss of life from landslides. Geology 40 (10), 927-930.

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19 July 2018

Ishkoman, Pakistan: a valley blocking glacial debris flow this week (updated with satellite imagery)

Ishkoman, Pakistan: a valley blocking glacial debris flow this week (updated with satellite imagery)

The Pamir Times has a report that earlier this week a significant valley blocking event occurred at Ishkoman, high up in the mountains of Gilgit in northern Pakistan.  This has also been reported in the mainstream media in Pakistan.    For example, Dawn reports that:-

“A small glacier melt has swollen Barsuwat Nullah in the Ishkoman valley of Ghizer district, Gilgit-Baltistan, creating an artificial lake and blocking the flow of the Immit River.  The water has submerged more than 30 houses, cultivated land, a link road and cattle farms and washed away over a dozen vehicles and hundreds of cattle head in the upstream areas.”

They also provide some more detail about the event itself:

“Deputy Commissioner of Ghizer Shuja Alam said that the Barsuwat glacier started melting on Tuesday at about 7pm. Water from the melting glacier, containing mud and stones, fell into Barsuwat Nullah and caused flooding. The nullah ultimately falls into the Immit River whose flow has been blocked and the stagnant water has created an artificial lake similar to Attabad Hunza lake, disconnecting upstream villages from other areas.”

The Pamir Times has tweeted this image of the aftermath of the event:-

Ishkoman

The aftermath of the glacial debris flow event at Ishkoman in Pakistan. Image tweeted by the Pamir Times.

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This is clearly a significant event, and it appears that a substantial volume of water has been impounded.  There are some suggestions that it might have started to drain however, but this is unclear.  It is very unlikely that the blockage will create a problem on the scale of the 2010 Attabad landslide given the low height of the debris pile.

(updated) This satellite image, via Planet Labs, shows the aftermath of the event (the lake has started developing; it appears to me that water flow around the distal side of the debris has started to develop at the time the image was collected).  It is a Planetscope image with 3 m resolution, collected at 05:16 UTC on 18th July (thanks to Jakob Steiner for finding it):-

Ishkoman

Planet Labs Planetscope image of the aftermath of the Ishkoman glacial debris flow. Image courtesy of Planet Labs, used with permission.

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Reference

Planet Team (2018). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com

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