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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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18 July 2018

Hidroituango: an update

Hidroituango: an update

I have not posted about Hidroituango (in Colombia) in the last few weeks, although the crisis has certainly not ended there.  Seasonal changes in weather have meant that the inflows from the upper reaches of the catchment have reduced, allowing a slow reduction in water level.  This has provided a welcome opportunity for the continued improvement of the dam, which is of course good news.

However, LAFM reports that last week a seismic event was recorded from within the power house cavern, which is interpreted as being a rockfall event.  This has reduced the flow of water by 5 to 10%, with fears that this might become worse.  One wonders about the state of the power house cavern, and indeed the remainder of the underground excavations, in light of these events.

Meanwhile, further imagery of the site has become available.  Last week, Planet Labs collected a high resolution image of the site using their 0.8 metre SkySat instrument:

Hidroituango

Planet Labs SkySat image of the Hidroituango site, collected on 9th July 2018 and used with permission.

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This highlights in particular the continued evolution of the slope failures just upstream of the dam, on the right bank:-

Hidroituango

Planet Labs SkySat image of the slope failures upstream of the Hidroituango dam. Image courtesy of Planet Labs, used with permission.

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Meanwhile, some instability is evident on the slopes above the reservoir as the slow drawdown continues.  This is to be expected.  On 11th July Andres Posada tweeted this image of landslides on the slopes at Hidroituango:-

Hidroituango

Drawdown landslides at Hidroituango. Image tweeted by Andres Posada on 11th July 2018.

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These slope failures can be seen on the Planet Labs imagery as well – this is a 3 m Planetscope image collecgted on 16th July 2018:-

Hidroituango

Planet Labs PlanetScope image of drawdown landslides at Hidroituango.  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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17 July 2018

Nanyu Township: a very large landslide in Gansu Province on Thursday 12th July 2018

Nanyu Township: a very large landslide in Gansu Province on Thursday 12th July 2018

Xinhua has posted some images of a very large, partially valley blocking landslide that occurred at Nanyu Township in Zhouqu County, located in Gansu Province, China.  The landslide, which was triggered by rainfall, is reported to have a volume of about 5 million cubic metres.  The best image of the landslide itself is this one, from Xinhua, which shows the lower portion of the displaced mass.  It is clear that it has greatly constricted the river channel:-

Nanyu township

The large landslide at Nanyu Township in Zhouqu County, northwest China’s Gansu Province. Image via Xinhua.

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The partial blockage of the river has caused extensive flooding:-

Nanyu township

Flooding upstream of the landslide at Nanyu township in Gansu Province. Image via Xinhua.

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On Google Earth the area affected by the landslide appears to be as below.  The location is 33.719, 104.421:-

Nanyu township

Google Earth image of the landslide at Nanyu township in Gansu Province

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My interpretation of this is that the failure is on a large, pre-existing landslide.  From the Google Earth imagery considerable slope modification has occurred.  The section of the slope that has failed in this event is shown in the image below:-

Google Earth image of the portion of slope that failed in the Nanyu township landslide

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This section of slope shows considerable signs of distress and instability, and it is interesting to note that the river has a series of rapids in this area.

Gansu Province has a long landslide history.  The following posts highlight landslides in this part of China:-

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16 July 2018

High resolution satellite imagery of the Japan landslide disaster

High resolution satellite imagery of the Japan landslide disaster

Planet Labs have now been able to collect some high resolution satellite imagery of the aftermath of the landslide and flood disaster that struck across Japan over the last few days.  This is a SkySat image, which has a resolution of 0.8 metres per pixel.  The image shows the area around Kure in the Hiroshima area, which was badly affected by the rains.  This is the full image:-

Japan landslide disaster

Planet Labs SkySat image of Kure, Japan showing the aftermath of the Japan landslide disaster. Image courtesy of Planet Labs, used with permission.

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Whilst there was a little bit of light cloud when the image was collected, the extremely large number of landslides is clear.  This is a part of the southern portion of the image:-

Japan landslide disaster

A portion of the Planet Labs SkySat image of Kure, Japan showing the aftermath of the Japan landslide disaster. Image courtesy of Planet Labs, used with permission.

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It is clear that there are dozens of landslides, mostly consisting of shallow slips that have transitioned into channelised debris flows, in the imagery.  The nature of these landslides is perhaps best illustrated by this set, in the northeast of the image:-

Japan landslide disaster

Detail of a portion of the Planet Labs SkySat image of Kure, Japan showing the aftermath of the Japan landslide disaster. Image courtesy of Planet Labs, used with permission.

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Here it is clear that the landslides started as small slips in the hilly, forested portion of the slopes.  The debris has entered the channels and then entrained channel material.  In many cases the same channel has seen slips from multiple slope portions.  The debris has run out onto the golf course, where deposition of the mobile mass has occurred.

Of course it also serves to illustrate the extraordinary quality of satellite imagery that is now available.  Many thanks to Robert Simmon at Planet Labs for his help with obtaining the imagery.

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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15 July 2018

Panjshir province, Afghanistan: using Planet Labs imagery to interpret the deadly debris flow

Panjshir province, Afghanistan: using Planet Labs imagery to interpret the deadly debris flow

On Thursday morning a deadly debris flow struck a small village, in some reports named as Pashgor (or Peshghor), in Panjshir province, Afghanistan, killing at least ten people.  There has been considerable speculation about the cause of this disaster, including landslides, melting icecaps and the breaching of lakes.  For example, Accuweather has an article claiming that melting snow caused a dike to melt, although the source of this information is not clear.  The Dhaka Tribune / AFP has the best image that I have seen of the aftermath of this event:-

Panjshir

The aftermath of the debris flow in Panjshir province, Afghanistan, on 12th July 2018

Fortunately, at this time of year this area of Afghanistan has little cloud, rendering satellite imagery a powerful tool to understand the event.  I have looked at Planet Labs imagery, which reveals the cause.  So, first, here is the before and after imagery of the downstream impacts of the debris flow.  The image below, collected on 11th July, shows the community struck by the debris flow before the event occurred:-

Panjshir

The community of Pashgor struck by the debris flow on 12th July 2018 in Panjshir Province, Afghanistan. Image, dated 11th July 2018, via Planet Labs, used with permission.

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This image shows the aftermath – the track of the debris flow, and the vast amount of new sediment in the main channel, are clear:-

Panjshir

Planet Labs imagery, dated 12th July 2018, of the aftermath of the debris flow in Panjshir province, Afghanistan. Image via Planet Labs, used with permission.

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It is not clear to me as to whether the channel is completely blocked. There is some chance that this might be the case.  But the imagery allows the course of the debris flow to be tracked upstream to find the source.  This lies about 10 km to the north as the crow flies, probably 15 km via the channel.  The source is at 35.47 N, 69.64 E if you are interested in looking at Google Earth.  At this location, at an elevation of about 4500 metres, we find this lake on the imagery before the disaster:-

Panjshir

The ephemeral lake in the mountains of Panjshir province, which caused the debris flow disaster on 12th July 2018. Image via Planet Labs, used with permission

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The image of the following day shows that the lake had completely drained, generating the debris flow that destroyed the village:-

Panjshir

Planet Labs image dated 12th July 2018 showing the drained ephemeral lake that caused the debris flow of 12th July 2018 in Panjshir province. Image, dated 12th July 2018, courtesy of Planet Labs, used with permission.

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The lake was about 400 metres long and 150 metres wide.  Interesting it was not present at any point last summer as far as I can tell, so it is likely to have been formed by temporary blocking of the valley by ice and/or debris (can anyone provide any insight into this process? I am assuming that this was probably an ice dam?).

Afghanistan is of course no stranger to landslide disasters.  It is somewhat frustrating to see some news agencies illustrating articles about this event with imagery from the dreadful Abe Barek landslide in May 2015.

Reference

Planet Team (2017). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com

 

 

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13 July 2018

Rohingya refugee camps: your help needed

Displaced Rohingya people living on cut slopes in the refugee camps of Cox’s Bazaar in Bangladesh. Image by Manish Swarup/AP , via Global Citizen

Rohingya refugee camps: your help needed

I have written before about the severe level of risk faced by the displaced Rohingya people from Myanmar, now living in refugee camps in the Cox’s Bazaar area of Bangladesh. About a million people are living in temporary camps across a hilly area that was previously mostly unpopulated.  The soils are weak, consisting of sands and soils, and of course this is an area with a monsoonal climate.  The monsoon is now building in intensity, and will last for the next three months or so.  Some fatalities associated with landslides have already occurred.

Rohingya

Rohingya houses on cut slopes in Cox’s Bazaar in Bangladesh. Image via a tweet by Manuel Marques Pereira

The hazards posed by landslides are severe.  In occupying this hilly land the people have had to cut the slopes to build benches to allow the construction of bamboo framed buildings.  Inevitably the cooking needs of so many displaced people has meant that the protective trees have been removed to be burnt.  As supplies of wood have dwindled the Rohingya people have been forced to dig up the roots to burn as well.  The consequences for slope stability are dire – the combination of weak materials (especially where the slopes are predominantly sandy), cut slopes, removal of vegetation and disruption of the soil is a toxic mix that means that landslides are inevitable.  There have already been some severe slope accidents.

The magnitude of the problem does not allow slope engineering as a widespread solution, although it may help in some particularly severe locations.  Across the area there is a very small number of rain gauges; the coverage is too low to provide a decent understanding of real time rainfall.  In a hilly area like this orographic effects mean that there will be considerable variation in rainfall patterns over a short distance.  In addition, the most serious rainfall events in the monsoon are likely to be convective – the so-called cloudburst events – meaning that a dense network is needed to be effective.

Your help is needed

I have been talking to one of a very small number of landslide experts in country trying to deal with the crisis, Marina Drazba.  This is a situation in which an early warning system of some sort might be helpful, but it is far from clear as to what an effective system, which can be implemented quickly, might consist of.  Given that we are talking about hundreds of small slopes over a large area, technology like slope radar is not going to be applicable.  So the questions that we are asking are:

Rohingya

Densely packed Rohingya houses on steep, weak slopes in Bangladesh. Image via VOA News

1. What effective systems are in place in similar circumstances elsewhere? Are there examples of good practice in other less developed countries?

2. What could an effective system look like in this situation?

3. How is it possible to communicate the hazard in real time if the alert is triggered?

4. How can you avoid, or manage, false alarms?

The aim here is to try to implement an early warning system quickly, if that is possible.  If you have answers to these questions, please could you post a comment.  Please help – we are open to any ideas or thoughts or ideas, or any experiences that you might have.

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