22 June 2017

A recent rock avalanche in the Yumthang Valley in Sikkim, northern India

A recent rock avalanche in the Yumthang Valley in Sikkim, northern India

A team of researchers from the Geological Survey of Norway (NGU; Reginald Hermanns, John Dehls and Ivanna Penna), the Norwegian Geotechnical Institute (NGI; Rajinder Bhasin), the Indian Institute of Technology Kharagpur (IIT; Sengupta Aniruddha), and the Wadia Institute of Himalayan Geology (WIHG; Vikram Gupta), have recently started a joint Indo-Norwegian project focused on the occurrence of landslides along two important road corridors connecting Sikkim (northeastern part of India) with China.  They have very kindly sent some details to me of a recent rock avalanche that they have found in the Yumthang valley in Sikkim, shown below.

Yumthang

The Yumthang rock avalanche. The upper image shows a view to the headscarp and deposits of the 2015 rock avalanche in Yumthang valley. The lower image provides a cross section that shows the asymmetric profile of the valley, and the height and run-out of the 2015 rock avalanche. Note how the propagation is controlled by triangular facets on outcrops

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They found this previously-unreported landslide during their first field visit.  The rock avalanche occurred between 20/01/2015 and 12/05/2015 (based on free Google Earth Imagery). The slope failure occurred on the western slope of the valley, and travelled about 1.4 km, damming the river and creating a lake with an area of 0.2 square kilometres. The Yumthang valley has a asymmetric profile in this sector, with a western slope inclining ca. 50° while the eastern dips 32° (see the cross-section above).

Before reaching the valley floor, the failed rock mass propagated in two branches, controlled by triangular facets developed on the outcrops. The travel angle of the rock avalanche is ~32 degrees. Three overlying lobate deposits on the northern part suggest three separate events. The deposits bracket an older rock avalanche deposit of unknown age, covered by native forest.

Yumthang

Figure 2. Past and current rock avalanche deposits in the lower section of the Yumthang valley.

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Fallen and aligned trees on the old rock avalanche deposits and the opposite slope of the valley extend up to 300 m from the distal part of the rock avalanche, highlighting the energy of the air blast, which can be seen in the image below. However, there is an asymmetric distribution of this air blast, probably controlled by local relief.

Yumthang

Damage to vegetation coverage caused by the air blast from the Yumthang rock avalanche

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21 June 2017

Much more detail about the Greenland landslide and tsunami, including images and video

Much more detail about the Greenland landslide and tsunami, including images and video

In the last 24 hours much more detail has emerged about the Greenland landslide and tsunami, which severely damaged the settlement of Nuugaatsiaq on Saturday.  The Arktisk Kommando, the Joint Arctic Command – have posted a series of images on their Facebook page that have resulted from reconnaissance missions over the site of the landslide.  The best overview of the landslide site is this one:-

Greenland landslide

Overview of the Greenland landslide, via the Facebook page of Arktisk Kommando.

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The landslide appears to consist of a large block failure of the bluff that has then run over the less steep lower slope. In the background of the image is the other section of distressed slope that is causing concern.  Above the winglet another large landslide with a clearly defined rear scarp can be seen.  The Arktisk Kommando have also posted this image of the landslide scar:-

Greenland landslide

The scar of the Greenland landslide, via Arktisk Kommando

 

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Meanwhile, my friends at Strasburg University, Clément Hibert, André Stumpf and Jean-Philippe Malet have kindly obtained two important pieces of information that they have kindly allowed me to share.  First, they have downloaded before and after images of the landslide site from the Sentinel-2 satellite:-

Greenland landslide

Before and after images of the Greenland landslide. Sentinel-2 data processed by Clement Hibert and colleagues from Strasbourg University.

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Importantly, this shows that the second landslide was present in the imagery in early June, which reduces the concern of imminent failure (but does not eliminate it by any means of course).  The Strasbourg team have noted that the early June image also appears to show the presence of landslide deposits in the area of the main landslide, suggesting that it might have been active before the major failure event.

Second, they have downloaded the data from the local seismic station:

Greenland landslide

Seismic data from the Greenland landslide, via processed by Clement Hibert and colleagues from Strasbourg University.

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This data definitively answers the question as to whether the earthquake was the trigger for the landslide, or was the signal from the landslide itself.  It was the latter – this signal was generated by the landslide.  I am no expert on this data, so I provide the observations by Clément Hibert, who most definitely is an expert:

The high-frequency seismic signal (1-20Hz) exhibits the ‘classical’ features of high-frequency signals generated by landslides (emergent onset, no phases, lots of energy in the high-frequency >1Hz). However the onset of the long-period signal (<0.1 Hz) is peculiar. The first phase, coherent and visible at other stations, is more characteristic of shear faulting. This might suggest a very fast destabilisation of the mass. This is my assumption and I think this should be more thoroughly investigated with inversion and modeling methods for example.

Finally, more information has now emerged about the tsunami that this landslide triggered.  In particular, new footage has been posted to Youtube:-

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This tsunami struck in the middle of the night.  It is simply terrifying.

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20 June 2017

Nuugaatsiaq tsunami: details emerge of the landslide

Nuugaatsiaq tsunami: details emerge of the landslide

In the last 24 hours details have started to emerge about the very large landslide that triggered the Nuugaatsiaq tsunami in Greenland on Saturday, which is now known to have killed four people, with a further nine people injured, two of them seriously.

The landslide occurred on Karrat Fjord, which according to Google Earth is the area shown below (although the location is far from clear at present).  Nuugaatsiaq is in the north of this image, on the plateau with the aeroplane symbol.

 Nuugaatsiaq tsunami

The location of the landslide that triggered the Nuugaatsiaq tsunami, via Google Earth.

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The landslide was reportedly 1,000 metres in length and 300 metres in width.  A helicopter video has emerged of the site of the landslide:

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The full version of the video may be available via the Facebook embed below:

Meget farligt

Posted by Kunuunnguaq Petersen Geisler on Sunday, June 18, 2017

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This image from the video suggests that the landslide may have been very deep-seated, and thus high volume, but we will need a better image of the slide to determine this properly:

Nuugaatsiaq tsunami

The scar of the landslide that triggered the Nuugaatsiaq tsunami; still from a Facebook video

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It remains unclear as to whether this landslide was triggered by the reported earthquake, or whether the seismic event was the signal from this landslide.  My sense remains that the latter is the most likely, but we await details of the seismic signal to know.

But perhaps the biggest current issue is the discovery of another potentially unstable slope immediately adjacent to the mass that has failed.  This is clearly shown in the video:-

Nuugaatsiaq tsunami

The potentially unstable rock mass adjacent to the landslide that triggered the Nuugaatsiaq tsunami; still from the Facebook video

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Clearly there is the potential for a further large landslide from this slope (although failure is not inevitable).  The plan is that one of the naval ships in the area will now keep a watch on this slope.  There is a need to establish proper monitoring at this location as a matter of some urgency.  In consequence the settlement of Nuugaatsiaq has been completely evacuated, and both Illorsuit and Viaqornat are being evacuated as well.

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19 June 2017

Nuugaatsiaq: A large landslide-induced tsunami on Saturday night?

Nuugaatsiaq: A large landslide-induced tsunami on Saturday night?

Late on Saturday the small community of Nuugaatsiaq in west Greenland was struck by a large but isolated tsunami.  The aftermath of this event was captured on a Youtube video that has been widely reported:

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Information about this event remains quite sketchy, but the English language media reports indicate that four people may be missing.  It appears that the local seismological bureau recorded the event as a magnitude 4.0 earthquake, with the tsunami striking a few minutes later.  Greenland is not a particularly seismically-active area, and as far as I can tell this earthquake has not been recorded more widely.  This, combined with the localised nature of the tsunami, suggest that the cause is most likely to have been a very large landslide, either from the fjord walls or under the water (or maybe both).  News reports in Greenland (in Danish) also speculate that the cause may have been a mass movement:-

It is still uncertain what caused the devastating tidal wave that hit Nuugaatsiaq on Saturday night, says a seismologist from GEUS [The National Geological Surveys for Denmark and Greenland]. 

“We have some signals at our earthquake stations resembling earthquakes, but they might also indicate that a landslide has been triggered,” says seismologist Peter Voss, from GEUS.  He explains that GEUS has a theory that it is a major slope from a mountain that has triggered the tide of waves:

“The slump has made a large part of the mountain collapse into the fjord and has created this wave,” says Peter Voss.

But GEUS can not conclude anything from the measurements alone…He also tells that the landslide could have been underwater, and then it will be difficult to detect.

Clearly the priority yesterday was to provide assistance to the affected villages, but news reports indicate that they will start to try to identify the source today.  This is important, given the potential for a secondary failure if a landslide was the cause.

This is the Google Earth image of the area affected by the tsunami:

Nuugaatsiaq

Google Earth image of the area affected by the Nuugaatsiaq tsunami

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Hopefully more information will emerge about this event today.

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16 June 2017

NTSB report: train collision with a landslide in Northfield, Vermont

NTSB report: train collision with a landslide in Northfield, Vermont

The NTSB in the USA has posted online a brief accident report for a train collision with a landslide at Northfield in Vermont on 5th October 2015.  This was a quite dramatic accident between a passenger train operated by Amtrack and a small rockslide.  The collision led to the derailment of the locomotive and four carriages.  One of the carriages slipped down a steep embankment; seven people were injured, four of whom were train crew.  The damage caused by the landslide exceeded $10 million.

This is an image of the aftermath of the accident from news reports at the time:-

Northfield derailment

CNN image of the derailment at Northfield in Vermont

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The NTSB report includes an image taken from the forward-facing video camera located on the locomotive:-

Northfield landslide

Imagery from the video camera mounted on the locomotive of the Northfield, Vermont landslide. Image from the NTSB report

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It is notable that this is a comparatively small landslide, probably caused by a failure on existing joints or other planes of weakness.  The debris appears to consist of quite large slabs, which may explain the derailment.  The train was travelling at 59 mph (about 95 kph) at the time of the collision.

The NTSB report makes some interesting observations about hazard management on this section of track:

Although the NECR [New England Central Railroad] had a safety program at the time of the accident, the NECR did not have a formalized hazard management and assessment program that addressed rock slide risk management and mitigation. Although track inspectors could notate anomalies along the right-of-way, the NECR did not keep or maintain the historical data on rock slides. The NECR had neither a rockfall detection program nor a rock face program maintenance initiative prior to the accident. After the accident, geologists identified two additional NECR locations where rock slide mitigation was recommended. The NECR implemented speed restrictions for trains at these two locations.

 

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13 June 2017

The Amyntaiou lignite mine landslide in Greece: more information

The Amyntaiou lignite mine landslide in Greece: more information

Over the last 24 hours more information has emerged about the Amyntaiou lignite mine landslide in Greece, which led to the permanent evacuation of the village of Anargyroi in Northern Greece on Saturday.  Perhaps most interestingly, a video has been posted on Youtube that shows the landslide as it occurred.  Whilst the quality of the video is not high, at about the 38 second mark it does seem to show one of the large excavators toppling:-

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The operator of the mine, PPC, has announced the formulation of a commission of inquiry to investigate the failure, with a committee drawn from industry and academia.

Meanwhile, a variety of information seems to have emerged about the losses from the landslide.  Greek Reporter has a rather extraordinary claim:-

Other than the total destruction of the Anargyroi village, the tectonic rupture caused by the lignite mine that belongs to the  Public Power Corporation (PPC) generated a huge financial loss to the already ailing company.

Specifically, 25 million tons of lignite worth 500 million euros and 100 million worth of excavating machinery and vehicles were buried under 80 million cubic meters of earth. According to PPC-GENOP union president Giorgos Adamidis, the total damage, including the end of operation of the Amyntaio power unit, may well exceed 1.5 billion euros.

The landslides also caused collateral losses to the stability of the power system as it is uncertain whether the two lignite power plants of Amyntaio, with total capacity of 600 megawatts, will operate again. Even though the two lignite units were fully operational from October to April, power supply shortages might occur.

Also, the effect of the landslides might be felt by 1,700 people who are at risk of finding themselves without a job. PPC was employing 850 workers at the Anargyroi mine, while there were 500 people employed by the contractors. Also, on Friday, one day before the landslide, another 350 seasonal employees were hired by PPC to work in the facilities.

PPC is denying these claims, claiming that losses are likely to be in the order of 200 million Euros.  Even so, this is an exceptionally expensive landslide.

Amyntaiou landslide

The Amyntaiou landslide in Greece. Image by Eurokinissi via CNN

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12 June 2017

Anargyroi: an 80 million cubic metre mining-induced landslide in Greece this weekend

Anargyroi: an 80 million cubic metre mining-induced landslide in Greece this weekend

Over the weekend, the village of Anargyroi, in northern Greece, has been permanently evacuated as a result of a huge mining-induced landslide.  The village, which is located at 40.603 21.612, was home to 182 people.  It will now be demolished.

The landslide appears to have been triggered by the collapse of an open case lignite mine.  Media reports suggest that the landslide is exceptionally large – 80 million cubic metres is being quoted by a number of sources.

This is a Google Earth image of the village and the mine, taken in 2014:

Anargyroi

Google Earth of the village of Anargyroi and the adjacent lignite mine

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Ekathimerini has this dramatic image of the edge of the mine showing enormous cracks extending across the landscape:

Anargyroi

Tension cracks extending from the margins of the mine at Anargyroi in Greece. Image via ekathimerini.com

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Meanwhile the best image that I have seen of the landslide itself is one the newsit.gr website, which has a fantastic gallery of views of the landslide:-

Anargyroi

The huge mining-induced landslide at Anargyroi in northern Greece, via newsit.gr.

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Meanwhile, this image (from the same source) gives an idea of the scale of the Anargyroi landslide:

Anargyroi

The extraordinary scale of the Anargyroi landslide in Greece, via newsit.gr

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A translation of the report on Newsit.gr yesterday suggests that the landslide is expected to continue for at least another 48 hours.  Movements started on 3rd June, but have clearly accelerated in the last few days.  This is an interesting part of the article (via Google Translate):

As a result of the landslide, cracks and damage occurred in about ten houses that are on the side of the mine front and were ordered by authorities to evacuate in order not to endanger human lives. Michalis Kavvadas Deputy Professor of Geotechnical Engineering, NTUA Polytechnic, who visited the area of ​​the mine and the Anargyroi area three days ago, stated in statements that the movements of soils at the mine of Amynousis activate the tectonic fault that passes through the village, causing larger cracks in the streets and in its homes.

This landslide is reminiscent of the enormous Collolar coal mine landslide in Turkey in 2011.

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11 June 2017

Landslides in Art Part 29: a Victorian view of Black Ven

Landslides in Art Part 29: a Victorian view of Black Ven

This is the latest edition of the long-running Landslides in Art series; in this edition I am looking at a Victorian view of the Black Ven landslide near to Lyme Regis in Dorset, southern England.  The previous edition is here.

Dorset is one of the most beautiful counties in England, and the coastal landscape around the town of Lyme Regis is perhaps the crowning glory.  This landscape has formed primarily through coastal landslides.  The downside is of course that these landslides represent a substantial hazard, and they regularly damage houses and roads.  Probably the largest landslide of all is Black Ven – a magnificent rotational landslide complex to the east of Lyme Regis.

This landslide is featured in a mid nineteenth century depiction that has been highlighted by the Marine Archaeology Trust in a case study that shows how archive images can be used to improve hazard management.  The image looks across Black Ven towards the town of Lyme Regis.  The artist is not known:-

Black Ven

A Victorian view of the Black Ven landslide in Dorset. A privately-owned image via the Marine Archaeology Trust

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This is a modern Google Earth image of the Black Ven landslide complex, looking towards Lyme Regis:

Black Ven

Google Earth image looking across the Black Ven landslide towards Lyme Regis

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The landscape of Lyme Regis itself is clearly recognisable in both images.  As the Google Earth view shows, Black Ven consists of a rotational landslide complex.  The large rotational blocks periodically slip and then degrade to form flows that pass over the benches lower down the slope.  The Victorian image appears to show one of these slipped blocks on the right side, and the degraded landscape downslope from there.  The apparent cliff in the foreground may well be the rear -scarp of a block that has more recently slipped.  There is a couple standing on the edge of this scarp, clearly enjoying the view across the landslides.  Is there just a hint of a crack between them and solid ground?

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8 June 2017

The enormous Green Lake landslide in New Zealand

The enormous Green Lake landslide in New Zealand

Worldwide there is a small number of landslides that a\re so large that they are almost impossible to comprehend.  The Green Lake landslide in Fjordland, New Zealand, is one such example.  This is a landslide that is so enormous that early mappers failed to recognise is at a slide; indeed the first proper description of the Green Lake landslide as a mass movement only occurred in 1983.

The best description of it is in a paper by Graham Hancox and Nick Perrin of GNS Science (Hancox and Perrin 2009), who note that:

  • The landslide consists of the collapse of a 9 km section of the Hunter Mountains in southern New Zealand (the location is -45.78, 167.36 if you want to take a look);
  • The volume of the slide is 27 cubic kilometres, making it one of the largest known landslides on earth, and the largest in New Zealand;
  • The landslide covers an area of 45 square kilometres;
  • The thickness of the landslide is up to 800 metres, although there is considerable uncertainty about this figure given the lack of subsurface information.

This is the Google Earth image of the landslide as it is today:-

Green Lake landslide

Google Earth image of the Green Lake landslide in New Zealand

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The best way to appreciate the scale of the landslide is to compare this image with the topographic map provided by Hancox and Perrin (2009):-

Green Lake landslide

Topographic map of Green Lake Landslide showing its main geomorphic features. From Hancox and Perrin (2009)

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Based on this I have attempted to draw the approximate boundaries of the landslide onto the Google Earth image:-

Green Lake landslide

The boundaries of the Green Lake landslide in New Zealand. Google Earth image.

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This landslide clearly occurred after the glaciers retreated, and thus must be younger than 14,000 years old.  Dating such a landslide is difficult, but Hancox and Perrin (2009) concluded that it probably happened 12,00 to 13,000 years ago.  The cause of the landslide is of course hard to determine, but the glaciers had probably left the landscape in an oversteepened and thus unstable state.  This part of New Zealand is subject to extremely large earthquakes.  Hancox and Perrin modeled the stability of the site based on a reconstruction of the original topography, and concluded that it was very sensitive to seismic accelerations.  Thus, a large earthquake is considered to have been the most likely trigger.

Reference

Hancox, G.T. and Perrin, N. 2009.  Green Lake Landslide and other giant and very large postglacial landslides in Fiordland, New Zealand. Quaternary Science Reviews, 28 (11-12), 1020-1036.

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6 June 2017

An update on the Bucium Hill landslide problem in Romania

An update on the Bucium Hill landslide problem in Romania

Back in March I posted an article about the Bucium Hill landslide problem on the A1 motorway in Romania.  To recap, this is a major road across the Transylvanian hills, recently constructed.  The slope has suffered repeated landslide problems, and as a result has had to be trimmed back repeatedly.  The slope still shows extensive indications of distress.

Two new videos are available of the site, both shot from drones.  The first is from 29th March 2017:

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And the second is from 21st May 2017:

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The slope continues to show extensive signs of movement, as this overview image demonstrates:-

Bucium Hill

An overview of the slope stability issues at Bucium Hill in Romania. Still from a Youtube video.

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There appears to be a notable change in the slope on the left side (looking towards the road).  This was this section of the slope in February:

Bucium Hill

The left flank of the Bucium Hill landslide in February 2017. Still from a Youtube video

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This is the same section in May 2017:

Bucium Hill

The left flank of the Bucium Hill landslide in May 2017. Still from a Youtube video.

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The lateral scarp in this area appears to have developed further over this period, indicating that the slope continues to deform.  Needless to say these broken drains and drainage channels are a problem.  The drains are of course designed to remove water from the slope in order to prevent erosion and to draw down the pore water pressure.  But in such cases maintenance of the drains is critical, as broken drainage channels can become a very effective conduit for feeding water into the slope in a concentrated manner.  In this case, as the images show, the drains will feed water directly into the shear surface.  This is exactly what one should avoid. Whilst I cannot say whether this slope is in a critical condition (I assume that proper monitoring is being undertaken to ascertain this),  the need to repair these drains is undeniable.

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