21 January 2021
Mount Darwin: another rock avalanche in New Zealand, with a groovy runout pattern
In the aftermath of the interesting rock avalanche on Mount Silberhorn in New Zealand, Simon Cox from GNS Science has alerted me to another recent rock avalanche, this time on Mount Darwin. This rock avalanche was also noted in a tweet by Ryan Dick (@ryandick207) of the University of Newcastle (the second tweet in the sequence below, though the Sentinel-2 images posted by Simon Gascoin – @hsgascoin – of the Mount Silberhorn landslide is also rather cool):-
Spotted this big one too, at the top of Tasman Gl. Sometime between 11-15 Jan based on Sentinel/Planet imagery pic.twitter.com/qECIpELWjo
— Ryan Dick (@ryandick207) January 19, 2021
The landslide was first spotted on 16 January 2021 at 08:30 local time, so it occurred at some point shortly before then. The location is 43.528° 170.336 at the head of the Tasman Glacier.
The source of the landslide is high on the slope, just below the ridge. The displaced mass has travelled down a very steep slope before a free fall on a talus slope covered in snow and ice. The runout is particularly interesting, with little evidence of spread. The bifurcation of the slide into a series of long runout fingers is quite unusual. These flows have split and then, in places, coincided. At the very right of the upper part of the flows here is a section with a different texture from the rest, probably involving more snow and ice. I am not sure whether this occurred at a different time to the main event, perhaps soon after.
Simon Cox has pointed out that this is not the first large landslide on Mount Darwin. In the GNS Science photo archive there is an image of a landslide taken in 1983, although this one did not have a long runout.
The recent rock avalanche on Mount Darwin is not a large landslide, but it is a very interesting case.
19 January 2021
A sensational high resolution satellite image of the Mount Silberhorn rock avalanche
On 31 December 2020 pilots from Mount Cook Ski Planes & Helicopters in New Zealand posted images of the aftermath of a large rockslide from Mount Silberhorn in New Zealand. Mount Silberhorn, with an elevation of 3303 m, is the fifth highest peak in New Zealand. It is located near to Aoraki/Mt Cook in the Southern Alps.
My friends at Planet Labs have very kindly collected a high resolution SkySat image of the landslide – and oh my, what an image this is:-
Clearly the source of the landslide is in the northwest of the image, with the slide moving towards the east and south. Note the clearly evident rock avalanche phase in the early part of the track – the image also picks up the dust staining of the snow around the landslide from this phase. In the lower part of the track the movement has transitioned into sliding, and there are the finger-like structures at the toe that might be associated with slow creep sliding at the end of the movement.
On the steep slopes of Mount Silberhorn there are a small number of separate landslides – one is toe the immediate south of the source area, with the debris moving towards the south. There are at least two others in this area. It is possible that these were triggered by the same process as for the main Mount Silberhorn rock avalanche, but I suspect that it is more likely that these were induced by the vibrations from the main landslide.
Perhaps the most remarkable thing about this image, which was captured on 12 January 2021, is that there is no post-event snowfall onto the landslide. This allows the features to be seen with ease.
Reference and acknowledgement
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
Thanks to Robert Simmon and his colleagues at Planet Labs for collecting this wonderful image.
18 January 2021
Gravity always wins: in New Zealand landslides are more deadly than earthquakes
New Zealand is a country with an abundance of natural hazards – earthquakes, volcanoes, floods, tsunami, cyclonic storms and landslides, amongst others. Of the geophysical hazards, it is earthquakes and volcanoes that attract most of the attention, driven by large events such as the Christchurch earthquake sequence, the Kaikoura earthquake and the Whakaari /White Island eruption. Landslides are generally not considered to be such a major issue around the world, and are often dismissed as a secondary hazard.
Interestingly though, my colleagues at GNS Science have been looking the comparative impact of landslides and earthquakes through time in New Zealand. The online news service Stuff has a good article about this work today. The simple conclusion is startling:
Landslides are significantly more dangerous than earthquakes, according to an analysis by GNS Science.
Interestingly the article provides some detail to this through some words from Jo Horrocks, the chief resilience and research officer of the Earthquake Commission (EQC), the national insurer against earthquakes (and landslides). She noted that landslides cost the country an average of NZ$250 to 300 million (about £125-150 million) and that over the last 160 years they have claimed about 1800 lives. This is considerably higher than the toll from earthquakes.
The reasons that they are under appreciated is that landslides tend to happen as frequent events from which the losses accumulate. Huge clusters of landslides do occur – the Kaikoura earthquake was a fine example – but of course these are usually triggered by another event, such as an earthquake or a cyclone. Very often it is the landslides that cause the losses.
I am sure that this effect is seen in many other countries as well. The article in Stuff has a nice quote, taken from an article in the Te Ara Encyclopaedia of NZ :
Gravity always wins
15 January 2021
The US National Landslide Preparedness Act
Amongst the remarkable political shenanigans in the United States in recent weeks, in which the term landslide has been used in an entirely different context, there has been one piece of good news. Earlier this week the President signed into law H.R. 8810, the National Landslide Preparedness Act.
This piece of legislation, initially proposed by Representative Suzan DelBene (D-WA), establishing a National Landslide Hazards Reduction Program in the USGS, with the aim of improving identification and understanding of landslide risks; of protecting communities; of saving lives and reducing property losses; and of improving emergency preparedness. This is a tremendous and very important step forwards, finally recognising at a federal level landslides as a significant hazard and establishing the means to start to improve their management.
The USGS shall, among other things
- develop and publish a national strategy for landslide hazards, risk reduction, and response in the United States (including territories);
- develop and maintain a publicly accessible national landslide hazard and risk inventory database;
- expand the early warning system for debris flow; and
- establish emergency response procedures for the rapid deployment of federal scientists, equipment, and services to areas impacted by a significant landslide event.
The USGS may provide grants to research, map, assess, and collect data on landslide hazards.
The National Science Foundation may provide grants to eligible entities for landslide research.
The USGS shall establish the 3D Elevation Program and the 3D Elevation Federal Interagency Coordinating Committee, and (2) may make grants and enter into cooperative agreements to facilitate the improvement of nationwide coverage of 3D elevation data.
There is a host of good things about this, including the development of a national strategy and the establishment of a LIDAR based programme to generate digital elevation data.
The timing is very pertinent, as earlier this week a really significant rainfall event occurred in the Pacific Northwest, triggering many landslides. The most significant appears to have occurred close to Dodson in Oregon, where a large debris flow killed a motorist, Jennifer Moore. A search is underway to try to recover her remains. Multnomah County Sheriff’s Office has tweeted this image of the site:-
13 January 2021
The 7 August 2020 landslide in Gokseong County, South Korea
In early August 2020 a period of heavy rainfall in South Korea triggered multiple landslides, killing several people. In terms of loss of life the most significant event occurred on 7 August 2020 in the village of Osan in Gokseong County, South Jeolla Province, in which five people were killed. There is an initial report on this landslide in the journal Landslides (Choi et al. 2021), which is really quite interesting.
The image below is taken from the paper, providing a vertical aerial photograph of the aftermath of the landslide:-
The landslide initiated at the bottom of the image and moved towards the north. It traveled a total distance of about 680 metres, with a volume in the order of 20,000 to 50,000 cubic metres. In the deposition zone it inundated five houses, killing all five of the victims.
As noted above the landslide was triggered by heavy rainfall. Choi et al. (2021) note that the cumulative rainfall in Gokseong County for the 3 days preceding the landslide was of 277 mm, with a peak intensity of over 50 mm per hour.
The most interesting aspect of this work though is the initiation of the landslide. As the image above shows, the crown of the landslide is adjacent to a road, and close examination of the image shows that road widening work was underway at the time of the failure. Choi et al. (2021) have observed that initiation was through the failure of a valley-filling embankment with embedded geogrids supporting the road, National Route 15. The failure surface of this fill slope removed a section of the under construction northbound lane of the highway. After failure it appears that the fill went through static liquefaction and transitioned into a debris flow that struck the houses. The debris flow included the concrete blocks that formed a part of the embankment, increasing its destructive power.
So, although his was a rainfall induced landslide, it is an anthropogenic slope that was responsible for the fatal landslide. Choi et al. (2021) speculate that during the temporary works the embankment might have lacked adequate drainage, allowing the landslide to occur.
Choi, S.K., Ramirez, R.A. & Kwon, T.H. 2021. Preliminary report of a catastrophic landslide that occurred in Gokseong County, South Jeolla Province, South Korea, on August 7, 2020. Landslides. https://doi.org/10.1007/s10346-020-01616-y
10 January 2021
Protecting the rescuers – a disastrous double landslide at Cihanjuang in Indonesia and a lucky escape in Italy
Protecting the rescuers – a disastrous double landslide at Cihanjuang in Indonesia and a lucky escape in Italy
I have noted previously that one of the great challenges in the aftermath of major landslide accidents is protecting the rescuers. In the recent Gjerdrum quick clay landslide the rescue proceeded slowly for this reason – in the immediate aftermath it was considered too risky to deploy rescue staff into an area in which another landslide might occur.
This problem has been brought home in vivid form through a disastrous double landslide in Indonesia on 9 January 2021. The events occurred in the village of Cihanjuang in West Java. The image below shows the aftermath of the landslide:-
Reports indicate that the first failure happened at 4 pm local time. Rescue operations were immediately undertaken, and evacuations were underway. A second landslide then struck the same location a little over three hours later. This is believed to have buried a number of rescue personnel.
At the time of writing the BBC is reporting that 12 people have been killed. Reuters is reporting that 18 people were injured. Unfortunately though the BBC is also reporting that a further 27 people are missing, although there will be considerable uncertainty in this figure.
Protecting the rescuers is a really challenging task, balancing the rapidly diminishing chances of trapped victims being able to survive against the likelihood of further landslides burying the rescue personnel. Decisions have to be made quickly on the ground, often in poor weather, and with inadequate information about what is happening. As the many landslide videos that are now available on Youtube illustrate so vividly. Landslides often strike two or more times at the same location in a short period of time.
Quickslide: a tragedy averted in Italy
Meanwhile, there was a remarkable escape in the Italian town of Bolzano on 5 January 2021 when a rock slope failure demolished a large part of Hotel Eberle, located on the hill of Santa Maddalena above the town of Bolzano. Fortunately the hotel was closed due to Covid-19 restrictions, so no-one was killed. The impact of the landslide was dramatic:-
The image below, from Tripadvisor, shows the hotel before the landslide. This was an extremely fortunate escape:-
8 January 2021
Brumadinho: signs of precursory deformation
The January 2019 Brumadinho tailings dam failure in Brazil remains one of the most serious mine waste failures in recent years. Despite the terrible toll, a positive legacy appears to be a genuine attempt by the mining industry to improve the management of these facilities, although we will wait to see how effective this proves to be in the long term. Mining is an industry littered with promises of improvement that have not been delivered.
The report of the Expert Panel came to a very surprising conclusion, which is that the dam showed no signs of distress prior to the collapse. This is a finding that has caused considerable concern. If a dam can collapse on this scale with no obvious short term external trigger and no indications of impending failure, then it becomes extremely difficult to know how to monitor these facilities. This is the wording in the report:-
The failure is also unique in that it occurred with no apparent signs of distress prior to failure. High quality video from a drone flown over Dam I only seven days prior to the failure also showed no signs of distress. The dam was extensively monitored using a combination of survey monuments along the crest of the dam, inclinometers to measure internal deformations, ground-based radar to monitor surface deformations of the face of the dam, and piezometers to measure changes in internal water levels, among other instruments. None of these methods detected any significant deformations or changes prior to failure. Post-failure satellite image analyses indicated slow and essentially continuous small downward deformations of less than 36 millimeters per year (mm/year) were occurring on the dam face in the year prior to the failure, with some acceleration of deformation during the wet season. In the lower part of the dam, the deformations measured in the 12 months prior to failure included horizontal deformations ranging from 10 to 30 mm. Such deformations are consistent with slow, long-term settlement of the dam, and would not alone be indicative of a precursor to failure.
However, there is hope at hand. A new open access paper, published in the journal Communications Earth and Environment (Grebby et al. 2021), has used a version on the well-known InSAR methodology called the Intermittent Small Baseline Subset (ISBAS) to evaluate deformations in the dam and in the tailings themselves in the period leading up to the failure. This is a really important and valuable study, originating from an independent multidisciplinary team from industry and academia. Crucially, their findings differ significantly from that of the expert panel. This is what the paper says:
We observed widespread deformation across the dam wall and tailings from two independent satellite tracks, revealing areas subject to consolidation settlement. However, in contrast to attempts using other InSAR techniques, we also detected evidence of anomalous deformation not consistent with consolidation on the dam wall and tailings beach, instead exhibiting a clear accelerated rate of deformation from about late October 2018 following a period of increased rainfall.
It is worth diving into this a little. The InSAR technique can provide a time history of deformation for both slopes and sediment stores, alongside maps of the deformation. This is one of the figures from Grebby et al. (2021):-
InSAR measures deformation along the line of sight of the satellite. The analysis used two different tracks of the satellite (in this case using Sentinel-1 C-band data) with different incidence angles, so two different deformation maps have been produced. Note that the general trend is subsidence, especially across the surface of the trainings but also in parts of the tailings dam. This is not dissimilar to the findings of the Expert Panel report.
However, Grebby et al. (2021) have found that the time history of the deformation is rather more complex than had been indicated previously. In particular they note that:
The results illustrate that some distinctive deformations observed on the dam wall, and front and back of the tailings beach were … nonlinear
The data suggest that across parts of the tailings pond the sediment was undergoing slow settlement at an approximately constant rate through most of 2018, but in November and December the rate of deformation started to accelerate. Over time through the back end of 2018 and January 2019 the area undergoing this rapid deformation increased as well.
There is an established technique for evaluating the time of failure for slopes called the inverse velocity method – I have undertaken some work on this approach. In some slopes (in general those undergoing brittle failure) the pattern of acceleration is hyperbolic with time. This means that if the inverse of velocity is plotted against time then a linear trend is generated. Failure occurs when 1/velocity is zero. This plot allows the time of failure to be predicted; in a range of settings it has been proven to be remarkably effective. It is an approach that is often used, with considerable success, in the monitoring of high wall mines for example.
Grebby et al. (2021) have plotted inverse velocity against time for these areas in which there was rapid acceleration:-
These are complex plots, and the data is noisy, meaning that analysing a single point is challenging. But if the ensemble of points is used the conclusion is that there was a linear trend in the inverse velocity graph (indicating that the sediments were following a brittle path to failure) and that the time of the dam collapse could have been predicted within a few days.
This is a really important finding for two reasons:
First, it implies that really high quality monitoring, and analysis of the data, could have allowed a warning to be given that the Brumadinho dam was developing serious stability issues. This is crucial – a separate (also open access) study (Lambruso et al. 2021) has found that a even a short term warning of dam failure would have saved many lives.
Second, it shows that even tailings dams that undergo very rapid failure probably show signs of distress that can be detected with appropriate monitoring and expert analysis of the data. This is reassuring for the mining industry, and the regulators, who will now need to step up to the plate to enact these systems.
Grebby, S., Sowter, A., Gluyas, J. et al. 2021. Advanced analysis of satellite data reveals ground deformation precursors to the Brumadinho Tailings Dam collapse. Communications Earth and Environment 2, 2. https://doi.org/10.1038/s43247-020-00079-2
Lumbroso, D., Davison, M., Body, R. and Petkovšek, G. 2021. Modelling the Brumadinho tailings dam failure, the subsequent loss of life and how it could have been reduced. Natural Hazards and Earth System Sciences, 21, 21–37.
5 January 2021
Planet Labs high resolution satellite image of the Gjerdrum landslide in Norway
Operations continue with some intensity of the site of the Gjerdrum landslide in the village of Ask in Norway. Sadly, the focus has now changed from rescue to recovery, with an acceptance that there are no more survivors. To date the remains of seven victims have been recovered, leaving three people missing. Operations have been made easier by an improvement in the conditions on the landslide, but finding those still missing will be a difficult task.
My friends at Planet Labs have now managed to capture an excellent SkySat high resolution satellite image of the site – once again can I note my thanks to them, and in particular to Rob Simmon, for their support. This is the first image that I have seen of the entirety of the site.
The crown of the landslide is of course where the losses occurred. The image below shows this area:
The form of this landslide is interesting, with a large main source area, and a smaller area to the north that has affected the houses with such catastrophic consequences. The reason for that morphology is not clear to me – on first inspection it appears that this was a retrogression from the main landslide bowl. If so, it will be important to understand why this happened at this particular location. Others will be better placed to comment on this than me, and I’m sure that the official investigation will provide an explanation.
The Planet Labs image also captured the whole of the landslide, which is very large. This is the image:-
Note the main source on the western side of the image. The main slide moved roughly towards the south, and then followed a very subtle channel towards the east. Mobility was high – the choked channel on the eastern side of the image demonstrates that the landslide moved over 2 2 km. In one location the slide has bifurcated, as seen on the helicopter image. There is a very substantial amount of debris at the toe of the landslide.
There is a great deal of speculation about the trigger of the Gjerdrum landslide. In the past, for example at Rissa, quick clay landslides have been triggered by excavations lower on the slope, which induced rapid liquefaction and expansion of the landslide. There is also some discussion about the role of modification of the topography too – the slope included both a golf course and the housing development. I am not in a position to comment on this, but the Wikipedia article on the Gjerdrum landslide has some details.
Planet Team (2020). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
4 January 2021
The Trotternish landslide complex on the Isle of Skye in Scotland
A few years ago I posted briefly about the Quiraing landslide (also sometimes spelt Quirang) on the Isle of Skye in Scotland, suggesting that it is the most beautiful landslide complex in the world. I stand by my view (but would welcome alternative suggestions of course). It is hard to beat this in my views:-
In fact the Quiraing is one part of a huge, ancient landslide complex located on the east side of the Trotternish peninsula in the northern part of the Isle of Skye. This landslide complex should be better known, but it is a long trip to visit it even from the major cities of Scotland. The complex, which is not active, dates from the period after the last glaciation, between about 13,000 and 5,000 years before present. The Google Earth image below shows the Trotternish peninsula and the location of the two best known landslides, the Quirang and the Storr:-
As the image shows, the Trotternish peninsula is dominated by a large escarpment running apprixmately north-south, formed from Tertiary basalts. At the Storr this has an elevation of about 720 metres. This escarpment, which extends for 23 km, has ancient landslides along its whole length. This is the complex known as the Trotternish landslides – it is the largest landslide complex in the UK by far.
Colin Ballantyne of the University of St Andrews wrote an excellent summary of this complex (Ballantyne 2008), which was published in the Scottish Geographical Magazine. He included this very nice summary of the general structure of the landslides at Trotternish:
As the diagram shows, these landslides consist of rotational failure through the basalt escarpment and the underlying Jurassic sediments, with the basal shear surface being defined by a resistant dolerite sill within the Jurassice rocks. There are multiple failures at the various sites, with the blocks buttressing those upslope. The rotated blocks become more degraded downslope.
This is a classic rotational landslide system, on a very large scale.
3 January 2021
Landslides in Art Part 34: Landslide (Bergsturz) from Intermezzi, Opus IV by Max Klinger
Max Klinger (1857 – 1920) was a German artist renowned for his paintings, sculptures, prints and graphgics, as well as extensive writings on art and graphics.
In 1881 he produced a folio, published as Intermezzi, Opus IV, comprising of seven etchings and aquatints with chine collé and five etchings with with chine collé. There is a copy in the Museum of Modern Art in New York.
Intermezzi, Opus IV provides a series of whimsical snapshots, arranged in sets of four works. One set of four etchings features the mythological lives of centaurs, and one of these is named Landslide (Bergstrutz):
The etching shows a simple but very beautiful landscape – Max Klinger had studied Japanese art, including the depiction of landscapes. The influences are clear in the work – look in particular at the representation of the mountains in the distance. But the main depiction is of a landslide in the centre of the etching. The landslide looks quite recent – note the smooth, unweathered topography of the landslide source and scar, and no track has yet been created across the deposit. On the edge of the lake is a boulder-rich landslide deposit – this was a rapid and energetic slide, which bifurcated to leave a bouldery heap on the lower part of the hillside.
Max Klinger has included in the etching six centaurs, three of whom are approaching the landslide with aplomb. One is distracted by a snake, to the evident frustration of the team leader. Clearly the centaurs are a team of engineering geologists, dispatched to investigate the landslide – indeed two are carrying ranging poles. Presumably the third is transporting a theodolite, out of sight. These centaurs are the ideal field geologists, with a human upper body but the stability and energy of a quadruped.
I imagine the centaurs will be quickly able to evaluate the landslide (once they have stopped being distracted by the snake); I wonder what they made of that fractured outcrop on the nearside of the landslide. I sense that there is a high risk of a toppling failure there, and there is a similarly precarious outcrop on the far side. The services of a roped access team might be required.