26 February 2020
The 1954 Prospect Point Rockfall at Niagara Falls
Regular reader George Haeh has very kindly pointed out a remarkable video on Youtube showing the 1954 Prospect Point Rockfall at Niagara Falls:-
This is an archive British Movietone newsreel, complete with dramatic music and rather elegant commentary. The associated text suggests that the rockfall had a mass of about 168,000 tonnes (185,000 tons). Niagara Frontier has this image of the rockfall:-
There is a good article about the Niagara Falls rockfall on the Niagara Frontier website. The rockfall occurred on 28 July 1954 on the American Falls side of the site. It appears that cracks at the site, shown in the video above, were first noticed by a nine-year old child the day before the failure. The rockfall left a large debris pile, which then became a tourist attraction in its own right. In the aftermath, the Niagara Frontier State Parks Commission undertook blasting to remove rock left in a precarious position, with large blasts on 6, 12 and 16 August 1954. Thereafter the site was deemed to be safe.
25 February 2020
Spatial and temporal patterns of landslide losses in Colombia
Back in 2012 I posted about the levels of landslide losses in Colombia, which is one of the most landslide prone countries, based on my fatal landslide database. I noted that levels of loss are high, especially in the western side of the country, and that Colombia needs to be a priority country if we are to reduce loss worldwide. It is good that the 13th International Symposium of Landslides will be held there later this year (COVID 19 permitting I guess), which will draw attention to the challenges in that country.
In that context, it is really good to see a new paper (Aristizábal and Sánchez 2019), published in the journal Disasters, which seeks to analyse losses from landslides in Colombia between 1900 and 2018. This is a truly epic piece of work – the authors have used multiple datasets at national and regional levels to record 30,730 landslides over the 118 year period of the study. As such this is one of the most detailed and comprehensive national landslide studies published to date.
There is much to take away from this study, but I’ll highlight some of the more interesting findings. First, not unexpectedly, the authors found that landslides are concentrated in the mountainous west of Colombia, as the map below shows:-
Of these landslides, 2,328 caused at least one fatality, with a total of 34,198 deaths. This is much higher than had been previously recorded. As always for these types of very long-term studies, the majority of landslide fatalities have occurred comparatively recently:-
It is really interesting to note that landslides, and the resultant fatalities appear, to have peaked in about 2011 after showing a notable increase with time, and have declined substantially since then. So, for example, the number of recorded landslides was 3,545 in 2011 but just 123 for 2016. The reasons for this are not entirely clear; Aristizábal and Sánchez (2019) suggest that:
“This might be due to advances in risk reduction in Colombia, especially making legally mandatory implementation of the land use planning programme (Planes de Ordenamiento Territorial), but it is too soon to say for sure. Much more analysis needs to be conducted and more evidence acquired to prove and compare the effectiveness of such risk reduction policies.”
If this is the case then it would be one of the most impressive landslide hazard management programmes undertaken at a national level to date. However, I also note that 123 landslides in a year in a country such as Colombia seems low to me, so I wonder if this might in part be an artifact of the data.
This is an excellent and very welcome study, which provides insight into the levels of loss in Colombia. It would be good to see more studies of this type for other landslide-prone countries.
Aristizábal, E. and Sánchez, O. 2019. Spatial and temporal patterns and the socioeconomic impacts of landslides in the tropical and mountainous Colombian Andes. Disasters. DOI: 10.1111/disa.12391
24 February 2020
The giant Kandersteg rock avalanche in the Bernese Alps in Switzerland
In a paper just published in the journal Landslides, Singeisen et al. (2020) provide a very comprehensive analysis of the landslide, including the deployment of a new set of dating methods to try to ascertain the timing of the failure. The description of the landslide is impressive – it started as a planar rockslide high on the mountain side. The authors estimate that 750 to 900 million cubic metres of limestones sandstones detached along pre-existing discontinuities from the northwest face of the Fisistock peak. As the image above shows, the landslide descended a very steep slope into the valley below – the schematic diagram below, from Singeisen et al. (2020), provides some details of the geometry of this part of the landslide:-
The large descent into the valley caused the rock mass to fragment, forming a rock avalanche that traveled northwards along the valley, during which time it entrained sediments from the valley floor. By the time the landslide stopped moving it had increased in volume to about 1,100 million cubic metres – i.e. 1.1 cubic kilometres. The landslide traveled a total distance of about 10 km, as the map from the paper below shows. The source zone of the landslide is the red area highlighted in the southeast corner of the map, whilst the landslide deposit is outlined in purple:-
The map above provides some of the dates from the research. Singeisen et al. (2020) suggest that this failure occurred about 3,200 years before the present. Of course it is hard to know what might have triggered this landslide, but the authors note that there is a cluster of large Alpine landslides with dates from about this time. There is some evidence that this was period in which glaciers advanced and conditions were wetter. However, giant landslide may collapse through progressive failure rather than triggering, so such interpretations are inevitably uncertain.
Singeisen, C., Ivy-Ochs, S., Wolter, A. et al. 2020. The Kandersteg rock avalanche (Switzerland): integrated analysis of a late Holocene catastrophic event. Landslides. https://doi.org/10.1007/s10346-020-01365-y
20 February 2020
Hardin County: a dramatic landslide in Tennessee
On Saturday 15 February 2020 a dramatic landslide occurred in the Chalk Bluff area of Hardin County in Tennessee, USA. The landslide, which is located at 35.385, -88.284, destroyed rather beautiful two houses located at the top of a bluff. Fortunately no-one was harmed, although the houses are a total loss.
Fox 17 News has posted some imagery and a video of the landslide, including this image of the early part of the failure:-
Whilst this image shows a later phase, when the slide had retrogressed significantly, causing the loss of the two properties:-
Google Earth imagery from November 2012 shows the site quite clearly, as the trees had no leaves:-
This image appears to show that a smaller landslide has been active for some years, and that it had encroached close to one of the two houses that were lost. The collapse on 15 February appears to be a significant increase in the size of this landslide, driven by a prolonged period of heavy rainfall. As the site is located on the outside of a gentle bend in the river, enhanced erosion would be expected.
The Jackson Sun has some more detail about the landslide. One of the houses, which were built in the 1990s, has been unoccupied, but the other was in daily use. The occupiers were able to recover only a small amount of their possessions before the house was destroyed.
18 February 2020
Further information about the Tylorstown landslide
Yesterday more information emerged about the Tylorstown landslide in South Wales on Sunday 16 February, which was caught on video. Many thanks to the various comments and observations that I’ve received.
The most useful information comes in the form of a pair of oblique aerial images that were tweeted by the National Police Air Service South West Region, who overflew the landslide. This is one of the two images:-
This image shows that the failure originated in the upper of the two spoil heaps. There can be little doubt that this is coal waste. The failure appears to have started as a rotational slip in the spoil, and a part of the rotated, back-tilted block is clearly visible. The lower part of the block has fragmented to form the flows that have reached and inundated the river.
These flows can be seen in more detail in the image below:-
This second image shows that the displaced block has failed to generate the flows, and the amount of material in the watercourse. Interestingly, it also hints that there may be a further failure developing to the right of the slipped mass, although better imagery is needed to be clear.
Rotational failure that transitions into a flow is the classic failure mode for coal waste in South Wales – indeed the official tribunal found that this was the mechanism for the Aberfan landslide. This was the description of the landslide:-
“On 21st October 1966 there were a number of slipping movements of a rotational kind accompanied by settlements of the crest of the tip. These movements gave rise about 9-10 a.m. to a flow slide, the relatively dry material in the flow slide pouring down the mountainside and into the village. it was this flow slide which engulfed the school and houses in Moy Road.”
The waste pile is not shown on the 25 inch OS map that was published in 1919, but it is depicted on the 1956 map. Interestingly the early maps show a stream flowing through the site. It is not clear as to what happened to this stream when the waste was dumped.
17 February 2020
Did South Wales suffer a coal waste landslide yesterday?
Yesterday morning the UK Met Office issued a rare red rainfall warning for South Wales, as a result of Storm Dennis. This was a prescient act as the rainfall duly triggered extensive flooding and a number of significant landslides. South Wales is a landslide prone environment – the Welsh Valleys have many natural landslides and, of course, many more that are a legacy of the mining coal mining that so dominated this area for many decades.
One particular landslide is of interest, and may be of real consequence. This occurred close to the village of Tylorstown, at approximately 51.656, -3.434. A part of the event was captured on a video that was posted to the front page of the BBC News website. There is a version of it on Youtube, though I suspect that this is not the original:-
On Twitter, Owen Griffiths posted a very helpful panoramic image of the site of the landslide at Tylorstown:-
Based upon that image, I interpret the landslide as occurring on the slope shown in the Google Earth image below:-
The origin of the landslide appears to be a spoil heap on the valley wall. The historic 1920-1940 Ordnance Survey map shows the route of the spoil conveyors from the Tylorstown Colliery (also shown on the map as Pendryrys Colliery) to this location, whilst the 1955-61 map shows spoil at this site:-
The photograph of the site suggests that the failure captured on video was only a small part of a larger failure. We need better images, but on first inspection is appears that a large mass has slipped, leaving the large scar that can be partially seen at the rear of the failure, and that a small part of this slipped and disrupted mass has then turned into the more mobile flow captured on video.
Much more detail is needed on this failure than is available at the moment, but since the clean up after the Aberfan landslide coal spoil tip failures have been rare in Wales. If (and this is an unknown at this point) this is a coal waste landslide then we need to know why it has occurred. Is it possible that the new, extreme rainfalls that we are now seeing as a result of global heating are rather greater than had been anticipated when the reprofiling was undertaken?
That is a pressing question that can only be addressed by examining this failure properly.
14 February 2020
Elkhorn City, Kentucky: a fiery train derailment by a landslide
On 13 February 2020 at about 7 am a freight train was derailed by a landslide close to Elkhorn City in Pike County in Kentucky, USA. Fortunately the train crew were able to escape the accident even though five carriages were derailed. The train consisted of three locomotives, 96 freight cars carrying ethanol, and two sand cars. Some of the carriages caught fire after the accident, meaning that the train crew had to be rescued by boat.
This image, tweeted by the Kentucky Energy & Environment Cabinet, shows the extremely messy aftermath of the accident:-
The landslide can be seen on the right hand side of the image, with debris that extends to the river. The lead locomotive is centre right, with the cab close to the river. Videos suggest that the train crew had to be rescued by boat from this location. Note the various derailed freight cars.
I have struggled to find a good image of the landslide itself, but a video posted by WYMT includes the following still:-
From this image the landslide appears to be a planar slide on a steep, wooded slope. Based on the news reports, my preliminary interpretation is that the landslide occurred on the slope shown below, which is at 37.333, -82.371:-
The landslide was undoubtedly caused by the prolonged heavy rainfall currently affecting large parts of the United States. Landslides have been reported elsewhere too, such as in West Virginia.
Landslides induced rail derailments are not unusual, fortunately in this case there has been no loss of life.
13 February 2020
The fast-moving Alpine Gardens landslide in New Zealand
My friends at GNS Science in New Zealand published an article on the Geonet website yesterday about the Alpine Gardens landslide in the Fox Glacier Valley in New Zealand. Featuring the work of a team led by Saskia de Vilder, who like me used to work at the University of Durham, the article highlights the impacts of a remarkably active landslide that has required the rerouting of the track to the Fox Glacier viewpoint, an important tourist destination on the west coast of South Island.
This is a large landslide – GNS estimate that it has a volume of 50 million cubic metres. Through Geonet, Saskia and her team have set up a GPS monitoring station on the slide. In the last year, that monitoring station has displaced by about 50 metres, with the rate of movement being dependent upon the groundwater level. This means that on average it is moving at over 11 cm per day, but on some days the displacement exceeds half a metre. This is an unusually large amount.
The landslide itself is remote, but as the image above shows, debris released by the landslide forms large debris flows that travel down the side valley and into the main channel. Large volumes of material are being mobilised – Saskia estimates that over the year to June 2019, about 6 million m³ of material was incorporated into debris flows. About half of that amount was deposited onto the debris fan, whilst the other half was transported away by the Fox Glacier.
The upshot is a remarkable level of geomorphological change. The Google Earth image below shows the same site in am image collected in May 2006:-
At that time there was little evidence of active movement on what has become the Alpine Gardens Landslide, and of course there are no debris flow deposits in the valley. It is intriguing to consider the possible causes of this high current level of activity.
11 February 2020
A seismic analysis of the 23 July 2019 Shuicheng landslide in China
On 23 July 2019 a large landslide occurred at Pingdi in Shuicheng County in western Guizhou Province, China, killing 51 people. I covered this large landslide, one of the more significant of 2019, at the time, and in August 2019 I posted the following high-resolution Planet Labs image of the slide:-
A first analysis of the Shuicheng landslide (Yan et al. 2020) has now been published in the journal Landslides. The most interesting element of this piece of work is that it uses a very detailed analysis of the seismic signals generated by the landslide to interpret its behaviour. This is one of the most detailed analyses of this type to date. It is particularly intriguing because of the behaviour of the slide, which I highlighted at the time, with an initial planar sliding component (in the vicinity of the road at the top of the slope, which is the bottom of the image above), bifurcation into two components in the middle part of the track, and then a single runout zone. Interestingly, Yan et al. (2020) have been able to back-analyse this behaviour from the seismic data.
As a consequence of this investigation, the authors have provided this schematic of the behaviour of the Shiucheng landslide:-
To my surprise, the data suggests that the Shuicheng landslide started below the road (Road A), not on the upslope side. Yan et al. (2020) suggest that this might have been the result of saturation of this part of the slope due to runoff from the road. This initial landslide was small, but it soon destabilised a wider area, such that a larger mass in the crown of the landslide began to move. Failure of this upper portion of the slope remained slow, but as the mass loaded the steeper slope below, the landslide both accelerated and increased in volume as material was entrained.
In the third stage of the Shuicheng landslide, the natural topography forced it to bifurcate into the two portions seen in the satellite image. The landslide was now rapid and was efficient in entraining debris.
Finally, the mass reached the bottom of the slope and was deposited in the valley. The seismic data indicates a rapid deceleration once the topography no longer supported sliding.
In my original posts I hypothesised that the road had destabilised the slope, but my interpretation was that it would have been the section upslope of the road that failed first. Yan et al. (2020), using quantitative data, have shown that whilst the road was indeed a key factor, it was the downhill portion that failed first.
This is a really nice example of the ways in which these new quantitative datasets can provide insight into landslide mechanisms.
Reference and acknowledgement
Yan, Y., Cui, Y., Tian, X. et al. 2020. Seismic signal recognition and interpretation of the 2019 “7.23” Shuicheng landslide by seismogram stations. Landslides. https://doi.org/10.1007/s10346-020-01358-x
Planet Team (2020). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
10 February 2020
The exceptional mobility of tailings dam failures
I’m continuing to write my paper for the keynote at the 13th International Symposium on Landslides in Colombia this year (the paper is due this month, so the pressure is on). As I noted in a post last week, I’ve been looking at the impact of landslides in less developed countries; one key component of this is the impact of failures associated with mining.
As part of this work I’m taking a look at the mobility of tailings failures in relation to other major landslides. Tailings dam failures inflict a huge impact in terms of loss of life, environmental effects and social damage. It is well established that the impacts can extend for tens or even hundreds of kilometres downstream – the Ok Tedi tailings failure in Papua New Guinea for example extended for 1,000 km and disrupted the lives of 50,000 people. Of course much of this damage was caused by remobilisation of the tailings by the river, but the issue of the runout of the landslide itself is very pertinent.
A good way to analyse the runout of landslides is to examine the so-called Fahrböschung angle, which is the ratio between the vertical change of the landslide (from crown to toe) to the length of the landslides (again from crown to toe). More mobile landslides have a lower Fahrböschung angle.
Using case studies described in the World Mine Tailings Failures (2020) catalogue, and going back to original topographic and satellite data, I have been able to calculate the Fahrböschung angle for 27 tailings dam failures. I have then compared these with the mobility of large landslides using data presented in a famous paper (Legros 2002) a couple of decades ago. I have also included in the graph data for coal waste landslides:-
Taking the large landslides first, it is well-known that the Fahrböschung angle decreases as landslide volume gets larger – the reasons for this remain a little unclear. Interestingly the same effect is seen for coal waste landslides and for tailings landslides, both of which are more mobile than large landslides. But, most significantly, the tailings landslides have a far lower Fahrböschung angle than that of the large landslides, but with much greater scatter too. Indeed, in many cases the Fahrböschung angle is two orders of magnitude lower – in other words, tailings landslides travel far further than other large landslides.
The reason for this high mobility is likely to the nature of the materials that are released in the tailings dam failure. Typically, the failure involves materials that have been crushed and that, at the point of failure, are saturated and have undergone liquefaction. The extreme mobility at the time of failure was of course illustrated rather elegantly by the Brumadinho failure in Brazil. Interestingly, many investigations of tailings dam failures tend to focus on the failure mechanism, and to ignore what happens thereafter. This needs attention.