8 July 2014
Komansu rock avalanche
The Komansu rock avalanche is described in a new paper by Robinson et al. (2014), which has recently been published online by the journal Landslides. The landslide is located in the Alai Valley of Kyrgyzstan, in the Trans Altai range of the Pamir Mountains. The landslide deposit is ancient – the slide has been dated at 5,000 to 11,000 years BP, which is the period after the retreat of the glaciers in this region.
The Komansu rock avalanche is both very large and quite hard to see. This is a perspective view Google Earth image of the landslide – I’ve annotated the key parts of the slide, based on the interpretation in Robinson et al. (2014):
The current landslide deposit has an estimated volume of 3 – 5 cubic kilometres (although a large part of the deposit has been eroded away), and covers an area of 64 square kilometres – i.e. this is a very large landslide indeed, and we’d expect such a large landslide in very steep, high terrain to have a long run-out. Empirical relationships from similar events suggest about 10 km. However, the Komansu rock avalanche has a run-out that is much longer than this – about 26 km – which asks real questions about the dynamics of the landslide. In other words, what was special about this landslide that allowed it to go so far? An obvious explanation is that the landslide volume was much larger than the modern deposit suggests, but given that the source area only has a volume of about 4 cubic kilometres, this then poses the question as to the origin of the additional material.
Robinson et al. (2014) have compared the hummocky topography of the landslide deposit with that of other large landslides from this region. This is a Google Earth perspective view of the deposit:
Whilst on the face of it the deposit might look a little strange, it is very similar to that found in many other large rock avalanches both in this area and more widely. From this perspective, the landslide is not unusual. The one mechanism that is known to generate usually long runouts is the presence of large amounts of snow and ice – i.e. that is a so-called rock-ice avalanche. However, such landslides tend to have a distinctive final morphology; Robinson et al. (2014) suggest that the Komansu rock avalanche deposit does not match this. An alternative, but similar possibility is that the landslide ran-out over a glacier within the valley, but again the morphology does not seem to match that observed from other known examples.
Robinson et al. (2014) suggest that the unusual mobility might be explained by the presence of a large amount of ice in the initial failure, and that the landslide then entrained a large volume of material from within the valley. So, the authors propose that the initial failure was about 4 cubic kilometres of rock together with about 500 million cubic metres of ice. This very large landslide then entrained about 4 cubic kilometres of sediment in the valley, plus additional glacial ice, to generate a flow that behaved in a manner that was similar to a volcanic debris flow, allowing the very long runout distance.
A final observation in the paper is that such landslides have substantial implications for hazard assessment in high mountain areas. These giant rock avalanches with long runout distances are clearly extremely destructive. As people increasingly populate the high mountains the likelihood of a mass fatality event, especially during a very large earthquake, increases.
Robinson, T.R., Davies, T.R.H., Reznichenko, N.V. and De Pascale, G.P. (2014). The extremely long-runout Komansu rock avalanche in the Trans Alai range, Pamir Mountains, southern Kyrgyzstan. Landslides, DOI: 10.1007/s10346-014-0492-y
7 July 2014
The Oso landslide in Washington State in March remains of great interest to the wider community, not least because of the number of lives lost and the unusually destructive nature of the landslide. A series of lawsuits have now been started in relation to the landslide. The Seattle Times has continued to investigate, and yesterday released a video that they obtained through a public-disclosure request showing continued landslide activity on the slope a month after the main failure. I have tried to embed the video, but if it does not work it can be viewed here.
The video was collected by Jeff Jones, Snohomish County geologist. It shows ongoing toppling failure from the landslide scarp. Such behaviour is quite normal as the stresses in the slope rebalance – in some ways this is anomalous to aftershocks after a big earthquake. Although the video is a bit jerky, the really interesting aspect if the mobility of the debris – even with these small slips the debris easily mobilised into a flow. Bear in mind that this is in a dry state, whereas the main failure was wet, and that the volume is a tiny fraction of the main event, and it is easy to understand why the main collapse was so destructive.
3 July 2014
Vietnam flash floods
Youtube has an interesting video of a very dramatic flash flood that appears to have occurred in Phin Pon, Sin Ho District of Lai Chau province in Vietnam on 5th June:
The new highway under construction in the background must be severely threatened by this event. The man who went down to try to recover the road roller was very lucky indeed to escape the surge towards the end of the video.
Thanks to Thomas Hodgson for finding this one.
1 July 2014
Zhaotong City landslide
The onset of the rainy season is China is, as usual, being marked by an increase in landslides. A number of news agencies have been carrying this footage of a slide occurring at Tuohe village in Daguan County, Zhaotong City in Yunnan Province on Saturday afternoon:
The landslide buried four local people, three of whom died. The heavy rains have also led to the death of a panda in Sichuan Province, apparently having been caught in a landslide, and to a landslide in Yunnan Province yesterday that killed two people and left a further 13 people missing.
20 June 2014
As I have noted previously, the global landslide cycle is dominated by the effects of the South Asia summer monsoon, which brings heavy and prolonged rainfall to the world’s most landslide prone region. In 2014 the monsoon has arrived late, which has meant that the level of landsliding across Pakistan, India, Nepal and Bangladesh is currently lower than is usually the case. This image, from the IMD, shows the monsoon precipitation deficit as of 19th June:
In South Asia, the highly landslide prone regions are in SW India (Kerala for example) and of course the Himalayan region, both of which are in a state of rainfall deficit at present.
However, the monsoon front is now advancing across the region, and with it comes reports of landslides. In Nepal overnight there were two major landslide incidents:
- In Aglung VDC- 8, Nipane, in Gulmi District a landslide buried a house, leaving nine people dead and seven missing (and assuming that they were in the house the likelihood of their having survived is very low). This is the worst landslide incident in Nepal this year.
- In Khung VDC in Pyuthan district a landslide killed five people and left another injured.
This apparently occurred in Rampur, which is in Uttar Pradesh, India; the actual date of the event is not given.
Meanwhile, over in Vietnam, the rainy season is already having an impact. This video is almost surreal – do watch to the end!
I guess there was no way back for those motorbikes. The landslide appears to be a reactivation of a previous event in deeply weathered soil. Note the precursory slips at the front of the landslide before the final collapse – the people near to the camera certainly saw this happening. Note also the flow of water that preceded the main landslide body down the road – this is often reported (and misinterpreted) for large events.
19 June 2014
The Devdoraki Landslide
The Devdoraki landslide was a large event in the Dariali Valley in Georgia that blocked the main road between Russia and Georgia a month ago. I featured some images of the landslide at the time, but (via Jorg Hanisch), I have been provided with a new set of very high quality photographs of the landslide. These images were collected by Georgy Gotsiridze of the Consulting Center “GeoGraphic”, Tbilisi, Georgia, who has made them available for free use. They are remarkable.
This is the source zone of the Devdoraki landslide:
Note the failure appears to have started as a rock mass failure on a very steep, ice-covered slope. This then appears to have entrained a very large volume of material as it loved down the steep slope. The dynamics are complex though – on the left side of the flow as seen from the camera the slide has spilled over a rock spur to create a second slide. Down-slope this merges again with the main slide, as shown in this image:
The most dramatic aspect of this image through is the extraordinary super-elevation of the slide when it reached the foot of the steepest slope and then needed to turn 90 degrees to follow the valley. Super-elevation is the term used when the slide travels up a slope, typically because of a sharp turn. On the right side of the image this super-elevation is very clear. This indicates that the landslide was travelling very fast at this point. The super-elevation is better illustrated in this image, showing the entire upper portion of the landslide:
Interestingly, from this point onwards the character of the slide appears to have changed markedly, I assume from a rock avalanche to a rapid debris flow. This is an image of the track of the landslide in the lower reaches:
There is some evidence of super-elevation on the outside of the bend, but to nothing like the extent upslope. The flow appears to have been strongly channelized in this portion. This is supported by this image of the slide, taken from a lower angle:
Finally, this is the landslide deposit at the point that it entered the main channel and stopped:
The diversion channel, which flowed into a tunnel, is clearly evident. The landslide does not seem to have traveled far, or to have spread dramatically, once it entered the main channel. There is little evidence of super-elevation as well. This supports the hypothesis that the movement rate was notably lower than for the initial stages.
This is a very unusual and interesting landslide – I hope that it will be analyzed and written up in detail.
17 June 2014
World Cup 2014
Alongside the World Cup 2014 tournament (for which the football has been wonderful, but let’s not talk about England…), parts of Brazil has been suffering from very heavy rainfall. The city of Natal, which yesterday hosted the match between Ghana and the USA, received extremely heavy rainfall over a 50 hour period at the start of this weekend, triggering a large landslide that destroyed 25 houses, but fortunately took no lives. This article has some images of the landslide:
The best coverage of the landslide is from some drone footage that has been placed on Youtube:
Note the extremely fine-grained nature of the soils, which make them very prone to erosion. The landslide appears to have a very unusual shape, with a planform that is similar to a cross. I would suspect that the two arms are the result of washout erosion once the main slide had occurred. Note the drainage pipes under the road on each side.
There is a very nice paper describing the geology of the Natal region of Brazil on JSTOR, dating from 1913. The paper describes the coastal region as being characterised by huge banks of sand blown in on the coastal winds, forming banks up to 75 feet (22 m high). This sand has become cemented to varying degrees.
11 June 2014
Vaðlavík (Vadlavik) landslide
A large landslide occurred at Vaðlavík (Vadlavik in the anglicised version) in eastern Iceland in April, but unfortunately this has only just come to my attention. The landslide, which is featured in an Icelandic news story dated 22nd April, has a long runout that ends in a lake. It is clear that a part of the deposit is now in the water. The bay in which this occurred in uninhabited in the winter, so the timing is unclear. RUV has some images of this impressive landslide, taken by Sigurbjörn Jonsson:
The geology of eastern Iceland is generally described as Tertiary bedrock. I am no expert on Icelandic geology, but I wonder if the slide has occurred in volcanic ash (tephra) layer overlying the solid geology. This would explain the fine-grained nature of the material and the mobility of the landslide. Interestingly I cannot see any signs of a displacement wave (small-scale tsunami).
Does anyone have any more information about this landslide?
10 June 2014
Ferebee Glacier rock avalanche
The Ferebee Glacier is located in the Alaska panhandle, in the same general area as a number of other rock avalanches that I’ve described in the last two years or so (e.g. Mount La Perouse, Mount Jarvis and Mount Lituya). Pilot Drake Olson, of Fly Drake, very kindly keeps his eyes open for such events in this area, and over the weekend spotted a new rock avalanche that has descended on to the upper reaches of the Ferebee Glacier (the location is 59.610, -135.625 if you want to take a look at the site). Marten Geertsema very kindly highlighted this event to me, and Colin Stark has also done a lot of work in the last 24 hours to characterise the slide from satellite imagery.
This is an image of the landslide, taken by Drake:
The slide has broken off a near vertical rock face and then has descended a steep ramp to flow out over the glacier. Note the lack of deposition on the ramp itself, the clear flow in the deposit (and see below) and the apparent deposit on the opposite flank. Colin has suggested, and I agree with him, that this might be the remains of a dust cloud. If so I suspect that the landslide was moving quite fast, given the size of the dust deposit. To give an idea of scale, the total vertical height difference of the landslide is over 700 m and the total distance traveled in over 2,000 m. Colin has done a rough calculation of the volume, which is in the order of 130,000 cubic metres.
Brett has also supplied this nice image of the landslide source – the bluff on the left side appears to be the one that has collapsed:
And this is a shot of the lower part of the landslide deposit:
On the right side of this image is the edge of the main landslide deposit. The fine, “fingered” structure of the deposit shown above is probably the result of late stage slow sliding – a mechanism that only came to our attention from the Mount Haast / Mount Dixon rock avalanche video.
The date of the landslide is unclear. There is a good quality Landsat 8 image from 7th May 2014 on which the landslide is not present, and another from 6th June 2014 in which it is. However, we do not have a fix from between these dates. Unfortunately, it is unlikely that this landslide generated a strong enough seismic signal to be detectable, so we may never know precisely..
9 June 2014
The Litochovice landslide occurred on 7th June 2013 in the Czech Republic. Until yesterday I hadn’t heard of this landslide, even though it is both large and interesting. GIM International, who have been undertaking a project to map the landslide using UAVs, have released this oblique aerial shot of the site:
The very obvious road at the foot of the slope (and now buried for a substantial section) is the under-construction D8 motorway linking Prague with Saxony in Germany. In this section the road is passing through the Czech Central Mountains, which are known to be landslide-prone. The road appears to be traversing a slope with a cutting on the upslope side of the highway – a working hypothesis might be that it has cut through the toe of a pre-existing landslide, which then destabilised in heavy rainfall. Note the roads across the surface of the displaced mass post-date the landslide (see images below).
The work undertaken by GIM International appears to be to map the landslide in detail, and they have made this youtube video of their GIS model of the Litochovice landslide available:
There is also a really nice image of the Litochovice landslide on a discussion forum on Skyscraper City:
An interesting aspect of the landslide is the location of the head scarp close to the quarry. An area for investigation will be whether any material from the quarry has been dumped on the upper reaches of the landslide, possibly further destabilising the slope. I suspect that the investigation team will also be very interested in the stability of the section of the slope between the landslide and the flyover that crosses the river, including the section with the two small bridges. Judging by the shape of the land I would be unsurprised to find that this section also has a history of instability.
The road is not expected to open within the next year.
I’ve also come across this interesting image of the landslide, apparently taken rather soon after the slide:
It is clear that the slide removed as a remarkably intact, coherent block – note that tracks on the slide body are essentially undisturbed. This supports the notion that this is a reactivation of an existing planar slip plane.