29 July 2015
Two new landslide videos
Two new landslide videos are now available. Unfortunately I cannot embed either, so you will need to follow the links. You won’t be disappointed!
1. A dramatic rockfall in Taiwan
The image above is taken from an amazing video of a complex rock topple / rockslide from Taiwan. The link to the video is as follows (note that this is to a Facebook page):
This is a terrific video, showing both the power and volume of a large rockfall. Judging by the geology this is from the eastern side of central or southern Taiwan, I’d imagine probably the Southern Cross Island Highway, but possibly the Central Cross Island Highway. The caption suggests that the crack in the slope was observed by a highway engineer and the road closed. If so, well done that person! I have seen the aftermath of cars being caught in an event like this on the Central Cross Island Highway on several occasions. The video will be worth detailed interpretation in the way that it shows precursory rockfall activity before the final failure, which is likely to be an indication of the way that the rock mass was straining and deforming as collapse progressed.
2. The Fukaminato River landslide in Japan
In Japan, a large landslide is causing considerable problems along the Fukaminato River in Tarumizu City, Kagoshima Prefecture. This landslide has had three large failures in the last month, of which the most recent occurred yesterday. This landslide was caught on video – and well, what can I say. The link is as follows:
The very dramatic fragmentation of this landslide, and the extremely rapid runout, are fascinating. I hope to write about this again in the next few days.
Thanks to Colin Stark of the Lamont-Doherty Earth Observatory at Columbia University for highlighting this one.
23 July 2015
Ambunti, Papua New Guinea
Via Twitter, Dr Phil Collins of Brunel University (@PhilCollins_UK) highlighted an interesting story on an Australian news website about a “sinkhole” that developed on Saturday on the banks of the Sepik River in Ambunti, Papua New Guinea. The original news report has some images:
Pacific Islands Report has a longer description of the landslide:
According to witnesses Jamie Asa and Frank Warakai, the sinkhole formed about midday last Saturday at the Forex Camp and Saksak Compound, along the Sepik River. “Sixteen houses went down as the earth opened up unexpectedly.
“The settlers panicked and scrambled out of their houses within minutes as the earth shook,” a shocked Warakai said, adding that his house was the first one to be sucked in by the sinkhole.
He said he was woken from his sleep by the movement of the earth and jumped out of his house. As he ran for safety, the earth gave way within seconds, causing a large stretch of land to immediately sink in, creating huge cracks that destroyed houses. Mr Asa said the people in the settlements also panicked and many managed to escape to higher grounds. He said the displaced people are seeking shelter in makeshift houses and at nearby villages.
Whilst this is being reported as a sinkhole, I am certain that this is a riverbank landslide. Unfortunately the Google Earth imagery for this location does not have a high resolution, but Ambunti appears to be on the outside of a sharp river bend, and there is a feature sticking into the river on the apex of the bend that looks suspiciously like an old landslide, but that is pure speculation at this stage:
22 July 2015
News 24 has posted the following video on Youtube in the last 24 hours. It was apparently shot in Chamoli District of Uttarakand in northern India, but I have no further information. It is a spectacular failure, as the screen shot below shows:-
I recommend fast forwarding to about 18 seconds to see the event properly:
Meanwhile heavy rains also appear to be causing problems in other parts of the mountains of Central and South Asia:
- In Chitral, northern Pakistan, reports suggest that 300,000 families have been displaced by flash floods. It is likely that many of these events will be debris flows.
- In Tajikistan, mudslides killed seven people in Vanch district of Gorno-Badakhshan.
- There are signs that the heavily remediated Varunavat Parvat landslide in Utterkashi, northern India, has reactivated.
- In Chechnya a minibus fell from a road near to the village of Kharachoy in Vedensky District , killing at least seven and possibly eleven people, and injuring a further six. Reports suggest that the vehicle was struck by a rockfall or landslide.
But on the brighter side, the impact of landslides in the earthquake affected areas of Nepal has been lower than feared, primarily because so far the rainfall has not been excessive to date. There is still a long way to go in the 2015 monsoon though, and the real danger is from cloud burst events that can occur at any time.
21 July 2015
A huge portion of the northern part of the island has been mined out. This is a mine that appears to be very prone to landslides – the image below shows an earlier collapse for example:
There is an excellent gallery of images of the landslide last week on the ABS CBN website, from which this image is taken:
The ABS CBN report suggests that this is a very large landslide – 374,000 cubic metres. The failure appears to be a rotational slip with quite a high level of mobility at the toe. The report also indicates that the slope was being monitored with prisms (i.e. optical surveying), so it is quite surprising that such high levels of loss occurred. I would be very interested to see the data.
Anyway, there is a video version of the news report on the Youtube website. This includes a section of video that I have not seen before – it starts about 20 seconds into the report – that shows an earlier (smaller) landslide in the same mine:
This is quite interesting in terms of the way that it starts as a comparatively small cliff collapse but then fragments on impact to transition into a high mobility flow. It is understandable that the effects are so dramatic when people get in the way of these landslides.
20 July 2015
The torrential rainfall of 30th June / 1st July in Darjeeling, northern India triggered large numbers of landslides, causing a substantial number of deaths. The Save the Hills blog has set out to document the landslides in the Kalimpong area, an exceptionally useful achievement. I don’t intend to reproduce their report here, but will highlight a few aspects. First, they have produced a map of the landslides, and are willing to make the coordinates of them available:
This is landslide number 1, which killed two people:
These are other major landslides in Kalimpong:
There are many more images on the Save the Hills website. I continue to share the view with Save the Hills that many of the landslides could be avoided with simple good management of the slopes. There is much to learn from elsewhere – this increase in losses from landslides in Darjeeling is both unnecessary and avoidable.
17 July 2015
Marzia Colonna is an Italian artist who is based in Dorset in southern England. Educated in The Accademia di Belle Arti and at Morley College, she now works in collae and scuplture. Marzia Colonna has an upcoming exhibition at the Sladers Yard Gallery in West Bay in Dorset. One of the pieces that will be in the exhibition is a collage entitled “Rockfall at Burton Bradstock”:-
This is a beautiful piece that captures both the majesty and the danger of these cliffs. In July 2012 a rockfall from these cliffs killed 22-year-old Charlotte Blackman from Derbyshire – this is the BGS image of the location, compiled using a terrestrial laser scan and orthorectified digital photograph:
The depiction in the collage of the variable properties of the cliff face, and in particular the colour changes associated with contrasts in the degree of weathering between fresh rockfall scars and older sections of cliff, is particularly impressive.
Part 22 of the Landslides in Art series can be found here
16 July 2015
Landslides on Pluto?
Overnight a series of stunning images of the surface of Pluto have been sent back to Earth by the NASA New Horizons spacecraft. These images are so good that they have even made the first story on the BBC News website – quite remarkable given the importance of the Greek debt crisis. The discovery that Pluto is geologically active seems astonishing, not least because a mechanism to drive active geological processes is not apparent.
The presence of mountains on the surface of the planet, and the absence of impact craters, suggests some form of active uplift process. On Planet Earth, active uplift is always accompanied by some level of active erosion, and in the presence of water this denudation is usually accomplished primarily by landslides. In extremely arid environments, erosion may be driven by seismically-induced landslides, as we explored in our recent paper on the 2010 Mexico earthquake (Barlow et al 2014). So a fascinating question is whether the creation of young mountains on Pluto also means that landslides (in this case ice avalanches presumably) are present too.
The image below has been generated by NASA, showing mountains rising 3500 m above the base surface near to Pluto’s equator. These mountains are thought to be formed from ice and are less than 100 million years old. Note the scale of the image, 50 miles is about 80 km:
Although I am no planetary scientist, on first inspection there are features on the surface that are reminiscent of active slope processes. This is an enlargement of the image in which I have annotated some key features:-
I am speculating here as to the nature of the features, but on many of the slopes there are streaks that look like landslide tracks, and there also appears to be debris at the slope toes in many places. In the mountain on the “north” side of the image there is a feature that could well be a landslide track with a displaced mass at the toe – this has many of the features of a terrestrial landslide, although of course this would be a very large body. Finally, and pushing the boundaries of speculation to an extreme, in the “southeast” portion of the image there is a mountain with a huge arcuate face and what appears to be debris at the toe. Could this be a giant mountain collapse landslide? If so it will be of enormous volume.
I am sure that the NASA scientists will be looking at these images in detail in the months ahead, and will be able to come to a much better conclusion about whether Pluto has landslides. But I will be surprised if it does not.
Barlow, J., Barisin, I., Rosser, N., Petley, D., Densmore, A. and Wright, T. 2014. Seismically-induced mass movements and volumetric fluxes resulting from the 2010 Mw = 7.2 earthquake in the Sierra Cucapah, Mexico, Geomorphology, Available online 24 November 2014, http://dx.doi.org/10.1016/j.geomorph.2014.11.012.
15 July 2015
The Judgement Cliff Rock Avalanche in Jamaica
At 11:43 am on 7th June 1692 an Mw=7.5 earthquake struck the town of Port Royal in Jamaica, killing an estimated 2000 people. The greatest impacts of the earthquake occurred in the town of Port Royal itself, in which there appears to have been a combination of a submarine landslide that removed 33 hectares of the town (this is sometimes interpreted as a liquefaction event, although this seems unlikely to me) and a tsunami (which could have been related to the landslide given the nature of the strike-slip faulting in Jamaica – I would not expect this earthquake to have been tsunamigenic in its own right).
Inland, the earthquake is associated with a large earthquake, known now at the Judgement Cliff Rock Avalanche. Strangely, it is a little unclear as to whether the landslide was triggered by the earthquake or by heavy rainfall a few days later (but it seems to me that a seismic origin is most likely given the depth of the shear surface). The landslide is very large – Maharaj (1994) provides a detailed description, estimating that it has a volume of between 131 and 181 million cubic metres, and extended over 440 metres vertically and 1763 metres horizontally. The landslide is very clear in contemporary photographs:
And on Google Earth images, even 320 years after the event:
Maharaj (1994) describes a landslide body consists of highly fragmented and disrupted limestone fragments and chert nodules, suggesting that the Judgement Cliff rock avalanche was very dynamic. The runout distance is quite large – the H/L (height / length) index is 0.25, implying a flow-type mechanism. Indeed as such this is an unusually mobile rock avalanche, comparable with for example, the Elm landslide in the Alps. As such this landslide would probably benefit from a more detailed investigation.
The Judgement Cliff Rock Avalanche was reported at the time to have killed at least 19 people. Thus, for example, a report compiled in 1809 on the basis of eye-witness accounts suggested that:
“a great mountain split and fell into the level land and covered several settlements and destroyed 19 white people” (Maharaj 1994, p. 243).
My interpretation is that the loss of life would have been rather higher, given that the account only appears to be concerned about the colonial settlers.
There is a nice account of the oral history of the landslide and the mythology that is associated with it in the Jamaica Observer from a few years ago.
Maharaj. R.J. 1994. The mprphology, geometry, and kinematics of Judgement Cliff Rock Avalanche, Blue Mountains, Jamaica, West Indies. Quarterly Journal of Engineering Geology, 27, 243-56.
13 July 2015
The 2011 Umyeonsan debris flows in South Korea
On 27th July 2011 an intense rainfall event in Umyeonsan, in Seoul,the capital of South Korea, killed 16 people and caused widespread damage. In a paper just published in the Journal Landslides, Jeong et al (2015) have analysed these landslides in detail. They report that the rainstorm, which had a peak intensity of 112.5 mm, triggered 33 debris flows and 151 landslides. The debris flows caused most of the damage, some of which were caught on dramatic videos:
The study by Jeong et al (2015) is impressively detailed. I will highlight two aspects here. First, the density of landslides in the Umyeonsan area is remarkably high. This image from the paper shows the debris flow gullies (in blue) and the landslide initiation points (yellow circles):
Jeong et al. (2015) ascribe this high density of landslides to a combination of thick colluvium associated with a fault zone, the intense and prolonged rainfall, the steep slopes and the vegetation, which is characterised by low root depths (thus providing little additional strength).
The debris flows themselves are in many ways classic for this type of environment, and are in many ways similar to those observed in natural terrain in Hong Kong. The debris flows started as small failures in colluvium on the hillside, in many cases with multiple small slips occurring in the same catchment. These small failures underwent a rapid mobilisation process and entered the main channel. Jeong et al. (2015) suggest that thereafter the flows eroded and incorporated sediment within the channel, rapidly increasing in size. It is likely that the flows created and broke a series of small dams, possibly partially caused by channel blockage by trees and other woody debris, allowing the creation of large volume, rapid failures. Based on the videos, the authors estimate that one of the failures was traveling at about 28.6 m/sec when it struck the road. This debris flow killed three people; the effects of such a catastrophic debris flow are truly catastrophic:-
Jeong, S., Kim, Y., Lee, J. and Kim, J. 2015. The 27 July 2011 debris flows at Umyeonsan, Seoul, Korea. Landslides. http://dx.doi.org/10.1007/s10346-015-0595-0
9 July 2015
The Straits Times in Singapore has an excellent article on the events on Mountain Kinabalu in Malaysia on the day of the earthquake last month. Focusing primarily on the party of Singapore school children that was caught in rockfalls on the mountain, the article powerfully describes the earthquake itself and the desperate attempts to get to safety afterwards:
On the Via Ferrata, about 12 to 15 pupils, with their teachers and guides, were on the rock face when boulders tumbled down from the broken peaks of Mount Kinabalu. Amal Ashley Lim, 12, was one of the students who had just started on the Via Ferrata. Linked by a rope to schoolmates El Wafeeq El Jauzy, Navdeep Singh Jaryal Raj Kumar and Sonia Jhala, they were led by teacher Madam Nur Uzaimah Fadzali. Behind them were Daanish Amran, the Singaporean guide, and a Mountain Torq trainer. “Rocks were falling. I almost fell but luckily I grabbed on to my teacher’s legs,” Amal Ashley told The New Paper. She was lucky enough not to be hurt by the falling rocks, which were half the size of car tyres. “They hit my backpack,” she said. Her teacher, Madam Uzaimah, had pulled her under a rock overhang, but went out again to find help. Another pupil, Emyr Uzayr, was saved by teacher Mohamed Faizal Abdul Salam. Mr Faizal cut the rope that bound him and the pupils, before cutting the ropes of Emyr’s harness. He used his body to shield him and two other pupils.
Mountain Torq trainer Hillary Augustinus, 34, was on the Walk the Torq with one group of students when he saw the rocks tumbling down. “When I look up, I can see a wave of rocks falling towards us, small, big boulders, with heavy clouds of dust. The rock face is shaking, we just lean there (on the rock),” he said.He slipped down the slope for a heart-stopping moment, but was held up by his backup safety rope; and through the rocks and dust, he saw a small crack to his right.“Out of instinct, I just crawl… to the crack. All I could do was to put my life in God’s hands,” he said. “It’s helpless, very helpless, you just couldn’t do anything.”When the quake stopped, his hands were bloodied and his right knee was hit by a rock. But he knew he had to move before more rocks fell, so he undid his rope and climbed up.A number of pupils were still clinging on to the rock face, frozen in shock.“I respect them, they were very strong, they were not crying,” he said.“We try to rescue as many as we can, one after another, and send them to the summit trail.”Despite the best efforts of the teachers and trainers, they could not save everyone.
Ten of them – most of whom were from the three groups who had started on the trail – did not live to see the sunrise from Mount Kinabalu.
There is a great deal more detail in the article, which I recommend.
The earthquake triggered extensive rockfalls from Mount Kinabalu. This image, from the Star Online, shows the fresh rockfall scars:
This is more or less the same view of Mount Kinabalu from the before the earthquake:
The earthquake appears to have triggered some shallow landslides in steep forested slopes and a very large number of rockfalls on the near vertical cliff faces of Mount Kinabalu. Interestingly, the less steep upper faces seem to have been affected far less. A detailed inspection suggests that there are in fact multiple comparatively small rockfall sources across the faces, each of which has triggered the release of material from the cliff face below to create a long rockfall scar. There are so many sources that the rockfalls have effectively removed large sections of the mountain side.