19 July 2017
Cold Springs swimming hole: a mudflow tragedy in Arizona
On 16th July a sudden mudflow and subsequent flash flood swept through the Cold Springs swimming hole in Tonto National Park in Arizona. This dramatic event came out of the blue for those at the swimming hole. It was immensely powerful – the latter stages of the flood component were caught on the video below, uploaded onto Youtube by AP:-
The Weather Channel also has a video of the event, which explains why it is right to cause this event a mudflow. This is a still from the video:-
It began as yet another scorching Saturday in central Arizona as scores of families flocked to the cool waters of a popular swimming hole, seeking relief from the 100-degree temperatures in the cities.
Among them was an extended family of 14 from Phoenix. They gathered at the Cold Springs swimming hole in the Tonto National Forest, near Payson, to celebrate Maria Raya’s 26th birthday, their relatives told local media.
At about 3 p.m., it was barely drizzling as the Raya family and others waded in the water and hiked along the narrow canyon, its scenic waterfall and granite rock formations in the backdrop.
Suddenly the adults and children swimming in the canyon heard a roar. As they turned to look upstream, they saw a massive wall of dark muddy water rushing toward them, carrying tree trunks and logs the sizes of vehicles, Ron Sattelmaier, Water Wheel Fire and Medical District fire chief, told The Washington Post, citing interviews with witnesses.
The flash flood’s six-foot tall, 40-foot wide torrents of murky water swept away Raya, her children and several other family members, spanning three generations, while other relatives grasped onto trees waiting to be rescued. By Sunday, nine people had been found dead. Authorities did not identify the dead, but relatives listed the names to local media.
It is likely that the final toll in the Cold Spings swimming hole landslide disaster will be ten people. The area upstream of the Cold Springs swimming hole has been affected by forest fires in recent months, explaining both the ferocity of the flow and the vast amount of wood that it transported. The area was swept by large thunderstorms on the day of the disaster.
17 July 2017
Two new landslide videos from China: Liuzhou
With thanks to Pasi Jokela, who brought them to my attention, there are two good new landslide videos from China, one from Liuzhou and one from Chamdo.
A rapid landslide from Liuzhou in Guangxi Zhuang Autonomous Region, China
First, a dramatic dashcam video of a slide from Liuzhuo in Guangxi Zhuang Autonomous Region on July 12. Reports suggest that the landslide injured three people (this video may not embed due to yet another WordPress quirk. Apologies if so):
The aftermath suggests that this was a very wet earthflow:
A riverbank collapse from Chamdo Prefecture, China
This dramatic riverbank collapse was captured from multiple angles.
Five storey building collapses due to flooding. A remarkable video has emerged from China showing a five-storey block of flats collapse into a flooded river. In the video, which was filmed in Chamdo Prefecture on July 8, the fast-flowing water appears to wash away the building’s foundations and it topples over into the river. Luckily the residents were evacuated in advance and there were no casualties. The clip also shows a empty lorry falling into the river as part of the river bank subsided.
14 July 2017
Understanding the La Palma mega-landslide hypothesis: part 2
Earlier this week I explored the main structural features of La Palma that have led some to propose that there is the potential for a mega-landslide there. This proposed volcanic flank collapse would be immense – the proposed volume is up to about 500 cubic kilometres. The idea that gained some popular traction is that this landslide could generate a tsunami that would devastate a large part of the coastline on both sides of the Atlantic.
Of course La Palma has undergone a previous flank collapse event, and there have been similar collapses elsewhere in the Canary Islands. Interestingly, none of these appear to have generated widespread tsunami deposits around the Atlantic basin. The key to the idea such an event developing again is the events of the major eruption in 1949. During this event, a fault structure was observed to develop along a part of the Cumbre Vieja ridge. This has been interpreted as indicating movement of the flank of the volcano towards the west, and thus the development of a potential flank collapse landslide on the southern part of La Palma. I spent a day up on Cumbre Vieja, with the main aim of taking a look at this fault scarp. Armed with a map from one of the key papers I roamed up and down the mountains on a most beautiful day. The feature that I found is remarkably unremarkable in landslide terms. Based upon the maps, the most obvious feature that I could find is the scarp shown below:-
This scarp is about 3 m high at the maximum – if you look carefully there is a person walking down the path for scale. It is reasonably clear in the landscape for some hundreds of metres before merging into the flank of one of the volcanic craters:
I have to admit that I struggle to believe that this feature is a key component of the mega-landslide hypothesis given its small size, but I could not find any more convincing alternative. Perhaps I missed the correct feature. The scarp suggests limited movement on the landslide, even if it is a correct interpretation, suggesting in turn that an actual failure would be unlikely in the foreseeable future.
This fault scarp did not reactivate in the smaller 1971 eruption. Monitoring of the flanks suggest that there is no sign of rapid current movement on this scale, but that there may be some signs from satellite data of very low velocity creep on this slope, which is not a surprise (this may well be true of all large slopes in weak materials). Thus, the mega-landslide hypothesis is that this volcano would only become unstable in a future eruption, and that in such circumstances the flank could collapse in a single coherent block to generate the tsunami. The paper that modeled the tsunami, Ward and Day (2001) modeled a landslide of about 450 cubic kilometres – i.e. they took the very largest volume that is imaginable. This seems a little odd to me – the rear scarp of their mega-landslide appears not to mobilise the scarp shown above, but one considerably to the east, creating a much larger block. I am not sure that I understand the reasoning for this. The model then assumes a series of extreme scenarios:
- The landslide occurs as a single coherent mass along the entirety of the ridge (thus over a distance of 25 kilometres);
- The landslide occurs as a single coherent mass through the cross-section (i.e. there is a single failure event over the 15 kilometre cross-section of the slope, rather than a series of retrogressive slip blocks);
- This huge block remains intact over a travel distance of 15 km before fragmenting;
- The landslide mass rapidly reaches a peak velocity of 100 m/sec (360 km/h)
A change (reduction) in any of these parameters would yield a much smaller tsunami. For example, subsequent work (Abadie et al. 2012) has taken the ““credible worst case scenario” (derived using slope stability analysis), to have a volume of 80 cubic kilometres (but note the factor of safety of the slope was found to be considerably higher than one, indicating that the slope is not particularly unstable). Modelling of the tsunami generated by such a landslide, using a more refined tsunami simulation, does generate a very significant wave close to La Palma. This wave would be significant as it crossed the continental shelf off the east coast of North America, but would lose a great deal of energy due to frictional effects in this region. Thus, for a 80 cubic kilometre “credible worst case scenario” flank collapse on La Palma, wave heights on the east coast of the USA were found by Tehranirad et al. (2015) to be less than 2 metres along the coastline.
This is not the disastrous scenario that the newspapers have so enjoyed featuring.
Abadie S., Harris J.C., Grilli S.T. and R. Fabre, 2012. Numerical modeling of tsunami waves generated by the flank collapse of the Cumbre Vieja Volcano (La Palma, Canary Islands) : tsunami source and near field effects. Journal of Geophysical Research, 117: C05030.
Tehranirad, B., Harris, J.C., Grilli, A.R. et al. 2015. Far-Field Tsunami Impact in the North Atlantic Basin from Large Scale Flank Collapses of the Cumbre Vieja Volcano, La Palma. Pure and Applied Geophysics 172: 3589.
Ward S. N. and S. Day, 2001. Cumbre Vieja Volcano potential collapse at La Palma, Canary Islands. Geophysical Research Letters, 28: 397–400.
12 July 2017
Understanding the La Palma mega-landslide hypothesis: part 1
As I noted in an earlier post, I spent a part of last week on the island of La Palma in the Canary Islands. Whilst my visit was to mark the opening of the GOTO telescope in my Vice-President role, I also took two days to explore the supposed mega-landslide that, it has been suggested, could generate a huge and very damaging tsunami. I have noted before that I do not subscribe to this hypothesis, but welcomed the opportunity to explore the site. In this and at least one subsequent post I will try to explain the mega-landslide hypothesis, and will also seek to outline why I do not think it stands up to scrutiny.
The La Palma volcanoes
The Google Earth image of La Palma below shows the main features of the island. I have provided an annotated version on the left alongside an unannotated version for clarity:-
The main features are, first, the Taburiente Volcano to the north. This is a large shield volcano that reaches almost 2500 metres above sea level (and thus about 6500 m above the sea floor). This started to form about 2 million years ago, and slowly extended to the south to form a ridge, called Cumbre Nueva. This is the Taburiente Volcano from the south:-
About 560,000 years ago the Cumbre Nueva ridge underwent a giant landslide, when up to 200 cubic kilometres of the volcano slipped towards the west into the ocean, leaving the giant Cumbre Nueva scarp. This feature can be clearly seen in the satellite image and in the photograph above, and is more obvious in the image below. The presence of this giant landslide has also been detected in the offshore bathymetric data. It is likely that this event generated a large local tsunami, but as far as I am aware no evidence has been found of a tsunami deposit from this event beyond the Canary Islands.
The easterly winds cause clouds to form as the air rises up the slopes of the volcano. These clouds then tumble over the landslide scar to form the cloud waterfall shown above.
Bejenado volcano erupted into the scar left by the Cumbre Nueva landslide, blocking a part of the drainage from Taburiente. This led to rapid erosion and formation of the enormous Calder de Taburiente, which can be seen in the image below:-
Thereafter volcanic activity has been mainly focused on the volcanoes to the south, which form the Cumbre Vieja ridge. These volcanoes remain active, and indeed erupted in both the 1940s and the 1970s. It is this part of La Palma that, it has been suggested, may be structurally unstable. This image shows one of the many volcanic cones along Cumbre Vieja:-
Note the major lava flow at the foot of the volcano.
In the next post I will explore the idea that the Cumbre Vieja volcano system may undergo a flank collapse event.
11 July 2017
Ngauranga Gorge: a landslide caught on video causes chaos in Wellington, New Zealand
The most important road in and out of the capital of New Zealand, Wellington, is State Highway 1, which passes through Nguaranga Gorge as it crosses the hills on the edge of the city. This afternoon, a landslide occurred on the walls of the gorge, with the debris ending up on three lanes of the carriageway. The rockslide came down when the road was busy, but fortunately did not strike any vehicles. The landslide was captured on the dashcam videos of two vehicles travelling through Ngauranga Gorge at the time. This vehicle had a near miss:
#WATCH The moment the landslide all came down on SH1! The road is currently BLOCKED!Video by Asispal Sandhu
Posted by Wellington – LIVE on Monday, July 10, 2017
The other video was recorded from a vehicle travelling in the opposite direction. WordPress no longer allows simple embedding of videos, so I cannot post this one, but you can view it here. The same news report has a nice image of the aftermath of the landslide:
This looks to be a comparatively small landslide, but it nonetheless caused very considerable traffic disruption. The stability of the Ngauranga Gorge has long been a concern, in particular in relation to a potential Wellington Fault earthquake. As an article from earlier this year noted:
New Zealand Transport Agency Wellington highways manager Neil Walker said the agency was investigating the stability of the Ngauranga Gorge, and expected to complete stabilisation improvements within two years.
I noted hazards associated with steep slopes in Wellington, in particular in the event of an earthquake, in a post earlier this year. The problems posed by the Ngauranga Gorge can be seen in this image from Google Earth, which looks down the road towards the city. At the foot of the hill, on the margin of the bay, is the trace of the active Wellington Fault. The gorge slopes would be likely to suffer various nearfield effects that make the behaviour somewhat unpredictable.
It is interesting that this slide came down in good weather.
10 July 2017
Spectacular landslide videos from Arunachal Pradesh in India
As we move into the main monsoon period, heavy rainfall has caused landslides across Arunchal Pradesh in northern India. A series of dramatic videos have appeared online, of which this is the most spectacular:-
This is a very interesting multi-phase movement. This one is genuinely interesting as well (and the footage shows a component of the first video too; it does get a bit repetitive though!):-
Meanwhile an excellent debris flow has been captured on the Manali to Kaza road in Himachal Pradesh:-
And finally, this news report captures a landslide in action in Zhongzhai Township in Guizhou Province, SW China on Saturday morning. The village had been evacuated in advance of the landslide:-
9 July 2017
The Willow Creek landslide: a large valley-blocking slide in Wyoming
The Jackson Hole News and Guide is carrying a report about the Willow Creek landslide, a new, large, valley-blocking slide in the Wyoming Range in the USA. The slide, located in Lincoln County, appears to be substantial:
The report gives some details about the landslide, and its discovery:
To [Dustin Child’s] eye the landslide was as high as 200 feet in places, covered 1/4 mile of the Willow Creek canyon and formed a 15- to 20-acre lake that’s probably 30 or 40 feet deep. As for the hazard, he didn’t think there was one.
“It could possibly could do something next spring, but there’s so much debris,” Child said. “It’s an unreal amount of debris. It dammed it up as far as it’s going to go, and now the river’s cut a stream between the debris pile and the far west side.”
It’s unclear when the yet-to-be named landslide was triggered, or if it all came down at once or slowly over the course of the spring. The remote geological phenomenon was discovered this past week, when a Bridger-Teton National Forest firefighter saw that a mountainside had given way from above.
“They were doing a flight, looking for a fire,” Bridger-Teton spokeswoman Mary Cernicek said. “They didn’t find the fire, but they found the landslide.”
Buckrail has some additional images of the landslide, taken by Tracy Shull:-
The slide appears to be a mobile earth / mud flow, which has entrained a significant amount of debris from within the channel. Note the deep erosion and sidewall cutting in the upper reaches of the landslide (before the major bend in the landslide track), and then the apparent deposition, starting a short distance downslope from this point.
This is of course not an unusual event for Wyoming. Previous examples include the spectacular Bighorn Mountains landslide in 2015 and the Snake River landslide in 2011 (including the brilliant video).
7 July 2017
Mishor Rotem – another tailings dam failure, this time in Israel
Although it has not really made the news, a major tailings dam failure occurred at Mishor Rotem in Israel on Friday 30th June 2017. Reuters has a detailed report about the event:-
Toxic wastewater that surged through a dry riverbed in southern Israel at the weekend left a wake of ecological destruction more than 20 km (12 miles) long. The flood began last Friday when the 60 meter (yard) high wall of a reservoir at a phosphate factory partially collapsed, letting loose 100,000 cubic meters (26.4 million gallons) of highly acidic wastewater in the Ashalim riverbed. That was enough fluid to fill 40 Olympic-sized pools. The toxic torrent snaked through the desert, singeing anything in its path, before collecting again hours later in a pool several kilometers from the Dead Sea, the lowest point on earth.
There are various images of the failure, of which this is the best:
There is also a decent Youtube video of the failure and its consequences downstream:-
Haaretz has a decent article on the implications of the failure, noting that the spill has damaged an area of important ecology. The tailings pond contains the waste from a fertiliser plant, owned by Rotem Amfert.
One can only speculate about the cause of the failure, although a slip in the embankment does not seem to have occurred. Overtopping or( perhaps more probably) a piping failure seem to be the prime candidates.
I have noted previously that the failure rate in tailings facilities is unacceptably high. There would be no tolerance of this rate of failure in any other of geotechnical work, especially given the consequences of these major leaks downstream. I remain deeply frustrated that this problem is allowed to persist.
4 July 2017
La Palma – initial images of the “mega-landslide”
I have spent the last three days on the island of La Palma, principally to represent the University of Sheffield at the inauguration of the new GOTO telescope, yesterday. I was able to take a couple of days over the weekend to visit the site of the famous “mega-landslide” that, some people have suggested, could create a damaging Atlantic tsunami (noting of course that I am, like many others, a real skeptic of this theory). I have written about this slide – and the rather extreme interpretation that is needed to generate the sort of tsunami that has hit the headlines – previously, but this was the first time I have visited. In the post I will provide some photos of the site; I will then examine the hypothesis in more detail in a subsequent post.
The first thing to note is that La Palma is gorgeous, it has been a pleasure to visit. The geology is remarkable too. The hypothesis is that “mega-landslide” would involve a huge mass on the southern end of the island slipping to the west. This is a slide on the flank of the Cumbre Vieja volcano – which is fact an elongated volcanic ridge consisting of multiple volcanic cones, some of which date from the 1970s. This is a view along the ridge from the north:-
This is a view of the Cumbre Vieja ridge from the south:
A hike along the ridge gives a good sense of the nature of the volcanic peaks that are supposedly being pulled apart by the potential landslide:-
Of course it would be remiss of me not to mention the telescopes that I was there to visit. This is sunset at the observatory:
Sometimes its not so hard to be a University Vice-President. I will post some more about the “mega-landslide” in the coming days,
28 June 2017
New landslide video: a large slip causes panic in China
The location of the landslide is not clear – the Youtube video describes it as Sichuan-Mao Xian, but this seems to be a confusion with the deadly slide on Saturday in Xinmo. Before the person making the video starts to flee (understandably) they capture the progression of the early phases of the landslide:
The Liveleak video includes some images of the aftermath:
Much of China has been suffering from very heavy rainfall in the last few days. Xinhua is warning of potential floods as these rains continue:
Provinces including Guangdong, Guizhou, Hubei, Hunan and Jiangxi have seen water levels in 175 rivers rise beyond their warning levels with five rivers at record-high levels. Flooding has forced more than 170,000 people to relocate in Hunan Province. In Jiangxi Province, 235,000 hectares of crops have been destroyed with direct economic losses of 4.5 billion yuan (660 million U.S. dollars). More rainfall is forecast for southern and southwestern parts of the country in the next ten days, with precipitation in some regions likely to reach 300 millimeters within 24 hours, the National Meteorological Center said Tuesday.
A different article suggests that the heavy rainfall in the last few days has had serious impacts in Zhejiang and Guizhou:
In Zhejiang, by 7 a.m. Tuesday, 765,000 people have been affected and 149,000 had been evacuated to safer places. Around 4,800 houses were damaged, and direct economic losses have been estimated at 2.08 billion yuan (304.6 million U.S. dollars), according to the provincial civil affairs authorities.
Guizhou’s civil affairs authorities said, by 7 a.m. Tuesday, more than 1.26 million people were affected, 13 people were reported dead or missing, and 110,000 had been evacuated to safer places. A total of 56,300 hectares of agricultural crops were affected and direct economic losses reached 1.33 billion yuan.
Thanks to Pasi Jokela for highlighting this event.