15 June 2016
The boulder that came to tea
The Croatian news website Dulist has a story this week about a boulder that came to tea in a house in Dubrovnik. The pictures are quite startling:-
According to a translation of the article, this landslide happened during heavy rainfall on Monday night. This block was part of a larger landslide on State Road D-8. The images suggest that this boulder bounced on the road before smashing through the broadside barrier:
And then bounced again in the garden of the house (note the huge divot in the grass), before trying to gain entry via the a bedroom window:-
This looks to be a classic case of a boulder that is rotating around its shortest axis, and so has gained a stable geometry as it travels down the hill. This situation creates the possibility of high velocities, large bounces and long travel distances.
I’d imagine that removing the boulder from the window is not going to be a trivial task
According to the Dulist article, the same house was struck by a boulder in 2012. The Google Translation of the article, which I have tidied up, says:
The Křečková house has already been hit by a big boulder, almost exactly four years ago, namely on 16 June 2012, when the rocks in the fall broke several trees, skipped the road, bounced off the railing of the road, glanced off the fence sound the driveway parking and travelled like a projectile through the roof of the house. Fortunately the roof structure was able to stop the rock.
All of this suggests that some work is needed quite urgently to assess the stability of the slope above the road. The article appears to suggest that there may be more unstable blocks.
13 June 2016
Three forthcoming landslide meetings of interest
I thought I would highlight three forthcoming landslide meetings:
1. GSA 2016 in Denver, Colorado
The 2016 GSA meeting will be held in Denver from 25th to 28th September 2016. There are three landslide sessions:
T21. Bridging the Gaps on Subaerial, Lacustrine, and Submarine Landslide Research
Lesli Wood, Lorena Moscardelli
Submarine landslides are never witnessed, but the aftermath is clear: destruction of seafloor infrastructure, disruption of biota, and tsunamigenic coastal threats. This session looks at researchers attempting to bridge between subaerial and submarine landslide processes.
T24. Landslide Hazards: Inventories, Hazard Maps, Risk Analysis, and Warning Systems (Posters)
William J. Burns, Stephen L. Slaughter, Matthew M. Crawford
This session is designed to highlight landslide hazards information especially as related to landslide inventories, hazard maps, risk analysis, and warning systems.
T25. Landslides, Debris Flow, and Rock Fall: Processes and Hazards
Rex L. Baum, Benjamin B. Mirus
This session will explore new insights about landslide processes and hazards. Contributions that address novel field and instrumental observations, analysis, and hazard assessments or that introduce tools and techniques applicable to any of these are especially welcome.
The abstract deadline is on 12th July. Details here.
2. Waiting for the End of the World: The Archaeology of Risk and its Perception in the Middle Ages
This meeting will be held in Oxford from 2nd to 4th December 2016. Details are as follows:
3. 2017 North American Symposium on Landslides
9 June 2016
The response of Californian earthflows to drought
A really interesting paper has just been published in Geophysical Research Letters examining the response of Californian earthflows to the ongoing, epic drought. This paper was led by Georgie Bennett, currently at the US Forest Service and Colorado State University, but who will be joining us here at the University of East Anglia in January 2017 as a full faculty member. California has been suffering a serious drought for many years now. In the paper, Bennett et al (2016) mapped 98 active earthflows in a 140 square kilometre area of the Eel River catchment in California. This is an area with multiple large, often deep earthflows that are an important part of the geomorphic system. I have taken one of the larger earthflows from Google Earth below:
The mapping was very detailed, undertaken using aerial photographs. The mapping focused not just on the boundaries of the landslides, but also on the displacement of trees located on the landslides, which allowed a calculation of the velocity of the landslides with time. This data was then compared with an index of drought, the commonly-used and widely accepted Palmer Drought Severity Index (PDSI), which has been used previously to show that the 2012-2015 drought in California is unprecedented.
The results are fascinating – I highlight here two key aspects. First, over the last 70 years or so the velocity of the earthflows has markedly decreased. This image shows the mean velocity, with error bars and the PDSI. It is notable that in recent years the PDSI has become exceptionally low, and the earthflows have responded by slowing down:
Bennett et al. (2016) also looked at the differential response of the Californian earthflows of different depths to the drought conditions. They found that the shallower (typically 5 – 15 m thick) landslides showed quite variable response to the drought conditions, with the majority slowing down but a few actually accelerating. However, all of those deeper than 15 metres decelerated. In some ways I find this a quite surprising result – I would have expected that the deep landslides would have been less susceptible to the climate than the shallow ones. The result is robust, but the cause is not clear and is intriguing. Bennett et al (2016) suggest that it could be that the shallow landslides respond to short term and local effects (vegetation change, a large storm) that might occur within a drought, whilst the deeper Californian earthflows are just responding to the climate forcing.
This is a really interesting study, showing very elegantly the ways in which the landslide system is responding to climate change. With greater changes to come in the years ahead as the global climate warms further, we will see many more responses of this type.
Bennett, G. L., Roering, J. J., Mackey, B. H., Handwerger, A. L., Schmidt, D. A. and Guillod, B. P. 2016. Historic drought puts the brakes on earthflows in Northern California. Geophysical Research Letters. Doi: http://dx.doi.org/10.1002/2016GL068378
8 June 2016
Copiah County: a fatal landslide accident in a gravel quarry
In Copiah County in Mississippi a landslide on Friday engulfed two quarry workers and an excavator. The landslide occurred at the Harmony Mine and Mill in Crystal Springs at about 1 pm. Efforts have been ongoing since to recover their bodies, but this is proving to be an extremely challenging operation. As of nightfall last night this had not been accomplished. MS News has a timeline of the events to date – on Sunday efforts were made to recover the excavator using a 230 ton crane, but without success.
WJTV12 has a report about the accident and the recovery works. This image appears to show the landslide mass and the buried excavator, of which just a small part is visible:
Based on this image the landslide appears to have been highly fluid – note the lack of surface morphology, suggesting that the landslide as flowed. This is likely to make the recovery operations very difficult as the deposit is probably very weak. Unfortunately there are likely to be be high suction forces, which makes extracting the machine without excavating around it very difficult.
The landslide occurred during very heavy rainfall. Clearly there will need to be some work to try to investigate and understand what happened to generate a landslide like this.
7 June 2016
Dam break risk for the Attabad landslide
In a paper just published in the journal Landslides, Chen et al. (2016) have analysed the stability of the Attabad landslide dam in northern Pakistan, and the potential impacts of such an event on downstream infrastructure. This is a very important study, given that the landslide continues to impound a vast quantity of water in a well-populated valley.
The paper contains some important and interesting background information, not least a graph of the water depth against time. This appears to be a similar dataset to the one that I was updating on a daily basis on the dedicated blog that I ran at the time, but the record is longer. It is not clear where the data has come from as I was not aware that there was monitoring by any other parties at the time. It’s good to see a full dataset. More importantly, the team have analysed the likelihood of a full dam break event using an empirical relationship derived from previous studies based on the so-called Dimensionless Blockage Index (DBI). Chen et al. (2016) conclude that:
The statistical analysis of the 84 natural landslide dams indicated that a dam is stable when DBI <2.75, quasi-stable when 2.75 < DBI < 3.08, and unstable when DBI >3.08…The DBI of the Attabad landslide dam is 4.62–4.85, which is greater than 3.08 and indicates that the dam is unstable and that there is a risk of a breach in the Attabad landslide dam.
However, the authors do not believe that a breach event would lead to release of all of the impounded water (this is probably correct in my view). This is fortunate as the authors have analysed the likely magnitude of a break flood at the site of the Attabad landslide dam itself. Such a full breach event would generate a calculated peak discharge of 175,145 cumecs (cubic metres per second), whilst a 50% breach would generate 44,904 cumecs. The flood would dissipate downstream, but a 50% breach is calculated to generate a peak flow of almost 16,000 cumecs at Gilgit Bridge, 100 km downstream.
Thus, the authors recommend that there is a continued need for risk management at the Attabad site. They conclude that:
In addition to continued monitoring of the upstream water inlet, lake water levels, and seepage and piping downstream of the dam, hazard zones and safe zones should be delineated in accordance with the results of the risk assessment of the Attabad landslide dam. Sanctuary sites, escape routes, and early warning signals should be pre-selected and pre-planned, and necessary material stockpiles should be prepared. A plan for construction during high-risk periods should be considered, and contingency plans for secondary disasters from the landslide lake should be distributed. The risks of disasters and potential losses should be reduced to the greatest extent possible.
I can only agree. The risks at the Attabad landslide dam site are far from negligible.
Chen, X., Cui, P., You, Y., Cheng, Z., Khan, A., Ye, C. and Zhang, S. 2016. Dam-break risk analysis of the Attabad landslide dam in Pakistan and emergency countermeasures. Landslides. Doi: 10.1007/s10346-016-0721-7
6 June 2016
Over the weekend an interesting, but to those involved distressing, landslide developed at the town on Granbury in Texas, threatening a four-storey apartment block. NBCDFW have a couple of decent images, including this one, of the landslide:
This image, showing most of the failed slope, is from Fox 4 News:
It is hard from the image to know what has happened at this site. It is clear that the retaining wall at the toe of the slope has buckled and displaced outwards. Did the slope fail, displacing the wall, or did the wall fail, triggering collapse of the slope? Or some combination of the two? There may be a hint in the Google Earth imagery, which seems to show something a little odd. This is the site, taken in late 2014:
In this image the lake / river level is much lower than it is at present. There appears to be some sort of structure below the wall – is this a toe weight, or some sort of erosion protection? The image seems to show that this body has large black structures. An initial interpretation might be that these are cracks and fissures, but I am unsure. If so they are very large (and similar structures are seen elsewhere on the riverfront too). I have no idea what these represent – an artifact on the image? Or signs that the toe of the slope was damaged? Sometimes landslides like this occur when the toe of the slope is damaged, unloading the foot of the landslide, decreasing stability. Then, as pore pressures rise during heavy rainfall, the slope fails from the toe upwards. But it is very hard to tell based only on these images, and no form conclusions can be drawn in this case.
I am sure that this will be investigated properly, so it’ll be interesting to see what emerges. In the meantime, the news items report that the insurance company has declined to cover the costs of the damage, which could be as much as $1 million. The owners of the property have set up a GoFundMe page. As of this morning this had raised $5 of the £2 million target.
5 June 2016
Colombia landslide video
During my work and travel-induced blog hiatus over the last fortnight, three new landslide videos have appeared on Youtube, from Hechi in China, Anatolia in Turkey and Colombia. None of the three provide much information. The first is apparently from Colombia, showing the collapse of a reinforced slope adjacent to a tunnel portal. The latter is destroyed in the landslide:-
I know no more about this landslide, but would observe that the reinforcement of the slope looks to be completely inadequate for the magnitude of the excavation. The failure seems to start directly above the tunnel portal, and then to propagate along the slope:-
A classic earth flow in Hechi, China
The second is a beautiful earth flow landslide on a road in Hechi, located in Guangxi Zhuang Autonomous Region in southern China:
The beauty of this landslide video is the way that it picks out the way in which the soil, that appears to be unsaturated, develops classic flow-like patterns. The occupants of the vehicles at the foot of the slope were extremely fortunate that the material was not more mobile.
A truck falling down a landslide tension crack
And finally, from Turkey a rather amazing video of a large articulated truck getting caught in a translational landslide, and falling down into the rapidly developing tension crack:
Note that the slope can be seen to be moving under the truck. It appears that the cab was sitting across the lateral shear of the landslide – as the slope moved outwards a tension crack opened, into which the truck could fall. According to the Daily Mail, this landslide occurred in a quarry in Tunceli province, which is in the Anatolia region.
These three videos do rather nicely illustrate the somewhat varied nature of landslides, the reason why so many of us find them to be fascinating. But note that all three have human causes.
21 May 2016
The mobility of the Aranayake landslide
An technically interesting aspect of the Aranayake landslide tragedy in Sri Lanka is the high levels of mobility that the debris has obviously shown. It is this mobility that has allowed the debris to travel so far, and of course so fast, which in combination is the reasons for so many fatalities. A video has been posted on Youtube showing a very small secondary failure of the landslide mass:
This failure is only a few cubic metres, a minute fraction of the devastating landslide of earlier this week. But its behaviour illustrates the problem beautifully. At the start of the video the failure is clearly just a standard small-scale landslide:
However, this quickly transitions into a highly fluid, very mobile mass:
One can only imagine what this must have looked like when the whole slope was on the move.
The Sri Lankan army today ceased its operations to rescue landslide victims, and instead turned to a recovery and relief mission. However, in a deeply surreal move, Nepal has reportedly donated $100,000 dollars towards “relief operations in the disaster zones”. Whilst the desire to assist a neighbour in distress is commendable, Nepal has many, many people living in the aftermath of an earthquake without any tangible assistance, and with the monsoon looming. There is reportedly a huge amount of unspent relief money, intended to assist the victims of the earthquake, so far unspent. This must surely be the priority for Nepal? Whilst the Aranayake landslide, and associated damage, is a disaster in Sri Lanka, the impacts are a fraction of those in the rural areas of Nepal. This should be the priority for the Nepal Government.
20 May 2016
The GFDRR ThinkHazard! tool
Yesterday the new GFDRR ThinkHazard tool was launched. This is a new web based system for developing countries that allows a basic assessment of hazard across a range of perils on a geographical basis. The GFDRR description is as follows:
The Global Facility for Disaster Reduction and Recovery (GFDRR) has created a new online tool for the development community, which enables non-experts to consider natural hazard information in project design. ThinkHazard! has been developed by GFDRR’s Innovation Lab, in collaboration with BRGM (the French geological survey), Camptocamp, and Deltares. Many other organizations and individuals have contributed data sets and expert input into information provided in the tool.
ThinkHazard! is a simple and quick, yet robust, analytical tool that enables a development specialist to determine for a given project location, the potential likelihood of eight natural hazards, and what actions they should take to make their project resilient. The tool analyzes hazard under current climate but also provides guidance from IPCC on how climate change may affect hazard frequency and intensity into the future.
This is the range of hazards that the tool covers:
I made a minor contribution to this project by writing the recommendations for the landslide part of the tool, and by benchmarking the results against the global landslide database that Melanie and I manage.
This is an example of the hazard maps that the tool can generate:
High hazard in this case is in red, etc. However, the tool does allow a higher level of detail, down to the district level. This is a district level map for Nepal for example:
For each level of hazard there are a set of recommendations as to how to go about determining the level of threat and to manage it. My sense is that this is an incredibly useful tool to both raise awareness of the likelihood of natural hazards in poor countries and to provide mechanisms to their mitigation. It is an impressive achievement.
19 May 2016
The Aranayake landslide in Sri Lanka
Aranayake landslide in Sri Lanka is now thought to have killed about 140 people, from which the remains of 19 victims have been recovered to date. The landslide was triggered by exceptional rainfall associated with a slow moving tropical cyclone. Some reports suggest more than 350 mm may have fallen. The best overview image of the landslide that I have seen to date is this one, by AP and posted on the BBC website:
This is a complex landslide. It appears to have started as a small landslide high on the hillslope – is there a hint of bedrock in that area? I suspect so, which might suggest regolith sliding on a bedrock interface. That then appears to have induced a much more substantial failure on the steeper sections downslope, with three main portions. There is certainly bedrock evident in this area, but the mobile material appears to be deeply weathered soil / regolith. Finally, the displaced material appears to have turned into a highly mobile flow that has channelised. It is this portion of the landslide that is likely to have caused the loss of life. I would also note from this image that the underlying geological structure here might be highly complex – note the different inclinations of the rock surface visible on the ridge to the left compared with the bedrock visible in the slide itself. This suggests that there could be a structural element to this as well, perhaps.
More detail is available about the sliding surface in this image, which was tweeted by the Sri Lanka Red Cross yesterday:
In this image it is clear that the main landslide on the steeper slopes consisted of regolith sliding on a bedrock interface. The Sri Lanka Red Cross have also tweeted this helicopter image of the lower portion of the landslide, which illustrates the highly mobile nature of the mass movement:
Reports today suggest that rescue operations have been suspended today due to further landslide movement associated with heavy rainfall. This will be a very dangerous site until the weather clears up and the ground dries out. The monsoon is not far away.
I believe that this Google Earth image shows the location of the landslide:
Pallebage (location: 6.9639, 80.4209) is reported to be one of the communities destroyed by the landslide. However, so far I have been unable to pin the location down more precisely. Viewing the Google Earth image from directly above leaves me with a suspicion that this might not have been the first major landslide on this hillside. I have indicated the location of a possible large, much older landslide: