This blog provides a commentary on landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings. The blog is written on a personal basis by Dave Petley, who is the Wilson Professor of Hazard and Risk in the Department of Geography at Durham University in the United Kingdom.

This blog is a personal project that does not seek to represent Durham University.

Wednesday, 29 July 2009

Landslide-induced train accident in China

The landslide misery in China continues, despite the strange lack of typhoons to date this summer. The latest incident occurred in Liuzhou City of Guangxi Province when a train struck a landslide and derailed. According to Xinhua four people were killed and 50 others were injured, at least ten of whom were seriously hurt. Xinhua has published a photograph of the aftermath of the incident:

Thus it appears that the landslide was comparatively small and occurred on a slope associated with a railway cutting.

This week there was also a (non-fatal) train derailment caused by a landslide near to Wellington in New Zealand (image from 3 News):


Earthworks failures on railway systems are surprisingly common. For example, Glendinning et al. (2009) reported the following for the UK rail network:

"Between January 2000 and March 2002, 91 earthwork slips occurred, each causing more that 750 minutes of train delays on Network Rail. While it is possible that the rate of failure on railway slopes may have reached equilibrium, this seems unlikely as the number of recorded earthworks failures rose from 47 in 2003/04 to 107 in 2007/08."

Fortunately of course the vast majority of slope failures on the railway network cause no more than disruption, but the potential for greater impact is always present.

Reference

S. Glendinning, J. Hall and L. Manning 2009. Asset-management strategies for infrastructure embankments. Proceedings of the Institution of Civil Engineers Engineering Sustainability 162, 111-20.

Monday, 27 July 2009

Landslide sessions as the AGU Fall meeting in San Francisco

The annual Fall Meeting of the American Geophysical Union (AGU) has long been the meeting of choice of the geoscience community, although these days it is being challenged by its European equivalent (the European Geosciences Union). The meeting this year is expected to attract about 16,000 earth and environmental scientists (I bet you didn't realise there were that many...).A frustration for the surface process and natural hazards communities has been the lack of representation at this meeting, but this year AGU has put this right.

Abstracts are due in early September, but I thought it would be helpful to pull together a list of the sessions potentially of interest to landslide scientists:

H56: Hydrometeorological Hazards in a Changing World
NH01: Natural Hazards General Contributions
NH03: Remote Sensing of Natural Hazards
NH04: The Development and Characterization of Natural Hazard Catalogs
NH06: Reducing Human Losses to Natural Hazards
NH14: Controls on Landslide Sizes and Size Distribution
NH18: Rainfall Induced Landslides: Prediction and Assessment
NH20: The Science of High-Probability, Unpredictable Hazards: From Theory to Practice
NH22: Extreme Natural Hazards: Risk Assessment and Forecasting
NH25: Energy in Natural Disaster Systems
EP02: Sediment Supply, Storage, and Delivery as Controlled by Hillslope-Channel Coupling

See you there!

Sunday, 26 July 2009

Two recent landslides at hydroelectric sites in China

In the past week China has suffered two rather extraordinary landslide accidents at hydroelectric plants.

The first occurred an 20th July 2009 near to the Xiaowan hydroelectric power station in Yunnan province. The dam, shown in the artist's impression below, will apparently be the world's tallest arched dam, standing 292 m high when finished. It is still under construction, with the first turbine expected to be operational later this year:


The image above is a bit fanciful as it doesn't show the lake or the extensive slope works that have been needed. The image below, taken in an earlier phase of construction, gives an idea of the state of the slopes:

Now interestingly, late last month there was a rather triumphant article in the Chinese media about the second stage filling of the site. The Google translation of the article says this:

"It is reported that the second phase of Xiaowan storage power station will be carried out in two steps, 20 July, water power stations will reach 1125 meters elevation; the end of August, water storage, power generation water level will reach 1160 meters elevation, the first unit into operation by the end of September this year power generation is just around the corner" (excuse the rather mangled English).

In other words, the lake level was being elevated for the first time to 1125 m elevation on 20th July. The landslide occurred on that day. The landslide itself was described thus:

"Waves up to 30 metres high swept 14 people into the turbulent upper reaches of the Mekong River following a huge landslide into the river in south-western China's Yunnan province, state media said on Tuesday. Rescue workers recovered two bodies from the river, which is known as the Lancang in China, and were still searching for 12 others missing since they were swept away in the early hours of Monday, the semi-official China News Service said. An estimated 13 hectares of land plunged into the river near the Xiaowan hydroelectric power station, creating giant waves that engulfed 14 farmers as they camped nearby, the agency said. "

This slide apparently had a surface area of 130,000 square metres and created displacement waves 30 m high. That is a very large landslide!

Then, on 23rd July 2009, another landslide disaster occurred, this time at the site of the Changheba Hydroelectric power (HEP) works in Kangding County, Sichuan Province. It appears that in this case a debris flow hit a construction camp for the dam, which will be a 2.2 GW plant across the Dadu river. Unfortunately, the very large (500,000 cubic metre) debris flow occurred at about the worst possible time, 3 am. It hit a major road and 136 temporary buildings housing workers. It is believed to have killed 57 people. The site of the landslide appears to be shown in this Xinhua image:

The rescue operations have been hampered by another large failure, this time on the access road to the site. Here it appears that a failure has occurred in a hillside store of boulders that are to be used in the construction of the dam:

The boulders clearly have been generated recently, as this close up image shows:

It appears that they were being retained by gabian walls above the road:


The collapse has blocked the highway, meaning that until today heavy machinery could not access the disaster site. This has hampered the rescue operation, although to be honest there seems to be very little chance that there could be any survivors from an event of this size.

If anything, 57 fatalities from 136 temporary houses would seem to be a surprisingly low number.

Monday, 20 July 2009

Update: the Nachterstedt landslide

This is an update with the latest news about the Nachterstedt landslide. The original post is here.

Further information has now emerged about the slide. This is summarised below.

1. The slide occurred in spoil from the mining operations.
In a comment in the original post, Florian Jenn (see his blog here) noted that the slide occurred in spoil dumped from earlier mining operations. This is consistent with the pictures, which seems to show a fine grained, reasonably homogeneous material. This type of material is also prone to gully erosion, which has clearly occurred. Thus, a liquefaction failure is quite possible.

2. This is the second failure at this site
A larger slide (6 million cubic metre) occurred at this site in 1959, resulting in a fatality. This will raise questions about the wisdom of the phased increase in lake level.

3. The lake was being filled through natural processes
If essentially the lake level was being increased essentially through rainwater (much of it flowing into the lake from the surrounding ground), then a possible explanation is that the heavy rainfall of late June has caused an increase in lake level over the last fortnight. Groundwater would have risen in response, perhaps triggering the failure.

4. The authorities have concluded that there is no possibility of survival for the three missing people
This is quite correct, assuming that they were in the building. Finding their remains will be a both challenging and dangerous.

Clearly this slide was both rapid and sudden. I guess it is hard to imagine such a slide. The first failure in this video, of the famous Pantai Remis slide in Malaysia, will give an indication of the speed and violence of a liquefaction-induced failure in the walls of an old mine:



There are more details of the Pantai Remis landslide here. Note that the latter part of the video is rather different from the Nachterstedt landslide as the sea was breaking through the wall of the mine.

Sunday, 19 July 2009

Intriguing landslide at Nachterstedt in Germany

NB: I have posted an update on this landslide here.

A somewhat intriguing landslide occurred on Saturday at Nachterstedt in Germany (the location is 51.808 N, 11.343 E for those who are interested). The site is the edge of Lake Concordia, a flooded open cast coal mine:

The mine apparently closed in 1991 whereupon it was converted into a recreation area. The lake was apparently created in 1994. Reports suggest that on Saturday the area received some rain, but that this was not exceptional in any way. The slide appears to have been rapid, with a volume of about 1 million cubic metres. Reports suggest that it created a mini-tsunami on the lake (not surprising given the images below), and that two houses were carried with the slide into the lake. It is thought that three adults were killed in one of the houses. The images of the site are quite remarkable:

Image published in the LA Times providing an over-view of the site

Image published in Deutsche Welle providing a more detailed of the landslide

Close up published in the LA Times of one of the houses affected by the landslide

This is quite an intriguing slide, both in terms of the mechanisms of the slide and of the trigger. In particular it is not at all clear to me why this slope has failed when the weather was not wet. Central Europe had heavy rain a fortnight ago, so this might be an interesting starting point to ponder. Earthtimes suggests that the area might have been underlain by old mine adits, though this is not obvious from the images above. The middle image does show what appears to be shallow coal seams on the right side, but I can't see any evidence of coal seams or abandoned workings elsewhere.

The Google Earth image of the site is quite high resolution. I have zoomed in below to show the area of the slide:


A few of things to note. First, the area that has slid appears to have been suffering some erosion of its toe. Second, this area also has extensive herringbone drains around the large gullies that cross it. I wonder why these gullies are there (they seem to be better developed than those elsewhere on the walls of the lake), and why these herringbone drains have been built. Is this an indication of a drainage problem. Third, there is another small slide on one of the images - see the right side of the Reuters image below:


This smaller slide also looks quite fresh (i.e. recent). It could of course be that this was triggered by the displacement wave, but it could also be an indication that there is a general stability problem. Finally, the presence of the ponds on the slide behind obviously displaced blocks suggests that there was some water in the slope.

The Earthtimes article suggests that the mine was still being progressively flooded, so it could be that the key issue here is instability under raised groundwater conditions.

NB: I have posted an update on this landslide here.

Thursday, 16 July 2009

Earthquake induced landslides

Every so often an event occurs to shake up out of our complacency. So often this is a disaster that is mind-bogglingly destructive, such as the Wenchuan Earthquake landslides last year. However, just occasionally something that happens that is far less damaging than would be expected. This of course is easier to ignore, but in fact can be just as informative as the big events.

Yesterday is just such a case. Sitting in a meeting I received a GDACS alert to say that there had been a Magnitude 8.2 earthquake in the far south of New Zealand. The earthquake was shallow - less than 20 km - and the south of New Zealand is highly mountainous, suggesting that it was likely to have induced a large number of landslides. The last big event in this area, the Fiordland earthquake of 21st August 2003, which was"only" Mw=7.2, triggered lots of slides (see the excellent Geonet report on this event), so the assumption that this large event would do the same was quite reasonable. Since the event the earthquake has been downgraded by the USGS to Mw=7.6 at a depth of 12 km - although smaller I would expect that this would still be a massive landslide-inducing event.

I'm wrong. In fact report coming from fly-over surveys of the epicentral area suggest that there were very few landslides triggered by the event. This is really surprising. Over the last 25 years, since the pioneering work by David Keefer at the USGS, a lot of work has been done examining the relationship between landslides and earthquakes. The map below shows the distribution of well-documented studies of earthquake-induced landsliding apologies if I missed out your particular study - please let me know!) - each yellow dot is an earthquake event for which extensive landslides have been documented. The background image is the GSHAP earthquake hazard map - dark areas have a high level of hazard:


The colours indicate the size of the earthquake and the dots are located at the epicentre of the earthquake (which is why some are obviously offshore). You will see that there is a pretty good coverage of areas that are obviously both seismically hazardous and have high relief, with some areas of high concentration because of proximity to research teams (Italy and California for example). You will also see that New Zealand, thanks to the efforts of GNS and Mike Crozier at Victoria University in Wellington, is pretty well covered.

For a substantial proportion of these earthquakes the area affected by landslides has been measured. Unsurprisingly, there is a pretty strong relationship between the area affected by landslides and the earthquake magnitude:

So when an earthquake occurs in a mountainous area we have a pretty good idea of the area that we would expect to be affected by landslides. Note that there is quite a large range for any given earthquake magnitude - this is the influence of earthquake depth, topography, prior weather conditions (i.e. has it been wet, in which case the ground is likely to be less stable), vegetation, humans, etc.

This map suggests that we should expect to see many landslides for the event yesterday. This is clearly not the case - which is something of a surprise. It will be interesting to see what happened here - for that we will have to wait for more detailed studies over the next few months. I wonder if the dynamics of this event might be slightly unusual, accounting for the vast difference in initial estimates of magnitude between the USGS and Geonet? Perhaps this translated into much lower ground accelerations than might be expected - and hence the low number of landslides.

Wednesday, 15 July 2009

June 2009 fatal landslide map

A little late, but here is the map of fatal landslides for June 2009. Regular readers will note a change in the quality of the map (for the better I hope). My achievement of the week is to teach myself GIS from scratch, so that now I can plot the data on decent quality maps. So here it is, plotted on the SRTM digital terrain model (Click on the map for a better view in a new window):
In total I recorded 22 landslides killing 155 people worldwide. Each dot above represents a single landslide. Sharp eyed readers will note that there is one missing from the above - there is a landslide in China that I have not yet located. The number killed is well below average (255 fatalities) for June, primarily because there are far fewer landslides in S. Asia than is normal for this time of year.

Update on the South Asian Monsoon

The seasonal landslide pattern in South Asia remains very substantively below the long term mean this year - to date at least the monsoon is failing. The level of the problem is illustrated rather well by this map of the monsoon season rainfall anomaly for India, from Monsoon Online:

The result is that the number of landslides in South Asia is very much below average, which is of course good news.

It is interesting to compare this year with 1997. This is part of a press release from 26th June 1997, put out by the Indian Institute of Tropical Meteorology:
"Unfavourable conditions trigger worry over south-west monsoon (26 June 1997)
Weather experts at the India Meteorological Department are keeping their fingers crossed over the performance of the south- west monsoon, as the waters of the Pacific Ocean are getting warmer. Warming of the Pacific is of significance since it means that there is no hope, at least for the time being, for the El Nino factor, which has a important influence on the monsoon, to become favourable. On the contrary, it only meant that it could have a more adverse impact than what was envisaged a month ago. To add to the problem, the Southern Oscillation, which is another global climatological phenomena that influences the monsoon, has also become more unfavourable. While El Nino is a reflection of the warming of some regions in the tropical Pacific Ocean, Southern Oscillation is an index of difference of pressure between the Pacific Ocean and the Indian Ocean. El Nino is considered favourable if the temperatures in the Pacific Ocean, particularly off the coast of Peru are low, and Southern Oscillation is considered to be advantageous if the atmosphere pressure in the Pacific Ocean is less than that in the Indian Ocean. The officials have, however, not given up hope on the ground that there was still a long way to go before the monsoon, which is active for four months, comes to an end in September. "

Interestingly the monsoon was 8-10 days late across most of the country that year. In the end the monsoon rainfall total was slightly above average, but characterised by very heavy rainfall, which caused floods and landslides, in late August.

1997 was of course the start of the largest El Nino in the last 60 years. It is unsurprising that the monsoon is currently showing a similar pattern as a new El Nino develops. The landslide pattern is apparently reflecting this.

Monday, 13 July 2009

Disastrous mining related landslide in Burma / Myanmar

A few days ago on 3rd July a major landslide occurred in northern Burma (Myanmar) that appears to have affected a huge number of people. The excellent ReliefWeb site is carrying reports of the UN OCHA response to the disaster. The OCHA report states that:

"On the 4th of July 2009, a landslide caused by heavy rains swept away a jade miners' settlement along the Uru River in Hpakant Township (also sometimes spelt Phakant), northern Kachin State. Another jade mining city, Seng Tawng, was also reported to have been affected by the floods. Villages in the surrounding area are also reported to be affected. In the absence of a credible assessment, initial information collected reveals a wide range of disparate mortality and affected population levels. It is anticipated that clearer fatality and casualty figures will be available within the next days. The New Light of Myanmar, a State-run newspaper, reports the number of fatalities to be 24 at this stage.In Hpakant, it is reported that a total of between 900 and 1,000 individuals are currently accommodated in a total of five informal displacement locations, including four monasteries and one school. Similarly, approximately 200 individuals are currently accommodated in a monastery in Tar Ma Hkan. The population in these locations is reported to include families"

So clearly this was a pretty serious event. Unfortunately, this is one of those occasions in which Google Earth just doesn't do the business due to the resolution of the imagery:


However, there is a local website for Hpakant set up by AKSYU (a campaigning human rights group from the Kachin area). Interesting, the website reports that:

"The death toll has risen to 70 in the aftermath of floods and landslides in Burma's Hpakant jade mining area in the country's northern Kachin State on July 4 and 5. Hundreds have been injured including over 10 people from local Kachin Baptist Churches, according to official figures available from Burmese Army authorities. The floods and mudslides were the biggest ever witnessed in Hpakant jade land. The devastation was said to have been caused because the ruling junta has been allowing indiscriminate jade mining activities with sophisticated machines following the ceasefire agreement between the regime and the Kachin Independence Organization (KIO) in 1994, said local environmentalists. The death toll was compiled till yesterday by the administrative office of the Hpakant Jade Mining City also called the City Peace and Development Council (Ma Ya Ka) of the junta, said Hpakant residents. The search for bodies in jade land is underway and an additional 30 bodies were found under soil and slush dug out from the jade mines yesterday evening, a resident of Hpakant told KNG today. Eyewitnesses said they saw dozens of bodies being carried in trucks while people were searching for more bodies under the soil heads which came crashing down in the heavy downpour. Most of the deaths resulted from the mudslides because of the high land dug for the jade mines and because most villages were constructed on low land near the Uru River, according to residents of Hpakant. The Hpakant government hospital is full of people with injuries as of Saturday night but a callous Burmese military authority is yet to launch any rescue mission for the victims, said residents of Hpakant. Residents expect the death toll to touch several hundred because over seven main jade mining villages were severely affected by the flood from the Uru River which brought down heaps of soil and mud dug out from thousands of jade mines near their villages. The three major jade mining cities of Hpakant, Lonkin (also called Lawng Hkang in Kachin) and Seng Tawng were flooded by the Uru River. However the water is receding since yesterday, added residents. Private and non-government rescue and relief missions were started yesterday in some of the flood and landslide affected areas like Hpakant city, Maw One, Seng Tawng and Lonkin after the rain and floods stopped, said locals. Soon after the floods, the Hpakant Regional Kachin Baptist Convention under the Kachin Baptist Convention (KBC), the biggest Kachin Christian body in the country formed an emergency committee. It is implementing rescue and relief missions, said a KBC staff member in Myitkyina, the capital of Kachin State. Roads in most villages in Hpakant jade land are covered with over three-foot of mud and slush allowing only ferry transportation, said local residents. Residents of Hpakant city are now busy cleaning their inundated homes. They are facing an acute shortage of clean water, said residents."

So is it possible that a death toll of several hundred could have occurred here, or is it an exaggeration? Well, let's take a look at a couple of the images of the mines in the Hpakant area that AKSYU have on their site, which can be accessed here:

(click on the images for a better view in a new window)

To call this a disaster just waiting to happen is something of an understatement. This image shows how the spoil dumping has occurred (note the people on the nearer slope for scale):


The combination of dumping at the angle of repose in dry conditions, and the villages in such close proximity to the mine dumps, makes a large-scale landslide disaster a distinct possibility:

It remains impossible to know what has happened - I will keep an eye on the UN and other web sites to see if anything appears. An flowslide type of failure must be a worry in this sort of setting though.

Wednesday, 8 July 2009

New landslide videos - slow moving slides affecting houses

I have come across yet another new landslide video. This one was shot in Brazil during the recent heavy rainfall there. This one is quite unusual as the landslide is large and slow moving, but in the video it overruns a house, causing it to collapse:

You should be able to play the movie below:



There is also a short video of a landslide removing the support from a deck at the back of a house, which then collapses, here:

Shallow landslides in County Mayo, Ireland

Last Thursday (2nd July) an unusually strong rainstorm passed across the northwest of Ireland. Considerable damage was caused, as recounted in this Irish Times article, with floods occurring across quite a large area. The rainfall in the Castlebar area was particularly intense - there is a quite nice article on this in the Mayo news. This rainfall appears to have triggered a set of large but shallow slides at Croaghmoyle. Castlebar News has two images, shown below, of the landslides:

The top (overview) shot is quite interesting. The large slide that is most obvious appears to have started as a very localised slip in what I think is probably a blanket peat layer high up on the slope (see annotated image below). The main slide is of the shallow regolith layer on the boundary with the underlying bedrock. It appears that a comparatively small change in gradient low on the slope caused the slide to cease to erode and start to deposit, although the material has moved a considerable distance over the land surface and onto the track. This is not unusual in this type of slide. The other slides appear to just be on the regolith / rock boundary.


The second image shows the debris on the road, which appears to be mostly peat and some entrained bedrock pebbles and cobbles. This road is the access track for a large television transmitter - two technicians were trapped on the wrong side by the landslides.

The Irish Meteorological Service has a short article on the rainfall here. The peak rainfall intensity in nearby Newport was 41.6 mm in 24 hours, which has an annual exceedance probability of 1 in 150. 60 mm of rainfall was recorded in total, with a maximum one minute intensity of 2.8 mm, and a maximum five minute intensity of 9.8 mm. The rainfall was thundery, so this image of lightning strikes shows the rain bands quite well:

Friday, 3 July 2009

The biggest landslide of them all - Saidmareh, Iran

As the summer begins and my mind starts to move over from administration to research, I was pondering really large landslides. As a result I thought that it was about time that I posted about the biggest known sub-aerial landslide - surprisingly it has received comparatively little attention to date.

The landslide itself was identified and written up by Harrison and Falcon in 1938 is a paper in the Journal of Geology that is freely available online through JSTOR. The landslide is located on the Kabir Kuh anticline in Southwest Iran at 33N, 47.65E :

(Click on the image for a better view in a new window)

This slide, which is called the Saidmareh landslide (sometimes also the Saidmarreh, the Seymareh or the Kubir Kuh landslide) is big...really, really big. The statistics defy imagination to be honest - it has a volume of about 20 cubic kilometres, a depth of 300 m, a travel distance of 14 km and a width of 5 km. This means that about 50 billion tonnes of rock moved in this single event!

Fortunately the slide is well covered by Google Earth - this is a perspective overview:


A slide this large is quite hard to understand, so I have annotated the image below. Note the scale!

So lets take a closer look at the source area of the landslide:

The image above shows that this is essentially a dip slope failure on a tectonic ridge - in other words, the landslide came off along an inclined bedding plane. You will see that, as is often the case in fact the slip plane stepped from one bedding plane to the next to exploit the weakest parts of the rock mass, which is mostly limestone with some marls. The maximum fall height was about 1600 m according to Harrison and Falcon (1938).

The deposit is huge, covering an area of about 166 square kilometres:

It is formed from very angular blocks of limestone, some of which are large enough to be seen on the Google Earth imagery:


The highly fragmented nature of the deposit and the long travel distance both suggest that this was a very energetic, high velocity landslide - a rock avalanche (sometimes called a sturzstrom).

The landslide blocked two rivers, allowing a pair of lakes to form, both of which have now drained away. However, the remains of one of them is clearly evident as the deposited sediment provides fertile farm land as shown below on the south side of the landslide. The lake appears to have breached across the landslide debris, creating a channel that has now been weathered. Subsequently the modern river has found a new course off the landslide mass:

The other lake is much larger, being located in the main valley that was blocked by the landslide:

This lake deposit is 39 km long and about 150 m thick close to the landslide.

The age of the landslide is not clear, but there is an ancient ruined Sassanid town bridge on the bed of the larger lake. The Sassanid era extended from 224 to 651 AD, so the landslide must be considerably older than this. One date was reported by Shoaei and Ghayoumian (1998) of 10,370+/-120 years BP.

Finally, what caused such a huge landslide? This is an area that is subject to intense seismic activity so it is highly likely that this was earthquake triggered. There is no evidence that the slide occurred as anything other than a one single, massive failure.

References:
Shoaei, Z. and Ghayoumian, J. 1998. Seimareh landslide, the largest complex slide in the world In: Moore D and Hungr O (eds) EIGHTH INTERNATIONAL CONGRESS OF THE INTERNATIONAL ASSOCIATION FOR ENGINEERING GEOLOGY AND THE ENVIRONMENT, PROCEEDINGS, VOLS 1-5 , 1337-1342.

J. V. Harrison and N. L. Falcon 1938. An Ancient Landslip at Saidmarreh in Southwestern Iran
The Journal of Geology, 46 [3], 296-309.