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.

Three new landslide / debris flow videos

Thanks to Lynn Highland at the USGS for drawing my attention to this video of a debris flow in Costa Rica:



This is a slightly strange event. It occurred on the Sarapiqui River in Costa Rica after the 16th January 2009 Cinchona earthquake. It is not all clear why the earthquake should have triggered such a debris flow given that there was no rainfall, but a suggestion is that there may have been mobilisation of shallow groundwater. Another possibility is the creation and then collapse of a barrier lake.

The same event also appears to have been captured in this video:



If anyone has any more information then I would be very interested in hearing about this event.

In Hong Kong last month I saw a video taken of a collapsing hillside during the Wenchuan earthquake. This appears to have been shot in the Wolong Panda Reserve area. The quality is poor, but the footage of the collapsing slope is dramatic:

The National Centre for Landslide Research, Studies and Management in India

Yesterday, the Indian National Disaster Management Authority held a press conference to announce the publication of a new set of "National Disaster Management Guidelines – Management of Landslides and Snow Avalanches". At this press conference it was also announced that the Indian Government will set up a National Centre for Landslide Research, Studies and Management, to be located in one of the most landslide-prone states (I would guess that this will either be in the north of the country or in the south-east). Unfortunately at the moment there is little information available about this centre, other than what was contained in the speech given by the Union Minister of Mines and DONER, Shri Bijoy Krishna Handique:

"The proposal for establishing a National Centre for landslides research, studies and management, as recommended by the guidelines is a welcome step in the direction of capacity building and research and development and I feel that GSI [Geological Survey of India] will be able to host this Centre as part of its core activities. Such a centre of excellence will ensure adequate national coverage, information flow, community participation, networking, and feedback with regard to landslides and snow avalanches, besides coordinating the effort of the states and other concerned central organizations. It will also foster, promote, and sustain a scientific culture in the management of slopes and landslides and encourage the transition to a culture of prevention, mitigation, preparedness and response."

Given that India has a pretty serious landslide problem that appears to be getting worse, this is a very sensible move.

I would like to get hold of a copy of the guidelines, but at the moment they are not available. However, the press conference suggested that they cover nine distinct areas:

• Landslide hazard, vulnerability, and risk assessment
• Multi-hazard conceptualisation
• Landslide remediation practice
• Research and development
• Monitoring and early warning of landslides
• Knowledge network and management
  
• Capacity building and training
• Public awareness and education
• Emergency preparedness and response
  
• Regulation and enforcement.

All of which sounds very sensible!

Chongqing landslide rescue update - 23rd June

Xinhua has a video report about the ongoing rescue attempts at the Chongqing landslide site. The report suggests that remotely sensed imagery allowed a number of locations in which the crags in the head scar area were found to be unstable and threatening the rescue teams. To this end, two artillery pieces were brought in and shells were fired at the crags to try to dislodge the unstable sections. This failed unfortunately, so now dynamite will be used instead.

Unfortunately there is no news of the rescue attempt itself.

Fatal landslides in 2009 so far - a review on the solstice

The summer solstice today seems like a good time to take stock of the position with fatal landslides to date, as collected in the Durham Fatal Landslide Database. Globally the fatal landslide season really starts in early June, the point at which the Asian monsoon starts to generate substantial amounts of rainfall in South and East Asia. Of course the greatest proportion of landslides occur in July and August, so we are before the main event.

So, how does the year look so far. Well, interesting actually. The graph below provides the cumulative number of recorded fatal landslides for 2007, 2008 and 2009, excluding the ones triggered by earthquakes (which obviously don't have a seasonal pattern). Obviously for 2007 and 2008 the full year graph is available.


You should be able to see that for 2007 and 2008 the normal S-shaped curve is clear, with a fairly low rate of increase in the first and last c.120 days. The time before this period, the northern hemisphere summer, shows a much greater rate of fatal landslides (i.e. a steeper line). It is also clear that in 2009 to date the number of fatal landslides is above the previous two years, although it is converging a little of late (of which more below). 2008 was anomalously low - 2007 is far more of an "average" year - although note that this is mostly because of the low number of recorded fatal landslides in the early part of the year.

The second graph, below, shows the recorded number of fatalities (again excluding those caused by earthquake-induced landslides). The coincidence between the patterns in 2007 and 2009 is very striking; again 2007 was very close to an average year on this measure. The comparatively low total at this point in 2008 is notable - but it is also clear that the rainy season resulted in a large number of fatalities (the large step is mostly due to hurricane-induced landslides in Haiti, plus a very active monsoon at this time).

One other aspects of this years data is really interesting. You may have noticed that in both the number of fatal landslides and the number of fatalities the trend in the last few weeks is a little anomalous. In particular, I would expect to see the steepening trend becoming clear as the Asian rainy season starts. However, this is clearly not the case as yet, as the graph below shows more clearly:

Here the blue line is the cumulative total of fatalities and the green line is the trend for fatal landslides. The recent flattening off is clear. This is mostly a clear indication of the rather strange pattern in the development of the South Asian monsoon this year. The northern passage of the monsoon appears to have stalled, as this map from the Indian Meteorological Agency shows:


Here the red lines are the average position of the monsoon front, whilst the green are the conditions observed this year. It appears that the northward advance is two weeks or so late at present - and it appears that this is being reflected in the fatal landslide data. However, the northward advance of the monsoon has apparently restarted this weekend, so the more usual trend may start to be displayed shortly.

Interestingly, there is some evidence that the SW Monsoon is weaker in El Nino years, and conditions are changing from La Nina to El Nino present. We are also recording more fatal landslides in South America than in recent years. However, it is far to early to tell whether the patterns that we are seeing this year are really associated with the possible El Nino conditions. It will be an interesting summer!

Chongqing landslide - NASA satellite image

NASA have provided the first decent overview of the Chongqing landslide via a high resolution satellite image. This can be found here.


The morphology of this is decidedly odd - I will spend some time trying understand it better. According to the NASA page the source is to the north and the landslide has moved southwards and then spread out to the southwest.

Meanwhile, the search for victims continues according to Xinhua.

Cayton Bay / Knipe Point landslide - report on options

A year or so ago I posted on an ongoing landslide at Cayton Bay in North Yorkshire, just an hour or so down the road from my base Durham. This landslide, which is no commonly called the Knipe Point landslide, was threatening 50 or so houses (see image below) - in the end three were demolished, although the rest are still under threat from the slide. Since my post the BGS have created a nice summary website here, from which this picture is taken:

The local council, Scarborough Borough, managed to find from a range of sources about £300,000 to pay for an investigation of the site, which was undertaken by Halcrow. This investigation was completed this week and will be discussed by the Council in a few days time. The Council has put out a press release here, although the report is not available online. The key findings are as follows:

a. The landslide is a deep seated, ancient landslide system. consisting of:
1. A main deep seated failure for which ground movement is controlled by the residual strength of the clay and a deep confined natural groundwater table;
2. Shallow mudslides in the overlying glacial tills for which the ground movement is controlled by an upper natural groundwater table. This slide is highly sensitive to small changes in the groundwater conditions.

I find the above quite surprising as the failures affecting the houses do not move that often - so this apparent high level of sensitivity is a little odd. I will need to read the report (I will try to get a copy).

The press release then discusses stabilisation issues - which is I am sure what the householders are worried about. It briefly mentions the constraints (minimal impact on the environment as the landslide contains a Site of Special Scientific Interest (SSSI), but a 50 year design life).

Three key actions are recommended:

1. "Maintain and continue monitoring of the surface and subsurface ground movement, groundwater and weather station network."
2. "Liase with stakeholders to review the findings of the report and discuss the way forward for managing the cliff instability risk at the site in the short and long term."
3. "Review funding options for promotion of the preferred engineering stabilisation options, and prepare an application for funding under the relevant and most appropriate legislation."

The preferred stabilisation option is unfortunately large and complex:

• Installation of deep drainage to reduce and control groundwater levels in the deeper water table.
• Construction of bored piles at Knipe Point to isolate the lower Cayton Cliff landslide system from the land above the cliff top.

The press suggest that this would cost £12 million (some reports suggest £20 million!). I would think that finding this sum of money is going to be tricky given the limited number of houses involved, although maybe the threat to the main road will help here.

The Chongqing landslide - update 16th June

The latest update on the Chongqing landslide rescue is provided by Xinhua. Key points:

• Rescue operations continue, with 3,000 people working on site;
  
• Ten small-scale landslides have occurred at the landslide site since Friday;
• southwest China's Chongqing Municipality from Friday, and rescuers continued to search for 64 missing for the 10th day on Tuesday.
• The water level in the barrier lake has dropped to 10 m below the top of the temporary embankment;
• The rescuers have not yet found the mine entrance.

Chongqing landslide update - 15th June 2009

An update on the Chongqing landslide rescue is provided by a CCTV report. Latest news:

• Contrary to the reports yesterday, rescue operations are continuing;
• The pumps to lower the barrier lake are now in operation and are succeeding. It will take about a week to empty the lake, whereupon construction of the channel will start.

The Chongqing landslide - the rescue is probably about to be abandoned

Xinhua is reporting that the rescue at the Chongqing landslide is likely to be abandoned shortly. Given the length of time that has elapsed since the failure the chances of rescuing the miners alive are now very small. More worryingly, there is an increasing risk of further failures at the site:

"According to a geologist with the rescue headquarters who declined to be identified, cracks with the span of eight to ten meters wide and up to 30 meters deep have appeared on the landslide-induced hills. "If the 1.75 million cubic meters of soil and rocks fell down from 80 to 100 meters high, another massive landslide shall occur," he said. Four remaining big stones that stood on the edge of the mountains are also likely to slip off when it rains, he said. Two landslides of smaller scale forced suspension of rescue work twice early Friday morning. The landslide site has entered the flood season, and landslide-induced lakes are likely to trigger mud-rock flows, said Zhu Xiansheng, head of the water conservancy bureau of Chongqing."

Such rescues are always a balance between the benefits of successfully rescuing the victims and the risks to the search teams. Given the time that has elapsed, the difficulties involved in the operation and the lack of indications that the miners are alive, the increasing risks to the rescue teams do suggest that stopping the operation is probably prudent, even though it is a very difficult decision to make. Thirty metre deep cracks that are widening are a strong indication that all is not well on the hillside, although failure is certainly not inevitable.

The latest update on the Chongqing landslide rescue

Xinhua and CCTV have published updates on the Chongqing landslide rescue. The picture is looking increasingly grim given that the estimated survival time of the miners was five to seven days, and it is now a week since the landslide. Highlights of the reports are as follows:

• Drilling continues but to date no signs of life have been detected. Drilling (or is this tunnel construction - see below) is only progressing at 5 m per day as they are creating an inclined hole to try to prevent secondary failures;
• Unfortunately the mine plans were buried in the landslide, so the exact location of the mine entrances is unknown. The chances of being able to build a tunnel that will intersect the mine entrance is considered to be less than 20%;
  
• A small landslide that a the drilling platform interrupted rescue operations today. No-one was injured. However, it is now believed that over a million cubic metres of the slope above the site is unstable, and the possibility of more landslides is considered to be "very high".
• The heavy lift helicopter is transporting heavy equipment onto the site (see image above). This is expected to increase the rate at which excavation can occur;
• The barrier lake now contains 40,000 cubic meters of water (this is a big increase in estimated volume compared with yesterday - but is still not a huge amount of water as these things go); The lake level rose by 0.5 m in the last 24 hours.
  
• The team continues to build an embankment to keep the water away from the rescue site. The water level is now 1 m below the embankment
• However, the drainage pipe is now in place and will start pumping today. With a capacity of 15,000 cubic metres per day this should keep the level below the maximum under current conditions;
• In due course a proper drainage channel will be needed, but at the moment the focus is on the rescue.

Three observations:
1. The news that the authorities do not know the actual location of the mine entrances is new - and very candid. One should not be critical of them for this - a characteristic of the Guinsaugon (Leyte) landslide was the huge difficulties that the rescuers, including the US Marine Corps, had in determining the former location of buildings and infrastructure;
2. It seems to me that there are two operations occurring simultaneously here - one to drill bore holes to allow detection equipment to be located and, I suspect, to try to find the mine entrances. This explains why 40 rigs are being used.
3. There is a double race occurring here - one associated with the limited survival time of the miners and the other to beat the seasonal rains. Unfortunately the slope could collapse even without further rain (i.e. through a progressive failure), so the danger to the rescuers is real and very immediate.