On the slide

Earthquake induced landslides

2009-07-16T21:17:00.006+01:00

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.

June 2009 fatal landslide map

2009-07-15T22:29:00.004+01:00

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

2009-07-15T17:40:00.004+01:00

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.

Disastrous mining related landslide in Burma / Myanmar

2009-07-13T20:35:00.009+01:00

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.

New landslide videos - slow moving slides affecting houses

2009-07-08T21:41:00.004+01:00

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

2009-07-08T08:12:00.005+01:00

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:

The biggest landslide of them all - Saidmareh, Iran

2009-07-03T15:16:00.014+01:00

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

2009-06-30T08:24:00.003+01:00

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

2009-06-23T21:13:00.003+01:00

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

2009-06-23T08:11:00.004+01:00

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

2009-06-22T00:01:00.000+01:00

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

2009-06-18T22:21:00.005+01:00

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

2009-06-17T21:51:00.004+01:00

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:

"Maintain and continue monitoring of the surface and subsurface ground movement, groundwater and weather station network."
"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."
"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

2009-06-16T09:31:00.002+01:00

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

2009-06-15T11:33:00.002+01:00

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

2009-06-14T17:03:00.005+01:00

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

2009-06-12T08:48:00.004+01:00

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.

Latest update on the Chongqing landslide

2009-06-11T19:48:00.003+01:00

The desperate rescue attempts continue at the site of the Chongqing landslide, but time is now clearly running out for the miners. The heavy lift helicopter, the same one that assisted at Tangjiashan, is now in full operation, and the drilling continues using 20 machines according to this report. The drilling operations have now reached 100 m below the surface and thus have reached the position of the portal. Unfortunately this appears to have collapsed (unsurprisingly). Additionally, the rescue teams have had to abandon their use of explosives due to the instability of the landslide mass.

There can be little hope for the trapped miners now, although it is still worth trying to get to them.

Meanwhile, according to this report the barrier lake volume has now reached 10,000 cubic metres (this is not a huge volume). Operations to lay a drainage pipe are ongoing.

Chongqing landslide update - 9th June

2009-06-09T21:06:00.004+01:00

Image source: http://uk.news.yahoo.com/19/20090609/img/pwl-china-landslide-death-9-6f14af6c0f4b.html

The latest news from the Chongqing landslide site is as follows:

Attempts to build a tunnel to the trapped miners continue. The heavy lift helicopter is now in operation. Electric cables and a generator have been installed to provide power to the ongoing operations;
Heavy rain has now reduced to drizzle, but the water depth in the barrier lake increased by a metre in 24 hours;
Operations to create a channel to drain the lake continue. The image above appears to show the barrier lake in the background;
The rescue teams are using sandbags to try to prevent water from the barrier lake entering the mine - this would of course be disastrous for the trapped miners.
Satellite imagery was expected to be available from today (I would like to see this!). Meanwhile, monitoring points have been established to provide warning of any further landslides.

Time must be running out for the miners, but it sounds as if the Chinese are undertaking a huge effort to rescue them.

Meanwhile, some additional pieces of background information have been published in China Daily:

The iron ore mine, which was called Sanlian, produced only 100 tonnes per day. This is very low.
A similar accident occurred 0n 30th April 1994, creating a landslide deposit that blocked the river;
Two days before the accident rockfalls were observed from the slope;
The local authorities warned the villagers about the potential for a landslide in 2003. They were offered 5,000 yuan (c.£450 or 520 Euros) to move. Most villagers refused to leave.

Background to the Chongqing landslide

2009-06-08T12:16:00.004+01:00

According to this report, rescue operations for the 27 miners trapped in a mine beneath the Chongqing landslide have been suspended due to bad weather. As I mentioned in my earlier post, working on a fresh rockslide deposit is exceptionally dangerous, so this is a wise decision. However, the outlook for the trapped miners must be looking increasingly bleak, given that it now appears that they are trapped 200 m underground and heavy machinery is not being used.

The above article has some very interesting and pertinent information about the context of the landslide. It quotes local residents as saying that the mine in question, which opened in 1949, was closed in 2000 "after being labelled dangerous by an official geological survey team". However, work resumed in 2004 under private ownership, whereupon landslides started to occur from the slope. In 2004 "masses fell from the mountain into the valley... after which the Tiekuang government offices, local school and circa 70 residencies were moved. But 40 of those people buried by the landslide decided to stay in the area, after local officials assured them that there were no problems."

The mine owner has been arrested, but the local people are critical that the local media is reporting the landslide as having been natural: “it wasn’t a natural disaster; human error is the only thing to blame for the tragedy”.

The race against time to save 27 miners trapped below the Chongqing landslide

2009-06-07T14:17:00.006+01:00

Image from: http://topiclinks.boston.com/photo/07Nr7zUf5l1W1

In China there is now a dramatic race against time being played out as rescuers race to reach 27 miners trapped below the Chongqing landslide. Xinhua is reporting that the two entrances to the Jiwei Mountain Iron Ore mine were blocked by the landslide. The trapped miners are likely to be able to survive for five to seven days, so there is very limited time available. Rescuers are now trying to blast a 40 m deep shaft through the landslide debris to reach the miners, as this Xinhua image shows:

To facilitate this the rescuers have build a road to bring in heavy machinery and now have access to a heavy lift helicopter.

However, we should not under-estimate the difficulties of this task. First, the landslide debris looks to be incredibly coarse, which will mean that digging a shaft or a tunnel is very difficult indeed, as this Xinhua image shows (note the rescuers for scale):

Third, the debris will be at its dry angle of repose and so is only just stable. Therefore, digging into will potentially destabilise the mass above. Supporting a tunnel or shaft in this material is not going to be easy. Finally, of course, rainfall would be very dangerous. The rainy season is just starting. Therefore, there are substantial risks to the rescuers as well as the miners.

Meanwhile, the slide, which is now estimated to have a volume of 12 million cubic metres, has also blocked the valley, such that a lake is forming. Once again the Chinese are having to build a drainage channel and evacuate people downstream and within the lake area.

The number killed by the landslide is very unclear at present, but the best estimate seems to be 79 buried by the landslide plus the 27 miners.

Illustration of the scale of the Chongqing rockslope failure

2009-06-06T17:54:00.003+01:00

The landslide at Chongqing is very large - it has an estimated volume of 3.5 million cubic metres. The scale of this is well-illustrated by this image from Suomen Kuvalehti, which shows rescuers walking across the landslide debris:

Update on the Chongqing landslide

2009-06-06T10:17:00.003+01:00

Xinhua is now reporting that 79 people have been killed in the catastrophic landslide in Chongqing. In addition, 27 miners are trapped in a mine whose adit has been buried.

Xinhua has also released an image of the source zone of the landslide (showing continued rockfall activity):

And also the landslide deposit. It is now appears that this is a massive and catastrophic rock slope failure:

UPDATE 2: Media reports of a very large landslide in China

2009-06-05T10:55:00.006+01:00

The Chinese State news agency Xinhua is reporting that a landslide in Chongqing Municipality has buried about 60 people.

UPDATE 2: The Chinese state media are now reporting 80 fatalities:

"At least 80 people are feared buried in a landslide at an iron ore mining area in southwest China's Chongqing Municipality on Friday, according to the local government. Rescuers had pulled out seven injured people, including four seriously hurt, from the debris as of 8:30 p.m., according to the publicity department of Wulong County, the site of the accident. The landslide happened at about 3 p.m. in the Jiwei Mountain area, in Tiekuang Township, about 170 kilometers southeast of the downtown area. Millions of cubic meters of rock filled a valley and buried an iron ore plant and six houses."

Interestingly, TRMM 3 day rainfall data does not suggest that the Chongqing area is subject to heavy rainfall at the moment (see image below - Chongqing is in central west China). I wonder whether this is another flowslide?

I'll post again when more info is available.

Are satellite-based landslide hazard algorithms useful?

2009-06-03T20:48:00.006+01:00

In some parts of the world, such as the Seattle area of the USA, wide area landslide warning systems are operated on the basis of rainfall thresholds. These are comparatively simple in essence - basically the combination of short term and long term rainfall that is needed to trigger landslides is determined, often using historical records of landslide events. A critical threshold is determined for the combination of these two rainfall amounts - so for example, it might require 100 mm of rainfall in hours after a dry spell, but 50 mm after a wet period. These threshold rainfall levels have been determined for many areas; indeed, there is even a website dedicated to the thresholds!

In 1997 NASA and JAXA launched a satellite known as TRMM (Tropical Rainfall Monitoring Mission), which uses a suite of sensors to measure rainfall in the tropical regions. Given that it orbits the Earth 16 times per day most tropical areas get pretty good coverage. A few years ago Bob Adler, Yang Hong and their colleagues started to work on the use of TRMM for landslide warnings using a modified version of rainfall thresholds. Most recently, this work has been developed by Dalia Bach Kirschbaum - and we have all watched the development of this project with great interest. The results have now been published in a paper (Kirschbaum et al. 2009) in the EGU journal Natural Hazards and Earth Systems Science - which is great because NHESS is an open access journal, meaning that you can download it for free from here.

Of course a rainfall threshold on its own doesn't tell you enough about the likelihood of a landslide. For example, it doesn't matter how hard it rains, if the area affected is in a flat, lowland plain then a landslide is not going to occur. To overcome this, the team generated a simple susceptibility index based upon weighted, normalised values of slope, soil type, soil texture, elevation, land cover and drainage density. The resulting susceptibility map is shown below, with landslides that occurred in 2003 and 2007 indicated on the map:

A simple rainfall threshold was then applied as shown below:

Thus, if an area is considered to have high landslide susceptibility and to lie above the threshold line shown above based upon an analysis using 3-hour data from TRMM, then a warning can be issued.

Kirschbaum et al. (2009) have analysed the results of their study using the landslide inventory datasets shown in the map above. Great care is needed in the interpretation of these datasets as they are derived primarily from media reports, which of course are heavily biased in many ways. Examination of the map above does show this - look for example at the number of landslide reports for the UK compared with New Zealand. The apparent number is much higher than in NZ, even though the latter is far more landslide prone. However, in New Zealand the population is small, the news media is lower profile, and landslides are an accepted part of life. However, so long as one is aware of these limitations then this is a reasonable starting point for analysing the effectiveness of the technique.

So, how did the technique do? Well, at a first look not so well:

In many cases the technique failed to forecast many of the landslides that actually occurred, whilst it also over-forecasted (i.e. forecasted landslides in areas in which there were none recorded) dramatically. However, one must bear in mind the limitations of the dataset. It is very possible that landslides occurred but were not recorded, so at least to a degree the real results are probably better than the paper indicates. Otherwise, the authors admit that the susceptibility tool is probably far too crude and the rainfall data to imprecise to get the level of precision that is required. However, against this one should note that the algorithm does very well (as indicated by the green pixels on the map above) in some of the key landslide-prone areas - e.g. along the Himalayan Arc, in Java, in SW India, the Philippines, the Rio de Janeiro area, parts of the Caribbean, and the mountains around the Chengdu basin. In places there is marked under-estimation - e.g. in Pakistan, Parts of Europe and N. America. In other places there was dramatic over-estimation, especially in the Amazon Basin, most of India, Central Africa and China.

All of this suggests that the algorithm is not ready for use as an operational landslide warning system. Against that though the approach does show some real promise. I suspect that an improved algorithm for susceptibility would help a great deal (maybe using the World bank Hotspots approach), perhaps together with a threshold that varies according to area (i.e. it is clear that the threshold rainfall for Taiwan is very different to that of the UK). Kirschbaum et al. (2009) have have produced a really interesting piece of work that represents a substantial step along the way. One can only hope that this is developed further and that, in due course, an improved version of TRMM is launched (preferably using a constellation of satellites to give better temporal and spatial coverage). That would of course be a far better use of resource than spending $4,500 million on the James Webb Space Telescope.

Reference
Kirschbaum, D. B., Adler, R., Hong, Y., and Lerner-Lam, A. 2009. Evaluation of a preliminary satellite-based landslide hazard algorithm using global landslide inventories. Natural Hazards and Earth System Science, 9, 673-686.