Chongqing landslide update - 9th June

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:

1. 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;
2. Heavy rain has now reduced to drizzle, but the water depth in the barrier lake increased by a metre in 24 hours;
3. Operations to create a channel to drain the lake continue. The image above appears to show the barrier lake in the background;
4. 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.
5. 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

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

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

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

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

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?

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.