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.

Sunday, 31 May 2009

Landslides and the Kailash Mansarovar yatra

One of the great pilgrimages of the Hindu faith is the Kailash Mansarovar Yatra, which is a 400 km trek up to Lake Mansarovar in Tibet. This pilgrimage is very demanding - the lake is at 4550 m above sea level. It is undertaken in groups of 60 people over 26 days. Each year the first group sets off on 1st June.

The route is shown below (from here):


This year the pilgrimage is going to have an additional challenge. I posted back in February about the Chautuldhar landslide in northern India, which was causing major problems in the close area of Tawaghat in Dharchula. The landslide is not quite where I thought it was back then - it now looks as if it is on the section of slope shown on the Google Earth perspective view below:


A close look at the map above will show that Tawaghat is right on the route of the pilgrimage. Unfortunately, the landslide remains active - indeed David Hopkins has been kind enough to send a translation of an article in a local paper for this area, dated 27th May:

"During the past sixty hours rocks and stones have been showering down from the mountain in Chautuldhar. Following the recent rains the mountain in Chautuldhar is on the move again. The temporary road made across the slide has been swallowed up by the river below. People are taking their lives into their hands to cross the slide. With two bulldozers of the BRO (Border Roads Organisation) stuck on the Tawaghat side problems have only increased. From Friday to Sunday following very heavy rains, rocks and boulders are continually raining down from the mountain."


To deal with this problem a diversion has been created, but this is reported to be "treacherous" and likely to add two days to the length of the trek.

Large fatal landslide in Papua New Guinea

On 25th May there was a large landslide in Papua New Guinea that reportedly killed 19 people. Reports about this event have been rather hard to come by, so I went searching through the Papua New Guinea only newspaper sites. The most dramatic image is this one, from The National:


It is clear that this is very large landslide (see below). The dynamics are fascinating as the source area appears to be very small. The slide has then scoured out what appears to be colluvium deposits from within a channel on the upper part of the hillside, before transitioning into a large -scale, highly energetic flow.

I also came across these images and this report on the pages of the Papua New Guinea Post Courier.

This image shows the track of the landslide

This image reportedly shows the landslide deposit.

The report (shortened here) states that:
"A family is counting its luck after all its members survived a massive landslide that killed 19 of their relatives between
the gorges of Firangka in the Sialum district of Morobe Province. The family of five survived by metres when the landslide swept down the mountainside and engulfed six houses, missing their hamlet in Zongefifi in the early hours of Monday...Locals retrieved three bodies, two male and one female while the other 16 bodies were still buried. The landslide started from the top of the mountain, slid down the gorge for about half a kilometre with debris strewn over
200 metres wide before dropping down the steep terrain.

Mr Gamato [deputy administrator] said the landslide was caused by water underneath the coronus limestone which had built up and caused the ground to become unstable, causing a massive slip. He also warned that the months of May, June and July were a time of continuous rainfall in the province and those travelling by sea, living along river banks and under mountainous terrains should take extra precaution because of the rain in the province in recent weeks."

Wednesday, 27 May 2009

Landslides from Cyclone Alia in Darjeeling

One of the most admirable landslide websites that I know is the Save the Hills blog, which is the mouthpiece of a community level group trying to raise awareness of the problems of landslides in Darjeeling in NE India. I have featured this site several times before.

As Cyclone Alia has closed in on the area over the last few days See below) they have been warning of the danger of landslides triggered by the rainfall that the cyclone would inevitably bring. The Cyclone passed across the area yesterday - and sure enough reports are now emerging of the landslides that the rainfall has triggered. At the time of writing Sify is reporting 22 killed in landslides, with 10 injured and another six people reported missing. Over 100 landslides have been reported. The Times of India reports that 245 mm of rainfall fell in a 24 hour period.

Meanwhile, in the last few days there are also reports of a large landslide in Sialum District in Morobe province of Papua New Guinea, which is reported to have killed 19 people (although the picture is still rather unclear), landslides in Bhutan with at least one fatality, mudslides in Uttar Pradesh in India that killed eight people, and landslides in Guangdong that have killed four. Finally, there are some very unclear reports about the magnitude of the impact of heavy rainfall in Afghanistan, with reports of about 95 people killed in landslides and floods.

Sadly, none of this is particularly unusual as we are seeing the impacts of the development of the summer monsoon across Asia.

Tuesday, 26 May 2009

The Pareechu landslide and flood, 2005

In July 2003 a landslide occurred on the Pareechu stream at 32.322N, 78.735E, a remote tributary of the Satluj River in Tibet (see Fig. 1). The landslide was quite large, blocking the river and allowing a lake to form that eventually breached. In this post I will try to use the range of satellite imagery and reports that are now available to describe the sequence of events.

Fig. 1: Google Earth location map of the Pareechu landslide (click on the image for a better view in a new window)

NASA produced an ASTER image of the site that was collected in October 2003, before the landslide occurred (Fig. 2). This shows the rather strange landform at this site - i.e. a broadening of the river in which there has clearly been extensive sedimentation.

Fig. 2: NASA ASTER image of the Pareechu landslide site before failure

It is not clear what triggered the landslide, but another ASTER image collected in July 2004 very clearly shows the immediate aftermath of the slide (Fig. 3).

Fig. 3: NASA ASTER image of the Pareechu landslide site after failure

Note that the basin is now being filled by a lake. The landslide itself is not particularly clear, although the extensive dust kicked up by the slide is fairly obvious as a whitish colour mantling the slopes just to the east of the lake. It is certainly clear that the valley is blocked. An enlargement of this area helps a little (Fig. 4).


Fig. 4: Enlargement of the NASA ASTER image of the Pareechu landslide site after failure

There is an image available in the following presentation (slide 7) that provides a view of the site in August 2004 (Fig 5):
http://www.managingclimaterisk.org/document/SAARC.pdf

Fig. 5: Presentation image of the Pareechu landslide site after failure

The landslide is clearer here, but note also that there is water flow clearly evident, so presumably at this point the landslide had overtopped the barrier. Note also though that the lake is still present, so presumably the flow was not large enough to induce significant erosion.

The next available image is from 20th February 2005 (Fig. 6). Of course this is the middle of winter, so unsurprisingly everything is frozen up. Nonetheless the lake is clearly still present.

Fig. 6: Google Earth image of the Pareechu landslide site in February 2005. The site is of course mantled with snow.

It does appear that there is some flow in the river, but not over the dam, presumably indicating that some seepage was occurring. This high resolution image also gives the first opportunity to get a good look at the slide, especially when the Google Earth terrain model perspective view is used (Fig. 7).

Fig. 7: Perspective Google Earth image of the Pareechu landslide site in February 2005.

It is clear that the landslide here was actually a comparatively small failure of a much larger rock slope failure. However, in turn this active section is part of a much larger rock slope failure that is delineated by a large fracture running across the hillside. I have highlighted this on Fig. 8.

Fig. 8: Annotated Google Earth image of the Pareechu landslide site in February 2005.

At its maximum the lake was 2,100 m long, 1,100 m wide and about 40 m deep storing about 64 million cubic metres of water, according to Gupta and Sah (2008). The dam appears to have failed at about 11 am on 26th June 2005, releasing a flood wave down the river that had a maximum measured discharge of about 2000 cubic metres per second. Fortunately, according to Gupta and Soh (2008) no lives were lost, although press reports at the time indicated that a small number of bodies were washed into India from Tibet. In India the flood did wash away 8 bridges, 15 km of road and caused damage estimated at US$177 million. It is not clear how much damage was caused in Tibet.

The final image, also from Google Earth and dated 4th September 2006, shows the site after the dam breach (Fig. 9).


Fig. 9: The most recent (Sept 2006) Google Earth image of the Pareechu landslide site

Note that the dam is still holding back a little water, but that this volume is now quite low. However, the slope above still looks highly unstable, so a repeat looks inevitable in due course.

Reference
Gupta, V. and Sah, M.P. 2008. Impact of the Trans-Himalayan Landslide Lake Outburst Flood (LLOF) in the Satluj catchment, Himachal Pradesh, India. Natural Hazards, 45, 379-90.

Monday, 25 May 2009

Fatal landslide map for 2009 to date

I have been a little remiss in posting these maps of late due to other pressures. Below is the distribution of fatal landslides that I have recorded in 2009 to date. Each red dot represents a single landslide that killed at least one person. All types of landslide (including debris flows and rockfalls) are included:


You can click on the map for a better version in a new window. One thing to note is that I have not heard of any fatal landslides from the L'Aquilla earthquake in Italy - but I would be surprised if there were none in reality.

Below I have plotted the same data, but colour coded the dots. In this case, the coding goes dark blue for January moving to lighter blue for February, blue-green for March, and light green for April and dark green for May:

It is reasonably clear that for Asia the blue colours cluster in the Philippines and Indonesia, whilst the greens are in South Asia. This is of course explained by the seasonality of rainfall.

For info, in 2009 to date I have recorded fatal landslides, killing 715 people. This is about par for this time of year, with the main landslide season about to begin.

Sunday, 24 May 2009

Malaysian Slope Safety Web Site

CKC, the slope engineering division of the Malaysian Public Works Department, have put together a website to provide advice to the public on slope safety:

http://slopes.jkr.gov.my/Slopesafety/default.html


Using a very simple structure, it provides a mass of very straightforward advice on what landslides are, why they happen, how to determine whether a slope problem is developing, and what to do in the event of a landslide. Whilst it clearly has a very strong Malaysian focus, it contains a wealth of information that is pertinent to other places.

Friday, 22 May 2009

Sinorock conference report - the Wenchuan Earthquake session

Yesterday there was a special session of the Sinorock Conference in Hong Kong, focused on the Wenchuan Earthquake. This involved six presentations and then a lively round-table discussion. This is a brief review.

The first talk was given by colleagues from Chengdu University of Technology on the topic of the landslides triggered by the earthquake. This was visually spectacular, emphasising the scale, density and impact of the landslides that were triggered. The CDUT team have completed an impressive amount of analysis of the data that they have collected now. An interesting addition was some small scale shaking table tests to investigate whether the morphologies that they observed can be replicated in the laboratory - the conclusion was that they can - and the videos made good viewing, although great care is needed in the interpretations due to the well-known problems of scaling the stresses and displacements.

Next up was Li Yong, also from CDUT, who talked about the mechanics of the earthquake itself. Interestingly, he highlighted the work that he and his co-workers had done with my colleague at Durham Dr Alex Densmore, in particular noting that their 2007 paper on the Longmenshan fault system had highlighted before the earthquake the threat posed by this active fault system. Dating of the sediments excavated from trenches along the fault suggest that the last major rupture was about 950 years before the present. However, his final note was quite chilling - this is that there are three large parallel faults in the Longmenshan system, but only two ruptured...

The third presentation was by the ever-impressive Chen Zuyu, who gave a wonderful talk about the mitigation of the Tangjiashan barrier lake, of which most readers will be very familiar. Prof. Chen focussed on the pressures that were on them during the successful drainage operation, the unanswerable questions that they faced, and the scientific data that they collected during the breaching. They measured the discharge as the breach proceeded and have a paper in with the ASCE at the moment. He pledged to release the data once the paper is published - so please can the ASCE make a quick decision!

An interesting issue that he highlighted was the state of Tangjiashan now. How noted that a debris flow blocked the river again on 24th September, forcing a 7 m rise in the lake level. The channel has now been widened and deepened ahead of the monsoon (this is what they were doing when I was there). More worrying, he noted that above the back scarp of the landslide scar there are tension cracks. Monitoring suggested very substantial amounts of ongoing movement, but this has now been terminated due to a lack of funds. This must be a very serious concern given the impending monsoon.

Finally before the break, He Chuan reviewed damage to lifeline engineering. Most of this went over my head, but I was interested in the fact that they examined the behaviour of rockslope reinforcement and retaining walls. In the case of rockslope reinforcement they noted that rock anchors and grids worked much better than mesh and shotcrete (not a surprise actually). The case of retaining walls they noted that walls on convex bends in the road performed poorly, whilst those on straight sections did OK. I am not sure whether this is because of the underlying materials (maybe walls on bends are holding up large colluvial bodies) or something to do with the dynamics of the earthquake shaking, or something else (presence of water?), but it is an intriguing result.

After coffee there were two brief presentations. The first was by Alexander Strom, who compared the impact of the earthquake in China with a potential event in the Tien Shan, noting that the presence of similar earthquake landforms (fault scarps, offset terraces, large landslides) suggest that an area that is considered to be of low seismic hazard may actually be quite risky. The second was by Xu Wenjie, who considered the ways in which the Xiajiapiao landslide blocked a river, and the ways in which it was breached. The fact that 14 tonnes of explosives were used to drain it sticks in the mind. I was also good to see some outcomes of modelling of the slides, but this did highlight the concerns about using models with rigid blocks to simulate materials that can fracture and fragment. The use of rigid blocks generates very high local stresses that cause ballistic behaviour of debris within the lodel. This does not mean that the the landslide did this (to be fair the author did not suggest that it did, but the audience might misinterpret the plots).

The discussion focused upon the availability of seismic data (apparently it has now been released in a book - I will try to get a copy), models of landslide initiation, topographic amplification, and the ways in which we understand the behaviour of coarse materials in landslide dams. It was all pretty interesting and there was some disagreement, which was good.

Overall I learnt a great deal but I am increasingly concerned that the opportunities presented by the event to gain scientific knowledge about landslides might be getting away from us. This is not the fault of our Chinese academic colleagues - who are impressively proactive and skilled - more of the global scientific system. This is very frustrating!

Incidentally, the Great Firewall of China has now blocked access to blogger across the whole of China. This is a great shame, and a retrograde step in terms of sharing knowledge.

Sinorock presentation file on the Wenchuan (Sichuan) Earthquake

Today there was a session on the Wenchuan Earthquake at the Sinorock conference in Hong Kong. I was invited to participate in the panel discussion, for which I put together the following presentation highlighting a few critical issues:


Uploaded on authorSTREAM by Dr_Dave

You should be able to review the presentation above or to download it the Powerpoint file if you wish (from here if necessary).

I will write a review of the presentations and discussion over the next day or so. It was very interesting indeed!

Tuesday, 19 May 2009

To explore or to research? That is not the question.

Some readers will be aware that there has been a rumpus during the last few months at the Royal Geographical Society (RGS-IBG) over its policy not to organise and run its own expeditions. A small but influential group (the Beagle Campaign) petitioned for, and got, a Special General Meeting of the Fellows of the Society, culminating in a vote on the issue, on Monday. The resolution, which was opposed unanimously by members of the Council, was defeated (but the vote was quite close on a large turn-out), meaning that the current policy is retained, although this policy was always scheduled to be reviewed over the next year.

You may wonder why I am posting on this issue on a landslide blog? Well, I am an Honorary Secretary of the RGS-IBG, and thus am a member of the Council. In the months leading up to the vote I have been careful not to comment in any public forum on the issue - I felt that in the interests of fairness it was best to remain silent (whilst encouraging all Fellows, regardless of their views of the resolution, to vote) - but now that the vote is over I will explain why I was opposed to the resolution. I write only from absolutely personal perspective - I was in Hong Kong on the day of the vote and have been here since. I have not discussed the vote with any other Council members, and I most certainly do not write on behalf of the Society.

First and foremost, the RGS-IBG has a long and proud tradition of fieldwork. I am a great advocate of field research - my early career was to a large degree built upon it - and I strongly believe that there is a great deal to learn from fieldwork that cannot be learnt from lab studies or from models. The key question therefore is not whether field research should be undertaken (every member of the Council is resolute about the importance of field research), but how should it be organised and funded. I guess in a sense this is where the Beagle Campaign followers and I disagree. They argue, passionately and impressively, that it is best undertaken through large, reasonably long-term expeditions. I argue that it is best undertaken through larger numbers of smaller scale, focused studies. Let me explain why.

In my view there is no doubt at all that the world is facing some pretty serious challenges. Climate change is the most widely discussed, but population growth, urbanisation, deforestation, biodiversity collapse, energy security, inequality and oceanic environmental degradation for example are serious challenges too in my view (some may be more serious than climate change actually). To help us to deal with these issues we need the best research undertaken by the best researchers in the optimum locations. The clock is ticking (loudly), we cannot be complacent. Geographers undoubtedly have a substantial part to play - which other discipline covers all of the above issues? Therefore, the RGS-IBG, as one of the premier Geography organisations, must take a lead. I think that the society is so doing, and am proud of my (very small) role in this.

Unfortunately, the amount of resource that the RGS-IBG has at its disposal is comparatively small. A key question therefore is what is the best way for the Society to use that resource to achieve the necessary aims? My view is that it is to direct comparatively small amounts of money at very high quality research that addresses fundamental issues (and by fundamental I mean key issues conceptually or in terms of influence). This occurs at almost every level - substantial shares go to undergraduate groups, to postgraduates, to early career researchers and to established researchers. The funds are generally used to "leverage" (dreadful word) other funds to great effect. The funding is thus both efficient and effective.

Other pots support more adventurous activities. The Land Rover sponsored Go Beyomd bursary for example provides funding and a Land Rover Defender to allow non-scientific expeditions (my own car is a Defender - there is no better vehicle for this).

Unfortunately, I just cannot see how the large-scale, multi-researcher but single location expedition approach can achieve what the current approach achieves. Almost any location is ideal for only a small range of contemporary problems. What is good for climate change (e.g. the high latitudes) does not facilitate research in another (e.g. urbanisation), meaning that the RGS-IBG would have to balance one threat against another. The current approach allows the Society to adress a wide range of issues in a wide range of environments by all levels of researchers, and still to produice world class research. The RGS-IBG should be proud of this - it is a remarkable achievement.

The newspaper articles supporting the Beagle Campaign (of which there were many) gave the impression that both models are possible - i.e. the RGS-IBG could organise both its own expeditions and support smaller-scale field research projects. Superficially this is attractive, but I think one must be realistic. The available pot of funding to support the Society is inevitably at best static, and possibly contracting, in the current economic climate. I can find no reasons to believe that in this context the RGS-IBG would be able to maintain its existing activities and support large-scale expeditions. I might be wrong, but to try to do so would be immensely risky.

Therefore I believe that the current policy is the right one. However, I recognise that the planned review may recommend a change policy - and that once all the factors have been taken into account then would be the right way to go. The review will undoubtedly be thorough and balanced, and it will then be up to Council to decide on the best way forward once the recommendations have been made. Given that there are elections for places on Council next month - and one of the positions being contested is the one that I currently hold - there are plenty of opportunities to influence this policy.

Your comments are welcome.

Dave Petley
Hong Kong,
20th May 2009

Landslide in Campostela Valley, Philippines: >25 people killed

Image of the September 2008 landslide in Campostela Valley that killed >20 people (image from here)

A range of news agencies, including Al Jazeera and AFP, are reporting that there was a major landslide in Campostela Valley in the Philippines yesterday. Regular readers of this blog will be fairly familiar with this location, which appears to have a major fatal landslide every few months.

The event yesterday occurred in barangay Napnapan, Pantukan town in Campostela Valley province (see map below). The approximate coordinates are 7.15N 125.95E. I will try to pin down the location in more detail.

Campostela Valley has a large number of fatal landslides largely because the combination of tropical soils, intense rainfall events and unregulated mining is a very toxic mix. This slide is reported to have killed 26 people and left a further 19 missing (although I wouldn't be surprised if this latter number is an over-estimate - it often is). The scenario of the slide is a little confused - some reports suggest that it buried 20 houses in a shanty town, whilst others say that the victims were resting in a bunkhouse. The trigger appears to have been heavy rainfall.

I'll post an update when more info is available.

Monday, 18 May 2009

Culvert failure video

Whilst this is not strictly a landslide, the video below of the failure of a culvert makes very interesting viewing. The ability of the channelled water to erode rapidly is a lesson that is often forgotten.



The video was captured by MWTW.com photojournalist Kevyn Fowler in Freeport, Maine during a storm.

Sunday, 17 May 2009

Landslide causes apartment block collapse in China

Xinhua is reporting that a landslide triggered the partial collapse of an apartment block housing 32 families in Lanzhou, Gansu Province, on Saturday evening. They have published a couple of pictures of the aftermath, of which this is one:

To date two bodies have been recovered and one injured person has been rescued. Judging by the above picture, and given the time of day in which the slide occurred, this total is almost certain to rise.

More as it becomes available.

Landslides and the UN's Global Assessment Report on Disaster Risk Reduction

The UN ISDR is today launching with a great fanfare the first Global Assessment Report on Disaster Risk Reduction. This report "provides hard-hitting evidence to demonstrate how, where and why disaster risk is increasing globally and presents key findings from a global analysis of disaster risk patterns and trends, including where high mortality and economic loss is concentrated. ." The report is online now and can be downloaded here.

I haven't yet had time to read the whole of the 200 page document - I will do so in due course - but have taken some time this morning to look at the landslide hazard / risk section in Chapter 2n. This was generated by the Norwegian Geotechnical Institute and has been peer reviewed by some eminent people. So how does it look?

I think a good starting point is to say that it has to be recognised that this is a very difficult thing to do. There are all sorts of problems in the collation and analysis of this type of data. However, I also have to say that I have some reservations about the outcomes, which don't to me seem to correspond to what we actually observe.

The landslides section starts with a premise that I find bizarre. The opening sentence is as follows: "Observed mortality in landslides triggered by high precipitation is approximately six times higher than in landslides triggered by earthquakes." Huh? No source or justification is provided for this statement. I just cannot see how it can be justified. In recent years we have large numbers of fatalities from landslides in the Kashmir earthquake and the Wenchuan earthquake, bit of which swamp the fatality signal from rainfall events. Perhaps this study was done before the impact of these events could be included, but there is plenty of documentation of mass fatalities from earthquake-induced landslides even before this event. Perhaps the problem here is that earthquake-induced landslides are included in the earthquake hazard section, but we should be under no illusions that the impact of this is ponce again to greatly under-estimate the risk associated with landslides. This is very frustrating!

The upshot is that the risk model considers only precipitation-induced landslides. We need to keep this is mind when evaluating the study. The headline result of the analysis seems to be (this is a direct quote) "The predicted mortality risk, even in very large countries such as India or China, is less than 100 deaths per year". Being blunt, if this is the mortality risk analysis then the model is frankly wrong as the measured losses are much higher than this. Taking 2008 as an example, a year in which precipitation-induced landslide occurrence was not exceptional, I recorded 778 rainfall-induced landslide fatalities in China, 700 in Haiti and 252 in India. This is typical and is supported by official figures. Of course, every few years these countries suffer a very large landslide disaster (e.g. the Leyte landslide in the Philippines), which increases the average annual numbers. Therefore, the study has fundamentally under-estimated the risks of rainfall-induced landslide mortality still further.

So let's take a look at the maps. They have produced landslide risk maps on a 10 x 10 km grid. Three maps have been generated, which I reproduce below. The maps are for Asia, Central America (plus the NW of S. America) and Central Africa, presumably because these are the three areas with the highest level of landslide risk. Click on the maps for a better view in a new window. Note that the label on the legend of "tropical cyclone risk" is presumably just an error, albeit a rather serious one.

This is my map of fatal landslides for 2006, 7 and 8. Each black dot represents a single fatal landslide:

This map is close to being a direct realisation of the mortality risk analysis, although care must be taken given the short time period that my map covers and to remember that population density may be an important factor. The first thing to note is that the C. American and Asian areas are well-chosen given the high incidence of fatal landslides that I record. I am far less sure of the African area - I really don't record much for that part of the world, although I recognise that this might be because I just don't capture events in this part of the world, perhaps. In Asia the distribution seems to be vaguely right in that it picks up the swathe of events through the Himalayan arc and the high risk in Java, etc. However, it does appear to fail to pick up the landslide risk associated with Central China at all well. This may reflect the high population density here (i.e. although there are lots of fatal landslides, the risk to individuals is low), but I doubt that this is the whole story. My feeling is that the analysis is failing to represent landslides in this area well. A similar problem occurs in SW India, which is a notable hotspot. In Central / S. America the analysis seems to do rather better.

Overall I am left feeling that the representation of landslide risk is really unsatisfactory. It must be possible to do this better. I hope that the analysis of the other hazards is rather better - I am sure that it must be.

Comments welcome.

Friday, 15 May 2009

Another Chinese tailings dam failure

The Chinese media are reporting another tailings dam failure, this time in Hunan province. Fortunately, the effects appear to be far less devastating than this event last year. The reports suggest that a manganese ore tailings dam failed in Huayuan County, Xiangxi Autonomous Prefecture in Hunan Province early on Thursday morning, releasing a flowslide that hit a house, killing three people and injuring four more.

Wednesday, 13 May 2009

So what have we learnt from the Wenchuan (Sichuan) Earthquake?

Driving home from work last night, and bored with listening to endless discussions on the radio about the ways in which politicians use the system to personal gain, I started pondering what we have learnt from the Wenchuan Earthquake a year ago. The media yesterday understandably focused on collapsed schools. We have known for years that critical buildings in earthquake zones need seismic reinforcement, so this is hardly new. These are the key things that I think we have learnt (you may have more, so I welcome comments):


1. Our current rapidly-generated maps of the distribution of earthquake shaking are not good enough.


In China it is clear that the area of maximum damage occurred on the hanging wall (NW side) of the fault, with the peak being very close to the surface trace of the fault. Many of the early maps suggested that maxim,um damage would be in a zone centred around the epicentre. Unfortunately this meant that at least a part of the rescue effort was misdirected. The need for strong motion instruments across an earthquake-vulnerable area that can telemeter (send) the data back to a central station is clear. This is what happened in 1999 in Taiwan. Additionally, further work is clearly needed to allow the rapid generation of reliable shake maps.

2. Communications are critical.


In China there was a major problem with communications from the most seriously-affected areas. With no telephones or power, and with all of the roads blocked by literally hundreds of landslides, getting information out about the impact proved impossible. This was compounded by a lack of understanding from the Chinese government about the likely level of damage. On the afternoon of the earthquake the Chinese Premier Wen Jiabao ordered that the roads to the epicentral areas should be reopened by before 12 p.m the day after the earthquake. Clearly there was no comprehension of what things were like in the mountain regions - and Wen is a geologist! This is not a criticism of Wen or the Chinese government - how could they possibly have known that things were so bad - but rather of the landslide community - of which I am a part - for failing to make governments aware of the implications of landslides in mountainous earthquake zones (see below).

3. Landslides play a major role in mountain area earthquakes.


Until now the earthquake community has failed to appreciate the major role that landslides cause in earthquakes in upland areas. About a third of the fatalities occurred as a result of landslides; landslides also to a large degree prevented the delivery of aid; landslides blocked valleys causing a major secondary hazard (see below); and landslides now generate much of the long term hazard in the affected areas.

4. Valley blocking landslides can be mitigated.


This is the first large earthquake in modern times that has created very large numbers of valley-blocking landslides. The Chinese demonstrated that these hazards can be successfully mitigated, but that it requires the availability of the right tools, experience and resources. The Chinese achievement is extraordinary - I wonder if the rest of the world could cope so well?

5. Satellite tools are still not up to the job.


For years we have been hearing that satellites provide the capability to get an almost instant view of what has happened in disaster zones. There are more satellites available than ever, but imagery proved to be of almost no use at all in the recovery phase. The problems remain that the instruments with the highest resolutions cannot see through clouds and it is very difficult to get the data into a format that is usable on the ground.

Monday, 11 May 2009

The Wenchuan Earthquake - one year on

No words can do justice to the first anniversary of the Wenchuan (Sichuan) earthquake, so I won't even try. Instead I post these pictures as a silent memorial to the victims.



Wednesday, 6 May 2009

Early May is the start of the landslide season

Whilst the transition towards the Northern Hemisphere summer is rather pleasant for many of us, the start of May also marks the start of the landslide season in the Northern Hemisphere. Of course the main problems kick in when the SW monsoon really gets going in Asia and the tropical cyclone season properly begins in the N. Pacific and N. Atlantic basins, but already there are clear signs that the land is starting to move. Overnight, a number of Pakistani news agencies have reported a large landslide in the Neelam Valley:

"At least 28 people were trampled to death due to landslide in Neelam Valley on Tuesday, Geo news reported. According to sources 28 people have been trapped under the landslide in Jora area here in Neelam Valley, part of Azad Jammu and Kashmir (AJK). The rescue activities have been kicked off after the tragic incident and the trapped dead bodies of the unfortunates are being dug out, sources added."

Of course the Neelam Valley was pretty badly affected by the 2005 earthquake (the image below shows a part of the valley in 2006), so ongoing landslide problems here are not a surprise.


Meanwhile, the Philippines has already been battered by one typhoon (named Kajira in the Pacific-wide system, or Dante in the Philippines), which triggered a landslide in Sorsogan that killed 23 people. Unfortunately, there is another one (Chan-Hom) en route for northern Philippines at the moment (Tropical Storm Risk):


The good news is that Tropical Storm Risk (see long term forecast here) are forecasting a below average season for typhoons (activity is anticipated to be 20% below the long term mean). The long term forecast for the monsoon in India is essentially average (forecast rainfall = 96% +/-5% of long term mean.

Tuesday, 5 May 2009

Nailing Jell-o to a wall...

This is a guest post from Bill Rabenaldt from California about a novel soil nail mitifation technique.

Can you nail jell-o to a wall? Not easily. Can you nail a landslide area, levee or bluff before it fails? You bet!


The valley floors around Aspen, Telluride and other resort areas in the Rockies are all but built out. Where do business and families go? The surrounding hills and mountain sides are all that is available. I’ve seen pictures of several of these homes and they are spectacular. Generally, the home theaters and pools are built into the mountain side due to local height restrictions.

How are they doing it?

For the past 10 years, I have been a member of the Pismo Beach City Council. Our community is on the Central Coast of California half way between San Francisco and Los Angeles, just north of Santa Barbara. During that time, I’ve learned a lot. As an example, our bluff has eroded faster than expected in some areas and we are in immediate danger of losing our highway, force mains and our underground utilities. Pebble Beach was another coastal community that was in danger of having their main arterial fall into the ocean. Trying to figure out how we can overcome these natural and man-made disasters has been my personal and political motivation for many years.

There are also the devastating fires we’ve had around the world. Rains are causing landslides of varying proportion. Our once stable private and public property is now vulnerable to the forces of nature. Our levee system is old and decaying.

There is a company I’ve been following for about 7 years. I first met them at the League of California Cities meeting in Sacramento. Soil Nail Launcher had a booth at the event and I was interested in how an 8 foot nail could be driven into an embankment. Over the years, I understand they have driven many nails and have protected a whole lot of property. Not only that, they have done it for less than half the cost of traditional methods.

Here is a short story you will enjoy:

In WW2, Great Britain developed a gas canister launcher to stop the enemy’s progress. A canister could be launched as far as 3 miles away. Several years ago, a company bought this equipment and all the patents and converted it to a “soil nail launcher”. 2,500 psi is built up in a chamber and launches a nail at 220 mph into the unstable soil. These nails are typically between 12 and 20 feet long with a Super Launcher that penetrates up to 80 feet. The area is then left to nature or a shotcrete surface can be applied.

If you would like to see what intrigued me the most, go to their website: www.landslidesolutions.com to see what they have accomplished. Their services are averaging half of the cost of traditional “fixes”, they were approved by the California Coastal Commission, they have recently received a GSA (General Services Administration) contract number from the Federal Government for emergency services. They can solve geotechnical, construction and public safety problems.


A recent report by the geological society on the new faults found along the infamous San Andreas Fault causes serious doubt as to the earlier government findings of “acceptable standards” for construction, land use issues, and a host of other many other conclusions that must be reviewed. Many may need to be reconsidered and/or revised with this new information. Reinforcement may be the only logical solution.

Sunday, 3 May 2009

Turkish landslide statistics



Just a short post to point out some interesting statistics on rockslides in Turkey. The source of the data is the General Directorate of Disaster Affairs in Turkey, reported here. The statistics are:
Total area at risk from rockslides in Turkey: 194,000 square kilometres
Number of people at risk: 8 million (11% of the population)
Number of fatalities from rockslides between 1980 and 2000: 177.

Given the high seismic hazard in Turkey, these statistics are quite interesting.

An ancient tsunami in New York

The BBC are running a slightly strange story today about the possibility that the News York area was hit by a tsunami about 2,300 years ago. Given that by far the most likely source of a tsunami is a submarine landslide, this is of some interest. The odd part of this is the timing of the story - I cannot quite work out why it has popped up again now. A very similar story made the news in November last year - see here - and again in December (see here), so I can't quite see what has changed to bring this back to the forefront again. Perhaps a paper regarding this is about to be published - but there is no reference to this in the news report on the BBC.



The BBC news report focuses upon work being undertaken by Steve Goodbred and colleagues at Vanderbilt University in Tennessee. They have identified what appears to be a tsunami deposit from cores across New York and New Jersey. Tsunami deposits are interesting as the wave can transport coarse-grained particles (typically gravels) and even marine fossils from the near continental shelf to deposit them some way inland. Thus, they tend to be quite distinctive. Unfortunately, a major problem is that storm surges associated with very large storms can also bring in coarse shallow marine materials, which means that determining for sure that a deposit was generated by a tsunami is difficult.

In the case of the New York area, a quite extensive deposit has been found. Dr Goodbred and his colleagues suggest in the BBC article that this is probably a tsunami created by a submarine landslide, much like the 1929 Grand Banks (Newfoundland) event.



My sense is that considerable further work is needed here. First, we should all be distinctly pleased that there is no suggestion being made that this tsunami deposit was generated by the ludicrous hypothesis postulated a few years ago by Ward and Day that occasional flank collapses on the volcanoes of the Canary Islands can generate tsunamis that devastate the whole North Atlantic basin. However, the November 2008 news stories centred around a suggestion that a research team from Harvard and Colombia University had found evidence of an impact event origin for the tsunami deposit - i.e. that the wave was generated by a meteorite impact into the ocean. They claim that the deposit contains the types of particles that such an event would generate. I note that there does appear to be some difference in the size of the wave that the teams believe occurred - Goodbred suggests c.5 m, whilst the Harvard team suggest 20 m.

Personally I would like to see some peer reviewed publications on this before we make too much of it. There are a whole series of strands here that really need to go through peer review:
1. The structure of the deposit and its distribution;
2. Its age;
3. Analyses of its origin, looking in particular at its composition (particle mineralogies and sizes, fossil materials; etc), variations in its thickness, the presence of nano-diamonds that are supposedly indicative of an impact event, etc.

Of course the media interest in this is that the potential destruction of New York by a tsunami is rather exciting. We do need to understand Atlantic tsunamis rather better, but there is little doubt that they are really pretty rare and have rather localised impacts in terms of the tsunamis that they generate.