EGU Day 3 - Dave Keefers Sergey Soloviev lecture

On Wednesday morning I attended the presentation by Dave Keefer, the winner of the Sergei Soloviev medal.  Dave has single-handedly defined the field of seismically-induced landslides, an area of great importance.  In the lat five years alone such slides have killed over 50,000 people, and the ongoing landslide activity in the aftermath of big earthquake events means that the legacy of the shaking continues for decades after the main shock.

Dave started by showing that in general losses from natural hazards are increasing both in social and economic terms.  Seismically-induced landslides are a key component of this.  Dave looked at the historic development of research into seismically-induced landslides, dividing the last century into three key phases. The first era was defined as from the beginning of time to 1947, during which time it was increasingly recognised that there was a problem with earthquake induced landslides.  However, documentation of events was patchy in almost every case,

The second era was defined as 1948 to 1988, during which “complete” mapping of landslides was initiated, including the development of quantification of landslide impacts.  He highlighted three key events in this period:

1964 Prince William Sound earthquake in Alaska, which saw landslides over an area of 270,000 square kilometres, causing 56% of the economic losses and at least 45 0f 130 deaths in the earthquake.
1970 Yungay earthquake in Peru that triggered the Huascaran landslide, which killed 6000 people and travelled over 180 km.
1976 Guatemala earthquake ,which triggered over  50,000 landslides over an area 16,000 square kilometres.

Dave used these data to write 1984 paper based upon 40 historic earthquakes with good data across a wide range of magnitudes with a broad geographic distribution.  This paper is of course a classic and, remarkably, subsequent analyses using modern techniques to generate far better datasets have hardly changed the main findings.  It is rarely reported that the study also looked at landslide type, finding that 86% of triggered mass movements were disrupted slides and falls on very steep slopes. 

Dave also highlighted the importance during this period of the development of the Newmark analysis, which then allowed the development of hazard maps over large areas.

Finally, Dave highlighted the modern era, which has seen detailed mapping of landslide events plus site specific data collection, plus some palaeo analyses.  Dave highlighted three key earthquakes:
1989 Loma Prieta, which saw the first GIS based landslide inventory, in this case for the Santa Cruz mountains.  This showed an exponential decay of landslide concentration with distance from epicentre and from fault.
1994 Northridge: similar analyses but more detailed than Loma Prieta, but this time developed to produce a regional scale Newmark analysis based hazard map, calibrated using the actual landslides.
1999 Chi—Chi earthquake in Taiwan, which remains the best studied seismically-induced landslide event of all time.  Most up to date analyses suggest that 13,000 landslides were triggered.  Dave described this events as unleashing an explosion of research on this topic.

Finaly, Dave highlighted the need to overcome our current limitations of knowledge, in particular highlighting a number of research needs:

1.    Urgent need to locate accelographs onto slopes to measure ground motion modification by slope properties;
2.    The need to develop automated mapping of landslides from remote sensing to allow the development of proper inventories;
3.    The need to further develop slope-stability and hazard mapping techniques;
4.    More detailed modelling and analysis of landslide mechanisms
5.    The need for complete mapping and characterisation of a great (M>8) earthquake, when such an event occurs.
In questions Dave highlighted the urgent need for better data from landslide inventories and on site specific effects.

EGU Day 2 - afternoon sessions on vulnerability, plus Italian landslide statistics

In the afternoon of Day 2 I decided to focus more on the human / vulnerability side of natural hazards, and went to two sessions on Social Sciences in Natural Hazards Research.  First up was Katie Oven from Durham, with a number of co-authors , who talked about landslide hazards in Nepal .  Now I was the principal supervisor of this research, but I am going to write about it anyway, so forgive me but understand my bias!  Katie set out to look at some fundamental questions around the interactions between landslides and people in upland Nepal. 

Katie started with the work that we published a few years ago on the occurrence of fatal landslides, which we wrote up for Natural Hazards (paper available here), and in particular on the reasons why Nepal is suffering an increase in landslides.  The question is whether this is due to physical problems – e.g. climate change, deforestation – or human factors – e.g. population growth, urbanisation.  The key issue that underpins this is that landslide vulnerability is far less well understood than is the physical hazard.  So Katie wanted to know who is vulnerable to landslides and why are they vulnerable.   To do this she looked at the upper Bhote Kosi landslide in Nepal.  In this paper she presented three case studies, all of landslide prone communities.  She found that in recent years (the last 20-30 years or so) there has been a major migration of people from  upper hillslope communities to live by the  road.  This changes their exposure to hazard, in particular putting them into the path of high energy flows that are very capable of killing people.  It is clear that people have made a conscious decision to increase their vulnerability to landslide risk because the location decreases vulnerability to other risks – i.e. they have better access to health, education, income-generating opportunities.

So, the key thing is that there is a tendency in the science community to over-estimate the role of natural hazards compared with other risks in the lives of the vulnerable people.  Decisions might appear to be illogical viewed through only the prism of hazards, but once the range other risks are taken into consideration moving into an area of higher hazard looks entirely sensible.  This of course means that we probably need to think differently about how to manage hazards in a way that really works for people.  Unfortunately, all bets will be off when Nepal suffers the earthquake that is well overdue; that is a truly terrifying possibility, but again the risks to individuals need to be considered alongside the everyday risks that the people in this are face. 

The next talk that caught my eye was that of  Marjory Angignard and her co-author looked at now affected people perceive natural hazards.  This study came out of the Mountain Risks training network project of 17 PhD students and post-doctoral researchers across Europe, working together to try to understand differences between public and expert cultures of risk.  The study presented here compared Italian and French perceptions of risk from natural hazards, and found quite large differences not only in the hazard perception (not surprising given that the hazards are different) but also that people’s source of information differed substantively between the two, presumably representing deeper cultural differences. This means that there is no silver bullet that solves the communication problems; for each area the approach needs to be locally tailored.

Eric Lindquist and Katrina Mosher-Howe looked at natural hazard problem and solution definition in the news media, based upon a study of reporting of Tropical Storm Allison in the USA.  Alison brought  five days of rainfall from 5th to 9th June 2001, inducing 22 fatalities, 70,000 houses flooded, the death of 30,000 lab animals in a flooded basement, and $5 billlion of damage.  In particular the storm caused very serious flooding in Houston.  The study looked at 500 news articles on the event from the Houston Chronicle, examining them for variables such as cause, impact, damage, blame, solutions, manifestations of harm, etc. 

A number of things came out.  First, as expected there was a very clear exponential decay in coverage of the event over several years.  Most media attention focussed on home-owners, even though this group was not the most affected.  News articles tended to blame local government, there was little blame to developers because this is a very powerful group in Houston.

Major causes articulated the causes as being associated with physical/topographic factors and drainage problems – i.e. the hazard was seen as an external process imposed on a vulnerable population.  Lots of emphasis was placed on poor infrastructure – e.g. poor drainage, etc.  However, the solutions proposed in the articles focussed on “soft” approaches – i.e. economic, development, social, infrastructure, political changes, and suchlike.

 They then looked at what actually happened in the aftermath of the event.  Interestingly, most of the changes were associated with “hard” engineering – for example Harris County spent $750 million on improvements and the City of Houston spent $250 million.  The soft solutions were poorly resourced.  Thus, there was a mismatch between the proposed solutions and actual answers. 

Very interesting stuff, but I wonder whether that newspaper has a particular political perspective that might have influenced its coverage?

Alessandro Trigila and colleagues focussed on the impact of landslides on urban areas and infrastructure in Italy, based upon the nationwide, amusingly titled but hugely impressive IFFI project.   Some of the statistics on landslide hazards in Italy defy belief:

• The project has documented 480,000 landslides covering 20,700 square km
• Landslides represent 6.9% of the land mass of Italy
• 5708 Italian municipalities are affected by landslides, representing >70% of the total number.  
• 992,403 people are at risk, representing 1.7% of population).
• There are 43,621 hazardous locations along the transportation network.

EGU Day 2 - morning landslide sessions

For this year's EGU General Assembly I intend to only blog on talks that really catch my eye.  This morning there was a fabulous session on Landslide Forecasting with series of great talks.  Of these,  Samuele Segoni and colleagues presented a very interesting paper on a hugely ambitious project to develop a regional landslide warning system for Tuscany based on rainfall thresholds.  The project appears to be extraordinarily successful – it appears to work with very few false alarms or missed forecasts.  However, to do this the area had to be split into 25 warning zones, using c.330 rain gauges.  As most such systems do, the approach uses an intensity – duration power law relationship. Thus, to make these systems work requires a huge infrastructure.  Interestingly, now that it is clear that such a system can work from a technical perspective, the emphasis needs to shift to the societal problems of trying to disseminate warnings effectively, and getting people to react appropriately to them.  That is a real challenge.

The second paper that caught my attention was by Peter Lehmann and Dani Or, looking at precursor events in the initiation of landslides using concepts of self-organised criticality.  Their starting point was that in the home country, Switzerland, 6% of landscape is prone to instability. In 2005 a rainfall event triggered over 1000 landslides, causing damage estimated at over $3 billion.  Essentially they seek to explain landslide initiation by considering processes that provide a cascade effect, as in the sand pile models of criticality.  Here they model the landslide as being controlled by fibres and fibre bundles, which are analogues of the loss of strength of the landslide material.  They showed that precursor events can be observed as weakening and breakage of the bundles occurs, replicating observed behaviour.  It was very neat and very interesting, and provided potentially important insights into failure initiation.

Next up was Nejan Huvaj-Sarihan from Turkey, presenting her doctoral work undertaken at the University of Illinois.  This was an experimental investigation of failure time prediction in landslides, using creep-rupture as the basic concept.  She built a simple direct shear machine to investigate the creep-rupture process, and showed two key things:
1.    She observed creep at even very low shear stresses (<20% peak strength).  She used this to infer that all slopes creep, which is correct;
2.    She could initiate creep rupture failure when factor of safety was greater than one, but that the time to failure depended upon how close to FoS = 1 the system is. 
Using this data she then explored whether failure prediction can be undertaken using the range of techniques available, concluding that it can in all three cases.  This is a very neat study, although I am surprised to see creep-rupture in pre-sheared materials.

During questions someone made the point that there is a “geotechnical disease” to ignore the time element.  This was a very provocative statement, but is quite correct.

Oded Katz and his colleagues followed this up with a model based study that sought to look  material disintegration in controlling the geometry and size of landslides.  Again, this was a neat bit of work that came to some key conclusions.  For me the most important one was that the power law roll-over in landslides is indicative of the change in material properties, and that the collapsing of the power law relationships onto each other occurs because there is such a narrow range of residual strengths available in natural systems.  However, the talk also demonstrated beautifully that failure is associated with breakage of inter-particle bonds.  Initiation of movement in the models occurred only when shear surface was fully developed through bond breakage, which links with the previous three presentations.

Those three talks (Lehmann, Huvaj-Sarihan and Katz) together present an extraordinary level of insight into landslide processes that on their own justifies my attendance at the meeting.

In the after coffee session I would like to highlight just one talk, that of Monique Fort and her colleagues on debris flow initiation in the Ghatte Khola watershed of Nepal.  This watershed suffers extraordinary pre-monsoon rainfall events – she quoted a storm in 1974 that had over 300 mm of rainfall in an hour – can this really be right?  Anyways this small ( 7.8 square kilometre) catchment generates debris flows that result from shallow slides that block the tributary valley, then collapse, creating flows.  These in turn enter the main valley, which is then blocked in turn, and another flow occurs down the main channel.  There are two interesting things here – first, how a small failure can initiate a bigger flow that in turn blocks the main valley, generating an even larger one – who would try to forecast hazards when this sort of situation occurs?  Second, she highlighted the ignorance of road builders in Nepal to these processes, resulting in inappropriate designs that then fail in the next storm.  This is a hobby-horse of mine; I could not agree with Monique more.

EGU presentation on landslide fatalities in 2008

I thought that it would be helpful to make available my Powerpoint file for the presentation that I am giving on the occurrence of landslide fatalities in 2008. This presentation details the fatalities that I recorded on the database over the course of the year, providing maps and tables of some of the data. I hope that you will find it useful.

The file should be visible below:


Uploaded on authorSTREAM by Dr_Dave

And you should be able to download the file from the link above or from the following site:

http://www.authorstream.com/User-Presentations/Dr_Dave/

EGU Day 3

I am just going to write up one session from today's meeting as it contained the most interesting talks that I heard. This was an annual session on landslides induced by volcanoes and earthquakes, the first three talks of which focussed on the Wenchuan event. Regular readers will know that I am very interested indeed in this event (see here for example).

So first up was Ed Harp and two colleagues from USGS. They provided a pretty general overview of the landslides triggered by the earthquake, but supplemented with some very nice satellite imagery of key sites. He highlighted the death toll associated with the earthquake-induced landslides (20,000+) and the huge number of dams that needed clearing (he quoted 33 that required mitigation). The tour included Beichuan, Tangjiashan, etc. I guess there wasn't much new or scientifically-challenging here, but it was a good start. The final part of the talk highlighted the collaboration between USGS and the China Geological Survey, which is going to allow transfer of techniques for seismic landslide hazard analysis, data collation to test the USGS PAGER model and quantification of the sediment flux. In questioning Ed said that the planned seismic hazard analysis tool is Newmark Displacement. I do wonder whether this is the right tool in this part of China - it is probably appropriate for the initiation of the slides, but most of the failures that I saw have lower sections that are very complex, with massive entrainment of slope debris and colluvium. This is where the people and infrastructure are, so it seems to me that without substantial modification Newmark is going to be quite problematic.

Second up was Gorum and his colleagues from ITC. The poor chap had the misfortune of giving his first international conference talk to a packed house about a set of landslides that he had not visited! In that context he did very well indeed. He gave a slightly broader overview, making use of some of the data collected by the Chengdu University of Technology from their mapping. In particular, he highlighted that the landslide are focused close to the fault trace (NB this focus is not on the epicentral region), with many slides on the lower gorges. Using satellite imagery they have mapped an initial 11,308 landslides, compared with 1,638 before the earthquake. They also noted that they had mapped 256 valley blocking slides, with the highest concentration being on the fault trace. They are now working with the Chinese to understand the landslide distribution (very challenging) and to undertake a multi-hazard analysis. I cannot quite see how the latter will be done - the presenter seemed to imply that they will use the existing landslide distribution to drive a modelling exercise. I hope that this is not the case as the seismically-induced landslides will not give a good indication as to where rainfall-triggered slides will occur in a post-earthquake landscape.

The final talk from Wenchuan was by Chigira and his colleagues from Kyoto, with substantial co-authorship from China. This was the best judges of the three, provising a nice summary of the key points issues, well-illustrated using good images. They highlighted the role of dissolution in raising landslide susceptibility - the point being that dissolving limestone beds creates voids that allows drainage of groundwater, reducing susceptibility to rainfall induced slides, but creating point-to-point contacts that increases susceptibility to earthquake induced sliding. This is a nice point. He concluded by looking at some of the very largest slides, concluding that the geomorphology before the earthquake showed depressions and dips on the big slides that indicated that they were potentially unstable. Thus, the biggest slides were considered to be predictable. I am not sure that I agree with the latter point completely (unless all slopes with these features failed, which I don't think is the case), the observations about the morphology are well-made.

The penultimate talk upon which I will comment was by Niels Hovious from Cambridge, with co-authors from Taiwan and elsewhere. Niels used the 1999 Chi-Chi earthquake in Taiwan to examine the distribution of landslides that are generated, and then to look at the production of sediment. First, Niels argues that the landslides closely map onto the distribution of ground shaking, with which I agree, but then argued that the highest landslide density occurs around the epicentre. This may well be true for Chi-Chi, but it was not for one of jis other examples (Northridge) and it was not true for Pakistan, where the highest densities are at the fault rupture. Most importantly, it is also not true for Wenchuan, where again the highest densities lie close to the surface expression of the fault rupture and not around the epicentre. Niels then showed that the density of landslides increased remarkably in the aftermath of the Chi-Chi earthquake - in the Chenyoulan ctachment that they studied the number of landslides before the earthquake was 8123, with a further 3,800 being triggered in the event. However, in the nearly ten years since a further 48,370 landslides have been triggered. However, Niels showed that the sediment concentration in the rivers is now close to base level again, suggesting that the earthquake's impacts are now reducing. This is good stuff but, given that the landscape is affected by typhoons that are exceptionally extreme events one wonders how applicable it is to other places. It seems to me that they need to work in China! An important aside is that this talk does highlight the importance of being prepared for massive sediment production in China.

The final talk that I shall briefly mention is that of Merri and his colleagues from Italy, who are using a finite difference model (FLAC3D to simulate the impacts of magma intrusion on the stability of the Stromboli volcanic edifice. The presentation was quite nice, but the model seems a little flawed. First, it assumes that the volcano is geologically homogenous - volcanoes certainly are not, and given that deposits are layed down in slope parallel layers, this heterogeneity can be a big factor in slope instability. Second, the model appears to ignore pore pressure affects (I asked whether pore pressures are being modelled - the presenter ducked the issue by talking about over-stress. Given that injections of hot material cause increases in pore pressure for certain, and these may well be very important in understanding slope stability - this is a substantial omission.

Comments welcome as ever, especially from the presenters and other attendees. Do feel free to comment if you disagree with what I have written. Finally, apologies for typos, spelling mistakes, etc. The spell check function isn't working and I don't have time to check.

EGU Day 2

The landslide elements of Day 2 at EGU were split between two sessions on landslide forecasting and two on landslide risk. The latter is of comparatively little interest to me, and I had a load of work to do and meetings to attend, so I only attended the morning sessions.

In terms of landslide forecasting, there was some pretty good stuff presented. I would say that some speakers need to think a little more about their audience - using endless meteorological acronyms might work well if you are talking to weather specialists, but when the audience is mostly composed of landslide geologists it is a surefire way to lose the focus of your audience.

The first talk that caught my eye was that of Brunetti and colleagues from Italy, who used datasets culled from the literature to look at the statistical properties of landslide volumes. This sounds pretty terminal, but actually it is interesting as the distribution of landslide sizes in any given area follows a very specific relationship - a so-called power law. The paper examined the caharctersitics of this power law for a range of landslides, finding that there were consistent patterns that appeared to be determined by the mechanism of failure - i.e. soil slides formed a group, irrespective of location, that was distinctly different from the group associated with rockfalls. This felt like a substantial step forward - power lay relationships have been around for a while but we have struggled to understand what this tells us. Detailed studies like this will help greatly.

The next talk was a slightly odd one, by Peter Lehmann and his co-author on self-organised criticality. This relates to the power law issue above, but here the starting point appeared to be that avalanches in a sand pile also show power law behaviour and that this is associated with self-organised criticality. Ergo, landslides occur because of self-organised criticality, which means that the characteristics associated with SOC can be used to look at precursors to slope failure. This step may be problematic because the SOC displayed by sand piles is associated with frictional systems, whereas landslides are generally cohesive. Therefore I remain to be convinced that tje same precursors will occur in SOC for natural slopes. Clearly there is more work to do here, so I will watch with interest. This is one of those things that could be brilliant or it could be very esoteric.

Matthias Jakob went next, talking about the design of a debris flow warning system for N. Vancouver in Canada. His starting point was that given the risk of debris flows some sort of warning system is needed, but the cost of a full blown deterministic system is too high given the area covered. So, using 30 years of very high quality data, they had looked at understanding the relationship between debris flows and rainfall. Interestingly, they have rejected the standard intensity - duration relationship, instead undertaking a discriminant function analysis on the data to find that the three key factors are:

• long term antecedent rainfall (fills up the groundwater stores)
• medium term antecedent rainfall (tops up groundwater)
• short term rainfall intensity (triggers failure)

The upshot was an equation that allows warnings to be issued. Three alert levels will be used (no debris flows, debris flow watch, debris flow warning). The authors thought that on average five warnings will be issued each year, of which two on average will generate debris flows. The system has worked well in trials this year, but it will be interesting to see how the community reacts to so many warnings.

A rather peculiar presentation was given by Thiebes and his colleagues from the Department of Geography at Vienna. The talk was well delivered and the topic was both interesting and scientifically valid. So what was odd? Well, the team are part of the ILEWS consortium that is trying to develop early warning systems for landslides. To do so they have instrumented a landslide in the Swabian Alb area. The aim is to use the instruments to drive an online data collection and analysis tool that incorporates end-user driven modelling via the CHASM code. This is great - and I fully support such initiatives. The odd thing is that the landslide that they are instrumenting has moved 1 cm in the last 2.5 years - this hardly sounds like a slide that needs an early warning system! This is a shame as there are so many slides around that do need such a system.

Serval Miller from Chester University presented a very detailed analysis of a landslide susceptibility mapping exercise that he had undertaken in Jamaica. Interestingly, they had tested a range of GIS based techniques, concluding that a Bayesian Model provided the best results. Second best was a straight forward layer combination model. This was quite interesting, but with this and other presentations on landslide susceptibility analysis I do end up wondering whether the time spent would be better used to provide a geomorphological map that indicated where landslides are considered likely. I wonder whether this would really be any less accurate?

Finally, I would like to note the work of Devoli and her colleagues, who have been trying, with some success, to implement a landslide risk reduction programme in Nicaragua in the aftermath of Hurricane Mitch a decade ago. Although the in-country team is small (three geologists), a huge amount appears to have been achieved through SINAPRED, the national emergency commission. This presentation highlighted two web resources that are well worth a look:

Georiesgos-ca.info, which provides georisk information across all of Central America (in Spanish)
http://mapserver.ineter.gob.ni/website/mapas/Estudios/viewer.htm, which is a mapping server that provides access to hazard maps for Nicaragua.

Updated: European Geosciences Union Day 1

Updated to include the afternoon sessions
This week is the annual European Geosciences Union assembly in Vienna. This is the biggest annual landslide meeting - there are >300 landslide related papers this time around - and since I am the scientific secretary for the landslide session I cannot allow the opportunity to comment on what I see to pass. So here are my thoughts on Day 1. My intention is not to comment on everything that I see, but instead on those that I found interesting.

Morning sessions
The first, unfortunately poorly attended, session focused on landslides associated with loess deposits. Dr Meng and colleagues from China presented a very well illustrated overview of landslides on the loess plateau. There were some remarkable statistics - for example, in the 20th Century over 60,000 people were killed by loess landslides in China, whilst in Gansu province alone in the decade between 1875and 1985 there were over 1000 disastrous landslides, killing in total >2000 people! Interestingly, the key factor determining the spatial occurrence of landslides was the neotectonic activity - areas of active uplift have far more slides than those that are subsiding, presumably because of undercutting and oversteepening during incision. The presence of sinkholes was also shown to be rather important.

Mamyrova and her colleagues presented a paper on the investigation of the mechanics of two loess landslides in Kyrgyzstan, a place about which we here far too little from a landslide perspective. She presented some rather nice repeat pass Quickbird imagery to show the evolution of the landslides, demonstrating in particular that one of the slopes showed clear tension crack development before the main failure event. Perhaps most interestingly, the initiation of the main failure event occurred in a wet, but not exceptionally wet, year (1994). A month or so earlier there was a magnitude 3.9 earthquake just 17 km from the landslide. The authors speculated as to whether this might have played a role. This project is clearly in its early stages, but the combination of an under-reported area, a very strong research team and an aspiration to combine FLAC (finite difference) and PFC (discrete particle) modelling makes it one to watch for sure.

Later in the morning, in a far better attended session (I ended up sitting on the floor!), there was a very nice presentation by Dewez and his colleagues frim BRGM in France on the use of terrestrial laser scanning to look at coastal cliff hazards in chalk. In many ways this mirrored the work that my colleagues and I do on cliffs in NE. England and, unsurprisingly, the results were similar. Over about 1 km of cliff, and scanning from eight stations, the survey picked up 8567 individual rockfall events. The most interesting thing for me was the investigation that they had done of the role of large vs small events in erosion on the cliffs, showing that over this time a single large event contributed 85% of the volume change, and that 99.8% of the volume change comes from rockfalls that are >1 cubic metre. This is quite a different result from our observations in layered sedimentary rocks in N. Yorkshire, emphasising the role that geology plays. It should be noted though that the comparatively short duration of this study (ours is >twice as long) may mean that the results are biased by the large events that happened to occur. The authors recognised that there is a need to extend the time-base - I do really hope that this is possible as the development of long datasets is crucial if we are to understand rockfalls properly.

Travelletti and his colleagues, also from France, presented a study of the use of terrestrial laser scanning for the monitoring of a large mudslide - in this case the Super Sauze slide. In my view the application of TLS for monitoring this type of slide is too rarely presented. In this case they have used the system to look at the evolution of the steep source area and to examine the movement of the toe of the flow. Both were pretty convincing, but I was particularly impressed with the work that they had done tracing the movement of boulders to generate displacement fields. In some cases they saw 16 m of movement in a single summer, which is far greater than the c.0.25 m error in the technique at this location. This is looking like a mature technique now that really justifies more extensive use.

Afternoon
The afternoon landslide sessions focused upon geophysical techniques, many of which are a little beyond my area of expertise. I will comment on a couple of presentations though. A general point to note is that, as the chair of the session pointed out, geophysical approaches to landslide analysis have moved from being rather esoteric and obscure to generating quite a lot of interest in a very short period. This is primarily because these techniques are increasingly good at discriminating between different types of wet sediment and debris, which means that they are useful. However, I do note that the presentations that I heard were on the whole about the geophysics, and not about the landslide, so these methods are not really in the mainstream yet.

There were two presentations on the Trieve landslide complex in France, the first by Kneiss and the second by Renalier. The former focused upon the use of seismic noise to map out the subsurface geology of the slope. In particular, they used a technique that they called the H/V method to delineate the soft sediment – bedrock boundary. The story was pretty nice in that the 3D topography that they showed explains the dynamics of the movement, although it does seem to be based on a slightly simplistic view of the mechanics of the slides. Personally I would like to see some verification of the 3d model (perhaps a couple of extra boreholes to see if they can predict where the drill will meet rockhead), but overall it is a pretty nice piece of work. The second was by Florence Renalier, who was a little nervous I suspect, but did a good job (well done if she reads this). The intriguing result here was that they showed that shear wave velocity is inversely correlated with displacement rate for the landslide that they studied (in the same complex as the previous paper). That seems to me to be a pretty fundamental result, but it was not really dwelt upon. In questions the team said that they think that the shear wave velocity is related to microcrack density. I would like to hear a lot more about this to be honest.

The next paper that caught my eye was by Clara Levy and her colleagues, also from Grenoble (are they trying to corner the market in research level landslide geophysics?). This was a study of the seismic precursors to a rockfall that occurred from chalk cliffs in 2002. By luck or good design (or both) the team had a seismic network in place before the 2000 cubic metre failure occurred. It was collecting data at 30 kHz, which must be a mind boggling dataset, but what they captured was 200 seismic events in the 2 hours before the collapse. They attribute this to breaking of the remaining rock bridges (which seems reasonable). They have tried to model this effect, but have chosen to do so with a Mohr-Coulomb failure model, which is perhaps not ideal. Nonetheless, the model does show how the failure propagates through the rock bridges, with those at the toe of the slope being the last to go. The model is I think not really faithful to reality, but it is an interesting piece of work.

Finally, Arnhardt and his colleagues from Aachen decided to break up the French – Italian axis by presenting a paper looking at the use of low cost sensor networks for monitoring landslides. This is highly worthy work, but I seem to have heard numerous similar presentations, all of which come to nothing. The problem is that the low cost sensors in question are usually designed for use in nice, controlled, clean, stable environments (like in cars, high tech production lines and hospitals). Landslides are the exact opposite – wet, cold (or hot), dirty and mobile, which means that the sensors that work so well in the lab really don’t function well. This is the same issue that Pen Hadow and his friends are having in their misjudged nightmare in the high latitudes. I guess someone will crack this problem in the end – and the team from Aachen seem sufficiently serious to be the ones to do it – but I do hope that they realise just how hard it will be. I really do wish them luck and will watch their progress with interest.

Overall it has been an excellent day (thanks to all the speakers), with some great science presented. Tomorrow we have two sessions on landslide forecasting and two on landslide risk. I can’t wait!

Landslide sessions at EGU in 2009

Around this time of the year I always start to turn my attention to the European Geociences Union meeting in April. This is a huge get-together of earth scientists from around the world (last year >8,500 people attended). One of the largest divisions is "Natural Hazards", and the landslide section, of which I am the secretary, is the biggest single part of NH. Next year (2009) the meeting will be held in Vienna on 19th-24th April and it looks to be the best yet - we have seventeen proposed sessions for which we are inviting abstracts. These are as follows:

NH4.1/GM6.3: Landslides, ground-failures and mass movements induced by earthquakes and volcanic activity
Convener: V. Del Gaudio | Co-Conveners: R. W. Jibson , D. Keefer , J. Wasowski

NH4.2/HS11.7: Hydrological processes in landslide research: analysis and quantification
Convener: T.A. Bogaard | Co-Conveners: L. Borgatti , F. Lindenmaier , J.-P. Malet , E. Zehe

NH4.3: Landslides Triggered by Rainfall Events
Convener: K.-t. Chang | Co-Convener: M. Borga

HS11.1/NH4.4: Rainfall triggered landslides and debris flows and their effect on erosion and sediment yield in river catchments
Convener: J. Bathurst | Co-Conveners: G. Crosta , P. Frattini

GM6.2/NH4.5: Processes and rates of rock slope erosion: weathering, detachment, and transport
Convener: JR Moore | Co-Conveners: M. Krautblacher , S. Loew

NH4.6: Hydrological, hydraulic and mechanical effects of plants for slope stability
Convener: F. Florineth | Co-Conveners: F. Graf , H. P. Rauch , F. Rey

NH4.7/HS2.7: Natural and anthropogenic hazards related to water reservoirs
Convener: J. Rohn | Co-Conveners: L. King , T. Scholten

NH4.8: Large slope instabilities: from dating, triggering, monitoring and evolution modelling to hazard assessment
Convener: G. Crosta | Co-Conveners: L. H. Blikra , M. Jaboyedoff , O. Korup

NH4.9: Landslides monitoring and characterization using high resolution DEM, LIDAR and other DEM techniques
Convener: M. Jaboyedoff | Co-Conveners: R. Couture , M.-H. Derron , C. Froese

NH4.10: Impacts of climate change and land-use change on landslides
Convener: J. Wasowski | Co-Conveners: T. Dijkstra , N. Dixon , M. Winter

NH4.11: Time and intensity prediction in landslide hazard assessment
Convener: F. Catani | Co-Conveners: J.-P. Malet , J. L. Zezere

NH4.12: Remote sensing and geophysical techniques for investigating unstable slopes
Convener: J. Wasowski | Co-Conveners: V. Del Gaudio , H.-B. Havenith

NH4.13: Terrain Instability Analysis and Mass Movement Prevention
Convener: X. Meng | Co-Conveners: J. Ma , D. Wang

NH4.14/HS11.6: Landslide Forecasting
Convener: F. Guzzetti | Co-Conveners: G. G.R. Iovine , M. Parise

NH4.15: Landslide risk assessment methods and strategies
Convener: P. Reichenbach | Co-Conveners: A. Guenther , F. Guzzetti

NH4.16: Documentation and monitoring of landslides and debris flows for mathematical modelling and design of mitigation measures
Convener: L. FRANZI | Co-Conveners: M. Arattano , F. Tagliavini

NH4.17: Rockfalls - Analysis, Simulation and Protection
Convener: A. Volkwein | Co-Conveners: F. Berger , L. Dorren

This covers a vast range of landslide topics. Details are available here. Abstracts need to be submitted by 13th January 2009. Please do come along and join in!

EGU Day 4

I spent the morning in the session on the Characterization, monitoring and early warning related to large landslides. I was struck during the presentations by the degree to which the technologies for monitoring landslides have improved over the last decade or so. For example, Casagli and his colleagues gave a very polished presentation on the application of their ground-based radar LISA to the monitoring of the Ruinon landslide near to Bormio in Italy. This system, which costs about 100,000 Euros per annum to buy and operate, can produce a map of deformation with a 1 mm movement resolution at ranges of up to 1.8 km. In this case it is being used to monitor the movement of this somewhat hazardous slope failure to great effect. On the other hand, David Toll (a colleague from Engineering at Durham) presented the results of a new set of high precision tensiometers that are capable of measuring suction forces down to -2 MPa, a significant step forward for tropical soils for example. Thoeny and his collegaues introduced us to the use of dynamic fluid electric conductivity logging, which looks at changes in the electric consuductivity of saline water introduced into a deep boreholed drilled through the landslide. This technique was able to determine the locations at which water is entering and leaving the borehole, which gives a good indication of the location of, for example, the shear surface. This looks like a complex technique, but one that shows a great deal of promise once fully developed. The problem would seem to be the rather cumbersome and specialised processes involved in saturating the hole with saline water. I will watch this development with interest. Glimsdal et al. presented the results of tsunami modelling for the same slide as Thoeny, the Aknes landslide in Norway. The danger is that a large failure would trigger a tsunami that would rapidly inundate local villages. The paper introduced the initial results of modelling a potential tsunami. This is clearly work in progress, but looks interesting.

To me the key issue was highlighted by the paper of Ronchetti and colleagues, who attempted to analyse the data obtained from monitoring of a very large earthflow on Mount Modino near to Modena in Italy. They attempted to use the so-called Saito approach, which I have worked on extensively, to see whether prediction of the failure of the landslide was possible. The paper itself was interesting and there was some sign that movement could be used in this way. However, the data proved to be very noisy, such that identifying trends in real time would be an awesome challenge. This issue that this highlights is that we desperately need to develop better ways to analyse the data that wed are producing. At this meeting it has been clear that analysis is lagging well behind data production. This is surely the next challenge. I have been working with three first class PhD students - Angel Ng, Jon Carey and Chris Massey, all of whom are making really substantial progress in this area for landslide movement at least. It is clear that this is a fertile area for development and that considerable more work is needed.

In the afternoon, I attended the sessions on Rockfalls and large catastrophic landslides. This was a bizarre session in that the quality of the science presented was exceptionally variable. I won't go into detail regarding the weaker end of the spectrum. At the strong end, I was taken by a couple of presentations in particular. Pichler and his colleagues presented a very comprehensive and detailed analysis of the threat to hydrocarbon pipelines associated with rockfalls. This included dropping large boulders 20 m from a crane onto a gravel pit to see what happened, wich looked great fun at least! The result of the subsequent analysis was a clear demonstration that a 3 m thick layer of gravel placed over the pipeline is enoough to protect it against a 10 tonne boulder falling from 100 m, which would seem to be a rather valuable thing to know! Meanwhile Sausgruber presented a great paper on a massive (1.3 cubic km) ancient kink band landslide in Austria. This slide has in the past moved about 60 m, but the computer model of the slides showed that development of flexural toppling has mobilised shear strength between the beds, which has effectively stabilised the slide. Waldmann and his colleagues reported attempts to model the potential generation of a landslide induced tsunami in Nordfjord in Norway, based upon the development of failure scenarios plus an analysis of two earlier events, one in 1905 (which killed 61 people) and one in 1936, which killed 74 people. Historic photos suggest that the earlier events had a run up height of up to 33 m, illustrating the threat posed. Again, this is work in progress, but it is a very nice piece of research. Finally, Agliardi and his colleagues have untaken the massive task of mapping deep seated gravitation slope deformations (these are massive creeping slope failures that occur in high mountain areas). The study is notable because:
1. It has made use of Google Earth as a primary data source, which shows waht a fantastic resource this has now becaome;
2. The task is epic - it took the individual concerned 2 months to do the mapping alone, which must have been somewhat tiresome;
3. The statistical analysis of the results show very nicely that these types of failure represent a part of the spectrum of mass movement types, and are not a seperate class of landslide in their own right.
Again, there is probably more to do here, but the study is really valuable and needs to be continued.

All-in-all a most interesting day. Once again I was struck by the tremendous range of material presented and by the very high quality of the science in general.

EGU day 2

Day 2 of EGU had less of interest to me than Day 1. I started out in the Historical Landslides session, in which my paper was the first. Most of the other five presentations were excellent. Notable amongst these was a paper by Jan Klimes and his colleagues on the landslide threat to Macchu Micchu. In recent years there have been some fairly lurid headlines about the threat to Machu Picchu as a result of landslide activity. An example is this from the BBC in 2001:

Machu Picchu 'in danger of collapse
Geologists have warned that the ancient Inca fortress of Machu Picchu in Peru is in danger of being destroyed by a landslide...Now, geologists from the Disaster Prevention Research Institute at Kyoto University have warned that the site may be in danger of collapsing.They have found that the land is sliding down at a rate of about one centimetre (0.4 inches) a month. Scientists say this is quite fast and is a precursor to a major landslide.

Pretty scary stuff, especially the part that says that this is a prfecursor to a major landslide. Klimes made a very measured presentation in which he first showed that this is an area with a large number of neotectonic features - which means that care is needed in the interpretation of features in the landscape. He then presented the results of high quality monitoring of the movement of the deep-seated landslides at Machu Picchu. The data clearly showed that the level of movement was orders of magnitude than that suggested above - in fact no more than 2 mm per year (and often less than that). He concluded that these are probably surface movements and that there is no evidence of movement of deep-seated landslides as has been suggested before. It should be noted that the teams monitoring has used more than one tried and tested technique over a prolonged period.

The team deserve great credit for taking on this task and for showing that the threat at Machu Picchu is massively over-stated. One can only hope that the other teams that have been dedicating so much resource to this issue now focus their attention on the real problem in Peru, which is the multiple active landslides that regularly kill and injure the poor population. Addressing these slides could actually make a difference.

In another presentation, Cees Van Westen from ITC showed the sort of thing that is needed. He
presented the work of his team in trying to assess landslide hazard in Guantanamo Province of Cuba. The approach used was to assess the runout of a (very) large landslide from 1963, and to use the parameters derived in a model to assess the likely runout, and thus the risk, associated with other landslides from the same ridge. The study was very impressive and detailed. The approach is not problem-free, but represents one of the most credible attempts to do this sort of thing that I have seen.

Later on I attended talks in the session focussed on the use laser scanning and DEM analysis for the evaluation of slopes. Laser-generated DEMs are probably the biggest single advance ion landslide studies in the last decade. A few years ago when my colleagues Nick Rosser and Mike Lim presented the results of their work using this technique there was a sort of stunned amazement. Now almost everyone uses it. However, I was slightly dispirited by the simplicity of the analyses being generated. In most cases the output seemed to be little more than slope maps and displacement records. The beauty of laser scanning is that we know that the structural and movement data that it can generate tells is a huge amount about what is happening inside the slope itself. It is in many ways like an X-ray of a broken bone, and a similar level of analysis and interpretation is needed. These techniques tell us about mechanisms and processes, and there is an urgent need to look at the data properly.

Tomorrow I won't be at the conference as I have to attend an editorial board meeting, so my next post will be on Thursday.

EGU day 1

Over the next few days I will try to write up some comments on issues that arise at the landslides sessions at the European Geosciences Union (EGU) meeting in Vienna. EGU is a massive meeting (c. 10,000 earth scientists), and the natural hazards section is one of the largest. The landslide field is the biggest component of natural hazards, so there is usually something for everyone. In total there are about 240 talks in the landslides sessions, so I clearly won’t comment on them all! I will instead focus on the matters that arise that interest me in a purely selfish way.

The first session on Monday was on remote sensing techniques and slope failures. Unfortunately I missed it as I was trying to track down my luggage, which once again had been lost by British Airways. Thanks to them once again - there are times when you make me so proud to be British. Oh, and by the way, if Terminal 5 is the answer to Heathrow's problems then I do have to ask what on earth the question was...

I did make it to the second session, which was on a combination of the role of vegetation on slope stability and on landslides and climate change. All six talks were of a very high standard – clear and concise, and covering a good range of material. I am intrigued by the paucity of papers on landslides and climate change, given that this is the topic of the moment. One paper that did address this issue head on, a presentation by Remaitre and colleagues looked at the impact of climate change on shallow and deep landslides in the French Alps. The results were refreshing as they indicated that projected climate changes will reduce the occurrence of slope movements due to a drop of 1-3 m in the groundwater level. Far too rarely do we hear of positive impacts of climate change, but here they are clear.

The previous paper, but Guthrie and colleagues, looked at landslide occurrence on Vancouver Island in Canada as a result of climate change. Whilst this was an interesting approach, the analysis was on the whole a bit over-simplified I think. However, the paper did very clearly highlight the ways in which logging triggers slope failures, demonstrating that clear cutting increases the occurrence of landslides by an order of magnitude or more in this steep, wet environment. The other presentations sought to try to understand why and how vegetation improves slope stability. All were highly competent, but it is clear that more work is needed given the spatial and temporal complexities involved.

All of which seems to highlight the fact that climate change is important, but land use change is much more so in the context of landslides. We should therefore be deeply alarmed by the current situation, in which concerns about climate change are driving land use changes to allow the production of biofuels. For example, felling of forest for palm oil plantations in tropical areas would seem to be deeply unwise. In addition, we are currently seeing massive increases in food and fuel prices, which is also likely to drive increased rates of forest loss.

The first session in the afternoon focussed on landslides triggered by earthquakes. A common theme emerged in terms of the role of topographic amplification in landslide triggering (this is the way in which earthquake waves interact with slopes to cause higher levels of ground shaking, which in turn triggers slope failures). Lee and colleagues presented an investigation of slope failures triggered by the 1999 Chi-Chi earthquake in Taiwan, showing that position on the slope (i.e. proximity to the crest) is the key issue in terms of triggering failure. Meunier et al presented a rather more conceptual analysis that agreed with this, although the topographic role was less strong than some maintain. The latter seems to be let down by the use of the full length of a landslide feature – presumably including the deposit - when really only the source zone should be used. This inevitably biases the results towards the foot of the slope. The observation that slope failures might be more likely on slopes orientated away from the epicentre is interesting, but is not supported by all earthquake events. My own observations from Kashmir do not support their suggestion that landslides cluster around the epicentre either, so I think rather more work is needed here to make this analysis convincing.

Two other presentations in the session focussed upon landslides triggered by MW=7.9 the 15^th August 2007 earthquake in Peru. Wartman and his colleagues focussed primarily on an impressive lateral spread that has in places moved by in the order of 20 m. The surface area of this failure is several square kilometres. Joseph Wartman has pictures of some of the landslides triggered by the earthquake linked from his web site, including a narrated slide show. Hermanns and his colleagues reported on landslides triggered by the same earthquake, but raised a different but very interesting issue. This part of the Andes is littered with large, ancient landslides and rock avalanches, which occur on both the coastal bluffs and in the high mountains. Hermanns noted that this earthquake actually triggered surprisingly few large landslides – and indeed no rock avalanches. What sized event is therefore needed to trigger the landslides that observed – is does this require a different type of event (e.g. a crustal earthquake). There are no answers to this at the moment, but it is a question that needs to be investigated urgently. Dating the ancient landslides, which should be possible for the rock avalanches at least using cosmogenic techniques, would be a good start.

The final session of the day was the Union meeting on forecasting natural hazards. Fausto Guzzetti gave a masterclass on assessing landslide hazard and risk, provoking a lively round of questions. The following speaker, who was talking on a non-landslide topic, impressed me rather less, so I called it a day.

I have the rather unlucky task of starting the first session tomorrow at 8:30 am – I am not expecting a big crowd!