15 April 2008

EGU day 2

Posted by Dave Petley

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.