Landslide Hazard and Risk

The case study presents an example of impact delivered via a project to assess landslide risk in Hong Kong undertaken by the UCL Hazard Centre. The work originated through a client (large UK insurance company) of Aon Benfield requesting to understand more about non-modelled perils (landslides, volcanism and earthquakes), which are not included in commercially available catastrophe models.

Recognising that Hong Kong is susceptible to landslides and has high insurance exposure, the project investigated the risk posed by landslides to the client’s exposure in the territory. The process involved developing a methodology for assessing landslide risk, and this used the results of EU Project RUNOUT that was coordinated by Dr Christopher Kilburn in 1998-2000. The key element of this research that was used was the theoretical basis for calculating the runout of landslides from the volume of the initial instability, which allowed estimates of areas of potential inundation from future landslides to be made.

The methodology used for assessing landslide risk in Hong Kong utilised the results of EU Project RUNOUT, which modelled catastrophic, large-volume landslides (sturzstroms) by investigating landslide dynamics and emplacement. The paragraph that follows is an extract taken from the executive summary of the results from Project RUNOUT, and it underpins the methodology developed for Hong Kong landslides.

“Applied to rapid large-volume slope movements, limits to dynamic regimes in granular flow have been quantified by scaling analysis and computer simulations. The essential features of sturzstrom emplacement can be explained if they lose kinetic energy through viscous deformation in one or more basal boundary layers. The boundary layers consist of rock fragments in a fine grained rock matrix. Crushed by the weight of overlying rock, the basal matrix acts as a viscous fluid. Comparison with results from computer simulations yields constraints on programme algorithms. During collapse itself, basal resistance is small compared with the gravitational force driving movement, so that there is a nearly perfect conversion from potential to kinetic energy until the landslide runs out on a subhorizontal surface. The new analysis provides a physical justification for using the volume of unstable material to forecast the potential runout length of a sturzstrom.”

The landslide volumes examined in Project RUNOUT were mostly of one million cubic metres or greater. The Hong Kong landslide project successfully demonstrated that the volume–runout relationship developed in Project RUNOUT can be meaningfully extrapolated to smaller volume (≤100,000 m3) landslides and be used as a general predictor of the length of landslide runout and area of potential inundation. Two UCL MSc projects undertaken in 2011 have also demonstrated that this relationship holds for smaller volume landslides in study regions in Australia, New Zealand and north-western USA.

Related Links:

• Kilburn CRJ, 2007. Giant catastrophic landslides. In, Sammonds PR, Thompson JMT (eds), Advances in Earth Science, Royal Society Series on Advances in Science 2, 213-228.
• Kilburn CRJ, Pasuto A, 2003. Major risk from rapid, large-volume landslides in Europe (EU Project RUNOUT). Geomorphology, 54, 3-9.
• Kilburn CRJ, Petley DN, 2003. Forecasting giant, catastrophic slope collapse: lessons from Vajont, Northern Italy. Geomorphology, 54, 21-32.
• Kilburn CRJ, 2001. The flow of giant rock landslides. In, Breigel U, Xiao W (eds), Paradoxes in Geology, 245-265. Elsevier 467pp.
• Kilburn CRJ, Sorensen SA, 1998. Runout lengths of sturzstroms: the control of initial conditions and of fragment dynamics. Journal of Geophysical Research, 103, 17,877-17,884.