2 November 2022
The role of atmospheric pressure in landslide triggering
Posted by Dave Petley
The role of atmospheric pressure in landslide triggering
A few years ago there was considerable surprise when high resolution monitoring of the Slumgullion landslide in the United States found that atmospheric pressure played a role in controlling movement. There has been some interest in this behaviour since – for example, it has not been clear as to whether Slumgullion is an exception. Is the stability state so marginal in this case that tiny fluctuations in inter-grain pressure affect stability – or has this type of response been missed because of the low resolution of most monitoring?
A new open access paper in the journal Natural Hazards and Earth System Science (Pelascini et al. 2022) has investigated this phenomenon in more detail. The test site was in Taiwan, which I have always considered to be the world’s greatest landslide laboratory (as well as an amazing place to visit). The weather conditions that drive the investigation were typhoons, which are really interesting because they bring both extreme rainfall and comparatively large fluctuations in atmospheric pressure. The researchers have used a model to explore the slope response to changes in pressure, driving by measured changes in pressure from the typhoon events.
The diagram below, from Pelascini et al. (2022), illustrates the potential drivers of the landslides. The graph on the left shows peak rainfall intensity for a range of typhoons in the study area plotted against the atmospheric pressure drop, with three key typhoons highlighted. On the right, the time series for the change in atmospheric pressure and the rainfall is shown for the three typhoons and a synthetic event.
(From the paper): (a) Typhoons over Taiwan sorted as a function of their maximum rainfall intensity and atmospheric pressure drop. The hydrological context is represented by the colour scale, showing the cumulated rainfall over the 6 months before the event. (b) Time series of rainfall and atmospheric pressure changes of the three typhoons and the synthetic event created from the average of every typhoon. Figure from Pelascini et al. (2022).
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When this data was fed into the landslide model, interesting results merged. Not surprisingly, the rainfall infiltration was able to induce large changes in pore water pressure, which are of course important for stability. However, the effects were delayed by hours or even days due to the time required for pressure change to diffuse through the soil. On the other hand, the atmospheric pressure changes were much smaller, but the impacts on the soil were instantaneous.
Pelascini et al. (2022) have made an interesting observation in that typhoons occur in or after the wet season in Taiwan, when slopes are already saturated. I would be interested in understanding the data that supports this key assertion. But, if so, then something else must finally trigger the landslides in the typhoon event. Their modelling suggests that this might be the atmospheric pressure drop.
This is a fascinating result. Of course, in the real world, this is a complex phenomenon, and the authors are careful to note the need for more research. In a typhoon, triggering will be controlled at the first level by rainfall – the slope will not fail until the pore water pressures are high – but Pelascini et al. (2022) have highlighted that the factor that might finally induce failure is the reduction in atmospheric pressure as the eye of the storm passes over or close to the slope. In a sense, the atmospheric pressure is the straw that breaks the camel’s back.
There is one other observation that is interesting in the paper. The models suggest that storm triggered landslides tend to initiate at the toe of the slope. This has been postulated previously, but it is good to see further evidence.
Overall, I think that this study is a really fascinating contribution, providing further evidence of the complexity of landslide initiation. It should be the trigger (if you’ll excuse the pun) for a range of studies involving slope scale monitoring and modelling, as well as landscape-scale investigations. I shall look forward to seeing further work in this area in the coming years.
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Reference
Pelascini, L., Steer, P., Mouyen, M., and Longuevergne, L. 2022. Finite-hillslope analysis of landslides triggered by excess pore water pressure: the roles of atmospheric pressure and rainfall infiltration during typhoons. Natural Hazards and Earth System Sciences, 22, 3125–3141, https://doi.org/10.5194/nhess-22-3125-2022.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
If the profile of matric suction with depth in the slope mass can be monitored together with the change of external atmospheric pressure above the slope surface, then it shall shed better light to understand the net change in interparticle stresses as a trigger to the slip. Sudden drop of 2 to 4kPa in atmospheric pressure is equivalent to 200mm to 400mm rise in phreatic surface in effective stress for deeper slip surface or reduction of effective stress in the vadose zone at shallow slope surface.
If I recall correctly, effective stress is total stress minus water level. A drop in atmospheric pressure (total stress) is an increase in effective stress. If the slope is near failure, that could do it. Put some pressure sensors in there recording pore pressure and barometric pressure.
Had another idea. This might be useful. http://pubs.usgs.gov/misc/FISC_1947-2006/pdf/1st-7thFISCs-CD/7thFISC/7Fisc-V1/7Posters.pdf Feel free to contact me. I have some of these left over.
During the last decades I took an interest in measuring pore water pressures in slopes in low permeable soils. My latest paper was published at ISFMG in London in September 2022:
https://www.issmge.org/uploads/publications/80/112/3._Shulze.pdf
In this paper guidance is provided on pore-water pressure measurements and compensation of atmospheric pressure effects. Detailed discussion would be appreciated.
Together with my former colleague H.-J. Koehler I was involved in spreading the idea worldwide, that falling atmospheric pressure may lead to the triggering of landslides in unstable slopes.
The current paper of Lucas Pelascini et al. deals with same idea.
Back in 1999 together with my colleague H.-J. Koehler we stated at ECSMGE in Amsterdam:
“[…] which suggests a connection between falling barometric pressure and landslide triggering. The instrumentation of an active landslide is briefly described. The acquired data lead to the introduction of falling barometric pressure as a novel and often decisive factor of landslide triggering.”
…and at FMGM in Singapore:
“[…] the fact needs to be acknowledged that changes of barometric air pressure play an important role concerning soil behaviour especially in low permeable soils. A connection between falling bar-ometric pressure and landslide triggering in unstable slopes is shown.”
Further information was provided at ISL in Cardiff in 2000:
“[…] that variations of barometric pressure acting on a slope may also influence pore water pressure conditions. Under certain conditions this effect may be decisive in triggering landslides. Own exten-sive field measurements have been performed in unstable clay slopes. In this paper recent results will be presented of these measurements in progress as well as results of back calculations.”
…and at FMGM in Oslo in 2003:
“[…] measurements and calculations suggest barometric pressure to be a new factor in slope stabil-ity. A further application of this concept suggests a pore water pressure release technique to stabi-lise slopes in low permeable soil.”
Bibliography:
Download of the papers at
http://hj-koehler.de/public/PublikationslisteK%f6hler092013.pdf
Schulze, R. & H.-J. Köhler 1999. Landslides in overconsolidated clay – geotechnical measure-ments and calculations. In F. B. J. Barends et al. (eds.), Geotechnical Engineering for Transporta-tion Infrastructure – Proc. 12th European Conference on Soil Mechanics, Amsterdam, 7-10 June 1999, 601-608. Rotterdam: Balkema.
Köhler, H.-J., R. Schulze & I. Feddersen 1999. Influence of barometric pressure changes on slope stability – measurements and geotechnical interpretations. Proc. 5th International Symposium on Field Measurements in Geomechanics, Singapore, 1-3 December 1999, 381-386. Rotterdam: Balkema.
Köhler H.-J. & R. Schulze 2000. Landslides Triggered in Clayey Soils – Geotechnical Measurements and Calculations. Bromhead et. al. (eds.), Proc. 8th International Symposium on Landslides, Cardiff (Wales), UK 26-30 June 2000, 837-842. London: Th. Telford.
Schulze, R. & H.-J. Köhler 2003. Stabilisation of endangered clay slopes by unconventional pore pressure release technique. Proc. 6th International Symposium on Field Measurements in Geome-chanics, Oslo, 15-18 September 2003, 347-353, Lisse: Balkema.
Schwab, R., H.-J. Köhler & R. Schulze 2004. Pore water compressibility and soil behaviour – exca-vations, slopes and draining effects. Proc. Skempton Memorial Conference, London, March 2004, 1169-1182, ISBN 0 7277 3264 1, Thomas Telford, London.
Schulze R. 2022: Influence of pore-water pressure and deformation effects on the long-term sta-bility of cut slopes in overconsolidated clay. Proc. 11th International Symposium on Field Monitor-ing in Geomechanics ISFMG, Imperial College, London, September 2022.