Category Archives: News

Inventory of shallow and spontaneous landslides and improvement of the methodology to establish hazard and risk maps for the Canton of Vaud

On contrary to hazards which have defined return time for establishing natural hazard maps (for example rock falls or floods), there is no similar methodology for shallow and spontaneous landslides. One way to improve the current methodology is proposed by Cedric Meier,  Marc-Henri Derron, Michel Jaboyedoff from RISK-UNIL and Christian Gerber, Veronica Artigue and Melanie Pigeon from the Vaud county administration. It includes the definition of 7 pilots zones based in Jura, Plateau and Alps, on riverbanks or mountain slopes. Based on the new airborne LiDAR acquisition, a former inventory from 1889 to 2013 and basics documents such as geological and topographical maps, air photos, about 110 landslides were registered.

Shallow landslide in the area of Ollon in 2018

The parameters of the source zone of the landslide, like length, width, estimated depth, area, slope angle and propagation angle (Farböschung) were recorded. For each landslide, 3 different volumes (with half-ellipsoid method, elliptical paraboloid method and Sloping Local Base Level or SLBL method, method developed and applied currently at the Institute of Earth Sciences, ISTE – UNIL) were calculated. A volume-frequency distribution, approximated by the Power Law site specific, but also depending on the slope type was developed. Figures showing the probability of the estimated depth or the volume depending on the area of the source zone were also prepared. For the propagation, only 4 % of the landslide have a propagation angle greater than 13°.

 
Probability of max depth in function of the surface area of the landslide

REFERENCES

Jaboyedoff M., & Derron M.-H. 2005: A new method to estimate the infilling of alluvial sediment of glacial valleys using a Sloping Local Base Level, Geogr.Fis.Dinam. Quat., 28, 37-46. 
VD (2017) : http://www.geo.vd.ch/theme/dangers_nat_thm

Hydrogeochemical characterization of alpine spring waters

With Hans-Ruedi Pfeifer (Hon. Prof. at the University of Lausanne), I had the pleasure to publish a paper in the Bulletin de la Société Vaudoise des Sciences Naturelles on the chemical composition of alpine spring waters. This paper is a review of water analysis (major and trace elements) according to the type of bedrock forming the catchment.

Although it is published in French, an extended abstract in English is available and reproduced below, with references to the most significant figures.

Derron M.-H., Pfeifer H.-R (2017) : Caractérisation hydrogéochimique des eaux de source alpines. Bull. Soc :Vaud. Sc.Nat, 96, 5-29.
https://www.e-periodica.ch/digbib/view?pid=bsv-002:2017:96#10
http://dx.doi.org/10.5169/seals-736800

Extended abstract
In order to investigate the influence of bedrock on the chemical composition of alpine spring waters, more than 700 chemical analyses for major and trace elements have been collected from regional reports or thesis. All these waters are from shallow aquifers (no deep or geothermal circulation), where water is cold and oxic, with pH neutral to basic. Five types of bedrock have been distinguished: granite, mafite, ultramafite, limestone and gypseous rocks (mostly gypseous dolomite). Classical physicochemical parameters (pH, temperature and electrical conductivity), major elements and, depending on the authors, about 15 trace elements are usually provided. The concentration ranges of each element in solution, for each type of bedrock, are provided as percentiles in annexes (online). These values are indicators of common water compositions encountered in moderate to high altitude alpine environment.
Results for major elements show that the total dissolved load depends directly on the nature of the bedrock: silicated, carbonated or sulfate-bearing rocks (Figure 1).

Figure 1: Total dissolved solid vs electrical conductivity for alpine waters from silicated rocks, limestones and gypseous rocks (N=696).

Classical diagrams of Schoeller (Figure 2) and Piper (Figure 3), as well as the hydrogeochemical facies of JAECKLI (1970), are used to characterize each water type, corresponding to the five types of rocks considered.

Figure 2: Schoeller’s diagram for the five types of alpine waters considered in this work (median concentrations for each type). 

Figure 3: Piper’s diagram of alpine spring waters for granite (N=98), mafic (61) and ultramafic (36) types on the left, limestones (294) and gypseous rocks (207) on the right.

Two types of water are well differentiated from the others. Waters of gypseous rocks are strongly enriched in Ca, Mg and SO4, with SO4/HCO3 >1. Waters from ultramafic rocks are enriched in Mg, with usually Mg/Ca>1. In all the other types of water (from granites, mafites or limestones), Ca and HCO3 strongly dominate. This convergence of compositions towards an undifferentiated calco-hydrogenocarbonated facies is known in metamorphic rocks. It can be attributed to traces of calcite in the silicate rocks and that metamorphic silicate minerals are much less reactive than calcite. In order to improve the discrimination of these water types, a new ternary diagram is proposed, using relative Ca, Mg and Si concentrations (Figure 4).

Figure 4: Ca-5Mg-10Si  ternary diagram (mMole/L) for alpine spring waters (N=442), with indicative isolines of electrical conductivity. The positions of main rock forming minerals are in the upper figure.

It appears from these analyzes that dissolution properties of minerals (i.e. solubility and dissolution rate) strongly control the content in major elements of these spring waters (Figure 9). In particular, a low amount of a highly soluble and rapidly dissolved mineral may play the main role: gypsum or anhydrite in gypseous rocks, brucite in ultramafites, or calcite in the other rock types.
Dissolved contents of trace elements are highly variables, several orders of magnitude for most of them. Median values and overall distributions, by type of rocks, are displayed in Figure 5 and Figure 6 respectively.

Figure 5: Median concentrations of trace elements in alpine spring waters by type of rocks and by valence. Speciation according to Stumm & Morgan 1996 (cmplx = aqueous complexe).

Figure 6: Wheel of trace elements in solution (inside a slice , the points are spread randomly on the radius that corresponds to the concentration).

For most of trace elements, there is no obvious relationship between rock contents and concentrations in solution. Some exceptions are: 1) water from gypseous rocks are enriched in Li, Rb and Sr; 2) concentrations of U, Mo, As are higher in water from granite. In order to interpret these data and to identify the processes regulating the concentrations of trace elements in solution, the valence, the speciation and a mobility index are used (Figure 10). Dissolution properties of minerals seem to control the concentrations of alkaline elements (Li, Rb, Sr, Ba). Very low concentrations of dissolved Fe, Al, Mn and Ti may be due to precipitation as oxy-hydroxides. Adsorption of transition metals (Co, Ni, Cu, Zn, Cd, Pb) on mineral surfaces or suspensions can regulate their concentrations in these basic waters. Higher valence elements (Si, U, Mo, Cr, As) form anionic complexes in natural waters. If they are present in soluble minerals, these anionic complexes may explain the observed enrichment of these elements in some specific types of water (granitic and gypseous).

Figure 9: Solubility vs dissolution rate for main rock forming minerals (pure water at 25°C and equilibrium with atmospheric CO2 and O2). The dissolution rate is expressed as lifetime of a 1mm diameter spherical grain. Both Goldich’s sequences are shown for silicates. The upper figure illustrates a typeical dissolution experiment, with: m = mass of dissolved mineral, kcin = dissolution rate at the beginning of the reaction [g/m2/s],  S = solubility [g/L], Areac= reactive surface of the mineral [m2/L].

Figure 10: Ratio of the median concentration in water on the concentration in rock (molar concentrations for both). The higher is this ratio, more the element is mobile in the system.

New publication in Environmental Earth Sciences about sinkhole-related risk

by Pierrick Nicolet, Marc Choffet, Marc-Henri Derron, Michel Jaboyedoff and Bertrand Lauraux: “Evaporite sinkhole risk for a building portfolio

Karst-related hazard can be a problem for buildings, especially in the case of evaporite karst. This study aims at evaluating the risk posed by evaporite karst for a building portfolio in western Switzerland, using a susceptibility map and an event inventory. Since the inventory is not complete, different corrections aim at obtaining a frequency of sinkhole events damaging a building as close as possible to the actual frequency. These corrections account for the variation of the building stock during the inventory period, the varying inventory quality among the municipalities and the partial knowledge, even in the best case. This approach is preferred here to estimating spatially the hazard, since the amount of information on the frequency and magnitude is insufficient to draw a proper hazard map. The distribution of loss ratios is also retrieved from the inventory, thanks to the estimated or actual price of the remedial works. Annual losses are then estimated using a Monte Carlo approach, which consists in sampling for a number of damaged buildings from a Poisson distribution, for a distribution of loss ratios and for a building value. Different exceedance curves relying on different hypotheses are presented, and the mean annual loss that the public insurance company might have to compensate is estimated at CHF 0.8–1.5 million.

The article can be accessed on Environmental Earth Sciences website. The full text can also be read on SharedIt

Flight at Bondo (GR)

Five people of the Risk Analysis Group went to Bondo, Canton of Graubünden, on 29 September 2017 to make a helicopter flight along the debris flow and cliff collapse of the August event. During a 25 minutes flight from the village of Bondo to the Piz Cengalo through the Val Bondasca, 11’400 pictures were taken by automatically and manually operated cameras . Those data will be used to get 3D models of the area by SfM processing.

 

Thesis on risk analysis available for download

Pierrick Nicolet defended publicly on the 9th of January his PhD entitled “Quantitative risk analysis for natural hazards at local and regional scales”. The thesis aims at improving the quantification of the potential consequences of natural events and is divided in two parts. The first part deals with risk analysis at local scale, which is particularly useful to prioritize the subsidies of protection measures. When it comes to the second part, regional stochastic models are proposed and are oriented towards the portfolio management for public buildings insurances companies.

Since the thesis was accepted, the full text is now available for download here, and the full abstract is available here.

Risk group @ EGU 2017 in Vienna

The Risk Group participated to the European Geosciences Union (EGU) General Assembly in Vienna, Austria, on 17 April to 22 May 2017. This huge meeting brought together 14’496 scientists from 107 countries with 4’849 orals, 11’312 posters and 1’238 PICO presentations.

It is always an excellent opportunity for our group to meet new people and other scientists we work with during the five days of the meeting. The Risk Group people presented 30 contributions as first authors whose titles are below.

4 orals:

  • Rockfall travel distances theoretical distributions Michel Jaboyedoff et al.
  • Rockfall monitoring of a poorly consolidated marly sandstone cliff by TLS and IR thermography Caroline Lefeuvre et al.
  • Characterization of the deformation and thermal behavior of granitic exfoliation sheets with LiDAR and infrared thermography (Yosemite Valley, USA) Antoine Guerin et al.
  • Optimizing the use of airborne LiDAR data for a better analysis and communication of 3D results​ François Noël et al.

4 PICO:

  • Debris flows susceptibility mapping under tropical rain conditions in Rwanda.
    Emmanuel Nduwayezu et al.
  • Five years database of landslides and floods affecting Swiss transportation networks Jérémie Voumard et al.
  • Three consecutive years of road closures due to natural hazards in the Weisstannen valley, Canton of St-Gallen, Switzerland Jérémie Voumard et al.
  • Experimental insights of liquid impacts onto granular beds of various packings : The packing influence over the excavated volumes Emmanuel Wyser et al.

9 posters:

  • Integrated risk management and communication: case study of Canton Vaud (Switzerland) Veronica Artigue et al.
  • Radiometric enhancements of thermal infrared images for rock slope investigation by coupling with groundbased LiDAR Marc-Henri Derron et al.
  • Landslide-Generated Tsunami model Martin Franz et al.
  • Introducing a moving time window in the analogue method for precipitation prediction to find better analogue situations at a sub-daily time step Pascal Horton et al.
  • Using genetic algorithms to achieve an automatic and global optimization of analogue methods for statistical downscaling of precipitation Pascal Hortonet al.
  • Development of a 3D rockfall simulation model for point cloud topography
    François Noël et al.
  • Understanding three decades of land use changes and a cloudburst in Phewa Lake Watershed, Western Nepal Karen Sudmeier-Rieux et al.
  • Automatic 3D relief acquisition and georeferencing of road sides by low-cost on-motion SfM Jérémie Voumard et al.
  • Preliminary 2D numerical modeling of common granular problems Emmanuel Wyser et al.

Michel Jaboyedoff received the DPRI Award 2017 in Kyoto University

Michel Jaboyedoff reciveing the DRPI Award from thge director of DPRI Prof. Kaoru Takara (Picture from http://www.dpri.kyoto-u.ac.jp/news_en/9141/)

On February 21st, Michel Jaboyedoff received the DPRI Award (Disaster Prevention Research Institute – Kyoto University). He expressed his gratitude to DPRI and Prof. Chigira when he received his award. He delivered a Memorial Lecture entitled: “Emerging Techniques and Impact of Human Activities in Landslide Risk Management: 3D Analysis and Human Induced Landslides” (video). The International Institute for Applied Systems Analysis (IIASA) received this award jointly.

DPRI Award: “The DPRI Award honours individuals and organizations that have contributed towards various joint research projects and activities of DPRI undertaken in Japan and abroad.” DPRI (from http://www.dpri.kyoto-u.ac.jp/dpriaward_en/)

Risk group @ RocExs 2017 – Barcelona

The Risk Group participated to 6th Interdisciplinary Workwhop on Rockfall Protection in Barcelona, Spain, on 22-24 May 2017.
The first two days, we followed the different presentations while the third day, we participated to a field trip in the Monserrat Massif whose theme was dedicated to rockfall management.
Presentations from the Risk Group:
  • 11 years of ground-based LiDAR monitoring in the West Face of the Drus (Mont-Blanc Massif, France) after the little rock avalanche of June 2005. Guerin et al.
  • The effect of slope roughness on 3D rockfall simulation results. Noël et al.
  • Multi-technique approach to assess rockfall propagation: a case study from Les Forges, Jura, Switzerland. Lefeuvre et al.

In memoriam Jacques Bechet

img_9698_2We have recently published two papers written with our former Master’s student Jacques Bechet who died tragically in a snow avalanches on 28 March, 2015. We dedicate these papers to Jacques Bechet (first author). Their content is an expression of his great ingenuity, curiosity and passion for research he shared with his co-worker Julien Duc. We will always remember his enthusiasm and his kindness. We sympathize with his family and with his friend Julien Duc who worked closely with him.

Bechet, J., Duc, J., Loye, A., Jaboyedoff, M., Mathys, N., Malet, J.-P., Klotz, S., Le Bouteiller, C., Rudaz, B., and Travelletti, J. 2016: Detection of seasonal cycles of erosion processes in a black marl gully from a time series of high-resolution digital elevation models (DEMs), Earth Surf. Dynam., 4, 781-798, doi:10.5194/esurf-4-781-2016. PDF

Bechet, J., Duc, J., Jaboyedoff, M., Loye, A., and Mathys, N. 2015: Erosion processes in black marl soils at the millimetre scale: preliminary insights from an analogous model, Hydrol. Earth Syst. Sci., 19, 1849-1855, doi:10.5194/hess-19-1849-2015. PDF

Risk group at the 12th International Symposium on Landslides (ISL)

Four persons of the Risk Group participated to the 12th International Symposium on Landslides (ISL) in Napoli, Italy, on 12 to 19 June 2016. We presented one lecture and three orals. All contributions at the symposium are collected into three books.
It was a great opportunity for us to meet scientists we work with during the five days of the Symposium.

Lecture:
Human-Induced Landslides: Toward the analysis of anthropogenic changes of the slope environment. M. Jaboyedoff et al.

Orals:
Rock slope pre-failure deformation database for improved transportation corridor risk management. R.A. Kromer et al.

Characteristics and influence of brittle structures and fold geometry in the development of slope deformations in Turtle Mountain (AB, Canada). F. Humair et al.

Minor landslides and floods events affecting transportation network in Switzerland, preliminary results. J. Voumard et al.

Napoli1

Location of the Symposium.

Napoli2

During the lecture on “Human-Induced Landlisdes”.