3rd Virtual Geosciences Conference

The 3rd Virtual Geosciences Conference took place in Kingston (Ontario) on 22-24 August 2018.  This conference is at the intersection of geomatics, visualization, computer vision, graphics and gaming, as well as virtual and augmented reality with applications to a range of geoscience subfields, such as geological mapping, geomorphology, geohazards, glaciology, volcanology, tunnelling, and mining. It was organized at Queen’s University, by Ryan Kromer, a former PhD student of Lausanne and Queen’s universities. 


MH Derron, S. Buckley, J. Chandler, M. Jaboyedoff and R. Kromer (Chairman of the 3rd VGC)

The first  VGC conference was in Lausanne in 2014 and then in Bergen in 2016. These events are fantastic opportunities to learn how new technologies can be used  in geosciences, gathering together people from different horizons. 

http://virtualoutcrop.com/vgc2018

Optimizing the use of 3D point clouds data for a better analysis and communication of 3D results. François Noël, Marc-Henri Derron, Michel Jaboyedoff, Catherine Cloutier  Jacques Locat
Infrared Thermal Imaging for Rock Slope Investigation – Potential and Issues. Marc-Henri Derron, Antoine Guérin, Michel Jaboyedoff

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

Aron Somazzi: Rockfall hazard and risk analysis in the Pichoux Gorges (Jura, Switzerland)

First, the potential sources of rockfalls are detected. These locations are determined using the slope histogram method. Then, one passes to the analysis and classification of the discontinuities present in the delimited zones. Density, direction, dip, spacing and persistence can give an idea of the state of the rock, the mode of rupture and the potentially mobilizable size. For this part, we link the measurements made in the field with those obtained digitally by remote sensing (terrestrial LIDAR, structure from motion from car or drone, handheld laser scanner). Then we go on to modeling of rockfall propagation. Four different simulation models were used: Eline, RocFall, Trajecto 3D and Rockyfor 3D. Results are then compared and analyzed.

Finally a hazard map is proposed and the risk assessed. In this study, we focus on the risk of direct block-car impact and the risk of collision with a block that is on the roadway. The sum of the risks gives us a value expressed in deaths per year or loss of francs per year.
After quantifying the value of the current risk, scenarios are proposed to reduce the risk. For this risk management part, cost-benefit analysis was used. This is an economic evaluation of the feasibility of the works of the protections proposed in relation to the costs.

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.

Barcelonnette field trip 2018

The field trip on gravitational slope movements for master students took place for the fifth year at Barcelonnette (French Southern Alps) at the beginning of June. During two weeks, the students had the opportunity to study the landslide of Lavalette, rockfalls around Meolans and debris flows in the Riou Bourdoux catchment. The quite intensive program was composed of mapping and terrestrial LiDAR in the field during day times, data analysis and numerical modelling the evening.

Hugo Collomb from RTM giving explanations on the debris flows mitigation measures in the Riou Bourdoux catchment

Once again we benefited from all the facilities provided by the Seolane center (center dedicated to host scientific stays at Barcelonnette), and we had the opportunity of a visit guided by Hugo Collomb of the French Office of Forest (ONF-RTM).

Séolane, Pôle d’accueil universitaire

Tunisian Geological Days on mapping georisks

The Journées de la Géologie Tunisienne was organized by the office national des mines in Hammamet from 23 to 25 March. This year, this conference was dedicated to the mapping of georisks. Mariam Ben Hammouda and Marc-Henri Derron from the group Risk took part to this conference, presenting advances in point cloud processing. It was also the opportunity to visit the Cap Bon area where Mariam is doing her PhD thesis.

Collapsed road at Cap Bon


Although blue sky, that was a chilly week of March

Field trip and visit in Taiwan

Beginning of March was a great opportunity for Marc-Henri Derron to visit sites and colleagues in Taiwan for the first time. Invited by Prof. C.W. Lin (National Cheng Kun Univ. in Tainan) and Prof. R.F. Chen (Chinese Culture Univ. in Taipei), Marc-Henri had the opportunity to visit large landslides in central Taiwan, as well as giving 3 presentations on various aspect of landslide investigation techniques.

Slope conditions, steep and weathered, are drastically different from those encountered in the Alps. This visit was the first one for a group Risk’s member and we are confident it will lead to further cooperation.

Emmanuel Wyser: Investigations phénoménologiques et numériques de l’impact de gouttes d’eau sur un milieu granulaire et du processus de diffusion

Emmanuel Wyser
Director: Prof. Michel Jaboyedoff
Supervisor: MSc. Benjamin Rudaz

Water erosion phenomenons are increasingly studied and understood but raindrop erosion is far more complex. Raindrop erosion includes subprocesses such as impact, cratering, rim formation, daughter drop splash and soil particle splash. This work is focused on modeling complex ballistic trajectories of soil particle splashes and particle dispersion process. The general purpose is first to recreate the splash effect in laboratory and second to provide optimal numerical models and a better understanding of the soil particle splash.

Since the complex multiphase interactions are difficult to model, it is easier to compute numerically the dispersion process. Physical based models are the most common approach in this investigation field. The first assumption is that the crater shape might be the controlling factor in the dispersion process governed by the average splash distance. Moreover, complex physical based models may govern ballistic trajectories. These assumptions have now to be proven.

Phenomenological observations are given by experiments in laboratory, on a setup inspired by Furbish et al. (2007) study. Fine soil samples are used in this work and advanced grain size analysis is performed using laser diffraction technique. High-speed camera acquisitions and micro-LiDAR records are used throughout experimental investigations. Then, impact velocities are measured as well as crater shape or particle dispersion. Measured velocities tend to be close to those computed by numerical simulations. High-speed photography analysis shows that the mean initial splash angle is dependent on the drop penetration depth. Moreover, the mean splash angle seems to be dependent on the slope at the crater edge.

Numerical computation is then performed to model the dispersion phenomenon. Using a
probabilistic algorithm, the grain size distribution can be taken into account throughout numerical simulation. The initial splash angle mean value is derived from previous assumption about the key role of the crater shape. Gravity, drag and buoyant forces are also taken into account. Model validation is performed by comparisons between experimental and numerical results using digitalized experimental dispersion photography and LiDAR scanning. Several differences between numerical and empirical results are noticed. The shape of the particle splashing distance distribution is found to be not similar. LiDAR acquisition analysis also shows a non-spherical shape for the crater. But a statistical trend exists for the mean crater gradient -mean splash distance relationship. However this has more to do with dierential initial velocities at the crater’s edge than with mean splash angle.

Further perspectives should be oriented in multiphase interactions ( fluid to soil particle) for a better understanding of the whole phenomenon.

Jaccaud Léonard: Étude de l’instabilité rocheuse du Kilchenstock, Glaris (Suisse)

Jaccaud Léonard
Directors: Prof. Michel Jaboyedoff and Prof. Stefan Schmalholz

The Kilchenstock peak is located in the Swiss Alps about 15 km south of the city Glarus. Many rockfalls from the Kilchenstock have been reported since the 19th century. The first study of this rock slope instability is done by Albert Heim in the 30s. The area is mainly composed of folded flysch with a stratigraphy predominantly dipping towards SSE. Heim reveals a sliding mass near the top of the mountain. This represents an unstable volume of 2.5 million cubic meters. At the foot of this area blocks break off and fall towards the town of Linthal 1000m below.

Heim measured velocities of the sliding mass from 1927 to 1932. On two occasions the displacement’s velocity has accelerated (up to 40mm per day) suggesting an imminent large rock-collapse. No catastrophic failure has occurred so far, however such an event remains possible and its characterization consists of the main objectives of the present study.

A detailed structural study is performed based on digital elevation model (DEM) as well as field investigations. The results show that the activity isn’t confined to the area described by Heim, but rather extends to the whole slope, suggesting a larger and deeper potential rock slope deformation at the Kilchenstock. This is supported by different signs of activity and geomorphic gravitation features such as rockfalls, scarps, double ridge, cracks. The existence of several contiguous or imbricated landslides constitute a complex instability who started with the retreat of the glacier

The final results of the study is a detailed geological map of the Kilchenstock and a cross-section in order to better explain which structural parameters constrain the unstable system.