Ryan Kromer is PhD graduate of Queen’s University and a post doctoral researcher at the Colorado School of Mines. He was a visiting PhD student at the University of Lausanne during 2015 and 2016 and is now visiting the Risk group from April to June 2019. During his visit, he will be conducting research on automated monitoring of landslides using terrestrial LiDAR and photogrammetry. The research visit is supported by the Herbette Foundation. Ryan is looking forward to another fruitfull visit with the group.
Active mountain fronts are subject to large scale slope collapses which have the capacity to run long distances on piedmont areas. Over time, fluvial activity and other gravitatory processes can intensively erode and mask primary features related to the collapses. Therefore, to reconstruct the history of their occurrence, further analyses are needed, like sedimentologic analyses. This work focuses on the occurrence of large rock avalanches in the Vinchina region, La Rioja (28°43’27.81” S / 68°00’25.42” W) on the western side of the Famatina range (Argentina). Here, photointerpretation of high-resolution satellite images (Google Earth) allowed us to identify two rock avalanches, with their main scarps at 2575 and 2750 masl. There are no determined absolute ages for these deposits, however by comparing their preservation degree with those dated further north (in similar climatic and landscape dynamics contexts), we can suggest these rock avalanches took place during the Pleistocene.We carried out a fieldwork survey in this remote area, including classical landslide mapping, structural analysis, deposits characterization and sampling. The deposits reach the valley bottom at around 1700 masl. with runouts about 5 km and 5.3 km long. In one of the cases, the morphology of the deposit is well preserved, allowing to accurately reconstruct its extension. However, in the second case, the deposits are strongly eroded by sources draining from the mountain front, therefore further analyses should be done to reconstruct its extension. In addition to morphologic interpretations, a multiscale grainsize analysis was done to di↵erentiate rock avalanches from other hillslope deposits: first 3D surface models of surface plots (5x5m) were built with SfM (structure from motion) photogrammetry; then classical sieving and finally laser grain-size analysis of deposits were performed. Samples were collected on different parts of the slope, but also along cross sections throughout the avalanche deposit. This deposits characterization was combined with results from mapping and image analysis to provide a first description of the sequence and the extension of events related to the evolution of this mountain front. The collected data helped to create a series of propagation models with the software DAN3D, developed by Hungr (2009). We chose a Voellmy rheology for the model with f = 0.10 ± 0.05 and ξ = 100 (m/s2) ± 50 (m/s2) for the rock avalanches and f = 0.10 ± 0.05 and ξ = 500 (m/s2) ± 200 (m/s2) for the debris flow. The results show a good propagation with more dispersion that we can see on the field. Part of the cover on the numerical model is not visible on the field, probably due to erosion and transport having moved the material, resulting in the current landscape.
Author: José Pullarello
Director: Marc-Henri Derron, Michel Jaboyedoff.
External Supervisor: Ivanna Penna.
Director: Prof. Dr. Michel Jaboyedoff
Jury: Dr. Marc-Henri Derron, Dr. Andrea Pedrazzini, Dr. Nicolas Pollet, Prof. Dr. Suren Erkmann
Geological and hydro-geological natural hazards, as landslides and floods, are a threat to many transport networks built in mountainous areas. These risks, that are often small in intensity, are poorly evaluated or unknown.
This doctoral thesis focuses on the characterization and quantification of natural hazards that impact Swiss communication tracks. It also explores various remote sensing techniques dedicated to the survey of areas around traffic lanes.
A database has been created to characterize the many small events that regularly affect roads and railway lines in order to compensate the lack of knowledge. The number of events and their trends – such as their spatio-temporal distribution, the weather, the geology, the direct damages or the types of affected tracks- are thus known at the national level over a period of five years (2012-2016). It shows that a natural event, on average, disrupts the traffic every 2.1 days and that the events occur mostly during the months of June and July, late afternoon. Direct costs were estimated at CHF 4 million per year, with an average cost per event estimated at 23 400 francs.
In order to characterize the approaches to roads and railways, we have developed and tested the photogrammetric technique “on-motion Structure from Motion”, whose cost is reasonable. This remote sensing technic makes possible to obtain colorized and georeferenced 3D point clouds from images taken by four action cameras placed on a moving vehicle. Its accuracy has been evaluated in laboratory conditions and on many sites. It was also compared with seven other traditional surveillance techniques to identify advantages and disadvantages.
This work highlights the impact and consequences of small-scale natural hazards that, taken as a whole, are not negligible for society. In addition, this study demonstrates that low-cost survey technic can compete with more expensive traditional survey techniques.
Keywords: Natural hazards, transportation networks, on-motion Structure for Motion, topographical survey.
François Noël, Teresa Gracchi and Emmanuel Wyser of the Risk Analysis Group (UNIL) went to Barcelonnette (France) from the 23rd to the 27th of September for an amazing experimental work in the field dealing with rock fall trajectories and associated topics (e.g. impact response, energy transfer, etc.), amongst other French researchers from Active Deformation Group of the University of Strasbourg (EOST, leaded by Jean-Philippe Malet) and the IRSTEA Institute of Grenoble (leaded by Franck Bourrier).
Several (30) rocks were thrown down into a short but steep gully while seismic signals (EOST) and high-speed imaging (IRSTEA & UNIL) were acquired. High resolution 3D imagings were acquired thanks to TLS and SfM.
Accelerometers (ISTE & EOST) were also included in few rocky blocks to monitor and acquire data to better understand impact response, angular velocity changes and other exciting data.
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.
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.
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
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.
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°.
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
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.
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.
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.
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.
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.
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).
Part of the Risk Analysis Group participated to the 7th Canadian Geohazard Conference from the Canadian Geotechnical Society (CGS) in Canmore, Canada, on 3 to 6 June 2018. It was a great opportunity to exchange about many topics related to natural hazards, geotechnics and rockfalls. The group presented four contributions whose titles are below:
- Real-size rockfall experiment: How different rockfall simulation impact models perform when confronted with reality? Noël F., Wyser E., Jaboyedoff, Derron M.-H., Cloutier C., Turmel D. and Locat J.
- Using Average Velocities Of Deep-Seated Landslides To Develop Intensity-Frequency Scenarios. Jaboyedoff M., Aye Z.A., & Derron M.-H., Artigue V. and Gerber C.
- Automated decision sight distance evaluation based on airborne topographical data for risk management along linear infrastructures. Cloutier C., Locat J., Noël F. and Jaboyedoff M.
- Comparison between three rock slope hazard assessment methodologies based on the Åknes case study from Norway. Oppikofer T., Hermanns R.L., Jaboyedoff M., Derron M.-H., Brideau M.-A., Jakob M., Sturzenegger M.
The conference also included a very interesting field visit where we did learn about the flooding that happened in Canmore in 2013 and how the local institutions did respond them. The trip continued with the visit of local sites with mitigation measures and concluded with a dinner on the Sulphur Mountain where we could enjoy a gorgeous view on the Rockies near Banff while exchanging with the other participants.