Once again the field course for master students in risk took place in the beautiful valley of Ubaye this year. During 11 days (end of May – beginning of June 2019), 12 students from environmental risk or geological risk had the opportunity to study the landslide of Lavalette, work on rockwall stability and discover the processes leading to debris flows. We had the pleasure to be hosted at the scientific center of Seolane in Barcelonnette.
Debris flow channel of the Riou Bourdoux torrent
The usual fieldtrip for bachelor students in risk took place in Les Diablerets . About twenty students took part to this course on 1-3 May 2019. The Pont Bourquin landslide was used for a mapping exercise and as a starting point for a risk analysis.
Example of a landslide map produced by students during 1 day mapping
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.
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.
In collaboration with the Fondazione Montagna Sicura, Michel Jaboyedoff, Antoine Guerin and Li Fei went to Entrèves (Aosta Valley, Italy) on 23 October 2018 to investigate the 1997 Brenva rockslide scar (3’870 m, Mont-Blanc massif), which reactivated in September 2016. A helicopter flight of about 25 minutes allowed acquiring hundreds of pictures (digital and thermal) of the rock mass in exceptional conditions, as the high mountain was dry in late autumn 2018. A high-resolution Structure-from-Motion model was then generated using these pictures, allowing us to analyze in detail the structural features and rockfall activity of the Sperone della Brenva.
View of the Mt BLanc and Brenva spur
3D point cloud model obtained by photogrammetry
Part of the Risk Analysis Group participated to the International Symposium on Rock Slope Stability 2018 in Chambéry, France, on 13 to 15 November 2018. It was a great opportunity to exchange about many topics related to natural hazards and rockfalls. The group presented two contributions as first authors whose titles are below:
1 Keynote
1 Oral
The symposium concluded with very interesting field visits where we did learn about the history of the Mont Granier and its previous rock collapses and about the different instabilities that affects the gorges of Arly and how the local institutions manage them.
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
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
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:
2 Orals
2 Posters
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.
Hugo Collomb from RTM giving explanations on the debris flows mitigation measures in the Riou Bourdoux catchment