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Many communication axes (roads and railways) erected along rocky outcrops are regularly damaged by rockfalls (Budetta, 2004). In these environments, rockfalls are a major and essentially unpredictable sources of danger. Thus, the assessment of their probability of occurrence is a major challenge for risk management (Delonca et al, 2014).
Geologic and geomorphological contexts of rocky outcrops influence both the frequency and magnitude of slope instabilities. The more a rockwall is weathered, the more it is unstable (Hantz et al., 2003, Matsuoka and Sakai, 1999). Nevertheless, it is usually external factors that control rockfalls triggering. Many studies highlight the predominant role of meteorological factors as heavy rainfalls and freeze-thaw cycles on rock surface instabilities (Brazdil et al., 2012, Delonca et al., 2014, Hantz et al., 2003). These events induce a change in the balance of forces acting in rock discontinuities.
Depending of climatic regions, occurrences of heavy rainfalls and temperature oscillations around the freezing point are concentrated within certain periods of the year. Since instabilities are largely correlated with meteorological variables, a good knowledge of the role these variables play on rockfalls would greatly support the development of a tool for statistical forecasting of rockfalls. Such a tool will help managers to establish effective preventive risk management plans.
The close relationship between meteorological variables and instability occurrences has been widely studied around the world (eg. Hall et al., 2002, Matsuoka and Murton, 2008). Nevertheless, studies that quantify the role of these variables are scarce (eg. D'Amato et al., 2016, Delonca et al., 2014) and do not support rockfall dynamics modelling. To date, there is no effective tool to develop the ability to predict rock fall based on meteorological triggering factors.
The main objective of my PhD project is to increase knowledge about the influence of meteorological variables on weathering of sedimentary rock cliff and on rockfall occurrence. To reach this goal, my project will build on the following three general objectives:
Evolution of freeze depth inside rock wall delimits depth of frost weathering and evolution of thaw depth in the spring dictates the size of rocks that are likely to fall following ice melt inside discontinuities of rock wall.
Meteorological variables such as rain, temperature, solar radiation or wind contribute to rock weathering and are trigger factors for rockfalls. Influence of these variables will be studied by focusing on daily, seasonal and annual dynamics.
Based on results from the first two objectives and on 21st century climate scenarios, we will seek to understand how magnitude and frequency of rockfalls will be modified in the climate change context.
Our study sites are all located in Haute-Gaspésie where two roads (132 and 198) are particularly affected by rockfalls. Between 2000 and 2012, 4720 rock falls reached the road on a portion of only 70 km. A preliminary analysis carried out by the Ministry of Transport, Sustainable Mobility and Transport Electrification (MTMDET) shows that most of rockfalls occurs in spring, during the thawing period of rock walls or during heavy rainfalls (M.T.Q., 2004). The hazard management strategy adopted by the MTMDET is based on development of a predictive capacity of rockfall, similar to that currently available for snow avalanches. This preventive management would rely primarily on a thorough understanding of meteorological variable role on rock instabilities. It would support manager’s planning and decisions making and thus limit the risks related to this hazard.
BRAZDIL, R., KAREL., S., TOMAS., P., PETR., D., LUCIE., K. & RADIM., T. 2012. The influence of meteorological factors on rockfall in the Morovskoslezské Beskydy Mts. Geografie, 117, 1-20.
BUDETTA, P. 2004. Assessment of rockfall risk along roads. Natural Hazards and Earth System Sciences, 4, 71–81.
BUNCE, C. C., DM & MORGENSTERN, N. 1997. Assessment of the hazard from rock fall on a highway. Can. Geotech., 34, 344-356.
D'AMATO, J., HANTZ, D., GUERIN, A., JABOYEDOFF, M., BAILLET, L. & MARISCAL, A. 2016. Influence of meteorological factors on rockfall occurrence in a middle mountain limestone cliff. Natural Hazards and Earth System Sciences, 16, 719-735.
DELONCA, A., GUNZBURGER, Y. & VERDEL, T. 2014. Statistical correlation between meteorological and rockfall databases. Natural Hazards and Earth System Science, 14, 1953-1964.
HALL, K., THORN, C. E., MATSUOKA, N. & PRICK, A. 2002. Weathering in cold regions: some thoughts and perspectives. Progress in Physical Geography, 26, 577-603.
HANTZ, D., DUSSAUGE-PEISSER, C., JEANNIN, M. & VENGEON, J.-M. 2003. Rock fall hazard assessment: from qualitative to quantitative failure probability. Picarelli. Int. Conf. on Fast Slope Movements, Prediction and Prevention for Risk Mitigation, 263-267.
HUNGR, O., EVANS, S. & HAZZARD, J. 1999. Magnitude and frequency of rock falls and rock slides along the main transportation corridors of southwestern British Columbia. Can. Geotech. J., 36, 224 - 238.
M.T.Q. 2004. Plan de transport de la Gaspésie-Îles-de-la-Madeleine. Direction du Bas-Saint-Laurent-Gaspésie-Îles-de-la-Madeleine. Ministère des Transports du Québec (MTQ), Rimouski (Québec), Bibliothèque nationale du Québec.
MATSUOKA, N. & MURTON, J. 2008. Frost weathering: recent advances and future directions. Permafrost and Periglacial Processes, 19, 195-210.
MATSUOKA, N. & SAKAI, H. 1999. Rockfall activity from an alpine cliff during thawing periods. Geomorphology, 28, 309-328.