Landsliding generated by thermomechanical interactions between rock columns and wedging blocks: Study case from the Larzac Plateau (Southern France)
1 Laboratoire Géosciences Montpellier, UMR 5243, Université de Montpellier, France
2 Laboratoire de Mécanique et Génie Civil, UMR5508, Université de Montpellier, France
3 CEREMA, Direction Territoriale Méditerranée, Laboratoire d’Aix-en-Provence, France
Published online: 30 June 2017
The Larzac Plateau is delimited by vertical cliffs whose geometry is controlled by vertical joints. Cliff’s erosion involves landslides initiated by incremental enlargement of joints that progressively detach rock columns at very low velocities (1.2 mm/yr). We find that enlargement of joints is linked to intraseasonal thermal cycles ranging between 2-15 days in relation with dilation/contraction of rock blocks trapped inside the joints. The mechanism involves two successive stages in which blocks create a wedging and a ratcheting effect on the rock column. Wedging is associated with compressional forces acting on the rock column, resulting from temperature increase and dilation of the shallow rocks. Ratcheting is associated with downward displacement of blocks by gravity to a new equilibrium position, resulting from temperature decrease and contraction of shallow rocks. The displacement vector in a thermal cycle is split into a plastic and a thermal component; plastic displacements range between 10 — 200 μm according to the seasons, and are absorbed along a shear plane dipping ~40° beneath the rock column: they are largest during autumn and winter, minor during spring and negligible in summer. This deformation mechanism is termed thermomechanical creep as permanent deformations are associated to mechanical forces induced by short-term thermal cycles.
© The Authors, published by EDP Sciences, 2017
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.