Sedimentation processes and facies on a semi-vegetated talus, Lousteau, southwestern France

Abstract

A two-year survey of clast displacements on a small rockfall talus at Lousteau, southwestern France, shows that creep reaches up to 19 cm/month near the talus apex, whereas the distal segment remains stable. Movements are not distributed homogeneously but concentrate in distinct areas because of the deflection of clasts by vegetation patches. Sections across the talus reveal stratified deposits, thought to result from the lateral shifting of the tongues of very mobile debris. Poorly sorted gravel layers alternate with coarser debris corresponding to former pavements developed where sedimentation is reduced due to the protective effect of vegetation. Similar deposits have been found in larger, semi-vegetated taluses from the forest belt of the French Alps. Interactions between vegetation development and sedimentation, possibly controlled by the climatic changes during postglacial times, may be responsible for their stratification.

Debris flow-dominated and rockfall-dominated talus slopes: Genetic models derived from GPR measurements

“…These models involve creep in Alpine solifluction lobes (Bertran et al, 1993), dry grain flows (Lowe, 1976), frost-coated flows (Hétu et al, 1994), debris flows and hyper-concentrated flows (Van Steijn, 1988;Bertran and Texier, 1994;Blair, 1999) as well as vegetational binding (Bertran and Texier, 1999). Centimetre-thick layers generated by supranival debris sliding and niveo-aeolian transport (Hétu and Vandelac, 1989;Hétu, 1991Hétu, , 1995 are too thin to be identified in the applied GPR resolution, and thus these processes should be excluded from our interpretation of GPR imagery.…”

“…Whereas stacked debris was first investigated in the French Pyrenees (Guillien, 1951), recent work has described similar deposits in temperate upland environments (Francou, 1990;Van Steijn, 1997;Gengnian et al, 1999;Hinchcliffe, 1999;Garcia-Ruiz et al, 2001) as well as in cold temperate environments worldwide (Bilkra and Nemec, 1998;Hétu and Gray, 2000). Stratified scree slopes are not only confined to high mountain regions, but also occur in vegetated upland environments (Bertran and Texier, 1999;Harris and Prick, 2000;Curry and Black, 2002). In these studies attention is paid to the question of whether the scree strata correspond to climatic fluctuations during the Pleistocene Pleniglacials, the Lateglacial and the Holocene.…”

Determination of the internal structure of alpine talus deposits using different geophysical methods (Lechtaler Alps, Austria)

“…Stacked sediments are widespread in many periglacial regions of the world (DeWulf, 1988); stratified talus accumulations were reported, e.g. by Hinchliffe et al (1997) in Scotland and Bertran and Teixier (1998) in southern France. Several possible reasons for these structures apply.…”

Cliff retreat and talus development at the caldera wall of Mount St. Helens: Computer simulation using a mathematical model

“…Geomorphologic processes on a talus slope have been examined by various authors (e.g. Kirkby and Statham, 1975;Pérez, 1988Pérez, , 1993Kotarba, 1997;Bertran and Texier, 1999;Decaulne and Saemundsson, 2006;Sass and Krautblatter, 2007). The inclination of talus slopes and the stability of a slope composed of granular materials have been studied in detail (e.g.…”