Paleotopographic control of landslides in lacustrine deposits (Trièves plateau, French western Alps)

Abstract

International audiencePaleotopography in Quaternary sedimentary environments can be an important factor that controls landslide movement. This study investigates the relation between paleotopography and landslide activity in two adjacent landslides in glaciolacustrine sediments located in the Trièves area (French western Alps). Although both are in slopes underlain by the same lacustrine deposits, the Avignonet and Harmalière landslides exhibit major differences in morphology and displacement rates. Through a combination of geological mapping, airborne light detection and ranging (LiDAR) data, aerial photographs, global positioning system (GPS), and seismic noise measurements, a three-dimensional impression was made of both landslides. The analysis reveals that the difference in kinematics between the two mass movements can be traced back to at least 50 years ago. The results show that the Harmalière slide, which failed catastrophically in 1981, is still much more active than the Avignonet landslide. The fear was that the Avignonet landslide might develop in a similar catastrophic manner, threatening a number of houses constructed on the landslide. A geophysical survey based on ambient noise measurements allowed us to map the base of the lacustrine clays, and the results indicate the presence of a N-S ridge of hard sediments (Jurassic bedrock and/or compact alluvial layers) on the eastern side of the Avignonet landslide. This ridge disappears when approaching the Harmalière landslide and makes a place to what can be interpreted as a NW-SE oriented paleovalley of the river Drac. We proposed that the ridge acts as a buttress that could mechanically prevent the Avignonet landslide from evolving as fast as the Harmalière. Furthermore, the NW-SE paleovalley located under the Harmalière landslide corresponds to the motion direction of the slide. Therefore, the different behaviour of the two landslides is partly controlled by the paleotopographic setting of Lake Trièves during the last Glacial Maximum extension. These results suggest a major influence of the bedrock paleotopography on the kinematics of the landslides

Ambient seismic noise monitoring of a clay landslide: Toward failure prediction

“…Of particular concern for hazard assessment is the triggering of earthflows and debris flows, the rheology of which switches from solid to fluid. This phenomenon has been widely reported in all types of recent clay deposits, including Quaternary marine sensitive [ Crawford , 1968; Eilertsen et al , 2008] or nonsensitive clays [ Picarelli et al , 2005] and lacustrine clay deposits [ Bièvre et al , 2011]. But flow‐like movements have also been frequently observed in fractured and weathered clay‐rich rocks, such as shales, marls and flyschs [ Angeli et al , 2000; Picarelli et al , 2005; Malet et al , 2005], and in volcanic rocks in which primary minerals were altered to clays [ Coe et al , 2003].…”

Shear‐wave velocity as an indicator for rheological changes in clay materials: Lessons from laboratory experiments

“…This paper aims to investigate through laboratory tests the potentiality of Vs as an indicator for rheological changes and the solid‐fluid transition in clay. The tested clay was sampled in the Trièves plateau (Western Alps, France), at the southern limit of the large Avignonet landslide [ Bièvre et al , 2011]. Atterberg limits were measured on 3 samples, yielding a mean value of LL = 0.44 ± 0.03, with a plasticity index of about 0.2.…”

1-D and 2-D resonances in an Alpine valley identified from ambient noise measurements and 3-D modelling

“…Bard 1998; Haghshenas et al 2008). Although the fundamentals of the H/V technique are still debated (Lermo & Chávez‐García 1994; Malischewsky & Scherbaum 2004; Bonnefoy‐Claudet et al 2006a; Albarello & Lunedei 2009; Lunedei & Albarello 2010; Tuan et al 2011; Sánchez‐Sesma et al 2011), this technique has been successfully used for mapping bedrock depth in sediment‐filled basins (among others, Ibs‐von Seht & Wohlenberg 1999; Delgado et al 2000; Parolai et al 2002; Hinzen et al 2004; Benjumea et al 2011; Bièvre et al 2011; Özalaybey et al 2011), using the relation between fundamental resonance frequency ( f 0 ), average shear wave velocity (β) and thickness of sediments ( H ) ( f 0 =β/4 H ). Since shear wave velocity profiles are not always available, authors most often calibrate locally a power‐law relationship that relates fundamental resonance frequency ( f HV ) and sediments thickness ( H ).…”