<p><span>Deep Seated Gravitational Slope Deformation (DSGSD) is defined as a set of rock mass characterized by a very slow movement (mm.yr-1) affecting large portions of slopes of a mountain range. </span><span>These typical slope&#160;</span><span>instabilities must not be neglected and need to be better identified and characterized to anticipate related hazard (e.g. landslides). Characterize them requires first of all to locate them as for example recently the inventories carried out for the European Alps or in France. These specific processes, which can lead to hazard and disasters (e.g. La Clapi&#232;re landslides), should not be neglected and need to be better identified and characterized to anticipate related hazard). Documenting the DSGSDs requires first of all to locate them as for example the recently published inventories initiated for the European Alps and France. These studies initiated approaches aiming at defining the factors controlling their evolution in time and space.</span></p><p><span>The research developed in this study targets a better understanding the short- (<100 yrs) and long-term (> 100 yrs) evolution of DSGSDs developed in the sedimentary rocks of the Queyras Massif (South-East French Alps). The main objective is to propose models of DSGSDs evolution with key interpretations of future developments to locate possible new landslide prone areas. The Queyras Massif was chosen because it represents an under-studied area of DSGSDs. The massif is characterized by Cenozoic marine sedimentary rocks accreted and metamorphized by the Alpine orogen. The massif is characterized by a regional schistosity plunging to the West and complex and active fault networks&#160;</span><span>mark the landscape (</span><span>Tricart et al., 2004)</span><span>.</span><span>&#160;The highest summits reach an altitude of 2500m a.s.l. and are separated by deep valleys incised by the Riss and W&#252;rm glaciers and currently by torrential streams.</span></p><p><span>The method is based on a geomorphological analysis of the landscape and landforms, field observations and image interpretation of remote sensing data. Results allow locating the DSGSD, estimating their degree of activity, and characterizing their structure. Several dating methods (</span><sup><span>14</span></sup><span>C,&#160;</span><sup><span>10</span></sup><span>Be or&#160;</span><sup><span>36</span></sup><span>Cl) complete the interpretations in order to reconstruct the history of the slopes and understand the factors that control their evolution.</span></p><p><span>At the scale of the massif, the DSGSDs were first identified using the approach proposed by&#160;</span><span><em>Blondea</em></span><span>u (2018).&#160;</span><span>Visual remote sensing&#160;</span><span>revealed the occurrence of thirty DSGSDs. These slopes were detected as they associate six common features commonly observed in DSGSDs</span><span><em>.&#160;</em></span><span>Eight DSGSDs were selected in order to investigate at the local scale their geomorphology, geology and hydrogeology and reconstruct their historical (millennial) and recent (last 50 years) evolution from dating methods&#160;</span><span>and&#160;</span><span>field observations. Through this multidisciplinary approach, present the observed bedrock and gravitational structural features and determine the predisposing factors of the formation of DSGSD. The research is part of the Program &#8220;R&#233;f&#233;rentiel G&#233;ologique de la France / RGF &#8211; Chantier Alpes&#8221;</span><span>&#160;which targets&#160;</span><span>to update the geological knowledge of the Alpine basement, surficial formations and associated hazards in three dimensions and in digital format.</span></p>
<p>"LONG AND SHORT TIME EVOLUTION OF DEEP SEATED GRAVITATIONAL SLOPE DEFORMATION: CONTRIBUTION TO KNOWLEDGE OF PHENOMENA FOR THE MANAGEMENT OF ALEA IN THE ALPINE MOUNTAINS"</p><p>&#160;</p><p>C.Boivin <sup>a</sup>, J.P. Malet <sup>a</sup>, C. Bertrand <sup>b</sup>, F. Chabaux <sup>c</sup>, J. van der Woerd <sup>a</sup>, Y. Thiery <sup>d</sup>, F. Lacquement <sup>d</sup></p><p><sup>a &#160;</sup>Institut de Physique du Globe de Strasbourg &#8211; IPGS/DA - UMR 7516 CNRS-Unistra</p><p><sup>b </sup>&#160;Laboratoire Chrono-Environnement &#8211; LCE / UMR 6249 CNRS &#8211; UFC</p><p><sup>c</sup>&#160; Laboratoire d&#8217;Hydrologie et de G&#233;ochimie de Strasbourg &#8211; BISE / UMR 7517 &#8211; Unistra</p><p><sup>d</sup>&#160; Bureau de Recherches G&#233;ologiques et Mini&#232;res</p><p>&#160;</p><p>&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; The <strong>Deep Seated Gravitational Slope Deformation (DSGSD)</strong> are defined like a set of rock mass characterized by a generally slow movement and which can affect all the slopes of a valley or a mountain range (Agliardi and al., 2001, 2009; Panek and Klimes., 2016). The DSGSD is identified in many mountains (ex: Alps, Alaska, Rocky Mountains, Andes&#8230;) and it can affect both isolated low relief and very high mountain ranges (Panek and Klimes., 2016). This deep instability are identified in many case like the origin zone for important landslide like the example of La Clapi&#232;re landslide in the Alpes Maritimes (Bigot-Cormier et al., 2005). The DSGSD represent an important object we must understand to anticipate catastrophic landslides.</p><p>&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; Actually, many factors that could be at the origin or controlling the evolution of DSGSD have been identified such as for example the structural heritage, the climate or the tectonic activity (Agliardi 2000; 2009; 2013; Jomard 2006; Sanchez et al., 2009; Zorzi et al., 2013; Panek and Klimes., 2016; Ostermann and Sanders., 2017; Blondeau 2018). The long-term and short-term evolution of DSGSD is still poorly understood but represents an important point to characterize in order to predict future major landslides. A first inventory of DSGSD began to be carried out by certain studies such as Blondeau 2018 or Crosta et al 2013 in the Alps. These same studies have also started to prioritize the factors controlling the evolution of DSGSD.</p><p>&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; It is in order to better understand the short-term (<100 years) and long-term (> 100 years) evolution of the DSGSD of the French Alpine massifs and the link with the occurrence of landslides, that this thesis project is developed. The main objective of this project, will be proposed models of the evolution of DSGSD since the last glaciations. But also to propose key interpretations of the future evolution to locate the areas likely to initiate landslides. Two study areas in the French Alpine massifs were chosen because they represent areas of referencing and localization gaps in DSGSD: Beaufortain and Queyras. They have the advantage of having a low lithological diversity making it possible to simplify the identification of the factors influencing the evolution of DSGSD. A geomorphological analysis on satellite data and on the ground is carried out to locate the DSGSD. Several dating (<sup>14</sup>C, <sup>10</sup>Be or <sup>36</sup>Cl) will be carried out to reconstruct the history of these objects and understand the factors that controlled their evolution.</p>
<p>Deep Seated Gravitational Slope Deformation (DSGSD) are gravitational processes damaging slopes over long periods of time. These processes may be reactived with the occurrence of smaller, shallow gravitational events. Thus, a better understanding of DSGSDs, from their formation to more catastrophic phases of activity, is an important goal&#160; for natural hazard prevention in mountainous areas. .A first inventory of DSGSD in the Western Alps has been proposed by Crosta et al. (2013) with 1057 DSGSDs identified. A similar work has been conducted more recently at the scale of the French Alps by Blondeau (2018) who identified nearly 460 DSGSDs. Despite the importance of these works, there are still many Alpine sub-massifs where high concentrations of DSGSDs (Blondeau., 2018) have been recognized but where no detailed studies have been conducted. This is the case of the Queyras Massif (South French Alps). It is in this context that this study is carried out, with both the objectives of locating and characterizing the DSGSDs observed in this area and identifying their recent activity.</p><p>The proposed approach is based on quantitative geomorphological studies combining photo-interpretation of multi-date aerial imagery, analysis of DSMs and field observations. Quantitative description criteria are proposed to identify DSGSDs and discriminate them from large deep-seated landslides. Thirty DSGSDs are inventoried and their lithological and structural setting is analyzed. Analysis of multi-date aerial photographs and InSAR derived landslide velocities (NSBAS processing of Sentinel-1 observations; e.g. Andr&#233; et al., XX?) allow characterizing their gravitational activity.</p>
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