The Cirque des Graves landslide in Normandy (N-W France) is a slow-moving and deep-seated coastal landslide characterized by surface displacement of a few centimeters per year (1-10 cm/yr) and regularly affected by brutal accelerations with several meters of displacements (January 1982, February 1988, March 1995 and March 2001). For these reasons, and because of the presence of economical and physical stakes, the landslide has been progressively monitored since 1985. Previous researches demonstrated qualitatively that these accelerations were controlled by the slope hydrology. To improve the knowledge on the slope dynamics, a combination of historical data and slope instrumentation is necessary. The actual monitoring system is based on twenty-four cemented benchmarks, three permanent GNSS receivers and several hydro-meteorological observation points. The aim of this study is to associate groundwater levels to the landslide kinematics to define critical piezometric thresholds to trigger landsliding. Thresholds have been identified using long-term continuous single point time series and shorter, but more spatially distributed, piezometric information. Empirical piezometric thresholds for the landslide triggering are defined taking into account the antecedent hydro-climatic conditions. Two main situations were identified: (1) major landsliding events associated to long-lasting rainfall periods (several month) with groundwater water elevation of more than two meters above the mean annual level observed for the period 1976-2013 (return period of over 6/7 years); and (2) moderate landsliding events associated to low intensity rainfall periods with a limited groundwater rise responsible for a moderate seasonal kinematics (return period of every years).

À l’extrémité nord-ouest du Pays d’Auge, les falaises des Vaches Noires constituent un site côtier long de 4,5 km à la morphologie unique de badlands, évoluant sous l’action combinée de processus subaériens et marins. Des glissements et éboulements de blocs calcaires/crayeux se produisent en partie sommitale. À l’aval, la morphologie chaotique est affectée par des coulées boueuses actives aux dynamiques et aux modalités d’extension diverses. L’escarpement basal (défini comme trait de côte) est battu par les houles. Ce dernier connaît alternativement des phases d’érosion en période de haute marée, puis d’accumulation grâce aux apports de matériaux issus de l’amont du versant côtier. Le fonctionnement non linéaire dans le temps et l’espace de ces falaises sont le résultat de relais et de combinaisons de processus que nous cherchons à définir et quantifier. Afin de déterminer l’évolution morphologique historique des versants, une analyse par emboîtement d’échelles spatiales et temporelles est menée. À l’aide de documents cartographiques anciens, de photographies aériennes de l’IGN, de MNT LIDAR, puis de documents historiques (archives, photographies, etc.), nous estimons des distances et des taux de recul de l’escarpement principal et secondaire, ainsi que l’évolution du trait de côte. L’analyse diachronique de différents documents permet d’estimer les vitesses et rythmes d’évolution des falaises des Vaches Noires sur des pas de temps longs (257 ans) et de les comparer aux vitesses des secteurs côtiers normands marneux avoisinants. Un cycle d’évolution complet des falaises est de 250 à 300 ans est également proposé.

Virtual reality is a technological development that, among others, has revolutionized Earth sciences. Its advantages include an opportunity to examine places otherwise difficult or impossible to access and it may also become an important component of education, fostering a better understanding of processes and landforms, geohazard awareness, and an appreciation of geoheritage. This paper reports on the GeoVT project, which aims to create a platform to build and disseminate Virtual Field Trips (VFTs) focused on geomorphology, natural hazards associated with geomorphological processes, and geoheritage sites. To put the GeoVT project in context, an overview of applications of VR in geosciences is provided. This paper subsequently proceeds with a presentation of the project and the GeoVT Authoring application, which is an innovative platform designed to help teachers and students, followed by brief presentations of a number of VFTs developed within the project. They address themes such as fluvial landforms and valley development, coastal landforms, evidence of past glaciation, coastal erosion, wildfire effects, mud volcanoes, and landslides.