Earthflow

Abstract: We use high-resolution electrical resistivity imaging to delineate the geometry of complex landslides in the Lucanian Apennine chain of southern Italy, to identify the discontinuity between the landslide material and bedrock, and to locate possible surfaces of reactivation. The Lucanian Apennine chain is characterized by high hydrogeological hazard and shows a complete panorama of mass movements. In this area, all typologies of landslides markedly predisposed and tightly controlled by the geostructural characteristics, are found: rotational and translational slides, rototranslational slides, earth and mudflows, as well as deep-seated gravitational slope phenomena with a predominance of rototranslational slides evolving as earthflow slides. Three test sites, characterized by complex geology and a high hydrogeologic hazard, are studied. The Giarrossa and Varco Izzo earthflow slides are located to the west and east of the town of Potenza, whereas the Latronico slide is located close to the town of Latronico....

Abstract: In mountainous landscapes with weak, fine-grained rocks, earthflows can dominate erosion and landscape evolution by supplying sediment to channels and controlling hillslope morphology. To estimate the contribution of earthflows to regional sediment budgets and identify patterns of landslide activity, earthflow movement needs to be quantified over significant spatial and temporal scales. Presently, there is a paucity of data that can be used to predict earthflow behavior beyond the seasonal scale or over spatially extensive study areas. Across 226 km^2 of rapidly eroding Franciscan Complex rocks of the Eel River catchment, northern California, we used a combination of LiDAR (light detection and ranging) and orthorectified historical aerial photographs to objectively map earthflow movement between 1944 and 2006. By tracking the displacement of trees growing on earthflow surfaces, we find that 7.3% of the study area experienced movement over this 62 yr interval, preferentially in sheared argillaceous lithology. This movement is distributed across 122 earthflow features that have intricate, elongate planform shapes, a preferred south-southwesterly aspect, and a mean longitudinal slope of 31%. The distribution of mapped earthflow areas is well-approximated by a lognormal distribution with a median size of 36,500 m^2. Approximately 6% of the study area is composed of earthflows that connect to major channels; these flows generated an average sediment yield of 19,000 t km^(−2) yr^(−1) (rock erosion rate of ∼7.6 mm/yr) over the 62 yr study period, equating to a regional yield of 1100 t km^(−2) yr^(−1) (∼0.45 mm/yr) if distributed across the study area. As such, a small fraction of the landscape can account for half of the regional denudation rate estimated from suspended sediment records (2200 t km^(−2) yr^(−1) or ∼0.9 mm/yr). We propose a conceptual model for long-term earthflow evolution wherein earthflows experience intermittent activity and long periods of dormancy when limited by the availability of readily mobilized sediment on upper slopes. Ultimately, high-order river channels and ephemeral gully networks may serve to destabilize hillslopes, controlling the evolution of earthflow-prone terrain.

Abstract: . The relationships between rainfall, hydrology and landslide movement are often difficult to establish. In this context, ground-water flow analyses and dynamic modelling can help to clarify these complex relations, simulate the landslide hydrological behaviour in real or hypothetical situations, and help to forecast future scenarios based on environmental change. The primary objective of this study is to investigate the possibility of including more temporal and spatial information in landslide hydrology forecasting, by using a physically based spatially distributed model. Results of the hydrological and geomorphological investigation of the Super-Sauze earthflow, one of the persistently active landslide occurring in clay-rich material of the French Alps, are presented. Field surveys, continuous monitoring and interpretation of the data have shown that, in such material, the groundwater level fluctuates on a seasonal time scale, with a strong influence of the unsaturated zone. Therefore a coupled unsaturated/saturated model, incorporating Darcian saturated flow, fissure flow and meltwater flow is needed to adequately represent the landslide hydrology. The conceptual model is implemented in a 2.5-D spatially distributed hydrological model. The model is calibrated and validated on a multi-parameters database acquired on the site since 1997. The complex time-dependent and three-dimensional groundwater regime is well described, in both the short- and long-term. The hydrological model is used to forecast the future hydrological behaviour of the earthflow in response to potential environmental changes.