Kinematics of active earthflows revealed by Digital Image Correlation and DEM of Difference techniques applied to multi-temporal LiDAR data

Earthflow-type landslides are persistent natural hazards having deep socio-economic and environmental consequences. They have significantly contributed to the geomorphic evolution of mountainous slopes in Europe since the Late Glacial. An understanding of their complex kinematics is crucial to better constrain the processes governing their occurrence and mobility. In this work, with reference of a large flow-type landslide locatedin the northern Apennines of Italy, we explored the possibility to quantify displacement vectors on a spatially distributed basis and to quantify volumetric transfer at the slope scale with the application of digital image correlation (DIC) and digital elevation model difference (DEMoD) techniques to multitemporal airborne LiDAR surveys of 2006, 2007 and 2009. DIC was applied to greyscale slope gradient maps retrieved after precise co-registration of LiDAR surveys, and allowed for a reconstruction and quantification of movement patterns over various sectors of the landslide (up to 60 m in the upper and main track of the landslide and up to about 27 m at the landslide toe). DEMoD analysis revealed significant mass transfer from the source to the tracks and toe zone, with the upper flow tracks acting as temporal storage of large amounts of material. The mass balance indicated that during reactivation events significant amounts of debris were actually eroded away from river erosion of the advancing toe. The combined analysis of results allowed discussing governing processes such as the transition from slide to flow, the influence of underlying topography on earthflow mobility and the role of undrained loading as a mechanism of toe zone reactivation. In conclusion, the successful application of DIC and DEMoD to the case study evidenced the added value of high-resolution DEMs in the analysis earthflows kinematics toward a better understanding of their role in the geomorphic evolution of slopes.