Latest advances in topographic data acquisition techniques have greatly enhanced the possibility to analyse landscapes in order to understand the processes that shaped them. High-resolution Digital Elevation Models (DEMs), such as LiDAR-derived ones, provide detailed topographic information. In particular, if multi-temporal DEMs are available, it is possible to carry out a detailed geomorphic change detection analysis. This analysis may provide information about the dynamics of large landslides and may thus, be useful for landslide risk assessments. However, LiDAR-derived DEMs are mostly available only as post-event surveys. The technique is relatively recent, and local or national authorities only started widespread surveys in the last decade. Therefore, it is of a certain interest to analyse the effectiveness of DEMs derived from technical cartography to produce reliable volumetric estimates related to large landslides. This study evaluates the use of a multi-source DEM of Difference (DoD) analysis for the investigation of a large landslide -Le Laste-, which occurred on November 12, 2014 on Mount Antelao (eastern Italian Alps). The landslide initiated as a 365,000 m3 rockslide close to the summit of the mountain and transformed into a debris avalanche during its runout. The comparison of pre- and post-event DEMs allowed for the identification and quantification of erosion and deposition areas, and for the estimation of landslide volume. A sound back-analysis of the landslide with the 3D numerical model DAN3D was based on this comparison and on seismic records of the event. These seismic records proved to be remarkably useful, as they allowed for the calibration of the simulated landslide velocity. This ensured the reliability of the model notwithstanding the topographic datasets, intrinsic uncertainties. We found that using a pre-event DEM derived from technical cartography tends to slightly overestimate the volume with respect to the use of the more accurate LiDAR-derived DEM. In recent years, the landslide risk around Mt. Antelao has been increasing alongside the ever-growing population and human activities in the area. Sediment accumulations produced by the Le Laste landslide significantly amplified the debris flow hazard by providing new sediment sources. Therefore, it is crucial to delineate the distribution of this material to enable an adequate debris flow hazard assessment. The material properties derived from the back-analysis of the Le Laste landslide can be used to simulate the runout of possible future events, and to generate reliable hazard zone maps, which are necessary for effective risk mitigation

Indices of connectivity are critical means for moving from qualitative to (semi-)quantitative evaluations of material (e.g., water, sediment and nutrients) transfer across the building blocks of a terrestrial system. In geomorphology, compared to closely related disciplines like ecology and hydrology, the development of indices has only recently started and as such presents opportunities and challenges that merit attention. In this paper, we review existing indices of sediment connectivity and suggest potential avenues of development for meeting current basic and applied research needs. Specifically, we focus on terrestrial geomorphic systems dominated by processes that are driven by hydro-meteorological forcing, neglecting seismically triggered events, karstic systems and environments controlled by eolian processes. We begin by setting a conceptual framework that combines external forcings (drivers) and system (intrinsic) structural and functional properties relevant to sediment connectivity. This framework guides our review of response variables suitable for sediment connectivity indices. In particular, we consider three sample applications concerned with sediment connectivity in_ (i) soil studies at the plot scale, (ii) bedload transport at the reach scale, and (iii) sediment budgets at the catchment scale. In relation to the set of response variables identified, we consider data availability and issues of data acquisition for use in indices of sediment connectivity. We classify currently available indices in raster based, object or network based, and indices based on effective catchment area. Virtually all existing indices address the degree of static, structural connectivity only, with limited attention for process-based, functional connectivity counterparts. Most recent developments in indices of sediment connectivity deal, to some extent, with different styles of anthropogenic and hydro-meteorological forcings and with the temporal variability of sediment connectivity, by incorporating additional variables and parameters in existing indices. We believe that, in order to use structural connectivity as explanatory or predictive tool, indices need to be interpretable in relation to geomorphic processes, material properties, and forcing styles and magnitude-frequency spectra. Improvements in this direction can be made through studies shaped to constrain structural-functional correlations across a range of hydro-meteorological scenarios, for example employing field-based techniques such as particle tracking and sediment provenance analysis, as well as numerical simulations. We further consider existing indices in relation to spatial and temporal scales. The latter have immediate implications on the distinction and application between indices and models of sediment connectivity. In this context, we suggest that sediment connectivity over millennial or longer time scales should be dealt with models, as opposed to indices.