Abstract
Spaceborne radar interferometry is a powerful tool to characterize landslides at local and regional scales. However, its application to very slow rock slope deformations in alpine environments (displacement rates < 5 cm/year) remains challenging, mainly due to low signal to noise ratio, atmospheric disturbances, snow cover effects, and complexities resulting from heterogeneous displacement in space and time. Here we combine SqueeSARTM data, targeted multi-temporal baseline DInSAR, GPS data, and detailed field morpho-structural mapping, to unravel the kinematics, internal segmentation, and style of activity of the Mt. Mater deep-seated gravitational slope deformation (DSGSD) in Valle Spluga (Italy). We retrieve slope kinematics by performing 2D decomposition (2D InSAR) of SqueeSARTM products derived from Sentinel-1 data acquired in ascending and descending orbits. To achieve a spatially-distributed characterization of DSGSD displacement patterns and activity, we process Sentinel-1 A/B images (2016-2019) with increasing temporal baselines (ranging from 24-days to 1-year) and generate several multi-temporal interferograms. Unwrapped displacement maps are validated using ground-based GPS data. Interferograms derived with different temporal baselines reveal a strong kinematic and morpho-structural heterogeneity and outline nested rockslides and active sectors, that arise from the background displacement signal of the main DSGSD. Seasonal interferograms, supported by GPS displacement measurements, reveal non-linear displacement trends suggesting a complex response of different slope sectors to rainfall and snowmelt. Our analyses clearly outline a composite slope instability with different nested sectors possibly undergoing different evolutionary trends towards failure. The results herein outline the potential of a targeted use of DInSAR for the detailed investigation of very slow rock slope deformations in different geological and geomorphological settings.
Highlights
Very slow rock slope deformations known as deep-seated gravitational slope deformations (DSGSD) are widespread in high mountain environments worldwide [1,2,3,4,5]
Even if displacement rates are low and apparently steady, DSGSDs result in large cumulative deformations that are mirrored by different morpho-structural field evidence
Mater DSGSD by exploiting the available SqueeSARTM dataset based on Sentinel-1 radar images (Figure 3a,b), from which we derived the products of 2D displacement rate vector decomposition (2DInSAR)
Summary
Very slow rock slope deformations known as deep-seated gravitational slope deformations (DSGSD) are widespread in high mountain environments worldwide [1,2,3,4,5] The evolution of these phenomena is strongly constrained by inherited geological structure and long-term climatic forcing and occurs through progressive damage accumulation. Even if displacement rates are low (usually smaller than 5 cm/year [11,12,13]) and apparently steady, DSGSDs result in large cumulative deformations that are mirrored by different morpho-structural field evidence These include extensional features as double-crested ridges, trenches, scarps, counterscarps, and half-grabens, usually dominating in the upper slope sectors, and compressional features like bulging, thrusting and folding, and nested large landslides in the middle-lower sectors. The kinematic interpretation of individual features and their associations provide critical information on the overall slope deformation mechanism and the patterns of both distributed and localized strain, reflecting deep-seated deformation mechanisms [14]
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