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We performed an extensive analysis of C-band SAR datasets provided by the European Space Agency (ESA) satellites ERS-1/2, Envisat ASAR, and Sentinel-1 in the period 1992–2020 aiming at reconstructing the multi-decadal spatial and temporal evolution of the surface displacements at the Brienz/Brinzauls landslide complex, located in canton Graubünden (Switzerland). To this end, we analyzed about 1000 SAR images by applying differential interferometry (InSAR), multitemporal stacking, and persistent scatterer interferometry (PSI) approaches. Moreover, we jointly considered digital image correlation (DIC) on high-resolution multi-temporal digital terrain models (DTM) generated from airborne surveys and InSAR results to compute 3-D surface deformation fields. The extensive network of GNSS stations across the Brienz landslide complex allowed us to extensively validate the deformation results obtained in our remote sensing analyses. Here, we illustrate the limitations occurring when relying on InSAR and/or PSI measurements for the analysis and interpretation of complex landslide scenarios, especially in cases of relevant spatial and temporal heterogeneities of the deformation field. The joint use of InSAR and DIC can deliver a better picture of the evolution of the deformation field, however, not for all displacement components. Since InSAR, PSI and DIC measurements are nowadays routinely used in the framework of local investigations, as well as in regional, national, and/or continental monitoring programs, our results are of major importance for users aiming at a comprehensive understanding of these datasets in landslide scenarios. [ABSTRACT FROM AUTHOR]

In this work, we assess the performance of Persistent Scatterer Interferometry (PSI) based on Sentinel-1 data in the Swiss Alps, focusing on the analysis of surface displacement in areas located in permafrost. To this end, we exploit a PSI dataset over Canton Wallis and the recently published permafrost and ground ice map of Switzerland (PGIM). First we evaluate the sensitivity to radar detection of the terrain, given a particular slope distribution and given satellite orbital geometries. We find that 92 % of the areas currently labeled as permafrost satisfy the geometric visibility criteria, which is a necessary but not sufficient condition for detection of ground movement by satellite radar. Second, we analyse the PSI surface velocity and displacement time series observed in Canton Wallis in the period 2015 to 2022. We find that the displacements rates appear to be correlated with the occurrence of permafrost and that there is a significant difference in displacement rates between ice-poor and ice-rich permafrost compared to no-permafrost zones. However, the difference between the surface velocities retrieved in ice-poor permafrost and no-permafrost zones are small and additional information would be needed to discriminate ice-poor permafrost zones. [ABSTRACT FROM AUTHOR]

We present a procedure to detect landslide events by analyzing in-sequence data acquired from regional broadband seismic networks and spaceborne radar imagery. The combined used of these techniques is meant to exploit their complementary elements and mitigate their limitations when used singularly. To test the method, we consider a series of six slope failures associated to the Piz Cengalo rock avalanche that recently occurred in the Swiss Alps, a region where we can benefit from high spatial density and quality of seismic data, as well as from the high spatial and temporal resolution of the European Space Agency (ESA) Copernicus Sentinel-1 radar satellites. The operational implementation of the proposed approach, in combination with the future increase in availability of seismic and satellite data, can offer a new and efficient solution to build and/or expand landslide catalogues based on quantitative measurements and, thus, help in hazard assessments and the definition of early warning systems at regional scales. [ABSTRACT FROM AUTHOR]

Investigating surface displacements in high alpine environments is often subject to challenges due to the difficult accessibility or harsh climatic conditions. Measurement systems have improved greatly in recent years regarding accuracy, range, or energy consumption. Continuously receiving high-precision, real-time monitoring data from a remote location can still support a better understanding of slope dynamics and risk. We present the design, construction, operation, and performance of a complex surface displacement monitoring system installed in the surroundings of the Great Aletsch Glacier in the Swiss Alps, based on two robotic total stations to continuously measure 3D displacements with high accuracies. In addition, GNSS stations are also considered in order to pass from a local to a geographic reference system, as well as to improve the measurement accuracy. The monitoring network is aimed at studying several types of deformation processes, i.e., (i) gravitationally driven and irreversible rockslide movements around the tongue of the Great Aletsch Glacier, (ii) reversible rock slope deformations caused by annual cycles of groundwater recharge and depletion, and (iii) small irreversible deformations of stable rock slopes resulting from progressive rock damage driven by glacier retreat and cyclic hydraulic and thermal loading. We describe the technical details of the monitoring system, which has been in operation successfully for 6 years, and discuss the system performance in terms of its robustness and accuracy. [ABSTRACT FROM AUTHOR]

The Moosfluh slope, located in the vicinity of the current tongue of the Great Aletsch glacier, Switzerland, hosts one of the largest active instabilities of the European Alps. Despite at this location accelerated slope displacement has been detected over the past decade, the rapid evolution observed between September and November 2016, locally reaching tens of meters, was largely unexpected. During this "crisis phase", the rock mass experienced substantial internal deformation mainly composed of toppling, formation of tensile scarps, and basal sliding. The large internal deformation caused also several local failure events in the form of single block falls and/or rock mass collapses of moderate size. Here we focus on the post-crisis, i.e. the period going between spring 2017 until today. The deformation occurring at the Moosfluh slope is still consistent and rock failure events are regularly going on, however, not in a dramatic fashion as observed in fall 2016. We show the results obtained by jointly investigating satellite, airborne, and ground based imagery, exploiting optical and radar sensors, as well as the data recorded from a local seismic network. In particular, we focus on the joint analysis of the information obtained from the optical imagery acquired with high temporal frequencies and the seismic waveforms associated to rock failure events. The combined remote sensing and geophysical dataset presented here is unique, and allows for a detailed interpretation of the rapid spatial and temporal rock mass disintegration in an alpine slope. Our results are of interest to understand mutual influences between predisposing slope instability factors (i.e., mainly due to geological, structural, and geomorphological conditions), and external driving factors (i.e., seismicity and meteo-climatic effects) on the progressive evolution of rock mass, specifically at the Moosfluh slope but also in similar case scenarios. [ABSTRACT FROM AUTHOR]

The analysis of Earth surface processes trough Space borne Synthetic Aperture Radar (SAR) observations is becoming more and more popular. The recent advent of the Copernicus Sentinel-1 constellation has boosted our capabilities to map and monitor surface changes globally, with unprecedented spatial and temporal resolutions. SAR data is nowadays invaluable to study surface changes due to the co-seismic and post-seismic effects of earthquakes, to analyze volcanic unrest and eruptions, and to monitor mass movements. In this contribution, I will focus on the application of space borne SAR to study rapid mass wasting, by discussing advantages and specific limitations, and showing real application scenarios in alpine areas and active volcanic regions. The examples presented will range from catastrophic slope failures, such as the rock avalanche of Piz Cengalo and the subsequent debris-flow recently occurred in the Swiss Alps, to the investigation of active volcanic environments, such as erosion and deposition processes due to pyroclastic flows and lahars at Colima volcano. [ABSTRACT FROM AUTHOR]

Fractured rock-masses deform in response to changes in pore pressure. In alpine catchments, groundwater flow dynamics is generally dominated by strong recharge signal from snowmelt infiltration in spring / early summer and in early winter, and punctuated by large rainstorms in snow-free periods. In crystalline rock slopes, infiltration occurs along discontinuities, such as faults and joints. Under constant normal stress joint apertures increase non-linearly during pore pressure increase, increasing the volume of saturated rock masses and leading to surface deformation. The latter can be measured with high-resolution geodetic monitoring systems and remote sensing methods such as DInSAR.In this work, we discuss temporal and spatial variations of reversible ground surface deformation measured in the Aletsch region, Switzerland. The study area is situated in the vicinity of the tongue of the Great Aletsch Glacier, central Swiss Alps, in the gneissic and granitic bedrock of the Aar massif. The valley (1550 to 2300 m.a.s.l.), is roughly oriented parallel to the main Alpine foliation (NE-SW) and to major fault zones. Total annual precipitation is less than 1 m/y, but snow depth frequently reaches 2 m during winter, with strong spatial variability. We use a network of 4 continuous Global Positioning System (cGPS) stations and 90 reflectors linked to 2 total stations (TPS), operating since 2014, to track deformation at millimetric to centimetric scale. We use weather and hydrological data from surrounding stations to estimate the timing of infiltration.At some locations in our study area we observe peak-to-peak magnitude of seasonal deformation over 2 cm, whereas other areas show no significant seasonal deformation. Measured displacement vectors are generally oriented towards the valley center in spring, when deformation rates are the highest (>0.5 mm/d). The start of the high-rate of deformation period also varies spatially. The South-facing slope starts deforming around 20 days earlier than the North-facing slope. The vertical component of motion is generally smaller than the horizontal one, and often below the noise level. Finally, we discuss possible factors (e.g. topography and slope orientation, discontinuities' orientation and density, lithology, groundwater recharge magnitudes and durations) that might influence the spatial and temporal variations of reversible deformation on the slopes adjacent to the tongue of the Great Aletsch Glacier. [ABSTRACT FROM AUTHOR]