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Rockfalls are a recurrent cause of disruption for transportation corridors running along the bottom of U-shaped alpine valleys. In some scenarios, risk may effectively be reduced only by implementing an early-warning system able to give notice of incipient failures on the slope. This paper describes a successful example of rockfall forecasting and risk management in proximity of the Gallivaggio sanctuary (San Giacomo Valley, Central Italian Alps). Since 2016, a Ground-Based Synthetic Aperture Radar continuously monitored a roughly 500-m high, sub-vertical granitic slope. Monitoring data evidenced the presence and continued movement of a ~ 5000 m3 highly unstable mass, having a projected fall trajectory directly threatening the sanctuary and the adjacent segment of a national road. Traffic and access to the sanctuary were regulated by a sequence of alert thresholds, and restrictive orders were issued according to the activity of the instability. The rock mass eventually fell, and the failure-time was accurately predicted several hours in advance. Despite damage to both the road and buildings, the timely evacuation of the area prevented any loss of life. The case study provides a reference framework to better manage rockfall risk in areas where the installation of adequate protective barriers is not technically feasible. [ABSTRACT FROM AUTHOR]

In recent years, space-borne InSAR (interferometric synthetic aperture radar) techniques have shown their capabilities to provide precise measurements of Earth surface displacements for monitoring natural processes. Landslides threaten human lives and structures, especially in urbanized areas, where the density of elements at risk sensitive to ground movements is high. The methodology described in this paper aims at detecting terrain motions and building deformations at the local scale, by means of satellite radar data combined with in situ validation campaigns. The proposed approach consists of deriving maximum settlement directions of the investigated buildings from displacement data revealed by radar measurements and then in the cross-comparison of these values with background geological data, constructive features and on-field evidence. This validation permits better understanding whether or not the detected movements correspond to visible and effective damages to buildings. The method has been applied to the southwestern sector of Volterra (Tuscany region, Italy), which is a landslide-affected and partially urbanized area, through the use of COSMO-SkyMed satellite images as input data. Moreover, we discuss issues and possible misinterpretations when dealing with PSI (Persistent Scatterer Interferometry) data referring to single manufactures and the consequent difficulty of attributing the motion rate to ground displacements, rather than to structural failures. [ABSTRACT FROM AUTHOR]

Ground-based synthetic aperture radar interferometry (GBInSAR) remote sensing technique has been repeatedly proved an effective tool for monitoring built environment affected by structural and geological criticalities. In this paper, it is described how this technique can be successfully applied for early-warning procedures and detection of ongoing deterioration processes on archeological and cultural heritage sites. An integrated approach of GBInSAR and terrestrial laser scanner (TLS) technologies was performed on Volterra test site (Tuscany, Italy), where a sudden collapse of a 35-m wide section of city walls occurred on January 31, 2014. The installed early-warning monitoring system is capable of an accurate and focused real-time displacement detection of the south-western side of the city including walls, buildings, and monuments, thus allowing prompt interventions for citizens safety and conservation purposes. The effectiveness of this alert technique became evident when the precursors of a second impressive wall collapse were clearly detected. From the beginning of the GBInSAR monitoring, we measured a constant displacement velocity of 0.1 mm/h in correspondence to a 15-m high wall sustaining the Acropolis and lying an underground parking. After a sudden increase of velocity values up to 1.7 mm/h, the local authorities were alerted so that they had time to interdict the area to citizens and to take adequate safety countermeasures two days before the collapse. [ABSTRACT FROM PUBLISHER]

Ground-Based Interferometric Synthetic Aperture Radar (GBInSAR) is an efficient technique for capturing short, subtle episodes of conduit pressurization in open vent volcanoes like Stromboli (Italy), because it can detect very shallow magma storage, which is difficult to identify using other methods. This technique allows the user to choose the optimal radar location for measuring the most significant deformation signal, provides an exceptional geometrical resolution, and allows for continuous monitoring of the deformation. Here, we present and model ground displacements collected at Stromboli by GBInSAR from January 2010 to August 2014. During this period, the volcano experienced several episodes of intense volcanic activity, culminated in the effusive flank eruption of August 2014. Modelling of the deformation allowed us to estimate a source depth of 482 ± 46 m a.s.l. The cumulative volume change was 4.7 ± 2.6 × 105 m3. The strain energy of the source was evaluated 3-5 times higher than the surface energy needed to open the 6-7 August eruptive fissure. The analysis proposed here can help forecast shifts in the eruptive style and especially the onset of flank eruptions at Stromboli and at similar volcanic systems (e.g. Etna, Piton de La Fournaise, Kilauea). [ABSTRACT FROM AUTHOR]

Volcano slope instability manifests in many forms, ranging from steady state to punctuated movement, or shallow erosion to deep-seated spreading. The interplay of gravity, magmatic or hydrothermal fluids, and often active tectonics on a volcanic edifice results in complex spatial and temporal variations in deformation kinematics. While this makes the recognition, assessment, and monitoring of volcano slope instability challenging, advancements in Synthetic Aperture Radar (SAR) technology have significantly accelerated our knowledge of instability phenomena and our ability to assess their hazards. This review discusses the applications and challenges of SAR imagery to various slope instabilities at volcanoes around the world. SAR amplitude images are powerful tools for mapping areas of geomorphological changes. These snapshots can be combined using Interferometric SAR (InSAR) to create multi-temporal deformation maps that provide unique information on the evolution of slope failures. Space-borne InSAR has become an economic way to detect changes at volcanoes at very high resolution. Ground-Based InSAR (GBInSAR) can produce frequent SAR images (on the order of seconds to minutes), propelling InSAR from monitoring to surveillance and early-warning applications. However, interpreting InSAR-derived ground deformation signals related to volcano slope instability is still challenging. Deformation from magma rise or variations in hydrothermal systems may be inseparable from persistent, deep-seated flank motion. Similarly, shallow or localized ground motion may occur in overlap with thermal contraction or subsidence of newly emplaced lava or tephra deposits. If triggered to failure, landslides can vary over several magnitudes, from small-volume rock falls that pose only a localized hazard, to large-volume debris avalanches capable of travelling tens of kilometers away from the source. These collapses can have cascading hazards if accompanied by directed blasts or tsunamis, emphasizing the need for continued advancement of our understanding of these events and their consequences. To highlight the utility of SAR for measuring and monitoring mass movement, two case studies of Stromboli (Italy) and Pacaya (Guatemala) volcanoes are discussed in detail, where recent instability events, persistent volcanic activity, and ground truth constraints have resulted in excellent case-histories in applying SAR imagery to understand these potentially hazardous slope instabilities. [ABSTRACT FROM AUTHOR]