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Stromboli volcano (Aeolian Archipelago, Southern Italy) experienced an increase in its volcanic activity from late December 2012 to March 2013, when it produced several lava overflows, major Strombolian explosions, crater-wall collapses pyroclastic density currents and intense spatter activity. An analysis of the displacement of the NE portion of the summit crater terrace and the unstable NW flank of the volcano (Sciara del Fuoco depression) has been performed with a ground- based interferometric synthetic aperture radar (GBInSAR) by dividing the monitored part of the volcano into five sectors, three in the summit vents region and two in the Sciara del Fuoco. Changes in the displacement rate were observed in sectors 2 and 3. Field and thermal surveys revealed the presence of an alignment of fumaroles confirming the existence of an area of structural discontinuity between sectors 2 and 3. High displacement rates in sector 2 are interpreted to indicate the increase in the magmastatic pressure within the shallow plumbing systems, related to the rise of the magma level within the conduits, while increased displacement rates in sector 3 are connected to the lateral expansion of the shallow plumbing system. The increases and decreases in the displacement rate registered by the GBInSAR system in the upper part of the volcano have been used as a proxy for changes in the pressure conditions in the shallow plumbing system of Stromboli volcano and hence to forecast the occurrence of phases of higher-intensity volcanic activity. [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]

We present a joint exploitation of space-borne and ground-based Synthetic Aperture Radar Interferometry (InSAR) and Multi Temporal (MT) InSAR measurements for investigating the Stromboli volcano (Italy) deformation phenomena. In particular, we focus our analysis on three periods: a) the time interval following the 2014 flank eruption, b) the July–August 2019 eruption and c) the following post-eruptive phase. To do this, we take advantage from an unprecedented set of space-borne and ground-based SAR data collected from April 2015 up to November 2019 along two (one ascending and one descending) Sentinel-1 (S-1) tracks, as well as, in the same period, by two ground-based systems installed along the Sciara del Fuoco northern rim. Such data availability permitted us to first characterize the volcano long-term 3D deformation behavior of the pre-eruptive period (April 2015–June 2019), by jointly inverting the space-borne and ground-based InSAR measurements. Then, the GB-SAR measurements allowed us to investigate the sin-eruptive time span (3rd July 2019 – 30th August 2019) which revealed rapid deformation episodes (e.g. more than 30 mm/h just 2 min before the 3rd July 2019 explosion) associated with the eruptive activity, that cannot be detected with the weekly S-1 temporal sampling. Finally, the S-1 measurements permitted to better constrain the post 2019 eruption deformations (31st August 2019 – 5th November 2019), which are mainly located outside the GB-SAR sensed area. The presented results demonstrate the effectiveness of the joint exploitation of the InSAR measurements obtained through satellite and terrestrial SAR systems, highlighting their strong complementarity to map and interpret the deformation phenomena affecting volcanic areas. • A joint exploitation of spaceborne and ground-based InSAR measurements is presented. • The InSAR analysis focuses on Stromboli volcano, from April 2015 to November 2019. • Two Sentinel-1 tracks and two independent GB-SAR systems have been used. • Results show a strong complementarity of spatial and terrestrial InSAR measurements. [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, results in complex spatial and temporal variations in deformation kinematics; deformation from magma rise or variations in hydrothermal systems may be inseparable from deep-seated and persistent flank motion. Similarly, shallow or localized ground motion may overlap with thermal contraction or subsidence of newly emplaced lava or tephra deposits. While this makes the recognition, assessment, and monitoring of volcano slope instability challenging, advancements in Synthetic Aperture Radar (SAR) technology have accelerated our knowledge of instability phenomena and our ability to assess their hazards. SAR amplitude images are powerful tools for mapping areas of geomorphological changes, which 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, propelling InSAR from monitoring to surveillance and early-warning applications. Various InSAR techniques have been used to measure persistent, transient, or surficial slope movement of at least ten volcanoes, some of which have had several periods or instances of flank motion. To highlight the utility of SAR for measuring and monitoring mass movements, studies at Stromboli (Italy) and Pacaya (Guatemala) volcanoes are reviewed 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. At Stromboli, years of monitoring with GBInSAR has led to an operational approach to mitigate landslide risks by defining a relationship between measured displacement rates and associated instability and eruptive hazards. This aided in anticipating a flank eruption 11 hours in advance in 2014. At Pacaya, the combined use of aerial and satellite InSAR time series successfully measured a large transient co-eruptive event in 2010. This was determined to have initiated a new stage of rifting, implicating new potential hazards for future eruptions. Monitoring slope instability over the world's volcanoes will continue to increase with new radar satellites schedule to launch around 2020-2022, including ALOS-4 PALSAR by JAXA, NISAR by NASA-India, and SAOCOM by Argentine Space Agency. These satellites will provide more frequent images and improved coherence and coverage than previous sensors, with the potential to move from observing and explaining volcanic slope instability to tracking and forecasting failures. However, this enhanced mitigation potential relies on the manageability, rapidity, and fusing of these large datasets, and the integration of measured persistent or flank unrest into emergency planning. [ABSTRACT FROM AUTHOR]