Volcano deformation may occur under different conditions. To understand how a volcano deforms, as well as relations with magmatic activity, we studied Mt. Etna in detail using interferometric synthetic aperture radar (InSAR) data from 1994 to 2008. From 1994 to 2000, the volcano inflated with a linear behavior. The inflation was accompanied by eastward and westward slip on the eastern and western flanks, respectively. The portions proximal to the summit showed higher inflation rates, whereas the distal portions showed several sectors bounded by faults, in some cases behaving as rigid blocks. From 2000 to 2003, the deformation became nonlinear, especially on the proximal eastern and western flanks, showing marked eastward and westward displacements, respectively. This behavior resulted from the deformation induced by the emplacement of feeder dikes during the 2001 and 2002–2003 eruptions. From 2003 to 2008, the deformation approached linearity again, even though the overall pattern continued to be influenced by the emplacement of the dikes from 2001 to 2002. The eastward velocity on the eastern flank showed a marked asymmetry between the faster sectors to the north and those (largely inactive) to the south. In addition, from 1994 to 2008 part of the volcano base (south, west, and north lower slopes) experienced a consistent trend of uplift on the order of ∼0.5 cm/yr. This study reveals that the flanks of Etna have undergone a complex instability resulting from three main processes. In the long term (103–104 years), the load of the volcano is responsible for the development of a peripheral bulge. In the intermediate term (≤101 years, observed from 1994 to 2000), inflation due to the accumulation of magma induces a moderate and linear uplift and outward slip of the flanks. In the short term (≤1 year, observed from 2001 to 2002), the emplacement of feeder dikes along the NE and south rifts results in a nonlinear, focused, and asymmetric deformation on the eastern and western flanks. Deformation due to flank instability is widespread at Mt. Etna, regardless of volcanic activity, and remains by far the predominant type of deformation on the volcano.

Starting in July 2011, anomalous seismicity was observed at El Hierro Island, a young oceanic island volcano. On 12 October 2011, the process led to the beginning of a submarine NW‐SE fissural eruption at ~15 km from the initial earthquake loci, indicative of significant lateral magma migration. Here we conduct a multifrequency, multisensor interferometric analysis of spaceborne radar images acquired using three different satellite systems (RADARSAT‐2, ENVISAT, and COSMO‐SkyMed (Constellation of Small Satellites for Mediterranean Basin Observation)). The data fully captures both the pre‐eruptive and coeruptive phases. Elastic modeling of the ground deformation is employed to constrain the dynamics associated with the magmatic activity. This study represents the first geodetically constrained active magmatic plumbing system model for any of the Canary Islands volcanoes, and one of the few examples of submarine volcanic activity to date. Geodetic results reveal two spatially distinct shallow (crustal) magma reservoirs, a deeper central source (9.5 ± 4.0 km), and a shallower magma reservoir at the flank of the southern rift (4.5 ± 2.0 km). The deeper source was recharged, explaining the relatively long basaltic eruption, contributing to the observed island‐wide uplift processes, and validating proposed active magma underplating. The shallowest source may be an incipient reservoir that facilitates fractional crystallization as observed at other Canary Islands. Data from this eruption supports a relationship between the depth of the shallow crustal magmatic systems and the long‐term magma supply rate and oceanic lithospheric age. Such a relationship implies that a factor controlling the existence/depth of shallow (crustal) magmatic systems in oceanic island volcanoes is the lithosphere thermomechanical behavior.

Volcanoes deform as a consequence of the rise and storage of magma; once magma reaches a critical pressure, an eruption occurs. However, how the edifice deformation relates to its eruptive behavior is poorly known. Here, we produce a joint interpretation of spaceborne InSAR deformation measurements and volcanic activity at Mt. Etna (Italy), between 1992 and 2006. We distinguish two volcano‐tectonic behaviors. Between 1993 and 2000, Etna inflated with a starting deformation rate of ∼1 cm yr−1 that progressively reduced with time, nearly vanishing between 1998 and 2000; moreover, low‐eruptive rate summit eruptions occurred, punctuated by lava fountains. Between 2001 and 2005, Etna deflated, feeding higher‐eruptive rate flank eruptions, along with large displacements of the entire East‐flank. These two behaviors, we suggest, result from the higher rate of magma stored between 1993 and June 2001, which triggered the emplacement of the dike responsible for the 2001 and 2002–2003 eruptions. Our results clearly show that the joint interpretation of volcano deformation and stored magma rates may be crucial in identifying impending volcanic eruptions.

We found the first evidence, in the last 30 years, of a renewed magmatic activity at Campi Flegrei caldera from January 2012 to June 2013. The ground deformation, observed through satellite interferometry and GPS measurements, have been interpreted as the effect of the intrusion at shallow depth (3090 ± 138 m) of 0.0042 ± 0.0002 km3 of magma within a sill. This interrupts about 28 years of dominant hydrothermal activity and occurs in the context of an unrest phase which began in 2005 and within a more general ground uplift that goes on since 1950. This discovery has implications on the evaluation of the volcanic risk and in the volcanic surveillance of this densely populated area.

A major goal in volcanology is to be able to constrain the physical properties of a volcanic system using surface observations. The behaviour of a volcanic system following an eruption can provide powerful constraints on these properties and can provide valuable information for understanding future hazard. We use spatially and temporally dense observations of surface deformation following the 12 June 2011 eruption of Nabro (Eritrea) to place constraints on the mechanics of its subsurface volcanic system. Nabro was imaged 129 times by TerraSAR-X and COSMO-SkyMed satellites during a 15-month period following the eruption. We have produced a detailed time series of the line-of-sight (LOS) displacements at Nabro, finding that the volcano subsides during the entire observation period at a decaying rate. We found significant atmospheric artefacts remained in the data set after a standard spatio-temporal filter was applied. Applying an empirical correction using a linear phase-elevation relationship removed artefacts but also removed real topographically correlated deformation. Instead, we were able to correct each SAR acquisition using independent delay estimates derived from the ECMWF ERA-Interim (ERA-I) global atmospheric model. The corrected time series can be modelled with the deflation of a Mogi source at ∼ 6.4 ± 0.3 km depth. Modelling the time series using viscoelastic relaxation of a shell which surrounds a spherical magma chamber can explain the observed subsidence without a source of further volume loss if the magma is compressible. CO 2 outgassing is also a possible cause of continued subsidence. Contraction due to cooling and crystallisation, however, is probably minor. If any post-eruptive recharge of the magmatic system at Nabro is occurring, the rate of recharge must be slower than the post-eruptive relaxation processes. Combined with the lack of pre-eruptive inflation, we suggest that recharge of the magmatic system at Nabro either occurs at a rate that is slower than our detection limit, or it occurs episodically. This case study demonstrates the power of long, dense geodetic time series at volcanoes.

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We investigate the Mw 6.5 Norcia (Central Italy) earthquake by exploiting seismological data, DInSAR measurements, and a numerical modelling approach. In particular, we first retrieve the vertical component (uplift and subsidence) of the displacements affecting the hangingwall and the footwall blocks of the seismogenic faults identified, at depth, through the hypocenters distribution analysis. To do this, we combine the DInSAR measurements obtained from coseismic SAR data pairs collected by the ALOS-2 sensor from ascending and descending orbits. The achieved vertical deformation map displays three main deformation patterns: (i) a major subsidence that reaches the maximum value of about 98 cm near the epicentral zones nearby the town of Norcia; (ii) two smaller uplift lobes that affect both the hangingwall (reaching maximum values of about 14 cm) and the footwall blocks (reaching maximum values of about 10 cm). Starting from this evidence, we compute the rock volumes affected by uplift and subsidence phenomena, highlighting that those involved by the retrieved subsidence are characterized by significantly higher deformation values than those affected by uplift (about 14 times). In order to provide a possible interpretation of this volumetric asymmetry, we extend our analysis by applying a 2D numerical modelling approach based on the finite element method, implemented in a structural-mechanic framework, and exploiting the available geological and seismological data, and the ground deformation measurements retrieved from the multi-orbit ALOS-2 DInSAR analysis. In this case, we consider two different scenarios: the first one based on a single SW-dipping fault, the latter on a main SW-dipping fault and an antithetic zone. In this context, the model characterized by the occurrence of an antithetic zone presents the retrieved best fit coseismic surface deformation pattern. This result allows us to interpret the subsidence and uplift phenomena caused by the Mw 6.5 Norcia earthquake as the result of the gravitational sliding of the hangingwall along the main fault plane and the frictional force acting in the opposite direction, consistently with the double couple fault plane mechanism.