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.

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The vertical transport of large volumes of silicic magma, which drives volcanic eruptions and the long‐term compositional evolution of the continental crust, is a highly debated problem. In recent years, dyking has been favored as the main ascent mechanism, but the structural connection between a distributed configuration of melt‐filled pores in the source region and shallow magma reservoirs remains unsolved. In the Central Andes, inversion of a new high‐resolution Bouguer anomaly data over the Altiplano‐Puna Magma Body (APMB) reveals ~15 km wide, vertically elongated, low‐density, 3D structures rooted at the top of the APMB at 20 km depth. We integrate our gravity inversion with the available geophysical, geological, and petrological observations, and in agreement with petrological/mechanical considerations propose that, in this region of the Andes, partially molten granitic bodies ascend diapirically through the hot ductile mid‐upper crust.

This paper presents a gravity inversion method for determining the volumes of bodies with pre-established density contrasts. The method works step-by-step on a prismatic partition of the subsurface volume, expanding the anomalous bodies to fit the observed gravity values in a systematic exploration of model possibilities. The process is treated in a 3-D context; at the same time, it can determine a simple regional trend. Moreover, positive and negative density contrasts are simultaneously accepted. The solution is obtained by a double condition: (1) the 2 -fitness to the observed gravity data (model fitness) and (2) the minimization of the total (weighted) anomalous mass (model smoothness). A positive parameter is used to balance the two minimization terms. The method is applied to a simulated example and also to a real example: the volcanic island of Gran Canaria (Canary Islands, Spain). In both cases, the results obtained show the possibilities of the method.

Changes in gravity and/or surface deformation are often associated with volcanic activity. Usually, bodies with simple geometry (e.g., point sources, prolate or oblate spheroids) are used to model these signals considering anomalous mass and/or pressure variations. We present a new method for the simultaneous, nonlinear inversion of gravity changes and surface deformation using bodies with a free geometry. Assuming simple homogenous elastic conditions, the method determines a general geometrical configuration of pressure and density sources. These sources are described as an aggregate of pressure and density point sources, fitting the whole data set (given some regularity conditions). The approach works in a growth step‐by‐step process that allows us to build very general geometrical configurations. The methodology is validated against an ellipsoidal body with anomalous pressure and a parallelepiped body with anomalous density, buried in an elastic medium. The simultaneous inversion of deformation and gravity values permits a good reconstruction of the assumed bodies. Finally, the inversion method is applied to the interpretation of gravity, leveling, and interferometric synthetic aperture radar (InSAR) data from the volcanic area of Campi Flegrei (Italy) for the period 1992–2000. For this period, a model with no significant mass change and an extended decreasing pressure region satisfactorily fits the data. The pressure source is located at about ∼1500 m depth, and it is interpreted as corresponding to the dynamics of the shallow (depth 1–2 km) hydrothermal system confined to the caldera fill materials.

Geophysical signals accompanying the reactivation of a volcano after a period of quiescence must be evaluated as potential precursors to impending eruption. Here we report on the reactivation of the central volcanic complex of Tenerife, Spain, in spring 2004 and present gravity change maps constructed by time‐lapse microgravity measurements taken between May 2004 and July 2005. The gravity changes indicate that the recent reactivation after almost a century of inactivity was accompanied by a sub‐surface mass addition, yet we did not detect widespread surface deformation. We find that the causative source was evolving in space and time and infer fluid migration at depth as the most likely cause for mass increase. Our results demonstrate that, even in the absence of previous baseline data and ground deformation, microgravity measurements early in developing crises provide crucial insight into the dynamic changes beneath a volcano.

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Volcano observatories provide near real-time information and, ultimately, forecasts about volcano activity. For this reason, multiple physical and chemical parameters are continuously monitored. Here, we present a new method to efficiently estimate the location and evolution of magmatic sources based on a stream of real-time surface deformation data, such as High-Rate GPS, and a free-geometry magmatic source model. The tool allows tracking inflation and deflation sources in time, providing estimates of where a volcano might erupt, which is important in understanding an on-going crisis. We show a successful simulated application to the pre-eruptive period of May 2008, at Mount Etna (Italy). The proposed methodology is able to track the fast dynamics of the magma migration by inverting the real-time data within seconds. This general method is suitable for integration in any volcano observatory. The method provides first order unsupervised and realistic estimates of the locations of magmatic sources and of potential eruption sites, information that is especially important for civil protection purposes.