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Active calderas are major volcanic features of the Earth’s crust associated with shallow magma reservoirs, high geothermal gradients, and geodynamic unrests often documented through historical time. As large caldera-forming eruptions are also among the most catastrophic events that may affect the Earth’s surface, calderas are ostensibly the sites of major interest for both the scientific community and governmental institutions worldwide. The Campi Flegrei is an active volcanic area located west of the city of Naples, largely on the continental shelf of the Eastern Tyrrhenian margin that has been characterized by dominantly explosive eruptions during the latest Quaternary. This is one among the highest volcanic risk-prone areas of the world and likely the only example in the historical record of a caldera where dramatic ground/seafloor deformation (more than 4 m of uplift between 1950 and 1984) was not followed by a volcanic eruption. This suggests some important role played by the heath and gas flow from the magma chamber and the dynamics of the shallow aquifers in the unrest episodes. Recent research offshore the Campi Flegrei has shown that a significant part of the volcaniclastic products and sedimentary processes are still largely unknown. The structure of the hydrothermal system associated with the offshore substructure of the caldera system is poorly constrained, and even the caldera-like diagnostic characters postulated for the older phase in the evolution of the Campi Flegrei, largely based on outcrop data, are somewhat questionable. Therefore, it has become clear that only drilling both the onshore and offshore parts of the caldera much deeper than conventional coring may provide a relatively complete stratigraphic record that could not be preserved on land. We propose 15 drill sites (1 deep drill site onland and 14 shallower drill sites offshore) that are necessary in order to reconstruct the Late Quaternary stratigraphy, structure, hydrothermal system and geodynamic evolution of the Campi Flegrei district as a component of the eastern Tyrrhenian margin. According with the outcomes of a MagellanPlus Workshop held in Napoli in February 2017, it was suggested the Campi Flegrei Caldera Drilling Project should be jointly submitted to IODP and ICDP as an Amphibious Drilling Proposal by the end of 2018. The Workshop participant agreed on the proposition that the IODP component of the proposal should focus on integrated stratigraphy of the caldera fill and resurgent structure, as well as on petrology and architecture of shallow structural levels (0-500 m depth), whereas the ICDP component should be designed to understand the rock-fluid properties, physical-chemical processes and the geothermal system at deeper structural levels (0-3000 m depth). Onshore drilling of a pilot hole has already been completed, enlightening many new results which shed completely new light on the volcanic history and on the extension and mechanisms of the caldera itself. The joint drilling project is hence based on solid grounds and can certainly become a key for a large step forwards in the knowledge of caldera dynamics and eruption prediction.

Dikes along rift zones propagate laterally downslope for tens of kilometers, often becoming arrested before topographic reliefs. We use analogue and numerical models to test the conditions controlling the lateral propagation and arrest of dikes, exploring the presence of a slope in connection with buoyancy and rigidity layering. A gentle downslope assists lateral propagation when combined with an effective barrier to magma ascent, e.g., gelatin stiffness contrasts, while antibuoyancy alone may be insufficient to prevent upward propagation. We also observe that experimental dikes become arrested when reaching a plain before opposite reliefs. Our numerical models show that below the plain the stress field induced by topography hinders further dike propagation. We suggest that lateral dike propagation requires an efficient barrier (rigidity) to upward propagation, assisting antibuoyancy, and a lateral pressure gradient perpendicular to the least compressive stress axis, while dike arrest may be induced by external reliefs.

Volcano deformation monitoring is crucial to understand how magma emplaces, propagates and erupts. Therefore, volcano deformation research projects are particularly important opportunities to improve our understanding of volcano dynamics. SAR4Volcanoes is a 2-year research project funded by the Italian Space Agency (ASI) within the framework of a cooperation agreement with the Japan Aerospace Exploration Agency (JAXA). It focuses on volcano deformation analysis through Differential SAR Interferometry (DInSAR) techniques by means of COSMOSkyMed and ALOS data, through the joint use of L-band and X-band SAR data. It also aims to the identification of methods and techniques to support decision making in emergency cases. Main target volcanoes in the projects are Etna, Vesuvio, Campi Flegrei and Stromboli (Italy) and Sakurajima and Kirishima (Japan). Secondary target volcanoes include recently or currently erupting volcanoes, as El Hierro (Spain), Nabro (Ethiopia) and Galapagos volcanoes (Ecuador). Since the project kickoff (July 2011) a large number of COSMO-SkyMed data has been acquired at these volcanoes; in some cases, the acquisitions are available almost at every satellite orbit, with an average interval down to 4 days. On these premises, the project represents an important opportunity to: (1) collect a significant amount of X-band data on active and erupting volcanoes and (2) study surface deformation to understand magma dynamics in different volcanic settings. We will present preliminary results on the ground deformation analysis of the main and secondary target volcanoes. In particular, target volcanoes without a pre-project archive are analyzed using single deformation maps, while those with archives are analysed through a time series approach, based on the SBAS technique.

Resurgent calderas are excellent targets for geothermal exploration, as they are associated with the shallow emplacement of magma, resulting in widespread and long-lasting hydrothermal activity. Resurgence is classically attributed to the uplift of a block or dome resulting from the inflation of the collapse-forming magma chamber due to the intrusion of new magma. The Los Humeros volcanic complex (LHVC; Mexico) consists of two nested calderas: the outer and older Los Humeros formed at 164 ka and the inner Los Potreros formed at 69 ka. The latter is resurgent and currently the site of an active and exploited geothermal field (63 MWe installed). Here we aim to better define the characteristics of the resurgence in Los Potreros by integrating fieldwork with analogue models and evaluating the spatio-temporal evolution of the deformation as well as the depth and extent of the intrusions responsible for the resurgence, which may also represent the local heat source(s). Structural field analysis and geological mapping show that the floor of the Los Potreros caldera is characterized by several lava domes and cryptodomes (with normal faulting at the top) that suggest multiple deformation sources localized in narrow areas. Analogue experiments are used to define the possible source of intrusion responsible for the observed surface deformation. We apply a tested relationship between the surface deformation structures and depth of elliptical sources to our experiments with sub-circular sources. We found that this relationship is independent of the source and surface dome eccentricity, and we suggest that the magmatic sources inducing the deformation in Los Potreros are located at very shallow depths (hundreds of metres), which is in agreement with the well data and field observations. We propose that the recent deformation at LHVC is not a classical resurgence associated with the bulk inflation of a deep magma reservoir; rather, it is related to the ascent of multiple magma bodies at shallow crustal conditions ( km depth). A similar multiple source model of the subsurface structure has also been proposed for other calderas with an active geothermal system (Usu volcano, Japan), suggesting that the model proposed may have wider applicability.