Key results

The main objectives of BRIDGE are (i) to explore and characterise shallow volcanic processes by using a novel interpretative approach, funded upon the combined analysis of co-acquired volcanic gas and geophysical (seismic, infrasonic, geodetic, thermal) signals; and (ii) to use this new interpretative framework to contribute improved models of volcanic degassing processes, with a particular focus on understanding the trigger mechanisms of explosive volcanic eruptions and the transition from passive degassing to eruption. A prerequisite for this joint analysis is bridging together the existing technological gap between geochemical and geophysical observations at volcanoes. To this aim, and as for the approved research timeline of BRIDGE, efforts of the BRIDGE science team in months 1-24 have been mostly focused on technological innovation. This activity has led us to designing, building-up, testing (in laboratory and then in the field) and finally field deploying the first prototypes of a new generation of volcanic gas sensing instruments. Efforts have been spent to contribute a significant step ahead in our ability to real-time measure volcanic gases at high-rate, and to make therefore the temporal resolution of gas measurements more comparable to that of geophysical observations. We have successfully realised the first prototypes of fully automated UV cameras that can be used to obtain continuous, unattended long-term imaging of SO2 flux emissions from active volcanoes with high temporal (0.5-25 Hz) and spatial resolution. These new UV-cameras systems have been field validated in a series of field expeditions, that have allowed us to characterise with unprecedented detail the degassing features of a series of volcanic targets in Italy (Etna and Stromboli), and abroad (Chile, Costa Rica, and Indonesia, among others). The first permanent network of volcanic SO2 imaging systems worldwide (at least to our knowledge) has then been released, installing four permanent UV camera systems at Etna and Stromboli. These new observational systems are now paving the way to improved understanding of the dynamics of volcanic degassing, and of what controls the switch from passive (quiescent) degassing to eruption. Using the much improved spatial/temporal resolution and temporal continuity of our SO2 flux records, we have fully captured, at both Etna and Stromboli, the volcanic degassing signatures typical of the transition from regular, quiescent degassing toward both effusive (ongoing on Stromboli by the time of writing) and paroxysmal explosive activity (Etna during summer 2014). In tandem-analysis of such volcanic gas data with co-acquired geophysical signals is now contributing to understand and model the volcanic processes leading to such transitions. We have studied, in particular, short-term periodicities and trends in passive degassing behaviour of open-vent volcanoes, to identify a link between the modes/rates of gas release and patterns in seismicity (volcanic tremor, LP and VLP seismicity). We have real-time characterised (via UV imaging) the onset, duration and degassing regime of hundreds of individual basaltic explosions, and compared their sin-explosive gas eruption rates/masses with the magnitude, shape and duration of the thermal, seismic and acoustic signals they irradiate. This activity has brought to significant advances in our understanding of the coupling between chemical and physical signals irradiated by active volcanism, and to initialise new models for the generation of basaltic explosive volcanism. A second gas that has been extensively studied in BRIDGE is CO2, the second most abundant species in volcanic gases but also one (with H2O) of the most difficult to probe with remote sensing techniques. Major efforts have been spent within the project to improve our ability to measure volcanic CO2 fluxes. This effort has been undertaken with several complementary approaches. We have refined existing technologies, such as the Multi-GAS, to compare long-term records of CO2 fluxes with seismological parameters, and to demonstrate that temporal fluctuations in CO2 emissions correlate well with shallow volcanic seismicity (e.g., that there is a coupling between degassing and seismicity). We have exploited recently developed techniques, such as Infra-Red Tunable Diode Lasers, to characterise (for the very first time) the rates of CO2 release from quiescent, hydrothermal volcanoes, and to compare temporal trends in degassing with geodetic (GPS) evidence of ground displacement (at Campi Flegrei volcano). Even more importantly, we have fully succeeded in the technological challenge of developing the first Lidar for volcanic CO2 sensing. Assembling and testing of this Lidar prototype has successfully been completed in September 2014. To our knowledge, this is the first example of a Lidar specifically designed to probe degassing of volcanic CO2, and represents a major step ahead in our ability to remotely sense volcanic emissions. Field validation of the Lidar has regularly started during summer/fall 2014, and the very first “direct” CO2 output estimate worldwide has been obtained in a field campaign at Campi Flegrei volcano in October 2014. This new instrument promises to contribute plenty of new CO2 flux information during moths 25-48 of BRIDGE. Overall, 23 papers on ISI journals have been published on BRIDGE-related science, plus a variety of dissemination activities of BRIDGE results at international meetings.