Abstract Understanding the behaviour of fluids in hydrothermal systems is a key factor in volcano monitoring. Measuring gas emissions in volcanic areas is strategic for detecting and interpreting precursory signals of variations in volcanic activity. The role of radon as a potential precursor of earthquakes has been extensively debated. However, radon anomalies appear to be better suited to forecast eruptive episodes as we know the loci of volcanic eruptions and we can follow the evolution of volcanic activity. Radon mapping is an effective tool in assessing diffuse and concentrated degassing at the surface. We hereby summarize the in-soil radon emissions collected worldwide and further discuss a collection of data on our key targets. These are closed-conduit and open-conduit volcanoes: Vesuvius (Italy) and La Soufrière (Guadeloupe, Lesser Antilles), Stromboli (Italy) and Villarrica (Chile), respectively. In all the above volcanoes, faults and fracture systems control radon degassing. Automatic and real-time measurements help us to detect major changes in volcanic activity. We present and discuss the radon time series associated with the last effusive eruption at Stromboli. Spectral analyses reveal diurnal and semi-diurnal cycles being probably modulated by atmospheric variations. Multiple linear regression (MLR) analyses have been performed by filtering the radon signals from the effects of local environmental parameters. The residuals do not show particular variations or precursory peaks as the gases have been released from this open-conduit volcano before the onset of the effusive phase (7 August 2014). It is finally emphasized that radon is not the sole precursor, and we should also rely on other geochemical and geophysical parameters. In this perspective, we propose a methodological procedure that can contribute to improving volcano surveillance in an attempt to mitigate volcanic risk.

Abstract Humans have long marvelled at (and feared) the odorous and colourful manifestations of volcanic emissions, and, in some cases, have harnessed them for their economic value. The degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions. Moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment, and climate. Even more fundamental are the relationships between the history of planetary outgassing, differentiation of the Earth’s interior, chemistry of the atmosphere and hydrosphere, and the origin and evolution of life. This book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma, the feedbacks between degassing and magma dynamics, and the composition, flux, and environmental, atmospheric and climatic impacts of volcanic gas emissions.