In populated areas, relatively small volcanic activities associated with the instability of magma-solicited hydrothermal systems (e.g., la Soufrière de Guadeloupe in 1976-77, and Campi Flegrei in 1982-84) have produced major impacts to local populations, determining far-reaching consequences on the economy and social fabric. These episodes are related to magmatic systems that have produced major explosive eruptions in historical times. For this reason, these events have generated long-standing debates about their actual origin, and particularly about the causal processes (magmatic vs hydrothermal) behind unrest episodes. This has fostered scientific and technical developments in geophysical and geochemical surveillance of volcanic-hydrothermal systems, which have been readily transferred to other volcanic contexts. Exceptional datasets have been produced during the last four decades that opened new perspectives about the understanding of volcanic unrest at explosive volcanoes, showing the crucial role of geochemistry-derived intensive thermodynamic (pressure, temperature and relative gas/liquid fractions) and extensive quantities (heat and mass fluxes) of the hydrothermal system. In the case of la Soufrière of Guadeloupe, an archetype andesitic volcano, we know from the 1976-77 phreatic eruption (though magmatic still-born) and the current unrest (the volcano reactivated in 1992 with a peak of activity in April 2018) that magmatic fluid transfer may take place rapidly, determining short-term (days to weeks) rapid heating and pressurization of the shallow hydrothermal system. For this reason, we aim to track the subtle evolution of the hydrothermal system and its eventual destabilization during supercritical fluid excursions. Forthcoming developments include the coupling of the OVSG-IPGP surveillance system with continuous muon-particle imaging, in order to provide efficient joint geophysical and geochemical monitoring for the detection of density changes at high-frequency and the real-time evaluation of the pressure, temperature and liquid/vapor ratio in the dome portion of the hydrothermal system.