Mid-term observation of the degassing dynamics of the Kolumbo submarine volcano (Aegean Sea) gained by new-generation stand-alone multidisciplinary seafloor observatory

The underwater volcanic activity associated with deep-seated mantle processes represents a primary driver of the chemical and biogeochemical evolution of the global oceans. Hydrothermal activity is often a manifestation of submarine volcanism, where fluxes of heat and magmatic volatiles confer both potential hazard and opportunities of resource exploitation. Despite this, research on shallow submarine arc volcanoes is still in an early stage and only a few continuous seafloor observing infrastructures have been developed until now.  The Kolumbo underwater volcano, located in the Aegean Sea, hosts one of the most active and dynamic hydrothermal vent fields, marking it - along with the proximity to the world-known Santorini island - a severe geohazard for a combination of reasons. Within the framework of the SANTORY (SANTORini’s seafloor volcanic observatorY) project, funded by the Hellenic Foundation for Research and Innovation and with the financial support of the Municipality of Thira, between 2022 and 2023, three oceanographic cruises were performed on submarine Kolumbo volcano. The oceanographic surveys were mainly aimed at the deployment of integrated operating sensors of state-of-the-art technology, for in situ monitoring. A new-generation stand-alone multiparametric observatory has been developed at INGV Palermo and deployed at the bottom of the crater (500 meters depth) for the first time in December 2022. The battery powered module has been able to operate autonomously for a 10-month-long period, collecting a dense, heterogeneous dataset able to describe the activity of the hydrothermal reservoir, highlighting its intense dynamic along the time.In June 2023, the observatory was recovered and re-deployed after brief maintenance operations including battery charging and data downloading. Finally, in October 2023, the observatory was definitely recovered.Here we present for the first time a mid-term-long chemical-physical data series acquired (pH, temperature, hydrostatic pressure, turbidity, conductivity, dissolved methane) along with passive acoustic and the preliminary findings of the system evolution within the observing window. A variety of local VT events likely sourced in the deeper portion of the plumbing system, together with several other minor seismic events related to fluid dynamics inside “fluid-filled” cracks and conduits has been revealed by passive acoustic data. Moreover the acoustic sensor recorded all the signals generated by the bubbles along the water column. The obtained results gave back an up to date picture of the ongoing Kolumbo degassing dynamics, hydrothermal and seismic activity.