Ground deformation prior to phreatic and phreatomagmatic eruptions at Rincón de la Vieja Volcano, Costa Rica

Rincón de la Vieja volcano is a highly active system in northern Costa Rica that experiences frequent phreatic and phreatomagmatic eruptions resulting in small-scale deformation. GNSS stations are set up and maintained by OVSICORI as part of their nationwide network including stations located 1 km southwest, 5 km southwest, 5 km northwest and 6 km northeast of the active vent. Between July 1, 2021, and December 31, 2023, Rincón de la Vieja experienced hundreds of eruptions associated with deformation at different timescales. Two periods of long-term inflation were detected between December 2021 and May 2022, as well as between November 2022 and November 2023. These periods resulted in 32 mm and 40 mm of uplift, respectively, which modelling indicates is the result of a deep (>4 km) magma body located below the active vent. These periods of uplift are associated with windows of significant eruptive activity (eruptions occurring >50% of days within a window). Between periods of long-term deformation, shorter periods of uplift up to 30 mm lasting 15 to 30 days are also recorded. Modelling of these shorter periods revealed resultant deformation was due to pressurization within the shallow (<1.5 km) hydrothermal system. We propose a model of two linked modes of activity where the shifting balance between the magmatic and hydrothermal system results in predominantly deep or shallow pressure sources respectively. This shift in magmatic and hydrothermal contributions produces the varied eruptive activity seen at Rincón de la Vieja. • GNSS reveals short- and long-term uplift at Rincón de la Vieja volcano. • Hydrothermal sealing drives shallow uplift and phreatic eruptions. • Deep magmatic pressurization produces long-term uplift and frequent eruptions.