Caudron Corentin auteur aut IRD Aoki Y. auteur aut IRD Lecocq T. auteur aut IRD De Plaen R. auteur aut IRD Soubestre J. auteur aut IRD Mordret A. auteur aut IRD Seydoux L. auteur aut IRD Terakawa T. auteur aut IRD text journalArticle eng text/pdf reformatted digital access A large fraction of volcanic eruptions does not expel magma at the surface. Such an eruption occurred at Mt Ontake in 2014, claiming the life of at least 58 hikers in what became the worst volcanic disaster in Japan in almost a century. Tens of scientific studies attempted to identify a precursor and to unravel the processes at work but overall remain inconclusive. By taking advantage of continuous seismic recordings, we uncover an intriguing sequence of correlated seismic velocity and volumetric strain changes starting 5 months before the eruption; a period previously considered as completely quiescent. We use various novel approaches such as covariance matrix eigenvalues distribution, cutting-edge deep-learning models, and ascribe such velocity pattern as reflecting critically stressed conditions in the upper portions of the volcano. These, in turn, later triggered detectable deformation and earthquakes. Our results shed light onto previously undetected pressurized fluids using stations located above the volcano-hydrothermal system and hold great potential for monitoring. specialized JAPON ONTAKE MONT 066 064 020 13 1 6145 [9 p.] 2022 https://www.documentation.ird.fr/hor/fdi:010086377 10.1038/s41467-022-32252-w [F B010086377] https://www.documentation.ird.fr/hor/fdi:010086377 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2022-12/010086377.pdf IRD - Base Horizon / Pleins textes 2022-12-09 2022-12-09 fdi:010086377 fre