title: Breathing of the Nevado del Ruiz volcano reservoir, Colombia, inferred from repeated seismic tomography.
abstract: Nevado del Ruiz volcano (NRV), Columbia, is one of the most dangerous volcanoes in the world and caused the death of 25,000 people in 1985. Using a new algorithm for repeated tomography, we have found a prominent seismic anomaly with high values of the Vp/Vs ratio at depths of 2-5 km below the surface, which is associated with a shallow magma reservoir. The amplitude and shape of this anomaly changed during the current phase of unrest which began in 2010. We interpret these changes as due to the ascent of gas bubbles through magma and to degassing of the reservoir. In 2011-2014, most of this gas escaped through permeable roof rocks, feeding surface fumarole activity and leading to a gradual decrease of the Vp/Vs ratio in the reservoir. This trend was reversed in 2015-2016 due to replenishment of the reservoir by a new batch of volatile-rich magma likely to sustain further volcanic activity. It is argued that the recurring "breathing" of the shallow reservoir is the main cause of current eruptions at NRV.
authors.affiliation: Universidad Nacional de Colombia, Department of Geosciences, Ciudad Universitaria, Bogota, Colombia.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Vargas
authors.affiliation: Trofimuk Institute of Petroleum Geology and Geophysics, SB RAS, Prospekt Koptyuga, 3, 630090, Novosibirsk, Russia.|Novosibirsk State University, Novosibirsk, Russia, Pirogova 2, 630090, Novosibirsk, Russia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Koulakov
authors.affiliation: Institut de Physique du Globe de Paris, Sorbonne Paris Cité, CNRS (UMR 7154), 1 rue Jussieu, 75238 Paris, Cedex 5, France.
authors.forename: Claude
authors.initials: C
authors.lastname: Jaupart
authors.affiliation: Trofimuk Institute of Petroleum Geology and Geophysics, SB RAS, Prospekt Koptyuga, 3, 630090, Novosibirsk, Russia.|Novosibirsk State University, Novosibirsk, Russia, Pirogova 2, 630090, Novosibirsk, Russia.
authors.forename: Valery
authors.initials: V
authors.lastname: Gladkov
authors.affiliation: Universidad Nacional de Colombia, Department of Geosciences, Ciudad Universitaria, Bogota, Colombia.
authors.forename: Eliana
authors.initials: E
authors.lastname: Gomez
authors.affiliation: King Saud University, Riyadh, Saudi Arabia, P.O. Box 2455, Riyadh, 11451, Saudi Arabia.|National Research Institute of Astronomy and Geophysics, NRIAG, 11421, Helwan, Egypt.
authors.forename: Sami
authors.initials: S
authors.lastname: El Khrepy
authors.affiliation: King Saud University, Riyadh, Saudi Arabia, P.O. Box 2455, Riyadh, 11451, Saudi Arabia.
authors.forename: Nassir
authors.initials: N
authors.lastname: Al-Arifi