title: Thermal vesiculation during volcanic eruptions.
abstract: Terrestrial volcanic eruptions are the consequence of magmas ascending to the surface of the Earth. This ascent is driven by buoyancy forces, which are enhanced by bubble nucleation and growth (vesiculation) that reduce the density of magma. The development of vesicularity also greatly reduces the 'strength' of magma, a material parameter controlling fragmentation and thus the explosive potential of the liquid rock. The development of vesicularity in magmas has until now been viewed (both thermodynamically and kinetically) in terms of the pressure dependence of the solubility of water in the magma, and its role in driving gas saturation, exsolution and expansion during decompression. In contrast, the possible effects of the well documented negative temperature dependence of solubility of water in magma has largely been ignored. Recently, petrological constraints have demonstrated that considerable heating of magma may indeed be a common result of the latent heat of crystallization as well as viscous and frictional heating in areas of strain localization. Here we present field and experimental observations of magma vesiculation and fragmentation resulting from heating (rather than decompression). Textural analysis of volcanic ash from Santiaguito volcano in Guatemala reveals the presence of chemically heterogeneous filaments hosting micrometre-scale vesicles. The textures mirror those developed by disequilibrium melting induced via rapid heating during fault friction experiments, demonstrating that friction can generate sufficient heat to induce melting and vesiculation of hydrated silicic magma. Consideration of the experimentally determined temperature and pressure dependence of water solubility in magma reveals that, for many ascent paths, exsolution may be more efficiently achieved by heating than by decompression. We conclude that the thermal path experienced by magma during ascent strongly controls degassing, vesiculation, magma strength and the effusive-explosive transition in volcanic eruptions.
authors.affiliation: Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 3GP, UK.
authors.forename: Yan
authors.initials: Y
authors.lastname: Lavallée
authors.affiliation: Department of Earth and Environmental Sciences, Ludwig Maximilian University of Munich, Theresienstrasse 41/III, 80333 Munich, Germany.
authors.forename: Donald B
authors.initials: DB
authors.lastname: Dingwell
authors.affiliation: Department of Geosciences, Boise State University, Boise, Idaho, USA.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Johnson
authors.affiliation: Department of Earth and Environmental Sciences, Ludwig Maximilian University of Munich, Theresienstrasse 41/III, 80333 Munich, Germany.
authors.forename: Corrado
authors.initials: C
authors.lastname: Cimarelli
authors.affiliation: Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 3GP, UK.
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Hornby
authors.affiliation: Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 3GP, UK.
authors.forename: Jackie E
authors.initials: JE
authors.lastname: Kendrick
authors.affiliation: Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 3GP, UK.
authors.forename: Felix W
authors.initials: FW
authors.lastname: von Aulock
authors.affiliation: Geological Sciences, University of Canterbury, Private Bag 4800, 8140 Christchurch, New Zealand.
authors.forename: Ben M
authors.initials: BM
authors.lastname: Kennedy
authors.affiliation: Department of Mineral Sciences, Smithsonian Institution, Washington, District of Columbia, USA.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Andrews
authors.affiliation: Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 3GP, UK.|Department of Earth and Environmental Sciences, Ludwig Maximilian University of Munich, Theresienstrasse 41/III, 80333 Munich, Germany.
authors.forename: Fabian B
authors.initials: FB
authors.lastname: Wadsworth
authors.affiliation: Geological Sciences, University of Canterbury, Private Bag 4800, 8140 Christchurch, New Zealand.
authors.forename: Emma
authors.initials: E
authors.lastname: Rhodes
authors.affiliation: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hydrologia (INSIVUMEH), 7a Avenue 14-57, Zone 13, Guatemala City, Guatemala.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Chigna