Variability of ash deposits at Piton de la Fournaise (La Reunion Island): insights into fragmentation processes at basal
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RESEARCH ARTICLE
Variability of ash deposits at Piton de la Fournaise (La Reunion Island) : insights into fragmentation processes at basaltic shield volcanoes Simon Thivet 1
&
Lucia Gurioli 1 & Andrea Di Muro 2 & Julia Eychenne 1 & Pascale Besson 3 & Jean-Marie Nedelec 4
Received: 11 March 2020 / Accepted: 30 June 2020 # International Association of Volcanology & Chemistry of the Earth's Interior 2020
Abstract It is commonly accepted that effusive activity emplaces the main emitted magmatic volume in basaltic shield volcanoes. At Piton de La Fournaise (La Réunion Island, France), eruptive activity occurs mostly within the non-populated Enclos Fouqué caldera and generally does not pose any risk to the population. However, historical observations, recent monitoring data, and field work on tephra deposits suggest that some eruptions have produced unusual and unexpected explosive phases. A comprehensive sampling of tephra from major historical and recent eruptions on this volcano allowed us to perform systematic componentry, grain size, and chemical and morphological analyses in order to characterize the eruptive dynamics involved in these explosive basaltic eruptions. This integrative approach reveals highly variable characteristics of the studied tephra reflecting different fragmentation efficiencies and multiple associated mechanisms. Primary ductile and partially brittle fragmentation of various intensity of juvenile magma emitted during Hawaiian fountaining or mild Strombolian explosions were identified as the most common fragmentation mechanisms, in particular during the 2014–2018 dominantly effusive eruptive sequence. In parallel, we distinguished more efficient short-lived fragmentation events related to (i) plug pressurization and brittle fragmentation enhanced by syn-eruptive crystallization, (ii) magma/water interactions, (iii) rare phreatic explosions, and (iv) secondary fragmentation producing fine ash during caldera collapse. We conclude that textural, geochemical, and morphological analyses make it possible to identify and characterize the variability in eruptive processes, with the grain size, and the componentry of the ash particles being probably the most important parameters to quantify both the efficiency and the nature of the fragmentation. Keywords Ash . Basaltic . Fragmentation . Grain size . Piton de la Fournaise . Texture
Editorial responsibility: U. Kueppers; Deputy Executive Editor: J. Tadeucci Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00445-020-01398-0) contains supplementary material, which is available to authorized users. * Simon Thivet [email protected] 1
Laboratoire Magmas et Volcans, Université Clermont Auvergne CNRS - IRD, OPGC, Campus Universitaire des Cézeaux, 6 Avenue Blaise Pascal, 63178 Aubière Cedex, France
2
Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, CNRS, F-97418, La Plaine des Cafres, La Réunion, Paris, France
3
Institu
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