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Magma fragmentation in scoria cones, a comparative study of Cinder Cone (California, USA), Sunset Crater (Arizona, USA) and Paricutin (Michoacan, Mexico)

Grégoire Pasdeloup 1, Pierre-Simon Ross1

Abstract

We present a comparative study between three scoria cone tephra sheets: Cinder Cone, Sunset Crater and Paricutin. Cinder Cone evolved from Hawaiian/Strombolian to violent Strombolian style, creating two main tephra units. Sunset Crater ranged from Hawaiian and Strombolian to subplinian, generating five main tephra units. Paricutin was composed of three different phases with the eruptive style reaching violent strombolian. We complete our dataset with Etna paroxysm episodes of lava fountaining from February-March 2021. We use the same methodology for all of our samples : we focus on three specific size fractions [coarse lapilli from 5.7 to 4 mm (− 2.5 to − 2ɸ), coarse ash from 0.71 to 0.5 mm (+ 0.5 to + 1ɸ), and very fine ash from 88 to 63 μm (+ 3.5 to + 4ɸ)] to compare componentry, morphometric parameters of individual juvenile fragments, and internal textures (crystallinity, vesicularity), based on microscope and SEM imaging. Our goal is to link measurable parameters of the particles to fragmentation processes and eruptive styles of the volcanoes. Our results show an importance of componentry for morphometric parameters and internal textures, sometimes more than between different tephra units during an eruption. The presence of different types of juvenile clasts in variable proportions could be a consequence of conduit zonation. Therefore, even if the eruptive style is responsible for the type of tephra deposits, the different types of juvenile components produced by local variations of magma (vesicularity, crystallinity) play a role in magmatic fragmentation.