Magma fragmentation: a perspective on emerging topics and future directions

Abstract

The breaking apart of magma into fragments is intimately related to the eruptive style and thus the nature and footprint of volcanic hazards. The size and shape distributions of the fragments, in turn, affect the efficiency of heat transfer within pyroclastic plumes and currents and the settling velocity, and so the residence time, of particles in the atmosphere. Fundamental work relating the glass transition to the fragmentation of magmas remains at the heart of conceptual and numerical models of volcanic eruptions. Current fragmentation criteria, however, do not predict the sizes and shapes of the resulting fragments, or fully account for the multiphase nature of magmas or ways in which magma can break in a fluidal manner or by thermal stress. The pulsatory, non-steady state nature of some eruptions, and related interactions with these fragmentation criteria, also requires further investigation. Here, we briefly review some recent advances in the field of magma fragmentation and provide a perspective on how integrated field, experimental and numerical modelling studies can address key outstanding challenges.

Late Quaternary explosive phonolitic volcanism of Petite-Terre (Mayotte, Western Indian Ocean)

“…Magmatic fragmentation is either caused by high strain rates during expansion of the gas phase leading to brittle fracture especially in the case of viscous magmas, or by bubble rupture and decompression during ascent, or by the combination of both (Cashman and Scheu, 2015; Jones et al, 2022;Sparks, 1978).…”

Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour

“…Fluctuations in intensity and style can occur between eruptive episodes, within a single episode, and simultaneously at different spatial locations 21 . Furthermore, the physical processes governing explosive eruption of low viscosity magmas are fundamentally different to those operating in the now relatively well-studied silicic systems 24 – 27 . Most commonly their fragmentation processes are fluid dynamic in nature such that breakage does not occur simply by decompression upon crossing the glass transition 7 , 27 – 29 .…”

“…Furthermore, the physical processes governing explosive eruption of low viscosity magmas are fundamentally different to those operating in the now relatively well-studied silicic systems 24 – 27 . Most commonly their fragmentation processes are fluid dynamic in nature such that breakage does not occur simply by decompression upon crossing the glass transition 7 , 27 – 29 . Instead, their low melt viscosities allow surface tension-driven reshaping and bubble nucleation, growth, and coalescence to operate on syn- and post-eruptive timescales.…”

The Morphology of Martian Pyroclastic Ramparts and Their Use in Determining Vent‐Proximal Eruption Dynamics

“…These are typically associated with low-intensity lava fountaining episodes of mafic magma (Houghton & Gonnermann, 2008;Parcheta et al, 2012Parcheta et al, , 2015Taddeucci et al, 2015). They represent eruptions on the cusp of explosive activity, fragmenting the erupted magma by predominantly ductile processes (Jones, Cashman, et al, 2022;Jones et al, 2019). However, to date on Mars, such products of (weakly) explosive volcanic eruptions have been rarely described (Hauber et al, 2009;Mouginis-Mark & Christensen, 2005;Wilson et al, 2009), and therefore, the understanding of explosive basaltic eruptions is still not fully constrained.…”