Skip to content

Do shape and size of erupted tephra reflect their porosity? An investigation of representative tephra from explosive eruptions at Mt Etna (Italy)

Alexandra Grace Lang 1, Daniele Andronico 2, Simona Caruso 2, Rosa Anna Corsaro 2, Antonio Cristaldi 2, Mattia Pistone 1

Abstract

Volcanic eruption forecasting is vital for ~1.1 billion people living near volcanoes worldwide, and remains incredibly challenging. It is crucial to develop new approaches for enhancing monitoring and forecasting of volcanic eruptions and applying promptly risk mitigation strategies. The size and porosity of erupted tephra are important parameters that can be variably used to determine the level of pre-eruptive gas storage and pressurization of magma, eruption style and intensity, and volcanic particle dispersion. To date, a potential correlation between the size of tephra with irregular shapes and porosity resulting from vesiculation in pre- and post-fragmentation stages of the erupted magma remains obscure. Here we present new data highlighting the possible correlation between tephra shape and size and porosity based on an interlaboratory analysis of a set of representative samples from Mt Etna (Italy) derived from fall-out deposits of the 122 B.C. Plinian eruption, 1669 initial strombolian phase, and paroxysms events of 2001 cycle, 2002-2003 phase, February 2021, February 2022, August 2023, and July 2024. We investigated lapilli size tephra ranging 2 and 30 mm using a dynamic image analysis on a CAMSIZER, a particle size and shape analyser. The porosity of selected samples is currently explored using a gas pycnometer. Tephra size and shape analysis shows monodisperse and polydisperse distributions that are currently being interpreted. We aim to demonstrate how dynamic image analysis via CAMSIZER may offer a prompt assessment of sample porosity resulting into a near-real-time monitoring of gas accumulation in magma during eruptions at Mt Etna.