Constraining proximal grainsize distribution of tephra from paroxysmal eruptions at Etna volcano

Abstract

This study examines proximal deposits associated with 17 lava fountains occurring at the South-East Crater between 16/02 and 1/04, 2021. This eruptive crisis gave rise to some of the most intense eruptions at Etna in the last decade. We studied products deposited from 1 to 3.2 km to the south of the vent. Tephra was preserved within and at the top of the snowpack and layers were correlated based on eruption chronology, remote sensing data on the plume dispersal, and precipitation chronology. The grainsize distribution of these proximal and ultra-proximal deposits is multimodal, with Mdɸ ranging from −2.79 and − 1.84, and σɸ 1.34 and 1.80. Refined data (50% of the main population range between Mdɸ −2.63 and − 1.63ɸ, and σɸ 1.01 and 1.41) were used in a comparative study with existing datasets for selected eruptions to assess the representativity of our data and define a Mdɸ/distance correlation along the dispersal axis. Finally, the contribution of proximal data on the total grainsize distribution suggest that they significantly affect the median grainsize values. A complete sampling could decrease it by up to 2 phi units when compared to distribution based only on medial to distal sampling. Results from this study reinforce the importance of collecting samples in proximal areas.