Simultaneous fall and flow during pyroclastic eruptions: A novel proximal hybrid facies

Abstract

The deposits of Plinian and subplinian eruptions provide critical insights into past volcanic events and inform numerical models that aim to mitigate against future hazards. However, pyroclastic deposits are often considered from either a fallout or pyroclastic density current (PDC) perspective, with little attention given to facies exhibiting characteristics of both processes. Such hybrid units may be created where fallout and PDCs act simultaneously, where a transitional phase between the two occurs, and/or due to reworking. This study presents analysis of a novel hybrid pyroclastic lithofacies found on Tenerife (Canary Islands) and Pantelleria (Italy). The coarse pumice block facies has an openwork texture and correlates with distal Plinian units, but it is cross-stratified and relatively poorly sorted with an erosional base. The facies is proposed to record the simultaneous interaction of very proximal fallout and turbulent PDCs, and it reveals a fuller spectrum of hybrid deposition than previously reported. This work highlights the importance of recognizing hybrid deposition both in the rock record and in hazard modeling.

Petrographic and geochemical analyses to characterise the source of built historical natural stones — a case study of the volcanic stones from historical quarries and Baoguosi Temple in the city of Ningbo, China

“…Tuff is a kind of pyroclastic rocks that can be considered as sedimentary rocks as well as igneous rocks, for the materials come from the explosive volcanic eruption whereas the way they formed is by deposit (Peterson 1985 ). Tuffs could be results of either plume (fallout) or pyroclastic density current (mixtures of pyroclastic particles and gas that move across the landscape under the effect of gravity) activity (Dowey and Williams 2022 ).

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Fig. 13 General scheme of fallout and pyroclastic density flow (PDC) processes in eruptions (Source: the authors, modified after Dowey and William 2022 )

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“…13 ; Acocella 2021 ). Until recently, depositional models of different pyroclastic density currents were developed by field observations, laboratory experiments, and numerical simulations (Sulpizio et al 2010 ; Dellino et al 2010 ; Dowey and Williams 2022 ). It has been recognised that the bigger clasts would go further before they fall and deposit because of higher kinetic energy (Sulpizio et al 2014 ).…”

Analytical Approaches to Characterize the Source of Meiyuanshi-stone Using Petrographic and Geochemical Methods

“…10; [38,43]). Until recently, depositional models of different pyroclastic density currents were developed by eld observations, laboratory experiments, and numerical simulations [40,44,45]. It has been recognized that the bigger clasts would go further before they fall and deposit because of more kinetic energy [44].…”

“…Tuff is a kind of pyroclastic rocks that can be considered as sedimentary rocks as well as igneous rocks, for the materials come from the explosive volcanic eruption whereas the way they formed is by deposit [39]. Tuffs could be results of either plume (fallout) or pyroclastic density current (mixtures of pyroclastic particles and gas that move across the landscape under the effect of gravity) activity [40].…”