Role of volatiles in highly explosive basaltic eruptions
Giuseppe La Spina, Fabio Arzilli, Mike Burton, Margherita Polacci, A. B. Clarke
Abstract
Abstract Water and carbon dioxide are the most abundant volatile components in terrestrial magmas. As they exsolve into magmatic vapour, they promote magma buoyancy, accelerating ascent and modulating eruptive dynamics. It is commonly thought that an increase in pre-eruptive volatile content produces an increase in eruption intensity. Using a conduit model for basaltic eruptions, covering the upper 6 km of conduit, we show that for the same chamber conditions mass eruption rate is not affected by CO 2 content, whereas an increase in H 2 O up to 10 wt.% produces an increase in eruption rate of an order of magnitude. It is only when CO 2 is injected in the magma reservoir from an external source that the resulting pressurisation will generate a strong increase in eruption rate. Results also show that ascent velocity and fragmentation depth are strongly affected by pre-eruptive volatile contents demonstrating a link between volatile content and eruptive style.