Role of volatiles in highly explosive basaltic eruptions

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 CO2 content, whereas an increase in H2O up to 10 wt.%
produces an increase in eruption rate of an order of magnitude. It is only when CO2 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.