Directly tapping crustal magma reveals storage conditions

The conditions under which magma accumulates and is stored are fundamental to unraveling the processes of crust formation, planetary differentiation, geothermal heat recharge, and volcanic eruptions. Storage pressure and temperature are typically inferred from erupted volcanic products. However, changes during kilometers of magma ascent induce disequilibrium crystallization and vesiculation, and inverting back to storage conditions comes with arguably unresolvable uncertainties. Here, we explore opportunities arising from magma drilling at Krafla volcano (Iceland) to reconstruct real, in situ magmatic conditions for the first time. The findings show that over the ∼5 min in which the magma is quenched, vapor bubbles consisting of H2O and CO2 exsolve, grow, and resorb, but the changes can be accounted for by careful multiparametric inversion (for chemistry, vesicularity, and vitrification), and that the magma was stored under lithostatic conditions, unlike previous assertions based on classic methods1. This constraint provides us with the unique pairing of precisely measured depth and pressure on a single magma body, and thus a robust method to improve our understanding of magma storage conditions and evolution.