Abstract

The rate of escape of magmatic gases from vesiculating, expanding magma is key to controlling the explosivity of an eruption. Permeating networks of bubbles may develop as magma rises and bubbles grow and impinge on one another. Geometric analysis shows that permeability develops anisotropically in the volcanic conduit: permeability across the conduit is enhanced and permeability along the conduit is hindered. The higher rate of horizontal gas loss that results has implications for the eruption rate and eruptive style – enhanced lateral degassing facilitates rapid gas escape, reducing the likelihood of magma fragmentation and mitigating eruption explosivity. The finding also calls into question the validity of eruption models which assume vertical gas flow, and paves the way for a new class of eruption model that resolves permeability throughout the volcanic system.