Tracking the permeable porous network during strain-dependent magmatic flow

We find that strain localisation during deformation leads to the rearrangement and closure of void space (a combination of pores and cracks) followed by preferentially aligned fracturing (in the direction of the maximum principal stress) to form damage zones as well as densification of other areas. In a dome setting, highly viscous, low permeability magmas carry the potential to block volcanic conduits with a magma plug, resulting in the build-up of pressures in the conduit. Above a certain threshold of strain (dependent upon stress/strain rate), the initiation, propagation and coalescence of fractures leads to mechanical degradation of the magma samples, which then supersedes magmatic flow and crystal rearrangement as the dominant form of deformation. This results in lower apparent viscosities than those anticipated for magma of such crystallinity, especially at high strain rates. In a lava dome, this could result in dome collapse and the concomitant depressurisation could trigger an explosive eruption.