That happened, for instance, at Bardarbunga a few years before the 2014 eruption when magma rose from 22 km to to 7 km, bypassing the lower magma chambers between 8 and 12 km. As gas continues to come out of the magma (CO 2 , H 2 O, SO 2 ), the magma develops froth and the frothy magma rises, creating a conduit if necessary. This is the normal process in Iceland: a slow start if old magma needs to be pushed out, a fast phase of fresh, gassy magma and a tapering off as the gas reduces, until a sudden end when the density of the magma is insufficient to overcome gravity and inertia.