Lava dome

A lava dome is the result of a slow extrusion of viscous lava, often rich in gas, giving a dome morphology generally resulting from the superimposition of successive lobes at the summit of the magma column. The sides of the domes are generally very steep and are frequently covered with unstable blocks deposited during or just after their extrusion. During an eruption they can disintegrate more or less explosively, but the last dome often remains at the end of the eruption and slowly cools, with the emissions from fumaroles.