The reduction of pressurein the mantle is a central reason behind Earth's volcanism. Mantle rock that rises adiabatically to a low enough pressure melts without any added heat source. The ascent may be actively driven by convection, as in mantle plumes, where hot, buoyant jets from the deep interior are thought to provide a rich source of material to fuel the volcanism. Or it may be passive, as at mid‐ocean ridges, where magma forms from the upwelling of rock into the gaps left by the spreading of tectonic plates. Deglaciation can also trigger volcanic pulses, as it did in Iceland at the end of the last ice age when the elastic plate rebounded from the melting of the ice cap. Meteorite impacts that excavate large craters at Earth's surface are yet another cause of pressure release.