Sustained blasts during large volcanic eruptions

We carried out numerical simulations to investigate magma ascent in wide conduits during large explosive eruptions. Wide conduits allow high discharge rates, low frictional pressure losses, and shallow levels of explosive fragmentation of the magma within the conduit. In contrast with the commonly modeled lower rate eruptions during which magma fragments inside the conduit at depth and feeds a vertical eruptive jet, we find that for sufficiently high discharge rates (>10 (super 10) kg.s (super -1) ) the fragmentation level may rise up to the surface. Gas-rich, unfragmented magma reaches the surface at high pressure and feeds a sustained volcanic blast. Geologic evidence for very high discharge rate eruptions, wide conduits, and shock waves in large pyroclastic flows supports the occurrence of this type of explosive eruption.