The role of magma vapors in volcanic tremors and rapid eruptions

A fracture dynamics model in which an igneous intrusion of magma within a crack occurs is used to describe the psysical processes of magma transport. A symbiotic relationship exists between the crack and the fluid. The crack tip cannot accelerate faster than the fluid within it can flow in the channel provided by the crack, and the speed of the fluid is limited by its own viscosity. A volatile phase at the tip of the crack at lithostatic pressures will allow the crack to accelerate to high speeds, since the viscosity of a volatile is small. It is proposed that periods of quiescence in volcanic activities may not in fact be quiet, but only periods where the crack velocity (and therefore the magma transport rate) is slow. At rapid crack velocities, where there is sufficient kinetic energy for the generation of abundant acoustic radiation, the crack generates a detectable seismic signal. From this point of view, seismic methods always underestimate the size of cracks. The analyses here apply fracture dynamics to the Kilauea cruption of 1963.