DIKE PROPAGATION THROUGH AN ELASTIC PLATE

We study the vertical propagation of a magma-filled crack which rises due to buoyancy through an elastic plate of finite thickness. The plat e rests on a magma source of large volume. Full time-dependent solutio ns of the coupled problem with elastic deformation and viscous flow in a thin fracture are obtained numerically. A range of initial conditio ns corresponding to different regimes of fracture filling, from passiv e conditions at negligible magma velocity to forceful injection, are i nvestigated. Three phases are distinguished during ascent. In a first phase, as the dike grows out of the initial magma-filled fracture, the elastic pressure distribution adjusts to a fully developed distributi on, with values close to buoyancy in a nose region and smaller values in a conduit region below the nose. Subsequently, the dike develops in creasingly wider conduit and nose regions. Close to the plate upper bo undary, stress and displacement fields become sensitive to the width o f the plate. The initial conditions determine quantitative characteris tics of subsequent dike propagation and, in particular, the flux of ma gma into the dike. As a dike propagates away from source, magma encoun ters increasingly colder rock but flows through an increasingly wider channel. This provides a self-shielding mechanism against freezing. At the upper boundary, eruption initially occurs out of the inflated nos e region and is driven by the relaxation of elastic stresses.