Effect of solidification on a propagating dike

Abstract

Magma migration through the brittle crust from depth occurs by the propagation of hydraulic fractures or dikes. Volcanic eruptions occur at the last stage if and when a propagating dike reaches the surface. Dike propagation involves complex physics because of several processes that are simultaneously occurring such as viscous flow of magma, rock fracture, elastic deformation of the host rock, and potentially large changes of the physical properties of the magma (crystallization, degassing, solidification, etc.). Currently the most practical way in the field or in terms of field measurements to follow the migration of magma before it reaches the surface is the analysis of the seismicity generated; nevertheless, a physical model that quantitatively relates the flux of magma in the dike to the seismicity is lacking. We present here laboratory experiments involving propagation of a fluid-filled crack such that the fluid solidifies upon contact with the cold elastic host. We show that this can lead to a way of estimating the flux of the injection as a function of the surface creation rate. The latter is shown to be a more reliable gauge of magma flux than the upward propagating velocity. In the geologic application of a propagating dike, the rate of creation of surface area may be related to the rate of release of seismic energy. Although this latter relation needs further work to be quantitatively reliable, our new model nevertheless indicates how a new general framework can be constructed.