Meredith Townsend, PhD student in Geological and Environmental Sciences at Stanford U., presents "Natural hydraulic fracturing around magmatic dikes as a precursor to the development of volcanic plugs" at the MIT Earth Resources Laboratory on December 11, 2015.

"Field relations between dikes and joints at Ship Rock, New Mexico, indicate that emplacement of magma results in the formation of orthogonal joint sets in the Mancos Shale host rock. One set, oriented parallel to the dike contacts, forms in response to the tensile stress concentration at the tip of a propagating dike. The second set, oriented perpendicular to the dike contacts, forms by thermal pressurization of pore fluids in the host rock. A mechanical analysis reveals that the most important factors that govern the formation of these natural hydraulic fractures include the difference in the remote horizontal stresses, the driving pressure, and the permeability of the host rock. Furthermore, field evidence suggests that fracturing of the host rock around magmatic dikes is a precursor to the development of large volcanic plugs."