Propagation of Vertical Fractures through Planetary Ice Shells: The Role of Basal Fractures at the Ice–Ocean Interface and Proximal Cracks

The presence of smooth, young surfaces indicates that regions of Enceladus and Europa have been resurfaced through recent or ongoing activity related to the eruption of liquid water from subsurface reservoirs. For interior material to erupt or flow out onto the surfaces of these satellites, fractures would have to vertically penetrate the ice shell to the depth of a subsurface reservoir or ocean. Here we use linear elastic fracture mechanics to show that accounting for fracture interactions makes it much more difficult for fractures to penetrate the entire ice shell than previous estimates. We found that fractures that originate from the surface are unlikely to penetrate the entire shell thickness, even for the upper range of tectonic stresses estimated for each moon. Tensile fractures that initiate from the bottom of the icy shell—as observed in terrestrial ice shelves—propagate further into the icy shell than surface crevasses but still do not penetrate the entire ice thickness. However, full ice shell thickness fracture is possible if shear failure connects the surface with deep-penetrating basal fractures in thinner ice shell thicknesses and under certain stress conditions. This suggests that the combination of tensile and shear failure may be important and necessary for the formation of a connection from the surface to the ocean below.