Formation of Europa’s Double Ridges Through Viscoelastoplastic Deformation Above Crystallizing Cryo-Volcanic Intrusions

Abstract:

Jupiter’s moon Europa is comprised of an icy shell and a ~100 km thick global ocean overlying a rocky core. Among the myriad topographic features etched across its enigmatic surface, double ridges, which consist of two raised flanks with a central trough, are the most pervasive. Often running for hundreds of kilometers, they frequently overprint and offset pre-existing features and appear to be genetically related to cracks in the icy shell. Yet, after nearly two decades of study, these ridge systems and the processes through which they form remain incompletely understood. Several mechanisms have been proposed for ridge formation, one of which is that they are the surface expression of cryovolcanic dikes. Previous mechanical models have considered the elastic response of the icy shell above a crystallizing cryo-volcanic intrusion. We present results from numerical models in which we treat the ice shell as a viscoelastoplastic medium and explore the variability of topographic expression due to varying rates of intrusion and tectonic extension/shortening. The irreversible viscous and plastic response of Europa’s ice shell during intrusion allows large-amplitude topography to develop, comparable to the topographic relief associated with double ridges.