Origin of Europa's Ridges by Incremental Ice-Wedging

Ridges are ubiquitous on Europa's surface. These ridges are narrow, linear features, up to a few hundred kilometers in length and 100-300 m in height. Many ridge-formation scenarios have been suggested, including tidal squeezing, linear diapir, up-warping by compression, linear volcanic activity buildup, shear heating along faults, or incremental ice-wedging. The previous quantitative studies have showed that shear heating can produce linear features comparable to Europa's ridges in height. However, the entral trough (one of the most characteristic features of Europa's ridges) was not reproduced in these studies. Here we extend the previous 2d numerical modeling to study whether incremental ice wedging can produce Europa's ridges using finite element code Tekton. We assume visco-elasticity and a power-law rheology in the models. We use the split node technique in Tekton to simulate the ice wedge opening. A vertical ice wedge is positioned in the center of the calculation domain, extending from 0 km to a depth of 0.6-1 km below the surface. Our simulations show that a ridge of 60 m or higher can be formed if the ice wedge increases to 200 m wide at a speed of 0.3-3 cm/yr. Our simulations also show that the ice wedge formation rate may have a strong effect on the ridge's shape and height. If the dike formation rate is slower (<1 cm/yr), a double ridge with central trough is generated. If the dike formation rate is faster (>1 cm/yr), a higher, single ridge (without central trough) is formed. In conclusion, ridges can be formed on Europa's surface by incremental ice-wedging under Europa's conditions.