Figure 3
Origin of Europan surface morphologies II: double ridges. A common feature for which many models have been proposed. These include (a) tidal squeezing, whereby daily tidal forces cause a crack to open and close, pumping material onto the surface (Greenberg et al., 1998); and (b) cryovolcanism, where a pre-existing crack provides a pathway for fissure eruptions that build the ridges cryoclastically (Kadel et al., 1998). In terrestrial volcanic systems the amount of subsurface magmatism tends to exceed the amount of surface volcanism. This should also be true on an icy satellite, since the cryomagma (i.e. water) is denser than the surface rock (i.e. ice). Thus while the ridge is being built as a cryoclastic fissure eruption, the cryomagma should form a sill at a depth corresponding to the neutral buoyancy of water within the ice shell. |