Stresses generated in cooling viscoelastic ice shells: Application to Europa

[1] A cooling viscoelastic ice shell overlying an ocean develops stresses due to two effects: thermal contraction of the ice due to cooling and the expansion of the shell due to the ice-water volume change. The former effect generates near-surface compression and deeper extension; the second effect generates extension only. In both cases, stresses are smaller at depth due to viscous creep. The resulting combined stresses are extensional except at shallow (<1 km) depths in thin ice shells. For ice shells thicker than 45 km, stresses are extensional throughout. The extensional stresses exceed 10 MPa for shells thicker than 20 km and thus dominate all other likely sources of stress as long as shell cooling occurs. The dominantly extensional nature of the stresses may help to explain the puzzling lack of compression observed on Europa and other large icy satellites. However, after 100 Myr of conductive cooling the maximum theoretical elastic strains for Europa are 0.35%, which are probably insufficient to explain the total amount of observed extension.