We investigate the hypothesis that the ~10 km diameter dome-shaped features seen on Europa's surface are caused by strongly temperature-dependent convection, in which upwellings form isolated diapirs or thermals. We use the observed lower limit on dome diameter of 4 km to deduce that the conductive (stagnant) lid thickness must be ≤5 km. Such a lid thickness implies a minimum surface heat flux of 90 mWm-2, compatible with recent estimates of tidal heating. We also use the mean observed dome diameter to infer a lower thermal boundary layer thickness of ~1 km. We find that the ice is probably deforming in the diffusion creep regime with a grain size in the range 0.02--0.06 mm. The fraction of internal heating is >0.5, the ice viscosity 1012--1013 Pa s, and the crustal solidification rate<5km/Ma.