Cycloidal features.
Cycloids are arcuate ridges like this:
Greg Hoppa has been able to explain the shape
and formation of these ridges by calculating the
tidal stresses on Europa over the span of several
orbits.
http://pirlwww.lpl.arizona.edu/~hoppa/
The span between two adjacent cusps is one
Europan day, corresponding to one tidal
push-pull cycle.
Conclusion: "Other icy satellites do not appear to have any analog to Europan cycloids, which suggests that only Europa has the unique characteristics necessary to form cycloidal features: A global ocean, substantial diurnal tidal stress, and a weak lithosphere."