Melted Ice

Caption NASA:"These drawings depict explanations for the source of intense heat that has been measured coming from Enceladus' South Polar Region. These models predict that water could exist in a deep layer as an ocean or sea and also near the Surface.

Cassini scientists infer that the temperature of the ice in the South Polar Region must be close to its melting point (shown in red). A layer of liquid water (dark blue) might exist between the ice and the silicate core (brown), allowing the ice to deform independent of the rock, providing even more mechanical energy and more flexing of the icy shell for extreme tidal heating.
Tidal heating could also cause friction in faults near the surface, leading to pockets of partially melted ice".