Geomorphic Features on EuropaChaos
Chaos regions are heavily disrupted regions on Europa's ice shell as seen in Figure 16. It appears to be regions where the ice crust has broken and shifted, forming ice blocks in a hummocky matrix. As described by Carr et al. (1998), the blocks of ice have flat tops and retain the features of the original, unbroken surface. Since this original surface features are present, one can construct the original layout and determine how the blocks have migrated. Analysis by Carr et al. indicate that the blocks have moved laterally up to several kilometers while also rotating. Some blocks have tilted inward, with their sides covered with inter-block hummocky material, and others appear sunken within the hummocky material.
Figure 16. Chaos region of broken ice shell. Courtesy NASA/JPL.
Carr et al. believe that the movement of the blocks is a result of plate movement where the blocks are contained. They suggest that as the plates moved, material below flowed upward through cracks. If this is true, it would suggest that thickness of the ice shell in the chaos region is only a few kilometers thick. They propose that the motion of the plates is due to diapirs, which are columns of mobile material rising to the surface creating an upward pressure on the ice shell. This kind of activity is predicted by models of tidally heated ice above sitting above a liquid water layer (e.g. Reynolds and Cassen 1979, Squyres and Croft 1986, Wang and Stevenson 2000). Thus, chaos regions are likely regions containing larger amounts of heat flow or even melting.