Diagram explaining formation of Europa chaos

Diagram explaining formation of Europa chaos
Diagram explaining formation of Europa chaos How Europa's chaos terrain is made, in sketch form. In (a), a plume of warm ice (not liquid water, but a solid ice plume, like the rocky plumes in Earth's mantle) rises upward. Above the upwelling plume, the surface might (but might not) warp upward. At great depth in Europa's crust, the pressure of the overlying ice overcomes the relatively warm temperatures to keep ice in solid form. On to (b): when the upwelling plume of warm ice pushes the nearer-surface ice upward, this balance is disturbed, and ice within the crust at a few kilometers below the surface begins to "sweat," partially melting. Liquid water is slightly denser than frozen ice, so takes up less volume. The reduced volume means that over the area of the melting, the surface sinks downward. The thicker crust at the edge of the downwarped area produces higher pressure on the liquid melt than the thinner crust at the center, so as more of the crust melts, the water flows from high pressure toward low pressure, producing a "lens" of water, thickest in the center and thinnest at the edges, and the melting water is pinned in a confined area above the uprising plume. Then comes (c): As the "lid" over the plume sinks downward, it also bends, and cracks open in the bottom of the lid to accommodate that bending. Briny liquid from the lake, under pressure from above, squirts into these cracks and percolates into the porous granular ice in the crust. In this way the crust never melts through but it is saturated with water, and large chunks of of crust can "calve" off as the fissures crack. If the blocks are narrow, they may tilt sideways. Finally, in (d), as the geologic activity subsides and the lens of liquid water refreezes, so does the water saturating the crust. Freezing water expands, so the brine-wetted matrix material in between the calved blocks domes upward. Nature Magazine