Gas-driven water volcanism and the resurfacing of Europa

Abstract

We have analyzed the problem of how pathways are created for the resurfacing by water or volatiles for a Europa model in which there is an ocean underlying a thin ice shell (∼10-km thickness). Open cracks propagating downward cannot reach the ocean unless the relative tension in the ice is both very high (∼100 bar) and applied very rapidly (⪅10^4−10^5sec); there is no known way to satisfy these criteria. Water-filled cracks propagating upward can approach the surface for relative tensions of 5–10 bar, comparable to the stresses induced by the eccentricity tide. Exsolution of plausible gas species (CO_2, CO, CH_4, SO_2) can then occur at the crack tip. The application of linear elastic fracture mechanics shows that the gas-filled portion of the crack pinches off from the water-filled portion and may rise rapidly to the surface, entraining some water. Many of these cracks may end up as intrusions rather than extrusions because of partial freeze-out of CO_2 and water on the walls of the crack. The resulting eruption is initially gas dominated, but may include a subsequent less extended eruption of foam. There may not be a direct relationship between the resurfacing process described here and the currently known geologic features observed on the surface. The main problem with this or any model for tapping the ocean is the propagation of cracks through the soft ice immediately overlying the ocean.

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