Europaquakes and Plumes Powered by Freezing-Driven Overpressure

We ask what may drive Europa’s putative intermittent plumes. We test whether shallow pockets of liquid water (i.e., sills) freezing within Europa's ice shell can power activity. We build a numerical model that couples heat flow, phase change, and pressure evolution, including the drop in melting temperature under pressure. As a sill freezes, the expansion of ice raises pressure; when a fracture opens, pressure falls and any supercooled liquid crystallizes quickly, producing bursts of solidification, pressure release, and re-pressurization. This cycle can yield sporadic venting and seismic events without a sustained conduit. Pressure-dependent melting shortens the total freezing time at depth and produces rarer but larger events, while elastic flexing of the ice roof reduces the event rate. For reasonable sill sizes and numbers, our model predicts late-stage spikes consistent with sporadic plumes and low-magnitude quakes. These results identify freezing sills as a self-contained engine for Europa’s activity and provide testable signatures for upcoming missions to seek Europaquakes and plumes.