Molecular models identify grain boundaries as accumulating dislocations and promoting creep in rock salt

The rheology of rock salt governs salt tectonics and dictates the long-term integrity of salt caverns used for energy storage. Traditional models inadequately address the coevolution of dislocation dynamics and pore networks under sustained loading. The micromechanical processes that control its creep behavior remain poorly quantified. Here, we integrate X-ray microcomputed tomography, electron backscatter diffraction, and molecular dynamics simulations to reveal the cross-scale mechanisms driving rock salt deformation under sustained load. We track the evolution of pore networks, dislocation densities, and ion-level energy landscapes, uncovering a mechanistic transition from transient to steady-state creep. This transition is marked by a shift in strain accommodation from grain boundary sliding to coordinated crystal slip plasticity. Steady-state creep is characterized by stable deformation rates, facilitated by interconnected dislocation networks within grains. Crucially, we identify a dual role for grain boundaries: they accumulate dislocations while simultaneously dissipating energy via structural adjustments like grain refinement and subgrain rotation. This sequential process of energy accumulation and dissipation at boundaries underpins the remarkable ductility of rock salt, enabling large strains without catastrophic failure. Our findings establish a fundamental link between atomic-scale defect evolution and macroscopic creep, providing key physics-based insights for predicting the long-term stability of geological and engineered salt systems.