Pattern Formation of Refrozen Melt Structures in Snowpack

Infiltration of surface-generated meltwater into snowpack is a spatially heterogeneous process due to the gravity fingering instability. Upon contact with deeper and colder snow, melt can refreeze into solid structures during infiltration. Refrozen meltwater forms as one of two primary structures within snowpack: (1) horizontal frozen structures that act as a barrier for infiltration, and (2) vertical frozen structures which may facilitate deeper meltwater infiltration. These two types of refrozen structures have been observed in the field and have profound effects on how meltwater and its residual thermal content distributes into the snowpack. However, a more detailed physics-based understanding of these structures has not yet been posed.

In this work, we use the thermodynamic nonequilibrium meltwater infiltration model developed by Moure et al. (2023) to investigate the formation of refrozen melt structures in an initially homogeneous snowpack. As the temperatures of the ice and water phases are tracked independently, the refreezing kinetics of infiltrated meltwater are governed by local thermodynamic conditions of each phase and thus do not rely on the assumption of a constant rate of freezing. We are able to recover the formation of ice lenses and ice pipes across a broad range of snowpack parameters. We identify the key thermal conditions that lead to the formation of these structures and how they continue to evolve in time under changing climatic conditions.