Title: Thermomechanics of meltwater floow through snow.

Abstract: Meltwater is produced on the surface of glaciers and ice sheets when the seasonal energy forcing warms the snow to  its melting temperature. This meltwater either percolates into the snow or runs off laterally in streams. The quantity of meltwater that is partitioned between these two modes of drainage is a key unknown for how glaciers and ice sheets will respond to climate change as well as contribute to future sea level rise. Here I address the question of meltwater partitioning through two problems. First, melting at high elevations on the Greenland Ice Sheet leads to refreezing layers, which are observed in ice cores. I solve for the motion of refreezing fronts and for the temperature increase due to the release of latent heat. I compare my model for freezing fronts to temperature observations from the Greenland Ice Sheet.  Second, I present a continuum firn hydrology model that includes heat conduction, meltwater percolation and refreezing, as well as mechanical compaction. The model is forced by surface mass and energy balances, and the percolation process is described using Darcy’s law, allowing for both partially and fully saturated pore space. Water is allowed to run off from the surface if the snow is fully saturated. This model applies to both accumulation and ablation areas and allows for a transition between the two as the surface energy forcing varies. The largest average firn temperatures occur at intermediate values of the surface forcing when perennial water storage is predicted. Together these studies provide a holistic picture for how meltwater is partitioned between snow storage and surface runoff. I show that as surface temperatures increase, the capacity for meltwater storage in snow decreases and surface runoff increases leading to sea level rise.