Why does snow densify faster at temperatures close to the melting point?

Snow densifies more rapidly at temperatures near the melting point because the processes that facilitate grain rounding and packing are significantly accelerated under these conditions.

At these temperatures, molecules evaporate from the sharp points of ice crystals and condense into hollows, causing grains to round and fit together more closely. Additionally, touching grains develop connecting necks of ice through a process called sintering. When liquid water is present, the rate of densification increases even further due to several factors:

• The melting of ice from grain extremities with subsequent refreezing elsewhere.
• The compacting force of surface tension.
• Refreezing after pressure melting (regelation).
• The freezing of water between grains.

These mechanisms allow the snowpack to reach higher densities much faster than in colder environments, where such molecular movement and phase changes occur more slowly.1