Sintering, or pressure sintering, is the physical process of bond formation between grains in the snowpack. It usually accompanies the rounding process. Sintering occurs when water vapour is deposited at the contact points between snow grains, forming necks. These necks then create strong bonds between grains, increasing the strength of the snow.
Hardening or compaction from any mechanical disturbance such as boots, skis, snowmobiles, groomers, wind, and avalanches produces rapid sintering by breaking up large grains and bringing grains into close contact.