3.4 Phase changes, including vapor diffusion

Radiation and conduction are processes that transfer thermal energy. Each induces changes in snowpack between solid ice, liquid water, and water vapor.

Melting is a phase change from solid ice to liquid water. As ice melts, it absorbs a great deal of energy from the surrounding environment, which significantly slows the warming of the snowpack. As a result, the temperature rise in a warming snowpack stalls at 0°C (the melting point) as ice changes to water. Illustration of the energy associated with melting snow
Freezing is a phase change from liquid water to solid ice. As water freezes, it actually releases heat, which significantly slows the cooling of the snowpack. Illustration of the energy associated with melting snow
Sublimation is a phase change from ice directly to water vapor. It occurs most commonly and quickly at the surface of a snowpack on dry, sunny days. Sublimation absorbs much more energy from the surrounding environment than melting, creating a shallow, stable layer just above the snowpack. This occurs despite the sunny conditions and inhibits the melting of the pack. Effect of sublimation on a snowpack