Constructive metamorphosis is caused by the upward movement of water vapor within the snowpack. Warmer temperatures are found closer to the ground because it receives heat from the core of the earth. Snow has a low thermal conductivity, so this heat is retained, creating a temperature gradient between the air underneath the snowpack and the air above it.
The process of constructive metamorphosis in snowpack is triggered by the upward movement of water vapor, which is influenced by the warming of the underlying surface due to heat transfer from the Earth's core. This warming creates a temperature gradient between the air beneath the snowpack and the surrounding atmosphere.