3.2 Gravity & conduction
The basic metamorphism processes that affect snowpack evolution are gravity, conduction, radiation, vapor diffusion, and, to a lesser extent, convection. We’ll describe each process on this and the following pages of this section.
Gravity
In general, gravity acts to pull snowpack straight downward toward the ground on flat slopes. It
increases the density of the snow after the snowpack becomes established in a process called settling.
Over sloped surfaces, a portion of the gravitational force is directed parallel to (along) the slope rather than vertically. This portion increases with slope steepness and is responsible for moving snow downhill.
Conduction
Conduction is the direct transfer of thermal energy from warmer to cooler substances that are
in contact with each other. Conduction is present in snowpack when there are changes in temperature within
the pack or at the top or bottom. Conduction often occurs in fall when ground temperatures are warmer than
the snowpack. A temperature gradient forms, causing the ground to heat the lower portion of the snowpack.
Note that ground temperatures just below the snowpack are typically near 0°C except in permafrost regions of the high latitudes, where they can be significantly colder. In these areas, snowpack temperatures more than a few centimeters away from the ground can be as low as -60°C depending on the ambient air temperature.