Facets are angular crystals formed under which condition?

• A. Round crystals formed by slow cooling
• B. Angular crystals formed under strong temperature gradients within the snowpack
• C. Dense packing of snow
• D. Large snow grains

Answer: (B)

Facets form when there is a strong temperature gradient within the snowpack. A large temperature difference between the surface and deeper layers drives water vapor to migrate through the snow: vapor sublimates from warmer areas and deposits on colder surfaces. This rapid, diffusion-driven metamorphism reshapes grains by removing mass from their edges and adding it to their faces, producing angular, flat-faced crystals—the faceted grains. This process is known as kinetic growth metamorphism and it creates a weak, fracture-prone layer that is important in avalanche behavior.

The other descriptions don’t capture this specific metamorphic process. Round crystals result from slow, low-gradient metamorphism where grains tend to smooth out and round; dense packing relates to how tightly packed the snow is rather than crystal shape; large snow grains describe size growth that doesn’t necessarily produce the angular facets formed by a strong temperature gradient.