Faceting in snow metamorphism occurs when the temperature gradient is at least 1°C per 10 cm. Which condition is associated with faceting?

• A. Less than 1°C per 10 cm
• B. No gradient
• C. Exactly 2°C per 10 cm
• D. At least 1°C per 10 cm

Answer: (D)

Faceting arises when the snowpack experiences a strong vertical temperature gradient, enough to drive rapid sublimation and re-deposition on crystal faces. The threshold is a gradient of at least 1°C per 10 cm. When that level is reached, vapor moves preferentially between faces, pruning edges and growing flat, smooth surfaces to form faceted crystals.

If the gradient is weaker than this threshold, the driving force isn’t strong enough to produce pronounced facets; grains tend to grow more uniformly or undergo other forms of metamorphism. With no gradient at all, facet formation doesn’t occur, and crystals don’t develop the characteristic angular faces.

Thus, any gradient that is at least 1°C per 10 cm supports faceting, including a gradient of exactly 2°C per 10 cm.