Surface hoar is a weak layer formed by which process?

• A. Frost crystals forming on the surface during clear nights
• B. Ice buildup due to pressure
• C. Wind erosion of surface
• D. Sintering of ice at depth

Answer: (A)

Surface hoar forms when water vapor in very cold, calm conditions deposits directly onto the snow surface as frost crystals during clear nights. Those large, delicate crystals bond weakly to the grains beneath, creating a soft, weak layer in the snowpack that can fail under additional loading. The other processes don’t produce this surface frost: pressure-driven ice buildup, wind erosion, or deep metamorphic bonding (sintering) all involve different mechanisms and layers within or on the snowpack rather than a surface frost layer forming from nighttime deposition.