Final answer:
Surface hoar forms a weak layer within the snowpack that can lead to an avalanche when it becomes buried under additional layers of snow and is subjected to further stress or weight.
Step-by-step explanation:
Surface hoar is a type of frost that forms when moisture in the air comes into contact with cold snow surfaces and then freezes. This can create a weak, crystalline layer on top of the snowpack.
When successive layers of snow fall on top of this fragile layer, the surface hoar can act as a sliding plane, leading to a potential avalanche under the right conditions. This is especially true if a significant load, such as new, heavy snowfall or an external force like a skier, is added on top.
Avalanche risk increases when this buried weak layer is disturbed and cannot support the weight above it, causing the snow to fracture and slide down the slope.