Some strength features of natural snow surfaces that affect snow drifting

The load, travel distance, and work index needed to break surface elements on 21 natural snow surfaces were measured with a motor-driven, spherical probe. The strongest and least brittle surfaces were fresh deposits of wind transported snow. The weakest surface was a new surface formed during snowfall with no sun and no wind. The most brittle surfaces were two cases of sun-softened snow that had refrozen before measurement. In new snow that had aged $\text{6–7}\text{1}\text{2}\text{h}$ with no sun and no wind, strength increased by a factor of 2–3, work index increased 10 times, and brittleness decreased by 4–9 times. On surfaces with both erosional and depositional features, the latter were stronger, less brittle, and had work indexes 10–100 times greater than the erosional features. The strength of snow surface elements as measured with the current hardness gage corresponded closely to the forces generated by saltating snow particles.