Final answer:
Snow above three feet with layers of ice and water is more susceptible to sliding, especially in high altitudes like the tierra Nevada zones above 15,000 feet. Snow stability is also influenced by the heat required for phase changes, even when the air temperature is above freezing.
Step-by-step explanation:
When the snow is above three feet and contains layers of ice and possibly water, it is more prone to sliding. This may occur due to various alternating layers of snow, ice, and water, which weaken the structural integrity of the snowpack. At high altitudes, such as above 15,000 feet in the tierra Nevada zones, snow and ice are more permanent due to the colder temperatures and less human activity.
An additional factor that contributes to snow stability is that even when daytime temperatures are above the freezing temperature, snow remains on mountain slopes because the phase change from solid to liquid requires significant heat. Hence, it takes time for the accumulated heat from the air to melt the snow, with warmer air speeding up this process.