4.2.8 High-density snow over low-density snow

Assume that the SWE of the new snow is 1.6 in (4.0 cm) rather than the 0.8 in (2.0 cm) that we just discussed, making it a very dense, wet snow layer. This type of snow tends to develop with warmer atmospheric and surface temperatures.

Higher-density snow overlying lower-density snow can lead to an unstable snowpack, one prone to collapse, since the bonds in the lower layer may not be strong enough to withstand the additional weight. Unstable snow situations occur in flat areas all the time but do not lead to avalanches due to insufficient slope steepness.

Scenario for an upside-down snowfall.

When the density of the snow increases during a single snow event, we get an upside-down snow situation. Generally speaking, the higher-density layer is stronger than the lower-density layer. In flat areas, the denser, upper layer speeds the compaction of the lower layer, but on a steep slope, the situation can lead to an avalanche.