Which category of avalanche can reach speeds of 15-40 mph?

The category of avalanche that can reach speeds of 15-40 mph is the Wet Flop avalanche. This type of avalanche occurs in conditions where melting snow becomes saturated with water, causing it to lose cohesion and become heavy. As the saturated snow moves, it flows rapidly down the slope, often resembling a slurry of water and snow. The significant speed range associated with Wet Flop avalanches is attributed to this combination of meltwater enhancing the flow and the gravitational pull acting on the heavy, wet mass.

In contrast, other types of avalanches have different characteristics and speed ranges. Gliding avalanches typically unfold more slowly as they are related to the movement of snow on the ground layer and often do not reach the speeds associated with Wet Flop avalanches. Loose snow avalanches can travel faster than gliding avalanches but generally do not achieve the same consistency and weight that contribute to the speed of Wet Flop events. Dry Flow avalanches tend to occur with less moisture content, resulting in a different flow behavior and speed. This context highlights why Wet Flop avalanches are notably swift in the specified speed range.