While any accumulation of snow can be termed a snowpack, the primary study and concern of snowpacks are typically in mountainous regions, such as the American Rocky Mountains and usually concern themselves with elevations above 3,000 feet. Even arid regions can have snowpacks that lock up millions of metric tons of fresh water that if released relatively quickly have massive potential for catastrophe, locally and farther down the continental divide as elevation declines, possibly spreading devastation many hundreds of miles away.
Because so much weight is locked up in snow at higher elevations, a rapid melt in the internal support at lower elevations can bring parts of the upper snowpack cascading down a mountainside. An avalanche not only brings many millions of tons of snow, but picks up trees, rocks and other debris and many reach speeds in excess of 80 miles per hour along a wide front. In spite of safety efforts, even when snowpacks are relatively stable, avalanches kill several people annually. Some recreational areas have preemptive methods for triggering potential avalanches during safe periods, but this cannot cover an entire mountain range. One such avalanche killed 12 people when it ripped through the Swiss canton of Valais in February 1999, so the risk is not specific to outdoor recreational enthusiasts.
The risk to skiers and small communities is evident, but the risk to ground routes through mountain passes has to also be considered for its potential to significantly disrupt commerce. Many mountain ranges have only a handful of passable routes and an avalanche along a critical road or rail line will cause more than just an inconvenience to travelers given how much ground freight moves daily throughout the world. An avalanche across one of these passes will cost more than just the clean up and rescue effort that is likely to take many days if it occurs and a rapidly melting snowpack can easily precipitate such an event.
By far, the most serious risk to a rapidly melting snowpack is from flood. Internationally, most waterways have flood control measures, often dams, to mitigate spring runoff and prevent a regular annual downriver catastrophe from occurring every spring. There are engineering limitations and a warm winter with better than average snowfall can bring spring floods earlier and with many more millions of gallons of water than the flood control measures can handle. While loss of life is not such a big factor (because flood waters take many days to move downriver), the loss to property, disruption to community and the widespread destructive nature of inundation across several square miles along rivers tends to cripple communities economically and drive up insurance costs nationally. The psychological impact from being a flood victim does not have a ready price tag, but that cost must also be taken into account from the potential for very bad events when the snowpack melts too fast.
