Lumivyöryjen

lumivyöryjen, or snow avalanches, are rapid flows of snow down a slope, triggered when the snowpack's internal stability fails. The instability arises from physical, environmental, and mechanical factors that alter the snowpack's structure. Weather plays a major role; sudden temperature rises, strong winds, or heavy precipitation can create layers of weak snow on top of denser layers, creating a natural lubrication that permits the onset of an avalanche. Snowpack shear stresses increase with slope gradients, most commonly between 30 ° and 45 °. Terrain features such as gullies, cliffs, and trees can accelerate the flow or alter its path, while the presence of ice-crystal layers or wind slabs can create “tenuous” zones of snow particularly susceptible to failure.

Avalanches are categorized both by the triggering event and the form the snow takes. Slab avalanches involve a cohesive block sliding off the surface, whereas powder or loose snow avalanches involve a more fluidized flow of finer material. The destructive capacity of an avalanche depends on snow depth, particle size, density, and the slope angle; large, dense slabs can travel meters or kilometres and are capable of burying infrastructure, homes, and even vehicles. In populated backcountry areas, avalanches constitute a major natural hazard, accounting for numerous casualties annually in mountainous regions.

To reduce the risk posed by lumivyöryjen, authorities maintain warning systems that monitor meteorological data, snow conditions, and slope stability through remote sensing, ground-based instruments, and visual inspection. Avalanche control methods include controlled detonations, loading of specific areas with additional weight, and the use of barriers or snow fences to slow or redirect flow. Public education, such as avalanche safety courses and real-time forecasting, helps skiers, mountaineers and emergency services prepare for and respond to avalanches, thereby mitigating their impact on human life and property.