Avalanches are making headlines

Over the recent weeks, it has been reported that the western U.S. has been in the middle of a snow drought. However, conditions recently changed, especially in the mountains of California. Several feet of fresh and unstable snow hit the Sierra Nevada mountains in California early last week. A group of people on a backcountry skiing adventure got caught in the state’s deadliest avalanche in modern history. There have also been deadly avalanches recently reported in Utah and a string of avalanches in Austria due to heavy snowfall.

Avalanches occur when a mass of snow becomes unstable and slides rapidly down a mountain slope under the force of gravity. Although they may appear sudden and unpredictable, avalanches usually result from a combination of weather conditions, snowpack structure and terrain features.

One of the primary causes of avalanches is heavy snowfall, as was the case with the recent disaster near Lake Tahoe. When a large amount of snow falls in a short period, the new snow may not bond well with the older layers beneath it. Snow usually accumulates in layers throughout the winter and each layer can have different strengths and weaknesses depending on temperature, wind and moisture at the time it formed. If a weak layer is buried under heavier, denser snow, it can collapse under pressure and trigger a slide.

Rapid warming also increases avalanche risk. When temperatures rise quickly or rain falls on snow, the snowpack can weaken. Meltwater seeps between snow grains, reducing friction and making it easier for the snow to move. Wet avalanches are especially common in late winter and spring when daytime temperatures climb above freezing.

Avalanches can be triggered by other natural forces or human activity. Natural triggers include additional snowfall or earthquakes. However, many modern avalanches are triggered by people traveling in backcountry areas, as the added weight of a person can stress a weak snow layer and cause it to fail.

The deadliest avalanche ever observed occurred in 1970 in Peru. The event was triggered by an earthquake as ice, mud, rock and snow from Mount Huascaran buried the town of Yungay and killed approximately 30,000 people.

Avalanches became a serious concern in Idaho during the late 1800s. A boom in mining resulted in towns being built in narrow valleys directly beneath steep, snow-loaded mountainsides. An example of this issue occurred during the severe winter of 1910. Heavy snowfall blanketed northern Idaho, increasing avalanche activity. That same year, the region was devastated by the Great Fire of 1910, one of the largest wildfires in U.S. history. Although the fire is more widely remembered, the extreme winter conditions leading up to it included numerous avalanches that disrupted rail lines and mountain communities.

The Silver Valley experienced repeated avalanche disasters during harsh winters in the late 19th and early 20th centuries. Railroads, which were critical for transporting ore, frequently crossed steep mountain passes and were highly vulnerable to slides. Avalanches damaged tracks, buried trains and isolated communities for days or weeks. Snow sheds were constructed to protect critical transportation corridors. These early engineering solutions marked some of the first organized attempts to reduce avalanche risk in the region.

By the mid-20th century, economic activity in Idaho shifted from mining toward recreation and transportation. Ski areas developed in the central and northern parts of the state and highways expanded through high mountain passes.

With more people traveling and recreating in avalanche-prone terrain State agencies responded by improving avalanche mitigation techniques. For example, the Idaho Transportation Department manages over 70 potential avalanche paths along a stretch of Highway 21. Explosives may be used to trigger smaller, controlled avalanches before snow builds to dangerous levels in other locations. Snow fences, barriers and improved road design have also reduced risk to travelers. Ski resorts will often conduct daily snowpack assessments and use explosives to secure slopes before opening them to the public.

Modern forecasting has become an essential tool in reducing risk. Organizations such as the Sawtooth Avalanche Center, the Idaho Panhandle Avalanche Center and the National Weather Service provide avalanche forecasts, danger ratings and educational programs. These forecasts analyze snowfall, wind loading, temperature changes and snowpack structure to inform the public about current and future conditions.

In terms of our local weather, snowfall totals at Cliff Harris’s station have been pushed over 20 inches for the 2025-26 season. With many microclimates, other totals in Coeur d’Alene and surrounding regions will vary depending on elevation and proximity to water.

Rain and snow are possible across the Inland Northwest later this week, with snow in the mountains. Despite the struggle for snow in the valley locations, the calendar still says winter. There is still the chance of measurable snowfall during the first two weeks of March as the long-range computer models are indicating a colder upper-level pattern developing across the region.

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Contact Randy Mann at [email protected].