Why does avalanche occur

Ensure you have an experienced group leader. Always stay within view of your group. Avalanches may reach the road without warning. Obey road closures. When the avalanche hazard is high, control work by explosives may be carried out at any time. If an avalanche blocks the highway, remain in your vehicle with seat belts on. Wait for assistance.

It is easier to find a car in the snow than it is to find a person. Heavy snowfall is the first, since it deposits snow in unstable areas and puts pressure on the snow-pack. Precipitation during the summer months is the leading cause of wet snow avalanches. Humans have contributed to the start of many avalanches in recent years. Winter sports that require steep slopes often put pressure on the snow-pack which it cannot deal. The use of All Terrain Vehicles and Snowmobiles creates vibrations within the snow that it cannot withstand.

Coupled with the gravitational pull, it is one of the quickest ways to cause an avalanche. There are conditions where snow is already on the mountains and has turned into ice. Then, fresh snow falls on top which can easily slide down. Disastrous avalanches occur when massive slabs of snow break loose from a mountainside. The mass of snow shatters like broken glass as it races downhill. These hazards can travel as fast as cars on a freeway, up to miles per hour, says Trautman.

Snow slides can start on mountain slopes with at least a degree incline, but they occur most frequently on slopes of degrees. Although avalanches need a slope to start, large avalanches accelerate downhill with sufficient momentum to cross flat terrain for short distances. In some cases, a large chunk of ice or small glacier breaks off a mountainside, gathering snow and momentum and rushing down in a dangerous steamroll.

One of the most deadly avalanches on Mount Everest , which killed 16 Sherpas, occurred when an ice mass the weight of buses plummeted down on top of hikers. Avalanches contain three main features : the starting zone, the avalanche track, and the runout zone.

Avalanches launch from the starting zone. Once the avalanche starts to slide, it continues down the avalanche track, the natural path it follows downhill. The avalanche finally comes to a stop at the bottom of a slope, in the runout zone, where the snow and debris pile up. Avalanches are most common during the winter, December to April in the Northern Hemisphere, but they do occur year-round. To get an avalanche, you need a surface bed of snow, a weaker layer that can collapse, and an overlaying snow slab.

The highest risk period is during and immediately after a snow storm. Underlying snowpack, overloaded by a quick deluge of snow, can cause a weak layer beneath the slab to fracture naturally. Human-triggered avalanches start when somebody walks or rides over a slab with an underlying weak layer. The weak layer collapses, causing the overlaying mass of snow to fracture and start to slide.

Earthquakes can also trigger strong avalanches. By digging a snow pit or profile , scientists can look at the composition of different snow layers that formed during a season, sort of like looking at the layers of a cake. The size and shape of the snowflakes in each layer provide clues about the weather events that occurred: big dumps of snow, drought, rain, a hard freeze, or loose, powdery snow.

Larger, looser snow crystals are weaker , because there are fewer points they can touch to interact with the other snow layers. The interaction of the snow layers can help predict the chances of an avalanche. He emphasizes that conditions can change rapidly with the weather, and this can be deadly. Slopes shaded from direct sun stay cooler, preventing bonding between snow layers and leading to more avalanches in cold conditions. Conversely, during the spring, sunny mountainsides have a higher risk for avalanches because of rapid warming and melting.

Precipitation type and intensity, temperature, wind, slope steepness and orientation the direction it faces , terrain, vegetation, and general snowpack conditions can influence whether and how snow moves down a slope. Moving across the terrain, slight changes in slope or how the mountainside is oriented towards the sun can create drastically different conditions. The Forest Service runs 14 backcountry avalanche centers in the United States to provide information for people recreating in snowy wilderness areas.

Forecasters use four main elements to describe conditions, assign a danger level , and help recreators make the best decisions in the backcountry. Field teams at avalanche centers document the snowpack—the thickness and type of snow layers—and combine those data with weather conditions to estimate danger levels.

The forecasts take into account the potential type and size of an avalanche, the likelihood it will occur, and the location. Before entering the backcountry, check online forecasts for the danger level in that area.

Each mountain range has unique snow properties and therefore, avalanche risks, so checking your specific region is critical.