Avalanche is a slide where any amount of snow slides down a mountain slope. It is also known as “snowslide”. The avalanche moving downslope when it reaches the bottom tends to gain power and speed; this can transform a small snowslide into a full-blown disaster.
Types of Avalanches
Avalanches can be categorized into two types based on their depth:
Surface Avalanche: Occurs when a layer of dry but loosely packed snow slides over a wet but dense layer of snow.
Full Depth Avalanche: It occurs when the full snow cover (top to the bottom surface) starts sliding.
Avalanches can also be categorized based on Snow Mass and Snow Type:
Slab Avalanche: When a plate of snow slides as a cohesive unit. The slabs are huge.
Loose Snow Avalanche: When snow that is loose slides downwards on a mountain slope. When loose slides are small, they are termed “sluffs”. Sluffs are not dangerous, as fatalities due to sluffs are rare.
Ice Fall Avalanche: When glaciers slide over a cliff, an ice equivalent of a waterfall.
Cornice Fall Avalanches: They are girder-like snow structures formed by the drifting of snow due to winds. The weight of a falling cornice produces an avalanche on the slope, or the cornice may break into pieces and transform into an avalanche.
Wet Avalanche: They usually occur when warm air temperature causes water to seep in beneath the snowpack and reduces its strength.
Glide Avalanche: It is quite similar to glaciers. In this case, the entire snowpack slowly slides as a unit. It is a very slow process.
Slush Avalanches: They are an unusual type because of their occurrences on gentle slopes. It mainly occurs in the permafrost soil that permits water to pile up, and the snowpack gets saturated; as a consequence, the snowpack loses its strength and slushes on a gentle plain.
Factors Causing Avalanches
Terrain: It constitutes slope profile, angle of slope and ground surface. Slope ranging between 25 to 45 degrees is prone to snow movement. The ruggedness and smoothness of surface rocks determine the pace of the movement of snow. Convex slopes allow more tension to develop hence augmenting the chances of a slab avalanche.
Climate: Due to excessive snowfall, the snow-built-up can be very rapid (2cm/hour), and it can create very unstable conditions. Sudden changes in temperature, wind speed and direction may also influence the stability of the snowpack. The Himalayan region becomes vicious from January to March. Generally, winters with heavy snowfall are associated with a major avalanche in the Himalayas.
Earthquakes: Himalayas is tectonically very active, and any tremors or earthquakes can result in a hazardous avalanche by breaking off large masses of snow, ice and rock.
Vibration or Movement: Vibrations produced by vehicles coupled with the gravitational pull it is one of the quickest ways to cause an avalanche. Construction work where the use of explosives is involved tends to weaken the snowpack and may trigger avalanches.
Human Interaction: Human interference is the reason behind 90 per cent of avalanches. The avalanche area of India lies along the northern part of our country, covering Jammu and Kashmir, Himachal Pradesh and the hills of Uttaranchal, extending up to Sikkim in the eastern region. The problem, however, is more acute in the western part of the Himalayas, where there is frequent interaction between troops and civilians with avalanches.
Avalanche Hazard
Major avalanche-prone areas of the World are located in higher latitudes or sub-tropical regions of high-altitude mountain regions. They occur frequently in France, Swiss, German, Austrian and Italian parts of the Alps mountains. Other regions are western Canada, Utah, Alaska, Colorado and the Himalayan mountains.
Impacts of Avalanches
Death and Fatalities: Victims of avalanches who are buried under snow die due to asphyxiation (suffocation), hypothermia and serious wounds. In February 2016 very heart rendering incident 10 soldiers of the Indian army buried under an avalanche, died near the 19000 feet high Siachen Glacier. In World, the most fatalities occurred in France, followed by Austria, the USA, Switzerland and Italy.
Damage to Property: It damages Infrastructure and causes a blockage that can adversely impact the livelihood of several people.
Flash floods: Flash floods are seen to happen after avalanches. It brings down all the debris with it and can cause havoc in low-lying areas.
Economic Impact: Various ski resorts depend on tourists to run their business. Ski resorts and other businesses are forced to close due to avalanches.
Risk Reduction
These are some of the passive methods adopted for Avalanche Hazard Mitigation in India:
Trying to increase the general awareness of the affected population through:
- Preparation and Publication of Hazard Map and Avalanche Atlas
- Training: Training in avalanche safety and rescue methods would go a long way to bring down avalanche casualties. SASE has been training army personnel in safety and rescue methods.
In India, the Snow Avalanche Study Establishment (SASE) has been forecasting and issuing warnings for snow avalanches; this is mostly done for the movement of the Indian army in the glaciated region. SASE has been using satellite imagery, Digital Terrain Model (DTM), and Stress Distribution Model (SDM) for better forecasting.
Some active methods have also been adopted in India to minimize the damage caused by avalanches. It includes:
- Structural controls such as snow bridges, snow rakes and snow nets.
- Afforestation
- The artificial Triggering method inhibits the disastrous build-up of snow cover on slopes.
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