26th November, 2021 Prelims



  • Avalanches are masses of snow, ice, and rocks that fall rapidly down a mountainside.


Anatomy of an Avalanche

Types of Avalanches

  • There are three main types of avalanches:

Slab avalanches

  • A slab avalanche occurs when the weak layer lies lower down in a snowpack. This layer is covered with other layers of compressed snow.
  • When the avalanche is triggered, the weak layer breaks off, pulling all the layers on top of it down the slope. These layers tumble and fall in a giant block, or slab.
  • Once a slab avalanche starts, the slab shatters into many separate blocks. These snow blocks break up into ever-smaller pieces. Some of the pieces rise into the air as a moving cloud of icy particles. The cloud races downhill at very high speeds.
  • The thickness and speed of slab avalanches make them a threat to skiers, snowboarders, mountaineers, and hikers.
  • Slab avalanches are, by far, the most dangerous types of avalanches for people.
  • A slab will move very quickly downhill, up to 130 km/h, starting off as a cohesive unit and shattering into smaller pieces as it descends.

Loose snow avalanches

  • Loose snow avalanches happen when poorly bonded surface snow slides downhill under it’s own weight.
  • They are common on steep slopes and are seen after a fresh snowfall.
  • Since the snow does not have time to settle down fully or has been made loose by sunlight, the snowpack is not very solid.
  • Such avalanches have a single point of origin, from where they widen as they travel down the slope.
  • Sometimes called sluffs, these types of avalanches are generally smaller and less dangerous than slab avalanches, but they can still pose a hazard in the wrong terrain.


  • Cornices are overhanging masses of wind-deposited snow that protrude from sharp terrain features like ridges or peaks.
  • These beautiful structures can be deadly, breaking off in response to changing weather or the weight of a person or machine.
  • When they fail, tonnes of snow fall on the slope below, forming an avalanche or potentially triggering an even bigger avalanche.

Powder Snow Avalanches

  • Powder Snow Avalanches are a mix of the other forms, Loose Snow and Slab.
  • The bottom half of this avalanche consists of a slab or a dense concentration of snow, ice and air.
  • Above this is a cloud of powdered snow, which can snowball into a larger avalanche as it progresses down the slope.
  • The speed attained by this avalanche can cross 190 miles per hour, and they can cross large distances.

Causes of Avalanches

Heavy Snowfall

  • Heavy snowfall is the first since it deposits snow in unstable areas and puts pressure on the snowpack.
  • Precipitation during the summer months is the leading cause of wet snow avalanches.


Human Activity

  • Humans have contributed to the start of many avalanches in recent years.
  • Winter sports that require steep slopes often put pressure on the snowpack, which it cannot deal with.
  • Combined with the heavy deforestation and soil erosion in mountain regions, it gives the snow little stability in the winter months.

Natural Causes

  • These include earthquakes and tremors since they can often create cracks in the snowpack.
  • New snow or rain can cause built-up snow to loosen and fall down the side of a mountain.
  • Sometimes the movement of animals has also been known to cause avalanches.


Vibration or Movement

  • The use of All Terrain Vehicles 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.
  • The other artificial triggers are off-piste skiers, gunshots and construction work done with explosives, which tend to weaken the entire surrounding area.


Layers of Snow

  • There are conditions where snow is already in the mountains and has turned into ice.
  • Then, fresh snow falls on top, which can easily slide down.


Steep Slopes

  • Layers of snow build-up and slide down the mountain at a faster rate as steep slopes can increase the speed of snow.
  • A rock or piece of huge ice can shake the snow and cause it to come down.


Warm Temperature

  • Warm temperatures that can last several hours a day can weaken some of the upper layers of snow and cause it to slide down.

Effects of Avalanches

Damage to Life and Property

  • A large number of casualties take place after avalanches hit heavily populated areas.
  • Infrastructure is damaged, and the blockage caused impacts the livelihood of many.
  • A powerful avalanche destroys buildings, and power supplies can be cut off.


Death or Injury

  • The biggest way in which avalanches affect people is by causing death or injury.
  • Asphyxiation is the most common cause of death, followed by death from injury and lastly, by hypothermia.


Flash floods

  • When an avalanche occurs, it brings down all the debris with it and can cause havoc in low lying areas.
  • Flash floods are seen to happen after avalanches, which is a long term problem many villagers and townspeople have to deal with.


Property and Transportation

  • Avalanches can completely destroy whatever is on its pathways such as houses, cabins and shacks.
  • Avalanches also can cause roads and railroad lines to close.
  • A large amount of snow can cover entire mountain passes and travel routes with cars and trains traveling on these routes.


Utilities and Communication

  • Avalanches can affect humans by damaging utilities and communication.
  • The power from these snow waves can completely destroy pipelines carrying gas or oil, thus causing leaks and spillage.
  • Broken power lines can cause a disruption in electricity and cause thousands of people to go without power.
  • Communication fields, such as telephone and cable lines, could go silent, causing a panic and a delay in response time and rescue.


Economic Impact

  • Businesses are forced to close until the avalanche decreases, and weather conditions become suitable.


Crop Failure

  • If the snow from an avalanche accumulates on farmland located at the lower altitudes, it can completely destroy the crop, causing crop failure and heavy economic losses for the farm.

Why have the Himalayas become prone to Avalanches?

  • Climate in the mighty yet fragile snow-covered Himalayas has been changing rapidly.
  • Researchers have found that winter temperatures in the northwestern Himalayas have risen on an average 0.65 degree Celsius over a period of 25 years from 1991 — higher than the global average rise of 0.44 degree Celsius.
  • During this period, total winter precipitation has increased with greater rainfall and lesser snowfall.
  • Rising temperatures have led to an increase in the frequency of avalanches since 1970, posing a threat to the road that provides access to the newly built Rohtang tunnel.

Do you know?

Some of the biggest shifts stemming from climate change are occurring in what scientists call the cryosphere, the regions of the world where water freezes seasonally, like the ice caps or mountain peaks. The Arctic, for example, is losing ice at its fastest rate in 1,500 years.

Coming to the Himalayas, even if carbon emissions are dramatically and rapidly cut and succeed in limiting global warming to 1.5C, 36% of the glaciers along in the Hindu Kush and Himalaya range will have gone by 2100. If emissions are not cut, the loss soars to two-thirds. – The Hindukush Himalaya Assessment Report 2019.


  • The tallest mountain range in the world — the Himalayas — are part of a region known as the “Third Pole.”
  • These mountains, alongside the Tibetan Plateau and the Hindu Kush Mountains, are home to the largest permanent ice mass outside of the Arctic and Antarctic.
  • More than 40 million people live in the Himalayas, and nearly 3 billion people live in the river basins that flow from the ice in the mountains.
  • Now that ice is melting faster, with sometimes deadly consequences.
  • Glaciers are retreating; permafrost is melting; and weather patterns are becoming more erratic, disrupting previously reliable water sources for millions and instigating more natural disasters like Avalanches.
  • In 2014, 16 sherpas were killed in an avalanche on Mount Everest. Another 22 people were killed in avalanches after an earthquake struck the region in 2015.
  • So, what'll happen if eventually the glaciers disappear one day? Our rivers will become bone dry. With no water for drinking and irrigation, life in any form would be impossible in the Indian peninsula.