What is an Avalanche and what causes them

An avalanche is a rapid flow of snow down a hill or mountainside. Although avalanches can occur on any slope given the right conditions, certain times of the year and certain locations are naturally more dangerous than others. Wintertime, particularly from December to April, is when most avalanches tend to happen. However, avalanche fatalities have been recorded for every month of the year.

All that is necessary for an avalanche is a mass of snow and a slope for it to slide down. For example, have you ever noticed the layer of snow on a car windshield after a snowfall? While the temperature remains low, the snow sticks to the surface and does not slide off. After the temperature increases, however, the snow will slide down the front of the windshield, often in small slabs. This is a miniature version of an avalanche on a much smaller scale.

Mountain avalanches are obviously much larger and the conditions that cause them are more complex. A large avalanche in North America might release 300,000 cubic yards of snow. That is the equivalent of 20 football fields filled 10 feet deep with snow. Large avalanches are often naturally released when the snowpack becomes unstable and layers of snow begin to fall. Skiers and recreationists usually trigger smaller, but often more deadly avalanches.

Large avalanches are often naturally released when the snowpack becomes unstable and layers of snow begin to fall. Skiers and recreationists usually trigger smaller, but often more deadly avalanches.


An avalanche has three main parts. The starting zone is the most volatile area of a slope, where unstable snow can fracture from the surrounding snow cover and begin to slide. Typical starting zones are higher up on slopes. However, given the right conditions, snow can fracture at any point on the slope.

The three parts of an avalanche path are the starting zone, avalanche track, and runout zone.

The avalanche track is the path or channel that an avalanche follows as it goes downhill. Large vertical swaths of trees missing from a slope or chute-like clearings are often signs that large avalanches run frequently there, creating their own tracks. There may also be a large pile-up of snow and debris at the bottom of the slope, indicating that avalanches have run.

The runout zone is where the snow and debris finally come to a stop. Similarly, this is also the location of the deposition zone, where the snow and debris pile the highest.


Several factors may affect the likelihood of an avalanche, including weather, temperature, slope steepness, slope orientation (whether the slope is facing north or south), wind direction, terrain, vegetation, and general snowpack conditions. Different combinations of these factors can create low, moderate, or extreme avalanche conditions. Some of these conditions, such as temperature and snowpack, can change on a daily or hourly basis.


Top 10 Deadliest Avalanches in history

10. Kolka Glacier, North Ossetia, Russia, September 2002 (125 deaths)

 A partial collapse of the Kolka glacier claimed 125 lives on September 20, 2002. The avalanche occurred on the northern slopes of the Kazbek massif in North Ossetia, Russia. Among the casualties were a film crew of 27, including the famous Russian actor Sergei Bodrov, Jr. The avalanche also buried a large part of the Russian village of Nijni Karmadon under snow and debris.

9. Gayari Military Base, Ghanche, Pakistan, April 2012 (138 deaths)

On April 7, 2012, an avalanche, occurring in the disputed Siachen region of Indo-Pakistan, claimed 138 victims. These included soldiers and civilian employees alike of the Northern Light Battalion at the Gayatri Military Base, Ghanche, Pakistan. This incident drew the attention of the governments of both India and Pakistan to resolve the Siachen dispute, which, since 1984, had led to the deaths of a large number of soldiers from both sides. These deaths were also primarily due to the harsh climatic conditions prevailing in the region.

8. Salang Avalanches, Hindu Kush, Afghanistan, February 2010 (172 deaths)

17 avalanches, triggered by heavy winds and rain and beginning at the southern approaches of the Salang Pass in the Hindu Kush Mountain range, buried more than 2 miles of highway and killed nearly 172 individuals in February of 2010. The avalanche entombed many cars, turning vehicles into icy coffins, and also shoved others into the mouths of death in the deep gorge below. A large number of cars were also trapped in the nearby two-mile-long tunnel that connects Kabul with northern Afghanistan.

7. 2012 Afghani Avalanches, Badakhshan, Afghanistan, March 2012 (201 deaths)

The Afghani Avalanches in the Badakshan Province of northeastern Afghanistan caused heavy losses to life and property in the region. On March 2, 2012, a series of three avalanches struck the region, burying villages on their way down under massive sheets of ice, snow, and debris. The village most affected in the disaster was so remote that the rescue forces were unable to reach its homes until two days later. In fact, there were no accessible roads connecting the village to the rest of the country. The locals of the Darwaz District and twenty-five aid workers from Tajikistan were among the first rescuers to arrive in the region.

6. Lahual Valley, India, March 6, 1979 (254 deaths)

The peace-loving denizens of the Lahual Valley of India are very protective about the forests in their region, as they consider the trees in the forest to be their guardians, shielding them against the rage of one of nature’s greatest furies: the deadly avalanches. One painful memory is etched into the minds of every member of the village, this being the memory of the avalanche that battered the villages in the Lahual Valley on March 6, 1979, claiming the lives of around 254 villagers in the region. A period of intense snowstorms were believed to have triggered the avalanches, which buried the valley under almost 6 meters of snow. Though extremely powerful, avalanches can even raze down large forests, and the trees definitely play an important role in stabilizing snow packs and halting small avalanches.

5. Winter of Terror, Austro-Swiss Alps, 1950-1951 (265 deaths)

The Winter of Terror was one of the worst periods in the history of the Alps, and one that saw a cascade of avalanches along the Austro-Swiss alpine border claimed over 265 human lives, and destroyed large areas of residential properties and other man-made structures in Austria and Switzerland alike as well. Both countries also lost thousands of acres of commercially valuable forests in the disaster. An atypical set of weather events is held responsible for the Winter of Terror. The tragic events occurred within a three-month period in the winter of 1950-1951.

4. 2015 Afghani Avalanches, Panjshir, Afghanistan, February 2015 (310 deaths)

In February of 2015, four north-eastern provinces in Afghanistan came under the attack of a series of deadly avalanches. The Panjshir province, around 60 miles north-east of the capital of Afghanistan, Kabul, was the worst affected by this disaster when the avalanches destroyed over 100 homes in the province. Rescue efforts in the region were slow to reach the villages, especially as heavy snowstorms and fallen trees slowed down the rescue personnel and vehicles on their way to the affected regions. There were around 310 casualties in the disaster.

3. 1962 Huascaran Avalanche, Peru, January 1962 (4,000 deaths)

Mount Huascaran, in the Andes Mountains of Peru, represents an extinct volcano, with many Peruvian communities settled at its base in the Rio Santa Valley. On the fateful day of January 10, 1962, a massive chunk of a giant glacier on the mountain broke apart from it and rushed down to the valley with thundering speed. As the people of the region were used to avalanches, they knew they had to seek refuge on higher grounds before the avalanche reached their homes. However, this time they had underestimated the speed of the avalanche, which covered a distance of 9.5 miles in only 7 mins, wiping away several communities in the valley before they could reach safe grounds. The deadly avalanche completely buried the towns of Ranrahirca and Huarascucho under 40 feet of snow, and continued on in its killing spree until it reached he Santa River. There, it blocked the river flow, subsequently causing massive flooding in the nearby areas. Over 4,000 people lost their lives in the disaster, with many bodies remaining undiscovered for long periods, still buried under several feet of snow. A large number of farm animals and millions of dollars of crops were also lost in the disaster.

2. White Friday/Alpine Front Line avalanches, Marmolada, Italy, December 1916 (10,000 deaths)

In December of 1916, during the worst days of World War I, a series of avalanches in the Italian Alps killed around 10,000 Italian and Austrian soldiers fighting against each other. Some witnesses claim that the avalanches were purposefully triggered by the activities of soldiers on both sides in efforts to destroy their respective oppositions’ forces. Heavy snowfall in the winter of 1916 had further catalyzed the possibility of avalanches in the region. On December 13th, the first avalanche, involving around 100,000 tons of ice, snow, and rocks, plunged down Mount Marmolada into the barracks of the Austrian soldiers lying directly in its path. Though 200 soldiers survived, 300 others died in this accident. However, this was just the beginning. Within the next few weeks, many other avalanches struck the area, with disturbingly high frequencies of snowfalls claiming several more thousands of lives.

1. 1970 Huascarán-Ancash, Peru, May/June 1970 (20,000 deaths)

The worst natural disaster in the history of Peru occurred on May 31, 1970, and is known as the Ancash Earthquake, or the Great Peruvian Earthquake. The earthquake triggered an avalanche that alone claimed the lives of almost 20,000 people, making it the deadliest avalanche in the recorded history of humankind. The epicenter of the earthquake was located 21 miles off the coast of Peru in the Pacific Ocean, and the Peruvian regions of Ancash and La Libertad were the worst affected by this disaster. A massive avalanche struck the towns of Yungay and Ranrahirca when the earthquake destabilized the northern walls of Mount Huascarán. A large chunk of ice and snow, 910 meters wide and 1.6 kilometers long, sped down the mountain at speeds of 280 to 335 kilometers per hour. As it moved, it completely devastated all that came in its path, with its massive volumes of ice, water, mud, and rock alike.