In winter we all hope for snow. In the Netherlands to be able to play in it with the children, make snowmen, have snowball fights or just walk in it. In the Alps everyone hopes for enough snow to be able to ski or snowboard. But for non-winter sports enthusiasts it is of course nice to be able to take beautiful walks in the white world. Snow always does very well in photos. All those snowy peaks are beautiful to see, but actually those snowy peaks are very dangerous. The amount of snow increases the risk of avalanches. In addition to snow avalanches, areas can also be affected by mud or stone avalanches.
Content
- What is an avalanche
- Creation of an avalanche
- Three factors responsible for the creation of an avalanche
- Avalanches
- Schneebrett avalanche
- Powder snow avalanche
- Dry snow avalanche
- Combination of all three types of avalanches
- Avalanche scale
- Scale 1 small – Yellow flag
- Scale 2 moderate – Yellow flag
- Scale 3 significant – Yellow-black checkered flag
- Scale 4 large – Yellow-black checkered flag
- Scale 5 very large – Black flag
- Rescue work in an avalanche
- Precautions to take yourself in a snow avalanche
- Mud and rock avalanches
- Disasters with avalanches
- Stone avalanche Randa elaborated
What is an avalanche
During an avalanche, a large mass comes rushing down a slope at great speed. This mass can consist of different types of material. This can be snow or mud, but it can also be rocks. On its way down, an avalanche really takes everything with it. These can be trees, but also cars and / or houses. The havoc after such an avalanche is often enormous.
An avalanche is called in it:
- English
- avalanche
- German
- Avalanche
- French
- avalanche
- Italian
- valanga
Creation of an avalanche
An avalanche can sometimes start suddenly, but often a direct cause can be found. For example by off-piste skiing. Because a skier or snowboarder skis over the snow, the load on the snow layer increases. If the snow layer has not yet attached itself properly, it can shift, resulting in an avalanche. The steeper the slope, the more likely the snow will slide. Avalanches are of course not always caused by off-piste skiing. It can also be caused by the amount of fresh snow that is sliding around. Snow can also suddenly less well adhere to the surface due to, for example, temperature increases. As a result, the top layer of snow melts and can therefore no longer adhere properly to the bottom layer and then starts to slide. This can also be caused by rainfall.
Three factors responsible for the creation of an avalanche
- steepness of the slope (minimum 25 degrees).
- relatively smooth surface.
- no good adhesion of new layer with substrate
In short: there is a combination of the above factors, but it is so complex that it is almost impossible to predict an avalanche in advance. Anyone – experienced or not – can be surprised by an avalanche. So the steeper the slope, the more likely the snow will shift. If snow is also on a fairly slippery surface, such as smooth rocks or tall grass, the snow cannot properly adhere to the surface and will slide.
Avalanches
There are four different types of avalanches.
- Schneebrett avalanche
- Powder snow avalanche
- Dry snow avalanche
- Combination of all three types of avalanches
Schneebrett avalanche
A schneebrett avalanche is an avalanche in which the top layer of snow slips completely. This is because the layers do not bond well with each other. The snow layer that slips can be compared to a plank, hence the German word Brett. By the way, this snow does not have to be hard. People who end up in such an avalanche are usually injured by being pressed against trees or rocks. There is less choking.
Powder snow avalanche
A powder snow avalanche is an avalanche that starts on steep slopes. Snow is falling down. As a result, more and more snow drifts on top, creating a mix of snow and air. At first, this rushes down at a speed of around 100 kilometers per hour. But that speed soon becomes many times higher. This creates pressure waves that are very dangerous.
Dry snow avalanche
There is one dry snow avalanche when fresh snow cannot hold its own weight. In German this avalanche shape is called Lockerschneelawine. Such an avalanche is shaped like a pear. The beginning is pointed and further on the snow mass is getting wider. They often start spontaneously.
Combination of all three types of avalanches
There is also one of all these types of avalanches combination possible. The names are also called roll avalanches and drift avalanches. At a roller avalanche the snow slides down at a slower speed, but takes a lot with it on its way down. When stationary, the snow is hard. People who have been swept up in such avalanches become buried under this hard layer of snow and often die from hypothermia and lack of oxygen. Help often comes too late. At a drift avalanche entire villages or roads become buried under snow. Often these avalanches are caused by fresh snow that has fallen in large quantities.
Avalanche scale
If there is a danger of avalanches, this is always indicated by means of a scale / flag. There are five different types of scales / flags that indicate the risk of an avalanche. These scales vary from small to very large.
Scale 1 small – Yellow flag
Here the risk of an avalanche is small. The snow layer is stable, no chance of spontaneous avalanches is to be expected. There is only a risk of an avalanche due to a large load and on steep slopes. This risk occurs about 1/5 of the winter.
Scale 2 moderate – Yellow flag
The chance of an avalanche is moderate because the snow layer does not adhere well on some slopes. The avalanche notice that applies to that region states which slopes are dangerous. Large groups of skiers / snowboarders can cause avalanches on normal slopes, this can be caused by a single skier / snowboarder on a steep slope. However, spontaneous small avalanches can occur in the spring. This risk arises during half of the winter.
Scale 3 significant – Yellow-black checkered flag
The chance of an avalanche is considerable. The snow has not adhered well on many slopes. On a normal slope, a single skier can cause an avalanche. Spontaneous avalanches develop on steep slopes. These avalanches can penetrate to flat and deeper areas. It is only allowed to ski off the slopes accompanied by an experienced guide. This risk occurs about 1/3 of the winter.
Scale 4 large – Yellow-black checkered flag
The danger of avalanches is great. All slopes are dangerous. Large avalanches arise spontaneously. It is perilous outside the groomed slopes. The risk of this danger is often only a few days per winter.
Scale 5 very large – Black flag
The avalanche danger is extreme. Skiing is not safe, the slopes are dangerous. Villages, roads and railways are threatened by avalanches. In some cases evacuations can take place. Fortunately, this is rare. It occurs on average about one day per winter.
Rescue work in an avalanche
As soon as there has been an avalanche, a rescue operation is started. After all, you never know whether people are buried under snow or rubble. There will be instant SAR dogs deployed. SAR stands for Search-And-Rescue. Dogs smell good there, they have enormous perseverance and are fast. In addition to dogs, the rescue team consists of people with diggers and sonars. The dogs lead the way and the rescue workers follow behind. Dogs that are often used for rescue work today are: Labradors, Golden Retreivers and sheepdogs. In addition, Saint Bernard and Bernese Senne dogs are used to a lesser extent.
Precautions to take yourself in a snow avalanche
If you want to go skiing off-piste, make sure you bring specific equipment in case of an emergency. This equipment consists of an avalanche transceiver, avalanche probe and a shovel. This equipment is also useful when skiing on groomed slopes, as an avalanche is often sudden. You can hear it coming from a distance, but due to the speed of the oncoming snow mass, the chance of escaping the avalanche is very small.
Mud and rock avalanches
In addition to snow avalanches, mud and / or stone avalanches also occur. These are caused by landslides. Landslides are devastating and often they arise out of nowhere. It is often not possible to give advance warning of an evacuation. If during a landslide a lot of ground suddenly starts moving and this causes rocks to be dragged, there is a stone avalanche. Another name is rock or rubble avalanche. Sometimes stone avalanches are also induced with mounting. A quantity of dynamite is then detonated in the rocks. This is done in a controlled manner to counteract the risk of spontaneous rock avalanches.
Heavy rainfall can also cause soil to shift. If the surface is completely saturated with water, it has no grip and will slide. If a mud flow then arises, it is a mud avalanche. It seems that mud avalanches are much more common. This may be due to climate change, which means that there is much more frequent heavy rainfall.
Disasters with avalanches
- In the winter of 1998/1999, as many as 31 people were killed in a snow avalanche in Austria in Galtür (Tyrol).
- In 1991 in Randa, Switzerland, many millions of cubic meters of rock broke off three times and this collapsed into the valley with frenetic violence. The railroad and highway were covered by a gigantic pile of stones. On April 23, 2015 there is another rock avalanche.
- On 17 February 2012, Prince Friso was caught in an avalanche while skiing off-piste in Lech (Austria). On August 12, 2013 he passed away from the consequences of his skiing accident.
- On April 18, 2014, 16 Sherpas on Mount Everest are killed in an avalanche.
- In April 2015, the severe earthquake in Nepal caused an avalanche. As a result, many mountaineers, guides and residents of a village die.
Stone avalanche Randa elaborated
In 1991, the village of Randa – which is located in the Swiss Mattertal – was startled three times by a rock avalanche as a result of a landslide. In 2020, there is still much to be seen from both road and rail of the impressive quantities (tons of cubic meters) of boulders that lie there. Slowly the larches start to grow again between the rocks.
- On April 18, 1991, 18 million cubic meters of boulders collapsed. The road, the train track and the river Vispa are buried with rubble.
- On April 21, 1991, another 100,000 cubic meters of rock falls down.
- On May 9, 1991, another rock avalanche takes place. This time, no less than 33 million cubic meters of boulders fall down.
The road had just been reopened, but this stone avalanche buried the road again under gigantic boulders. The same fate met the river Vispa. The river was dammed over a distance of 1.3 kilometers and this had serious consequences for the valley. The water could no longer escape. The train track was still buried under the boulders. Miraculously, no people were injured, but sheep and horses were killed. Much of the hamlet of Lerch has disappeared forever. We worked hard to make the railway accessible again. In a period of 10 weeks, the trains were able to run again, albeit on a new route.