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Avalanches
See if you've been taking notice in your geography lessons.

Avalanches

As part of your GCSE geography study of the effects of ice on the landscape, you will have looked at at least one case study of an area where a landscape that is actively affected by snow and ice attracts tourists. One of the problems in such areas is the successful management of the avalanche danger.

Avalanches occur quite often in areas of high and regular snowfall because they are generally mountainous regions with steep slopes. There are two main types of avalanche caused as the snow slides off the sides of hills and mountains - slab avalanches and loose snow (powder) avalanches. When they occur near centres offering winter tourism, they can cause disruption, damage and loss of life.

Slab avalanches are the more dangerous type. This type of avalanche begins when a large area of compacted or partially-compacted snow suddenly breaks away from the mountain.

Snow itself is surprisingly heavy and it can also pick up boulders, trees and other debris, making it very destructive. When it stops, it immediately becomes a very solid mass meaning anyone buried in it will find it extremely difficult to move. It is almost impossible to save yourself from within a slab avalanche, most victims suffocate - the snow is so solid, no air can reach the victim. Winter sports resorts use specially-trained dogs and search teams to locate people who have been buried.

A loose snow avalanche generally starts in a small spot and causes a lot less damage. If you have ever watched video clips of extreme skiers or snowboarders descending steep slopes, you will have seen this type of avalanche.

There are many reasons why an avalanche starts - several different episodes of snowfall followed by heavy snow, deforestation allowing large snow slabs to build up and vibrations are just three of them. In winter resorts, avalanche experts monitor the snow conditions closely, looking at how the snow is layered, the bonding between snow layers and other factors in order to decide on the avalanche risk and ways in which they can be managed.

Explosions are used to trigger avalanches to clear slopes of dangerously unstable snow. Snow fences and barriers can be set up to deflect avalanches and to absorb a lot of the energy, reforestation of slopes has much the same effect. Land can be zoned to ensure that no building is carried out in the areas most at risk. Where a road or railway track could be prone to avalanches, tunnels are built to allow any avalanches to pass harmlessly over.

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1.
An avalanche is ...
a gradual movement of a mass of snow towards the coast
a slow movement of ices towards a river
a rapid movement of snow over flat land
a sudden fast movement of snow down a steep slope
There is nothing gradual or slow about an avalanche!
2.
Which of the following is not a method used to manage avalanches in the area of a winter sports resort?
Brushing the snow off a slope
Setting off an explosion in the snow
Building a reinforced tunnel over a road
Using large fences and barriers
During the First World War in the Alps, opposing forces aimed their artillery towards the slopes above the enemy forces in order to try to create avalanches
3.
Which of the following is least likely to cause an avalanche?
The first light snowfall of the winter
Heavy snowfall
Skiing
An earthquake
The most likely avalanche conditions come after heavy snowfall
4.
Which of the following is a type of avalanche?
Lumpy
Block
Slab
Chunk
After snowfall, the new snow settles and becomes firmer forming a snow 'slab'. If this is not well-bonded to the snow underneath, it can slide downhill
5.
Why is the type of avalanche mentioned in the previous question more destructive than a loose snow avalanche?
It is made from a large volume of very compacted snow
It occurs over a wide area and travels a long way
It carries rocks, trees and other debris with it
All of the above
Loose snow avalanches usually occur on a smaller scale
6.
When is the main avalanche 'season' in mountain ranges in the Northern hemisphere?
July to September
October to December
January to March
April to June
This is when the most snow falls
7.
Which of the following statements about avalanches is correct?
Avalanches only occur in summer when melting snow becomes very soft
It is difficult to predict exactly when and where an avalanche will occur
All avalanches will destroy buildings that are in their path
Avalanches pose no threat to skiers because their skis keep them on the surface of the moving snow
An avalanche needs a trigger to set it off even if it is just a slight change in the snow slab created over a long period by gravity. Triggers are random events and cannot be predicted and snow slabs are extremely complex which adds to the difficulties. This unpredictability is one of the reasons that safety teams trigger avalanches using explosives
8.
Which of the following most closely describes some of the effects of avalanches on an area?
An increase in tourism because a lot of people come into the area hoping to watch more avalanches
The soil and grass is removed from the slopes of the mountain which decreases the agriculture of the meadows in the summer
It increases the number of wild animals and trees by sweeping away the rubbish left by tourists
Avalanches cause deforestation, destruction and damage to some buildings and financial losses to an area
Roads and other transport infrastructure are damaged by avalanches and areas can be closed to tourism whilst clearing up the debris and snow from avalanches
9.
What is the main cause of death from avalanches?
Crushing
Being hit on the head by rocks in the snow
Suffocation
Freezing
About 90% of people who are killed by an avalanche run out of air and suffocate long before the cold kills them
10.
When an avalanche is over ...
the snow becomes extremely solid
the snow rapidly melts because it is warmer lower down the slopes
the snow is very soft as it contains a lot of air
the snow becomes very powdery and easy to clear
After an avalanche, the snow becomes extremely solid which is the main reason that people and animals become trapped as they are unable to move their limbs to dig themselves out
Author:  Kev Woodward

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