Avalanche Flashcards
Define avalanche.
Is a rapid downhill movement of snow, ice and rocks.
Usually in mountainous environments.
They move down hill at speeds of up to 300km an hour.
Name the 3 types of avalanches?
Powder.
Slab.
Wet.
What are snow avalanches?
Usually powdery avalanches that start from a single point.
What are slab avalanches?
Large-scale avalanches formed when a slab of ice and snow breaks away from the main ice pack.
It has immense power causing a great deal of damage.
They occur naturally and can be triggered by humans.
Name human causes of avalanches?
Skiing.
Loud noses.
Tree removal.
How can skiers trigger an avalanche?
They can travel over unstable snow and make it become even more unstable.
How can loud noises trigger an avalanche?
Cause big vibrations and weaken the snow making it unstable.
How can tree removal trigger or help protect from an avalanche?
No interception to slow down or divert snow.
No barriers for protection.
Name physical causes of avalanches?
Heavy snowfall.
Steep slopes.
Temperature rising.
Heavy rainfall.
How can heavy snowfall trigger avalanches?
It puts pressure on the slope and destabilises the slope.
How can steep slopes trigger avalanches?
The snow will never be fully stable.
How can temperature rising trigger avalanches?
It melts snow and ice.
Lubricates the slope.
Weakens the bonds.
How can heavy rainfalll trigger avalanches?
Melts the snow and ice.
Snow becomes unstable and the heavy rainfall is making it heavier.
What is an important trigger?
Overloading.
The weight of the snow increases until it overcomes cohesion to the snow pack underneath.
What slope angle to most avalanches occur at?
25 and 400C.
How can vibration be caused?
By thunder, gun shot, explosions etc.
What natural disaster can cause avalanches?
Earthquakes.
Where is the avalanche problem more severe?
Europe than North America due to higher population densities in the Alp mountain range.
What are powder avalanches?
Often start from a single point and accumulates snow as it moves down the slope forming a snowball effect. This type is most common following heavy snowfall Without the cohesion with the snow layer underneath the snow is too heavy to settle.
How fast can powder avalanches travel?
62 and 186 miles per hour.
What are slab avalanches?
Most common type of winter avalanche due to the build up fresh snow.
A slab is a compact snow surface layer that can detach from a weaker snow layer underneath.
The slab slips forward as a whole block or breaks into pieces.
What are wet avalanches?
Often occurs after a warm spell or during the spring thaw.
Snow becomes heavier as it begins to turn into water. Occurs frequently and are generally small and generally easier to predict than the other types.
Name a recent avalanche in history?
The Cascade range, Washington (1910)
The worst avalanche disaster in the USA to date. Three snow-bound trains were swept into a canyon which killed 118 people.
