A comprehensive presentation about avalanches: definition, formation, causes, prevention and examples.

1. AVALANCHESAVALANCHESASASHAZARDSHAZARDS

2. WHAT IS AN AVALANCHE?WHAT IS AN AVALANCHE?
• An avalanche is a rapid flow of snow
down a slope.
• Can be naturally triggered or a consequence
of a human activity.
• It occurs in the mountains.
• An avalanche is a mix of water and snow.
• Powerful avalanches: ice, rocks, trees.

3. ROCKSLIDESROCKSLIDES
Slides of rocks or debris, behaving in a
similar way to snow, are also referred to as
avalanches (rockslide).

8. AFTER INITIATIONAFTER INITIATION
After initiation, avalanches usually
accelerate rapidly and grow in mass and
volume as they entrain more snow.
If the avalanche moves fast enough some
of the snow may mix with the air forming a
powder snow avalanche, which is a type
of gravity current.

10. SLAB AVALANCHESSLAB AVALANCHES
Slab avalanches form frequently in snow
that has been deposited, or redeposited
by wind. They have the characteristic
appearance of a block (slab) of snow cut out
from its surroundings by fractures. Slab
avalanches account for around 90% of
avalanche-related fatalities.

11. POWDER SNOW AVALANCHESPOWDER SNOW AVALANCHES
The largest avalanches form turbulent
suspension currents known as powder
snow avalanches or mixed avalanches.
These consist of a powder cloud, which
overlies a dense avalanche. They can
exceed speeds of 300 km/h, and masses
of 10,000,000 tonnes.

12. WET SNOW AVALANCHESWET SNOW AVALANCHES
In contrast to powder snow avalanches,
wet snow avalanches are a low velocity
suspension of snow and water, with the
flow confined to the track surface. The low
speed of travel is due to the friction
between the sliding surface of the track
and the water saturated flow.

16. BIG AVALANCHES IN HISTORYBIG AVALANCHES IN HISTORY

17. WORLD WAR 1 - ALPSWORLD WAR 1 - ALPS
During World War I, an estimated 40,000 to
80,000 soldiers died as a result of
avalanches during the mountain campaign
in the Alps at the Austrian-Italian front, many
of which were caused by artillery fire.

18. THE WINTER OF TERRORTHE WINTER OF TERROR
In the northern hemisphere winter of 1950–
1951 approximately 649 avalanches were
recorded in a three-month period throughout
the Alps in Austria, France, Switzerland, Italy
and Germany. This series of avalanches
killed around 265 people and was termed
the Winter of Terror.

19. THE GALTUR AVALANCHETHE GALTUR AVALANCHE
The Austrian village of Galtür was hit by the
avalanche in 1999. The village was thought
to be in a safe zone but the avalanche was
exceptionally large and flowed into the
village. Thirty-one people died.