General introduction of Avalanches

1. AVALANCHES

2. DEFINITION:
Words comes from the French word “avalance” meaning descent.
An avalanche is a mass of snow, debris and ice which travel down
the mountain slides destroying all in its path.
Size of an avalanche can vary from loose snow or a small shifting of
loose snow called sluffing to the displacement of large ice block
called slab.
The mass of avalanche snow may reach a speed of 130kmph.
Capable of destroying small forests and villages in its path.

3. TYPES OF AVALANCHES:
There are four types of avalanches:
1. Loose snow avalanche
2. 2. Slab avalanche
3. Powder snow avalanche
4. Wet snow avalanche

4. LOOSE SNOW AVALANCHE:
It is most commonly seen after a fresh snowfall on the steep slopes.
Snow does not settle down or made loose by the sunlight , the
snowpack is not very solid.
Such avalanches have single point of origin from where they widen as
they travel down the slope.

5. 2. SLAB AVALANCHE
Loose snow avalanche in turn could cause a slab avalanche
They are usually characterized by the fall of a large block of ice down
the slopes.
Damage caused by these avalanches could be of two types. Thin
slabs cause fairly small amount of damage, while thick block cause
major fatalities.

6. 3. POWDER SNOW AVALANCHE:
These are the mixture of other forms such as loose snow avalanche
and slab avalanche.
The bottom half of this avalanche is consist of slab or a dense
concentration of ice, air and snow.
The upper half of this avalanche is a cloud of powder snow which can
later snowball into a larger avalanche as it travel downs the slope.
Speed attained by this avalanche can cross 190 miles per hour.
It can cross large distances.

7. 4. WET SNOW AVALANCHE:
As its name indicates that this avalanche is consist of water and snow
at the beginning and later on it pick ups the speed of travelling down
the sloe.
On its way down it collects debris from the path due to the friction
and it travels slowly.
Considered the most dangerous form of avalanche.

8. CAUSES OF AVALANCHES
There are number of causes which triggers avalanches .
1. sandstorms and wind direction (while blowing up,it scours snow
off the surface)
2. heavy snowfall (depositing snow in unstable areas which put
pressure)
3.Human activity in form of winter sports and deforestation, soil
erosion (gives less stability to snow) and earthquake (produce cracks
in the snowpacks)
4. Vibration or movement in form of heavy traffic and snow
automobiles
5. Layers of snow
6. Steep slopes

9. EFFECTS OF AVALANCHES:
1. Major natural hazard for the local human population (2012 avalanche
incident in Siachen Glacier in Pakistan headquarters, took lives of more than
130 people).
2. Damage to the life and property
Infrastructure get damages, roads get blocked, impacts livelihood of many
people. Power supply can be cut off, destroy buildings. People who enjoy
skiing, snowboarding etc. are at major risk.
3. Flash floods.
Cause havoc in low lying areas, change in weather patterns cause crop
failure .
4. Economic impact:
Block everything in its way and restrict the normal movement of traffic. Ski
resort and other snow related business get closed until the normal condition
kick off.

10. PREDICTION OF AVALANCHES:
Accurate avalanche prediction requires
1. an experienced avalanche forecaster who works in the field to
gather snowpack information and
2. in the office with all the sophisticated tools including
Remotely accessed weather data
Detailed historical weather and avalanche databases
Weather models
Avalanche fore-casting models

11. PRECAUTIONS/ TECHNIQUES TO
AVOID AVALANCHES
1. Explosives are used to trigger avalanches on potentially unstable
slopes so that avalanche will occur when people are not
endangered.
This type of control is effective in ski areas and highway corridors.
2. Use of avalanche rakes, are used on the slope to hold snow in its
place.
wedges or dams are used as diversion tools at the base of slope to
stop, split or deflect the snow in avalanches .