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Journal for Studies in Management and Planning

Available at

http://edupediapublications.org/journals/index.php/JSMaP/

I SSN: 2395-0463

Vol ume 03 I s s ue 0 7

June 2017

Available online: http://edupediapublications.org/journals/index.php/JSMaP/ P a g e | 185

Landslide & Snow Avalanches: An Overview

RAHUL CHOUDHARY

Assistant Professor (Extension)

Department of Geography

Pt. N. R. S. Govt. College, Rohtak (HR)

rcsheoran.02@gmail.com

Abstract: A landslide, also known as a

landslip, is a form of mass wasting that

includes a wide range of ground

movements, such as rock falls, deep failure

of slopes, and shallow debris flows.

Landslides occur when the slope changes

from a stable to an unstable condition. A

change in the stability of a slope can be

caused by a number of factors, acting

together or alone. Landslides can be

triggered by rainfall, snowmelt, changes in

water level, stream erosion, and changes in

ground water, earthquakes, volcanic

activity, disturbance by human activities, or

any combination of these factors. An

avalanche (also called a snowslide or

snowslip) is a rapid flow of snow down a

sloping surface. Technically, an avalanche is

any amount of snow sliding down a

mountainside. It can be compared to a

landslide, only with snow instead of earth.

An avalanche can be composed of many

different kinds of snow depending on the

region, temperature and weather. It could

be compiled of loosely packed light fluffy

snow, which can still be very dangerous

even though it may not appear threatening.

It could also consist of a thick “slab” which

is an area of tightly packed together snow

that separates itself from the surroundings.

Although avalanches can occur on any slope

given the right conditions, certain times of

the year and certain locations are naturally

more dangerous than others. Wintertime,

particularly from December to April, is

when most avalanches tend to happen.

However, avalanche fatalities have been

recorded for every month of the year.

KEYWORDS: Landslides, Avalanche, Snow

Slide, Slopes, Flows, Temperature.

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June 2017

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Introduction: The word avalanche is derived

from the French word “avalanche” meaning

“descent”. An avalanche is a mass of snow,

often mixed with ice and debris which

travels down mountain sides, destroying all

in its path. It is a large mass of snow, ice,

etc., detached from a mountain slope and

sliding or falling on any slope, the snow is

piled up and supported by a snow-pack. It

keeps the snow from tumbling down all the

time. Avalanches occur when the snow- pack starts to weaken and allows the

buildup of snow to be released. Small

avalanches are generally made up of ice,

snow and air. The larger ones comprise of

rocks, trees, debris and even mud that is

resting on the lower slopes. Contrary to

belief, these snow slides are not random

events that occur without any warning

signs. Winter season is when they are most

common, often brought on after a large

storm in the area.

What Causes Avalanches ?

Avalanches occur due to any of the

following triggers: overloading,

temperature, slope angle, snow pack

conditions, and vibration. Overloading is an

important trigger, the weight of the snow

increases until it overcomes cohesion to the

snow pack underneath. Temperature has an

effect on the cohesion of snow; a rise in

temperature weakens the bonds creating

weakness, whilst a fall in temperature

increases the brittleness and tension of a

slab. Slope angle is important as most

avalanches occur on slopes between 25°C

and 40°C, although avalanches have been

noted on slopes as gentle as 15°Cand as

steep as 60°C. Snow pack conditions is a

significant factor as the layers below the

upper snow cannot be seen and it is difficult

to assess whether the slope is likely to fail.

Vibration is a physical trigger cause by

thunder, a gunshot, by explosions or other

loud noises such as shouting. Earthquakes

can start avalanches, as well as noise from

heavy machinery.

Slab 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. Elements of slab avalanches

include the following: a crown fracture at

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Journal for Studies in Management and Planning

Available at

http://edupediapublications.org/journals/index.php/JSMaP/

I SSN: 2395-0463

Vol ume 03 I s s ue 0 7

June 2017

Available online: http://edupediapublications.org/journals/index.php/JSMaP/ P a g e | 187

the top of the start zone, flank fractures on

the sides of the start zones, and a fracture

at the bottom called the staunch wall. The

crown and flank fractures are vertical walls

in the snow delineating the snow that was

entrained in the avalanche from the snow

that remained on the slope. Slabs can vary

in thickness from a few centimeters to

three metres. Slab avalanches account for

around 90% of avalanche-related fatalities

in backcountry users.

Loose Snow Avalanches: First of these are

the Loose Snow Avalanches. They are

common on steep slopes and are seen after

a fresh snowfall. Since the snow does not

have time to settle down fully or has been

made loose by sunlight, the snow-pack is

not very solid. Such avalanches have a

single point of origin, from where they

widen as they travel down the slope.

Powder Snow Avalanches: Powder Snow

Avalanches are a mix of the other forms,

Loose Snow and Slab. The bottom half of

this avalanche consists of a slab or a dense

concentration of snow, ice and air. Above

this is a cloud of powdered snow, which can

snowball into a larger avalanche as it

progresses down the slope. The speed

attained by this avalanche can cross 190

miles per hour and they can cross large

distances.

Wet Snow Avalanches: Finally, there are

Wet Snow Avalanches. These are quite

dangerous as they travel slowly due to

friction, which collects debris from the path

fairly easily. The avalanche comprises of

water and snow at the beginning, but

understanding of avalanches has showed us

that it can pick up speed with ease.

Effects of Avalanches: As such, there is little

damage to the overall ecological system

due to avalanches. They are a part of nature

and have been happening for thousands of

years. However, they are a major natural

hazard for the local human population.

1. Damage to Life and Property: A large

number of casualties takes place after

avalanches hit heavily populated areas.

Infrastructure is damaged and the blockage

caused, impacts the livelihood of many

people who enjoy skiing, snowboarding and

snowmobiling and thus are at a greater risk

of losing their lives. A powerful avalanche