Page 249 - Health, Population and Environment Education 9

Glacial Lake outburst flood (GLOF)
A type of outbrust flood that occurs due to
filling of the dam containing a glacial lake is
called glacial lake outburst flood. The dam
of the glacial lake consists of glacier, ice or
a terminal moraine. Failure of glacial lake
dam occurs due to erosion, water pressure,
avalanche, earthquake, volcanic erruption,
etc. As a result, a large amount of glacier
breaks off and displaces the water in a
glacial lake massively. Catastrophic failure
of the containing ice or glacial sediment can Fig: 13
release the water of the lake by glacier lake Glacier Lake outburst
outburst. Glacier lake outburst floods are
often compounded by a large amount of river bed erosion in the steep moraine villages.
The volume of glacial lakes varies, but may hold millions to hundred millions of cubic
meters of water.
There are many deadly glacial lake outburst floods identified worldwide. In Nepal, the
Tsho Rolpa glacier lake is situated in the Rolwaling valley. The lake is dammed by a 150
m high unconsolidated terminal moraine dam. This lake is growing larger every year due
to the melting and retreat of the Trakarding glacier. It has become most dangerous glacier
lake in Nepal storing 90 to 100 million cubic meters water.

Effects of glacier lake outburst
The major effect of glacier lake outburst flood are given below.

i. Destruction of lives and properties
ii. Destruction of land structures
iii. Sources of floods, soil erosion and landslides

iv. Destruction of fertile land and agricultural products
v. Destruction of physical infrastructures like human settlements, roads, bridges, etc. in
downstream

4. Avalanche
An avalanche is a rapid flow of snow down a
sloping surface. It is commonly called a snow slide.
Avalanches are typically trigged in a starting zone
from a mechanical failure in the snowpack. It occurs
when the forces on the snow exceeds its strength
but sometimes only with gradually widening. After
initiation, avalanches usually accelerate rapidly and
grow in mass and volume as they entrain more snow.
Fig: 14
The load on the snowpack may be only due to gravity Avalanche
GREEN Environment Population and Health Education Book-9 249