Thai
Sikh International School
Year
9 Geo Notes Topic 13 [Rivers from Source
to Mouth.]
1.
Explain
how the water cycle works.
The
water from the sea escapes in the form of evaporation and returns to the same
sea. This is called water cycle. Water cycle undergoes five stages. They are:
a. Evaporation:
The high temperature and warm winds change the sea water into gas (water vapor)
which rises into the atmosphere.
b. Evapotranspiration:
The vegetation absorbs the rain water through the roots and is eventually returned
to the atmosphere by transpiration leaves.
c. Condensation:
As water vapor is blown towards mountains by the winds; it is forced to rise,
cools and condenses into water droplets. These form clouds and falls as rain.
d. Interception:
Some rainfall is intercepted by plants and trees before reaching the ground.
Some falls on the ground and flows as small flowing streams.
e. Overland
flow: Upland streams flow downhill and join at confluences to form wider rivers
which finally join the sea or lake.
2.
Differentiate
between vertical and lateral erosion.
In
the upper course the stream flows over steep ground. The main process is
vertical erosion. The water running fast through the mountain cuts deep and
flows. This is vertical erosion.
In
the lower course the river flows over flatter ground. The water cuts the side
and widens the river. This side cutting is called lateral erosion.
3.
Explain
different types of river erosion?
a. Hydraulic action:
In this the erosion takes place due to the impact of moving water.
b. Corrasion. (Abrasion)
: The wearing away of the bed and banks of a river by the load being carried is
corrasion.
c. Attrition:
The wearing away of the load as the particles bumb against each other while
being carried in the river.
d. Solution (Corrosion):
It is the dissolving of material by the river water.
4. Mention the different land forms
formed due to erosion.
a. Waterfalls
and rapids.
b. V
shaped valleys and
c. Potholes
in river beds.
5.
Name
the different landforms formed by river deposition.
a. Meanders
and ox-bow lakes.
b. Flood
plains and
c. Deltas.
6.
How
do Meanders and Ox-bow lakes are formed?
Erosion
on the outside of bends and deposition in the inside of bends leads the river
‘swinging’ along the valley. This creates Meanders.
Ox-bow
lakes form when a meander is cut off from the main river.
7.
Explain
how flood plains and deltas are formed?
When
the river floods; it deposits material forming a wide flat valley floor. These
are flood plains.
When
the river slows on entering sea or lake it deposits more material than can be removed.
These are the Deltas.
13a,
b. [Niagara Falls, the Ganges delta.]
8.
Give
a description about the formation of Niagara Falls.
Niagara Falls consists of two waterfalls
on the Niagara River which marks the border between New York State, USA (the
American Falls) and Ontario, Canada (the Canadian or Horseshoe Falls).
The
formation of the falls began at the end of the ice Age in North America around
18000 years ago. Torrents of water were released into the great lakes as ice
melted into what is now the Niagara River.
9.
Give
a brief description about Bangladesh and its location.
Bangladesh
lies north of the Bay of Bengal and shares borders with India and Myanmar (Burma).
It is one of the most densely populated countries in the world, yet most of the
country is part of a huge low-lying delta. This has been formed by deposition
from some of the longest rivers in the world-The Ganges and its tributary,
Brahmaputra- and the Meghna River. Monsoon rains, Cyclones and floods regularly
cause natural disasters.
10. Why Bangladesh is called ‘the drain
of the Himalayas’?
Bangladesh
(formerly East Pakistan until1971) is an LEDC. Over two- thirds of the country
is made up of the Ganges delta. The Ganges River is over 2500km long, having
its source in snowmelt and rainfall in the Himalayan Mountains north of India. It
flows eastwards and empties into the Bay of Bengal after being joined by the
Brahmaputra and Meghna rivers from the east.
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