Chapter 2
The Earth and the
Changes on It
The surface of the
earth never remains the same. It
constantly undergoes changes. These
changes can be sudden or gradual. The
sudden changes originate inside the earth, due to volcanic or earthquake
activities. These forces bring radical
changes and are easily visible. On the
other hand, some changes are very slow and take place gradually over a very
long time. This could be due to natural
forces, such as carrying of soil by rain water, changes in the course of a
river, winds carrying soil particles with them, etc. Human factors can play an equally important
role in changing the surface of the earth.
The examples are cutting down of forests, construction of roads, bridges
and railway lines, large - scale mining, building of dams, etc. In this chapter, we will study about the
processes that are involved in bringing gradual changes upon the earth's
surface. a EXTERNAL PROCESS Any process
working on the earth's surface and bringing changes on it, is known as external
process. The external process may lower
the level of land by wearing away rock particles. It can also raise the level of land where the
soil particles are deposited, external processes include changes do you
know? on account of weathering and
Geomorphology is the science of study of landforms. gradation weathering The term weathering
refers to the process that breaks rocks into smaller particles. It includes erosion and deposition. They disintegrate as they are exposed to all
types of weather changes. The effect of
weathering can also be seen on stone monuments and buildings where pleces of
stones get flaked off and iron railings get rusted. Weathering 7
Do you know?
Gradation means levelling of land.
It occurs in two ways -agradation and degradation Agradation means
adding of sediments and raising the level of land. Degradation means breaking and wearing away of
sediments and lowering the level of land.
Erosion Erosion or Denudation refers to gradual wearing and carrying
away of all those loose particles of disintegrated rocks which lie exposed on
the earth's surface by the weathering agents of gradation, i.e. running water, wind, moving ice and sea
waves. Deposition Deposition refers to
the laying down of sediments which have been carried from distant parts of the
earth's surface by various agents of gradation.
The continuous process of deposition results in the formation of soil at
other places. The rate at which erosion
take place depends upon the temperature of a place, vegetation cover, rainfall,
slope of the land, type of soil and changes in land use. AGENTS OF GRADATION Running Water It is an
important agent of gradation. A river,
like any living form, has a 'life cycle'.
It takes birth in a mountain or a hill, becomes larger where it is met
by a number of tributaries, flows over plains and finally ends when it reaches
the sea. In its early stage, the river
is young. It flows over steep mountains
where its rate of erosion is maximum.
Due to down cutting work of a river, it forms striking youthful features
like 'I shaped and' V 'shaped valleys, waterfalls, etc. As the river enters into the plains, it comes
to the stage of maturity. Here, the
volume of water increases and the slope of land decreases, resulting in slow
speed of the river. During this stage,
the river is said to flow through meanders.
Meander
Shoreline Main river sediments before meeting the sea, the
river becomes large and sluggish and gets divided into several
distributaries. It now comes to its old
stage. The river, thus, deposits silt,
sand and sediments over a large area near its mouth. This large deposition helps in the formation
of a delta. The delta of Ganga and
Brahmaputra is the largest in the world.
Glacier Mouth It is believed that a million years ago, the climatic of a
river condition of the earth's surface was much cooler than Distributary
Channels what it is now. The earth's
surface was covered by ice but later, the temperature began to rise
gradually. This rise in Delta
temperature resulted in melting of the ice.
The mass of moving ice is called a Glacier. In India, the glaciers are found at high
altitudes of the Himalayas where temperature is below freezing point. Like running water, moving ice also erodes
loose particles or parts of rocks. It
takes them along and deposits them behind, when it melts. Huge masses of ice which cover large areas of
a continent are called Continental glaciers like Antarctica and Greenland. Other glaciers which occupy small areas over
the mountains are called mountain glaciers like Siachin glacier and Siachin
Glacier Gangotri glacier of the Himalayas in India. Do you know?
The snow line is a line on the high mountains above which the snow never
melts. Wind Do You Know? In the regions where there is little rainfall
and meagre vegetation, the land is exposed to strong winds. The loose rock particles are easily blown
away by the strong wind. Thus, the wind
is also an agent of gradation. The
action of the wind is most common in the desert regions. Air can neither be seen nor felt but the
swift horizontal movement of air is felt and it is called wind. 9
silt and clay. A
mixture of these particles gives rise to different types of soil as per their
proportion. The strong wind has the
capacity to rub and scrap rocks, resulting in strange shaped rocks like
mushroom rock. The carried material is
then deposited at a new place whenever the speed of wind slows down. This forms various types of sand dunes. Sand dunes can be found in the western parts
of Rajasthan in India. Sand dunes Sea
Waves Along the sea shore, sea waves are the most powerful agent of
gradation. The continuous striking of
sea waves breaks the rocks. Such
continuous erosion forms steep sided cliffs facing the sea. The eroded material may then be deposited
along the coast forming beaches. Human
beings also play a critical role in changing the face of the land. Over growing population and industrialisation
has disturbed the natural environment to Cliffs a large extent. The human activity involves diverse land use
like clearing of forests for agriculture, construction of roads and new human
settlements, etc. These are a few
examples which change the land surface.
Human beings need to take care of all the resources for carrying
ecological balance. This can be achieved
by sustainable development. SOIL Soil is
the loose material found on the surface of the earth. It is made of organic and inorganic
particles. The organic particles are derived
from dead remains of plants and animals.
In the course of time, these particles get decomposed and change into a
dark colored material called humus. The
humus present in the soil contributes to the fertility of the land. This is rapidly formed in humid areas due to
heavy growth of plants and rich animal life.
However, humus is low in desert soil.
The inorganic particles are derived from rocks. They include loose disintegrated particles of
different sizes. The large sized
particles are called gravel, while the smaller ones are called sand, These are
called sandy, loamy and clayey soils. 10
silt and clay. A
mixture of these particles gives rise to different types of soil as per their
proportion. The strong wind has the
capacity to rub and scrap rocks, resulting in strange shaped rocks like
mushroom rock. The carried material is
then deposited at a new place whenever the speed of wind slows down. This forms various types of sand dunes. Sand dunes can be found in the western parts
of Rajasthan in India. Sand dunes Sea
Waves Along the sea shore, sea waves are the most powerful agent of
gradation. The continuous striking of
sea waves breaks the rocks. Such
continuous erosion forms steep sided cliffs facing the sea. The eroded material may then be deposited
along the coast forming beaches. Human
beings also play a critical role in changing the face of the land. Over growing population and industrialisation
has disturbed the natural environment to Cliffs a large extent. The human activity involves diverse land use
like clearing of forests for agriculture, construction of roads and new human
settlements, etc. These are a few
examples which change the land surface.
Human beings need to take care of all the resources for carrying
ecological balance. This can be achieved
by sustainable development. SOIL Soil is
the loose material found on the surface of the earth. It is made of organic and inorganic
particles. The organic particles are
derived from dead remains of plants and animals. In the course of time, these particles get
decomposed and change into a dark colored material called humus. The humus present in the soil contributes to
the fertility of the land. This is
rapidly formed in humid areas due to heavy growth of plants and rich animal
life. However, humus is low in desert
soil. The inorganic particles are
derived from rocks. They include loose
disintegrated particles of different sizes.
The large sized particles are called gravel, while the smaller ones are
called sand, These are called sandy, loamy and clayey soils. 10
NOU Formation of Soil It is a very slow process. It takes thousands of years to form a thin
layer of soil. As mentioned earlier, the
weathering process breaks the rocks into small particles. These are then carried away by water, wind,
etc. , and later get deposited at a new
place. Such soil is called transported
soil. But, when the soil is formed by
the weathering of a parent rock and remains present on the same site, it is
called residual soil. Topsoil Subsoil
The soil forming process continues over a long span of time. It starts developing in layers, weathered one
over the other. These layers are called
rock horizons. From bottom to top, the
lowest horizon is called bed rock, then comes the horizon of weathered rock and
it is followed by Solid rock the sub soil and top soil. The topmost horizon is rich in humus. Soil layers INDIA MAIOR SOIL TYPES PAKISTAN
TINETI Distribution of Major Soil Types Soil is generally classified on the
basis of color and texture. Alluvial
soil: It is found over a large part of India.
It is mainly formed by the deposition of sediments by river and is
confined to northern and coastal plains.
This type of soil is very fertile and forms major agricultural land of
our country. Black soil: it is found in
Deccan plateau. This type of soil is
confined to some parts of Gujarat, Maharashtra and Karnataka. This soil has an ability to retain moisture
and become sticky when wet. It is
largely used for growing cotton and thus, is popularly known as cotton
soil. Red soil: As the name suggests,
this soil is red in color due to the presence of iron MYANMAR Forest Mount Ava
DAS Late and LANKA Major soil types 11
particles. Red soil is confined to peninsular India and
some patches of north - eastern parts of India.
It is highly porous, fine grained and deep. Laterite soil. It is found over the hill slopes of
peninsular plateau. The laterite soil is
found in the regions of heavy rainfall.
It is formed by the leaching process.
Apart from these four types, there are desert and mountain soils. They are found in their respective
regions. Removal of the top layer of
soil is called soil erosion. We must
understand that soil erosion is a serious problem cting land all over the
world, certain areas, soil erosion has become a menace which causes decline in
the crop yield. This is happening due to
wrong human practices like cutting of trees, overgrazing by animals, besides
many other reasons. Soil erosion needs
to be checked through appropriate measures of soil conservation, such as
plantation of trees, selective agricultural practices like crop rotation and
multiple cropping method, development and management of pasture land. We need mass awareness and adoption of these
practices at local level. Keywords
denudation: the wearing away of the earth's surface by weathering process and
agents of gradation. distributary: river
channels separating from the main river.
I shaped valley: erosional feature with narrow and vertical walls formed
by a river. It is also called
gorge. leaching: a natural process in
which rainy water dissolves minerals from the soil and carry them away. meander: sweeping curves of a river. tributary: small streams joining the main
river. V shaped valley: feature formed
by a downward cutting of rocks by a river.
It resembles the letter 'V. B. 12
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