NCERT Textbook - Geomorphic Processes | Geography (Prelims) by Valor Academy - UPSC PDF Download

 Page 1


LANDFORMS
This unit deals with
• Landforms and their evolution
• Geomorphic processes — weathering, mass wasting, erosion
and deposition; soils — formation
UNIT
III
2024-25
Page 2


LANDFORMS
This unit deals with
• Landforms and their evolution
• Geomorphic processes — weathering, mass wasting, erosion
and deposition; soils — formation
UNIT
III
2024-25
GEOMORPHIC PROCESSES
CHAPTER
A
fter learning about how the earth was
born, how it evolved its crust and other
inner layers, how its crustal plates
moved and are moving, and other information
on earthquakes, the forms of volcanism and
about the rocks and minerals the crust is
composed of, it is time to know in detail about
the surface of the earth on which we live. Let
us start with this question.
Why is the surface of the earth uneven?
The earth’s crust is dynamic. You are well
aware that it has moved and moves vertically
and horizontally. Of course, it moved a bit faster
in the past than the rate at which it is moving
now. The differences in the internal forces
operating from within the earth which built up
the crust have been responsible for the
variations in the outer surface of the crust. The
earth’s surface is being continuously subjected
to external forces induced basically by energy
(sunlight). Of course, the internal forces are still
active though with different intensities. That
means, the earth’s surface is being
continuously subjected to by external forces
originating within the earth’s atmosphere and
by internal forces from within the earth. The
external forces are known as exogenic forces
and the internal forces are known as endogenic
forces. The actions of exogenic forces result in
wearing down (degradation) of relief/elevations
and filling up (aggradation) of basins/
depressions, on the earth’s surface. The
phenomenon of wearing down of relief
variations of the surface of the earth through
erosion is known as gradation. The endogenic
forces continuously elevate or build up parts
of the earth’s surface and hence the exogenic
processes fail to even out the relief variations
of the surface of the earth. So, variations remain
as long as the opposing actions of exogenic and
endogenic forces continue. In general terms,
the endogenic forces are mainly land building
forces and the exogenic processes are mainly
land wearing forces. The surface of the earth is
sensitive. Humans depend on it for their
sustenance and have been using it extensively
and intensively. So, it is essential to understand
its nature in order to use it effectively without
disturbing its balance and diminishing its
potential for the future. Almost all organisms
contribute to sustain the earth’s environment.
However, humans have caused extensive
damage to the environment through over use
of resources. Use we must, but must also leave
it potential enough to sustain life through the
future. Most of the surface of the earth had and
has been shaped over very long periods of time
(hundreds and thousands of years) and
because of its use and misuse by humans its
potential is being diminished at a fast rate. If
the processes which shaped and are shaping
the surface of the earth into varieties of forms
(shapes) and the nature of materials of which
it is composed of, are understood, precautions
can be taken to minimise the detrimental effects
of human use and to preserve it for posterity.
GEOMORPHIC PROCESSES
You would like to know the meaning of
geomorphic processes. The endogenic and
exogenic forces causing physical stresses and
chemical actions on earth materials and
2024-25
Page 3


LANDFORMS
This unit deals with
• Landforms and their evolution
• Geomorphic processes — weathering, mass wasting, erosion
and deposition; soils — formation
UNIT
III
2024-25
GEOMORPHIC PROCESSES
CHAPTER
A
fter learning about how the earth was
born, how it evolved its crust and other
inner layers, how its crustal plates
moved and are moving, and other information
on earthquakes, the forms of volcanism and
about the rocks and minerals the crust is
composed of, it is time to know in detail about
the surface of the earth on which we live. Let
us start with this question.
Why is the surface of the earth uneven?
The earth’s crust is dynamic. You are well
aware that it has moved and moves vertically
and horizontally. Of course, it moved a bit faster
in the past than the rate at which it is moving
now. The differences in the internal forces
operating from within the earth which built up
the crust have been responsible for the
variations in the outer surface of the crust. The
earth’s surface is being continuously subjected
to external forces induced basically by energy
(sunlight). Of course, the internal forces are still
active though with different intensities. That
means, the earth’s surface is being
continuously subjected to by external forces
originating within the earth’s atmosphere and
by internal forces from within the earth. The
external forces are known as exogenic forces
and the internal forces are known as endogenic
forces. The actions of exogenic forces result in
wearing down (degradation) of relief/elevations
and filling up (aggradation) of basins/
depressions, on the earth’s surface. The
phenomenon of wearing down of relief
variations of the surface of the earth through
erosion is known as gradation. The endogenic
forces continuously elevate or build up parts
of the earth’s surface and hence the exogenic
processes fail to even out the relief variations
of the surface of the earth. So, variations remain
as long as the opposing actions of exogenic and
endogenic forces continue. In general terms,
the endogenic forces are mainly land building
forces and the exogenic processes are mainly
land wearing forces. The surface of the earth is
sensitive. Humans depend on it for their
sustenance and have been using it extensively
and intensively. So, it is essential to understand
its nature in order to use it effectively without
disturbing its balance and diminishing its
potential for the future. Almost all organisms
contribute to sustain the earth’s environment.
However, humans have caused extensive
damage to the environment through over use
of resources. Use we must, but must also leave
it potential enough to sustain life through the
future. Most of the surface of the earth had and
has been shaped over very long periods of time
(hundreds and thousands of years) and
because of its use and misuse by humans its
potential is being diminished at a fast rate. If
the processes which shaped and are shaping
the surface of the earth into varieties of forms
(shapes) and the nature of materials of which
it is composed of, are understood, precautions
can be taken to minimise the detrimental effects
of human use and to preserve it for posterity.
GEOMORPHIC PROCESSES
You would like to know the meaning of
geomorphic processes. The endogenic and
exogenic forces causing physical stresses and
chemical actions on earth materials and
2024-25
FUNDAMENTALS OF PHYSICAL GEOGRAPHY 38
bringing about changes in the configuration
of the surface of the earth are known as
geomorphic processes. Diastrophism and
volcanism are endogenic geomorphic
processes. These have already been discussed
in brief in the preceding unit. Weathering, mass
wasting, erosion and deposition are exogenic
geomorphic processes. These exogenic
processes are dealt with in detail in this chapter.
Any exogenic element of nature (like water,
ice, wind, etc.,) capable of acquiring and
transporting earth materials can be called a
geomorphic agent. When these elements of
nature become mobile due to gradients, they
remove the materials and transport them over
slopes and deposit them at lower level.
Geomorphic processes and geomorphic agents
especially exogenic, unless stated separately,
are one and the same.
A process is a force applied on earth
materials affecting the same.  An agent is a
mobile medium (like running water, moving ice
masses, wind, waves and currents etc.) which
removes, transports and deposits earth
materials. Running water, groundwater,
glaciers, wind, waves and currents, etc., can
be called geomorphic agents.
Do you think it is essential to distinguish
geomorphic agents and geomorphic
processes?
Gravity besides being a directional force
activating all downslope movements of matter
also causes stresses on the earth’s materials.
Indirect gravitational stresses activate wave and
tide induced currents and winds. Without
gravity and gradients there would be no
mobility and hence no erosion, transportation
and deposition are possible. So, gravitational
stresses are as important as the other
geomorphic processes. Gravity is the force that
is keeping us in contact with the surface and it
is the force that switches on the movement of
all surface material on earth. All the movements
either within the earth or on the surface of the
earth occur due to gradients — from higher
levels to lower levels, from high pressure to low
pressure areas etc.
ENDOGENIC PROCESSES
The energy emanating from within the earth is
the main force behind endogenic geomorphic
processes. This energy is mostly generated by
radioactivity, rotational and tidal friction and
primordial heat from the origin of the earth.
This energy due to geothermal gradients and
heat flow from within induces diastrophism
and volcanism in the lithosphere. Due to
variations in geothermal gradients and heat flow
from within, crustal thickness and strength,
the action of endogenic forces are not uniform
and hence the tectonically controlled original
crustal surface is uneven.
Diastrophism
All processes that move, elevate or build up
portions of the earth’s crust come under
diastrophism. They include: (i) orogenic
processes involving mountain building
through severe folding and affecting long and
narrow belts of the earth’s crust; (ii) epeirogenic
processes involving uplift or warping of large
parts of the earth’s crust; (iii) earthquakes
involving local relatively minor movements;
(iv) plate tectonics involving horizontal
movements of crustal plates.
In the process of orogeny, the crust is
severely deformed into folds. Due to epeirogeny,
there may be simple deformation. Orogeny is
a mountain building process whereas
epeirogeny is continental building process.
Through the processes of orogeny, epeirogeny,
earthquakes and plate tectonics, there can be
faulting and fracturing of the crust. All these
processes cause pressure, volume and
temperature (PVT) changes which in turn
induce metamorphism of rocks.
Epeirogeny and orogeny, cite the
differences.
Volcanism
Volcanism includes the movement of molten
rock (magma) onto or toward the earth’s
surface and also formation of many intrusive
and extrusive volcanic forms. Many aspects of
volcanism have already been dealt in detail
2024-25
Page 4


LANDFORMS
This unit deals with
• Landforms and their evolution
• Geomorphic processes — weathering, mass wasting, erosion
and deposition; soils — formation
UNIT
III
2024-25
GEOMORPHIC PROCESSES
CHAPTER
A
fter learning about how the earth was
born, how it evolved its crust and other
inner layers, how its crustal plates
moved and are moving, and other information
on earthquakes, the forms of volcanism and
about the rocks and minerals the crust is
composed of, it is time to know in detail about
the surface of the earth on which we live. Let
us start with this question.
Why is the surface of the earth uneven?
The earth’s crust is dynamic. You are well
aware that it has moved and moves vertically
and horizontally. Of course, it moved a bit faster
in the past than the rate at which it is moving
now. The differences in the internal forces
operating from within the earth which built up
the crust have been responsible for the
variations in the outer surface of the crust. The
earth’s surface is being continuously subjected
to external forces induced basically by energy
(sunlight). Of course, the internal forces are still
active though with different intensities. That
means, the earth’s surface is being
continuously subjected to by external forces
originating within the earth’s atmosphere and
by internal forces from within the earth. The
external forces are known as exogenic forces
and the internal forces are known as endogenic
forces. The actions of exogenic forces result in
wearing down (degradation) of relief/elevations
and filling up (aggradation) of basins/
depressions, on the earth’s surface. The
phenomenon of wearing down of relief
variations of the surface of the earth through
erosion is known as gradation. The endogenic
forces continuously elevate or build up parts
of the earth’s surface and hence the exogenic
processes fail to even out the relief variations
of the surface of the earth. So, variations remain
as long as the opposing actions of exogenic and
endogenic forces continue. In general terms,
the endogenic forces are mainly land building
forces and the exogenic processes are mainly
land wearing forces. The surface of the earth is
sensitive. Humans depend on it for their
sustenance and have been using it extensively
and intensively. So, it is essential to understand
its nature in order to use it effectively without
disturbing its balance and diminishing its
potential for the future. Almost all organisms
contribute to sustain the earth’s environment.
However, humans have caused extensive
damage to the environment through over use
of resources. Use we must, but must also leave
it potential enough to sustain life through the
future. Most of the surface of the earth had and
has been shaped over very long periods of time
(hundreds and thousands of years) and
because of its use and misuse by humans its
potential is being diminished at a fast rate. If
the processes which shaped and are shaping
the surface of the earth into varieties of forms
(shapes) and the nature of materials of which
it is composed of, are understood, precautions
can be taken to minimise the detrimental effects
of human use and to preserve it for posterity.
GEOMORPHIC PROCESSES
You would like to know the meaning of
geomorphic processes. The endogenic and
exogenic forces causing physical stresses and
chemical actions on earth materials and
2024-25
FUNDAMENTALS OF PHYSICAL GEOGRAPHY 38
bringing about changes in the configuration
of the surface of the earth are known as
geomorphic processes. Diastrophism and
volcanism are endogenic geomorphic
processes. These have already been discussed
in brief in the preceding unit. Weathering, mass
wasting, erosion and deposition are exogenic
geomorphic processes. These exogenic
processes are dealt with in detail in this chapter.
Any exogenic element of nature (like water,
ice, wind, etc.,) capable of acquiring and
transporting earth materials can be called a
geomorphic agent. When these elements of
nature become mobile due to gradients, they
remove the materials and transport them over
slopes and deposit them at lower level.
Geomorphic processes and geomorphic agents
especially exogenic, unless stated separately,
are one and the same.
A process is a force applied on earth
materials affecting the same.  An agent is a
mobile medium (like running water, moving ice
masses, wind, waves and currents etc.) which
removes, transports and deposits earth
materials. Running water, groundwater,
glaciers, wind, waves and currents, etc., can
be called geomorphic agents.
Do you think it is essential to distinguish
geomorphic agents and geomorphic
processes?
Gravity besides being a directional force
activating all downslope movements of matter
also causes stresses on the earth’s materials.
Indirect gravitational stresses activate wave and
tide induced currents and winds. Without
gravity and gradients there would be no
mobility and hence no erosion, transportation
and deposition are possible. So, gravitational
stresses are as important as the other
geomorphic processes. Gravity is the force that
is keeping us in contact with the surface and it
is the force that switches on the movement of
all surface material on earth. All the movements
either within the earth or on the surface of the
earth occur due to gradients — from higher
levels to lower levels, from high pressure to low
pressure areas etc.
ENDOGENIC PROCESSES
The energy emanating from within the earth is
the main force behind endogenic geomorphic
processes. This energy is mostly generated by
radioactivity, rotational and tidal friction and
primordial heat from the origin of the earth.
This energy due to geothermal gradients and
heat flow from within induces diastrophism
and volcanism in the lithosphere. Due to
variations in geothermal gradients and heat flow
from within, crustal thickness and strength,
the action of endogenic forces are not uniform
and hence the tectonically controlled original
crustal surface is uneven.
Diastrophism
All processes that move, elevate or build up
portions of the earth’s crust come under
diastrophism. They include: (i) orogenic
processes involving mountain building
through severe folding and affecting long and
narrow belts of the earth’s crust; (ii) epeirogenic
processes involving uplift or warping of large
parts of the earth’s crust; (iii) earthquakes
involving local relatively minor movements;
(iv) plate tectonics involving horizontal
movements of crustal plates.
In the process of orogeny, the crust is
severely deformed into folds. Due to epeirogeny,
there may be simple deformation. Orogeny is
a mountain building process whereas
epeirogeny is continental building process.
Through the processes of orogeny, epeirogeny,
earthquakes and plate tectonics, there can be
faulting and fracturing of the crust. All these
processes cause pressure, volume and
temperature (PVT) changes which in turn
induce metamorphism of rocks.
Epeirogeny and orogeny, cite the
differences.
Volcanism
Volcanism includes the movement of molten
rock (magma) onto or toward the earth’s
surface and also formation of many intrusive
and extrusive volcanic forms. Many aspects of
volcanism have already been dealt in detail
2024-25
GEOMORPHIC PROCESSES 39
driving forces. It should become clear from
this chart that for each process there exists a
distinct driving force or energy.
As there are different climatic regions owing
to variations in thermal gradients created by
latitudinal, seasonal, and land and water
spread on the surface of the earth, the exogenic
geomorphic processes vary from region to
region.  The density, type and distribution of
vegetation which largely depend upon
precipitation and temperature also exert
under volcanoes in the Unit II and under
igneous rocks in the preceding chapter in this
unit.
What do the words volcanism and
volcanoes indicate?
EXOGENIC PROCESSES
The exogenic processes derive their energy
from atmosphere determined by the ultimate
energy from the sun and also the gradients
created by tectonic factors.
Why do you think that the slopes or
gradients are created by tectonic factors?
Gravitational force acts upon all earth
materials having a sloping surface and tend
to produce movement of matter in down
slope direction. Force applied per unit area
is called stress. Stress is produced in a solid
by pushing or pulling. This induces
deformation. Forces acting along the faces of
earth materials are shear stresses (separating
forces). It is this stress that breaks rocks and
other earth materials. The shear stresses
result in angular displacement or slippage.
Besides the gravitational stress earth
materials become subjected to molecular
stresses that may be caused by a number of
factors amongst which temperature changes,
crystallisation and melting are the most
common. Chemical processes normally lead
to loosening of bonds between grains,
dissolving of soluble minerals or cementing
materials. Thus, the basic reason that leads
to weathering, mass movements, and erosion
is development of stresses in the body of the
earth materials.
 Temperature and precipitation are the
two important climatic elements that control
various processes.
All the exogenic geomorphic processes
are covered under a general term,
denudation. The word ‘denude’ means to
strip off or to uncover. Weathering, mass
wasting/movements, erosion and
transportation are included in denudation.
The flow chart (Figure 5.1) gives the
denudation processes and their respective
influence indirectly on exogenic geomorphic
processes. Within different climatic regions
there may be local variations of the effects of
different climatic elements due to altitudinal
differences, aspect variations and the variation
in the amount of insolation received by north
and south facing slopes as compared to east
and west facing slopes. Further, due to
differences in wind velocities and directions,
amount and kind of precipitation, its intensity,
the relation between precipitation and
evaporation, daily range of temperature,
freezing and thawing frequency, depth of frost
penetration, the geomorphic processes vary
within any climatic region.
What is the sole driving force behind all
the exogenic processes?
Climatic factors being equal, the intensity
of action of exogenic geomorphic processes
depends upon type and structure of rocks. The
term structure includes such aspects of rocks
as folds, faults, orientation and inclination of
beds, presence or absence of joints, bedding
planes, hardness or softness of constituent
minerals, chemical susceptibility of mineral
constituents; the permeability or impermeability
Figure 5.1 : Denudational processes and their
driving forces
2024-25
Page 5


LANDFORMS
This unit deals with
• Landforms and their evolution
• Geomorphic processes — weathering, mass wasting, erosion
and deposition; soils — formation
UNIT
III
2024-25
GEOMORPHIC PROCESSES
CHAPTER
A
fter learning about how the earth was
born, how it evolved its crust and other
inner layers, how its crustal plates
moved and are moving, and other information
on earthquakes, the forms of volcanism and
about the rocks and minerals the crust is
composed of, it is time to know in detail about
the surface of the earth on which we live. Let
us start with this question.
Why is the surface of the earth uneven?
The earth’s crust is dynamic. You are well
aware that it has moved and moves vertically
and horizontally. Of course, it moved a bit faster
in the past than the rate at which it is moving
now. The differences in the internal forces
operating from within the earth which built up
the crust have been responsible for the
variations in the outer surface of the crust. The
earth’s surface is being continuously subjected
to external forces induced basically by energy
(sunlight). Of course, the internal forces are still
active though with different intensities. That
means, the earth’s surface is being
continuously subjected to by external forces
originating within the earth’s atmosphere and
by internal forces from within the earth. The
external forces are known as exogenic forces
and the internal forces are known as endogenic
forces. The actions of exogenic forces result in
wearing down (degradation) of relief/elevations
and filling up (aggradation) of basins/
depressions, on the earth’s surface. The
phenomenon of wearing down of relief
variations of the surface of the earth through
erosion is known as gradation. The endogenic
forces continuously elevate or build up parts
of the earth’s surface and hence the exogenic
processes fail to even out the relief variations
of the surface of the earth. So, variations remain
as long as the opposing actions of exogenic and
endogenic forces continue. In general terms,
the endogenic forces are mainly land building
forces and the exogenic processes are mainly
land wearing forces. The surface of the earth is
sensitive. Humans depend on it for their
sustenance and have been using it extensively
and intensively. So, it is essential to understand
its nature in order to use it effectively without
disturbing its balance and diminishing its
potential for the future. Almost all organisms
contribute to sustain the earth’s environment.
However, humans have caused extensive
damage to the environment through over use
of resources. Use we must, but must also leave
it potential enough to sustain life through the
future. Most of the surface of the earth had and
has been shaped over very long periods of time
(hundreds and thousands of years) and
because of its use and misuse by humans its
potential is being diminished at a fast rate. If
the processes which shaped and are shaping
the surface of the earth into varieties of forms
(shapes) and the nature of materials of which
it is composed of, are understood, precautions
can be taken to minimise the detrimental effects
of human use and to preserve it for posterity.
GEOMORPHIC PROCESSES
You would like to know the meaning of
geomorphic processes. The endogenic and
exogenic forces causing physical stresses and
chemical actions on earth materials and
2024-25
FUNDAMENTALS OF PHYSICAL GEOGRAPHY 38
bringing about changes in the configuration
of the surface of the earth are known as
geomorphic processes. Diastrophism and
volcanism are endogenic geomorphic
processes. These have already been discussed
in brief in the preceding unit. Weathering, mass
wasting, erosion and deposition are exogenic
geomorphic processes. These exogenic
processes are dealt with in detail in this chapter.
Any exogenic element of nature (like water,
ice, wind, etc.,) capable of acquiring and
transporting earth materials can be called a
geomorphic agent. When these elements of
nature become mobile due to gradients, they
remove the materials and transport them over
slopes and deposit them at lower level.
Geomorphic processes and geomorphic agents
especially exogenic, unless stated separately,
are one and the same.
A process is a force applied on earth
materials affecting the same.  An agent is a
mobile medium (like running water, moving ice
masses, wind, waves and currents etc.) which
removes, transports and deposits earth
materials. Running water, groundwater,
glaciers, wind, waves and currents, etc., can
be called geomorphic agents.
Do you think it is essential to distinguish
geomorphic agents and geomorphic
processes?
Gravity besides being a directional force
activating all downslope movements of matter
also causes stresses on the earth’s materials.
Indirect gravitational stresses activate wave and
tide induced currents and winds. Without
gravity and gradients there would be no
mobility and hence no erosion, transportation
and deposition are possible. So, gravitational
stresses are as important as the other
geomorphic processes. Gravity is the force that
is keeping us in contact with the surface and it
is the force that switches on the movement of
all surface material on earth. All the movements
either within the earth or on the surface of the
earth occur due to gradients — from higher
levels to lower levels, from high pressure to low
pressure areas etc.
ENDOGENIC PROCESSES
The energy emanating from within the earth is
the main force behind endogenic geomorphic
processes. This energy is mostly generated by
radioactivity, rotational and tidal friction and
primordial heat from the origin of the earth.
This energy due to geothermal gradients and
heat flow from within induces diastrophism
and volcanism in the lithosphere. Due to
variations in geothermal gradients and heat flow
from within, crustal thickness and strength,
the action of endogenic forces are not uniform
and hence the tectonically controlled original
crustal surface is uneven.
Diastrophism
All processes that move, elevate or build up
portions of the earth’s crust come under
diastrophism. They include: (i) orogenic
processes involving mountain building
through severe folding and affecting long and
narrow belts of the earth’s crust; (ii) epeirogenic
processes involving uplift or warping of large
parts of the earth’s crust; (iii) earthquakes
involving local relatively minor movements;
(iv) plate tectonics involving horizontal
movements of crustal plates.
In the process of orogeny, the crust is
severely deformed into folds. Due to epeirogeny,
there may be simple deformation. Orogeny is
a mountain building process whereas
epeirogeny is continental building process.
Through the processes of orogeny, epeirogeny,
earthquakes and plate tectonics, there can be
faulting and fracturing of the crust. All these
processes cause pressure, volume and
temperature (PVT) changes which in turn
induce metamorphism of rocks.
Epeirogeny and orogeny, cite the
differences.
Volcanism
Volcanism includes the movement of molten
rock (magma) onto or toward the earth’s
surface and also formation of many intrusive
and extrusive volcanic forms. Many aspects of
volcanism have already been dealt in detail
2024-25
GEOMORPHIC PROCESSES 39
driving forces. It should become clear from
this chart that for each process there exists a
distinct driving force or energy.
As there are different climatic regions owing
to variations in thermal gradients created by
latitudinal, seasonal, and land and water
spread on the surface of the earth, the exogenic
geomorphic processes vary from region to
region.  The density, type and distribution of
vegetation which largely depend upon
precipitation and temperature also exert
under volcanoes in the Unit II and under
igneous rocks in the preceding chapter in this
unit.
What do the words volcanism and
volcanoes indicate?
EXOGENIC PROCESSES
The exogenic processes derive their energy
from atmosphere determined by the ultimate
energy from the sun and also the gradients
created by tectonic factors.
Why do you think that the slopes or
gradients are created by tectonic factors?
Gravitational force acts upon all earth
materials having a sloping surface and tend
to produce movement of matter in down
slope direction. Force applied per unit area
is called stress. Stress is produced in a solid
by pushing or pulling. This induces
deformation. Forces acting along the faces of
earth materials are shear stresses (separating
forces). It is this stress that breaks rocks and
other earth materials. The shear stresses
result in angular displacement or slippage.
Besides the gravitational stress earth
materials become subjected to molecular
stresses that may be caused by a number of
factors amongst which temperature changes,
crystallisation and melting are the most
common. Chemical processes normally lead
to loosening of bonds between grains,
dissolving of soluble minerals or cementing
materials. Thus, the basic reason that leads
to weathering, mass movements, and erosion
is development of stresses in the body of the
earth materials.
 Temperature and precipitation are the
two important climatic elements that control
various processes.
All the exogenic geomorphic processes
are covered under a general term,
denudation. The word ‘denude’ means to
strip off or to uncover. Weathering, mass
wasting/movements, erosion and
transportation are included in denudation.
The flow chart (Figure 5.1) gives the
denudation processes and their respective
influence indirectly on exogenic geomorphic
processes. Within different climatic regions
there may be local variations of the effects of
different climatic elements due to altitudinal
differences, aspect variations and the variation
in the amount of insolation received by north
and south facing slopes as compared to east
and west facing slopes. Further, due to
differences in wind velocities and directions,
amount and kind of precipitation, its intensity,
the relation between precipitation and
evaporation, daily range of temperature,
freezing and thawing frequency, depth of frost
penetration, the geomorphic processes vary
within any climatic region.
What is the sole driving force behind all
the exogenic processes?
Climatic factors being equal, the intensity
of action of exogenic geomorphic processes
depends upon type and structure of rocks. The
term structure includes such aspects of rocks
as folds, faults, orientation and inclination of
beds, presence or absence of joints, bedding
planes, hardness or softness of constituent
minerals, chemical susceptibility of mineral
constituents; the permeability or impermeability
Figure 5.1 : Denudational processes and their
driving forces
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FUNDAMENTALS OF PHYSICAL GEOGRAPHY 40
etc. Different types of rocks with differences in
their structure offer varying resistances to
various geomorphic processes. A particular
rock may be resistant to one process and non-
resistant to another. And, under varying
climatic conditions, particular rocks may
exhibit different degrees of resistance to
geomorphic processes and hence they operate
at differential rates and give rise to differences
in topography. The effects of most of the
exogenic geomorphic processes are small and
slow and may be imperceptible in a short time
span, but will in the long run affect the rocks
severely due to continued fatigue.
Finally, it boils down to one fact that the
differences on the surface of the earth though
originally related to the crustal evolution
continue to exist in some form or the other due
to differences in the type and structure of earth
materials, differences in geomorphic processes
and in their rates of operation.
Some of the exogenic geomorphic processes
have been dealt in detail here.
WEATHERING
Weathering is action of elements of weather and
climate over earth materials.  There are a
number of processes within weathering which
act either individually or together to affect the
earth materials in order to reduce them to
fragmental state.
Weathering is defined as mechanical
disintegration and chemical decom-
position of rocks through the actions of
various elements of weather and climate.
As very little or no motion of materials
takes place in weathering, it is an in-situ or
on-site process.
Is this little motion which can occur
sometimes due to weathering synonymous
with transportation?  If not, why?
Weathering processes are conditioned by
many complex geological, climatic, topographic
and vegetative factors.  Climate is of particular
importance. Not only weathering processes
differ from climate to climate, but also the depth
of the weathering mantle (Figure 5.2).
Figure 5.2 : Climatic regimes and depth of weathering
mantles (adapted and modified from Strakhov, 1967)
Activity
Mark the latitude values of different
climatic regimes in Figure 6.2 and
compare the details.
There are three major groups of weathering
processes : (i) chemical; (ii) physical or
mechanical; (iii) biological weathering processes.
Very rarely does any one of these processes ever
operate completely by itself, but quite often a
dominance of one process can be seen.
Chemical Weathering Processes
A group of weathering processes viz; solution,
carbonation, hydration, oxidation and
reduction act on the rocks to decompose,
dissolve or reduce them to a fine clastic state
through chemical reactions by oxygen, surface
and/or soil water and other acids.  Water and
air (oxygen and carbon dioxide) along with heat
must be present to speed up all chemical
reactions. Over and above the carbon dioxide
present in the air, decomposition of plants and
animals increases the quantity of carbon
dioxide underground. These chemical reactions
on various minerals are very much similar to
the chemical reactions in a laboratory.
Physical Weathering Processes
Physical or mechanical weathering processes
depend on some applied forces. The applied
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