EVOLUTION OF LANDFORMS
The surface of the earth constitutes a
great assemblage of physical features,
each having a form, dynamics, and
uniqueness. It is called landform. No landform
is permanent, each is changing � some slowly
while others fast. Landforms vary in size from
continents to minor rivulets.
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A D V E R T I S E M E N T
A host of internal and external forces are
involved in the creation of landforms. Tectonic
forces crumple rocks and push up continents
and mountain ranges. Moving water, air and
ice erode rocks and transport the eroded
debris to depositional sites and thus, change
the appearance of the landscapes with the
passage of time. The intensity of these agencies
varies from one region to another depending
on climate, vegetation and altitude.
Geomorphology is the genetic study of
landforms. Traditionally, the study was
essentially confined to origin and evolution of
landforms. According to some, the study and
interpretation of records left by erosion
constitute the major part of the science of
geomorphology. While others view geomorphology
not merely as a study of
landforms but also interaction, at the contact
surface, between the lithosphere and the
atmosphere. Two great geomorphologists,
S.W. Wooldridge and W.M. Davis considered
that landforms were the best indicators of the
earth�s history.
The view of the earth�s history proposed by
the catastrophists of the early nineteenth
century was of a succession of abrupt
upheavals culminating in a great flood. These
paroxysms were interpreted as the result of
Divine intervention. In contrast, C. Lyell and
J.Hutton hypothesised slow changes involving
a number of natural processes. J. Hutton in
the book Theory of the Earth with Proof and
Illustrations (1785) recognised the cyclical
nature of geological changes. He postulated
that ordinary processes, operating over long
time intervals could effect great changes. He
reasoned from observation that rocks slowly
decayed and disintegrated under the action of
water and air. Hutton observed mountains
being eroded, rivers carrying debris to the sea,
ocean waves pounding rocks, sands and mud
settling to the bottom and then being buried
on the sea floor. Nature behaves in a uniform
fashion all the time. Charles Lyell called it
Principle of Uniformitarianism. Actually what
remains uniform are the physical and chemical
laws that govern geological activities.
LANDFORM TYPES
Landforms that result from crustal movements
are of tectonic type. No sub-aerial relief can
occur until tectonic uplift has raised land
above sea level or they are constructed by
depositional (volcanic or sedimentational)
processes.
Terrestrial land forms can be classified
into the following hierarchy: first order
land forms, second order land forms, and third
order land forms.
The first order landforms include the
continents and ocean basins that comprise the
largest units of the earth�s relief. In the
light of Plate Tectonic Theory (discussed in
Chapter 5 of this book), the continents are
large masses that are rafted and rooted in the
mantle. As a consequence of this process new
oceans are formed.
The second order landform includes the
tectonic mountain belts, plateaus and plains.
Under the second order relief, the landscapes
are characterised primarily by their tectonic or
structural unity. The second order relief is
generally, created by internal or endogenic earth
processes driven by the energy source in the
form of volcanism and/or tectonic activity from
deep inside the earth. The Himalaya mountains
and the Deccan Plateau are examples of the
second order landforms.
The third order landform includes the
features produced by erosion such as carved
mountains, hills and valleys. Atmospheric
weathering and erosion are largely responsible
in giving rise to the landforms by destructional
or erosional processes. Complex series of
reactions take place when rocks are exposed to
water and air in the planet�s gravitational field.
The third order landforms are shaped by the
external or exogenic earth processes. External
processes, driven by solar energy, act through the
atmosphere and oceans where air and water
come in contact with the lithoshpere.
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AKHAND PRATAP SINGH
