NCERT Book Class 11 Geography (Fundamental of Physical Geography) Chapter 6 Landforms and their Evolution

CHAPTER

LANDFORMS AND THEIR
EVOLUTION

A
fter weathering processes have had part of the earth’s surface from one landform into
their actions on the earth materials another or transformation of individual
making up the surface of the earth, the landforms after they are once formed. That
geomorphic agents like running water, ground means, each and every landform has a history
water, wind, glaciers, waves perform erosion. of development and changes through time. A
It is already known to you that erosion causes landmass passes through stages of development
changes on the surface of the earth. Deposition somewhat comparable to the stages of life —
follows erosion and because of deposition too, youth, mature and old age.
changes occur on the surface of the earth.
As this chapter deals with landforms and What are the two important aspects of
their evolution ‘first’ start with the question, the evolution of landforms?
what is a landform? In simple words, small to
medium tracts or parcels of the earth’s surface
are called landforms. RUNNING WATER
In humid regions, which receive heavy rainfall
If landform is a small to medium sized
running water is considered the most important
part of the surface of the earth, what is a
of the geomorphic agents in bringing about
landscape?
the degradation of the land surface. There are
two components of running water. One is
Several related landforms together make
overland flow on general land surface as a
up landscapes, (large tracts of earth’s surface).
sheet. Another is linear flow as streams and
Each landform has its own physical shape,
size, materials and is a result of the action of rivers in valleys. Most of the erosional landforms
certain geomorphic processes and agent(s). made by running water are associated with
Actions of most of the geomorphic processes vigorous and youthful rivers flowing over steep
and agents are slow, and hence the results gradients. With time, stream channels over
take a long time to take shape. Every landform steep gradients turn gentler due to continued
has a beginning. Landforms once formed may erosion, and as a consequence, lose their
change in their shape, size and nature slowly velocity, facilitating active deposition. There
or fast due to continued action of geomorphic may be depositional forms associated with
processes and agents. streams flowing over steep slopes. But these
Due to changes in climatic conditions and phenomena will be on a small scale compared
vertical or horizontal movements of land- to those associated with rivers flowing over
masses, either the intensity of processes or the medium to gentle slopes. The gentler the river
processes themselves might change leading to channels in gradient or slope, the greater is
new modifications in the landforms. Evolution the deposition. When the stream beds turn
here implies stages of transformation of either a gentler due to continued erosion, downward