Page 111 - SST Class 07
P. 111

Vertical Movement                                       or fissures in the earth’s
                                                                    surface. The faulting can be
            Vertical movements result in a rise or fall of the
                                                                    horizontal or vertical, or
            earth’s  crust.   These    are   continent-building
            movements and cause a large scale uplift     (rising)   both    types   can    occur
                                                                    simultaneously.
            and subsidence  (sinking).                                                                    Faulting
            A plateau is formed at the place of an uplift, while     Landforms and Human Activity
            a valley is formed at the place of a subsidence.        In addition to various earth movements, humans
                                                                    also cause a change in the landforms on a large
            Horizontal Movement
                                                                    scale. Cutting down of trees; construction of
            When the tectonic plates compress against each          roads, buildings, dams and canals; mining; and
            other, it results in folding ; and when the tectonic    the use of explosives for construction or warfare
            plates cause tension, faulting  occurs.                 are some of human activities which cause a

            Folding :  Folding occurs when two plates collide.      change in the earth. Man has become so powerful
            The rocks often bend than break. This collision         that he has disturbed the ecological balance by his
            results in up-folds called anticlines  and down-folds   activities. Human activities are
            called  synclines .  The                                causing irreparable harm to the
            anticlines         cause                                environment. Time is ripe when
            mountains,     such    as                               we should become aware of
            Himalayas in India and                                  this problem and save the earth
            Andes     in   America,                                 from such changes.
            while synclines result in                                                                       A dam
                                               Folding
            valleys.                                                        Just Think!

            Faulting :  When tectonic plates move away from
            each other, a tension is caused resulting in cracks      How have human activities greatly changed the
                                                                     earth’s surface and harmed the environment?






            v The endogenic forces work within the earth and the exogenic forces outside it.
            v Earth movements can occur suddenly or gradually.

            v A volcano occurs when the magma erupts out of a fissure on the earth’s crust.
            v An earthquake occurs due to tectonic movements.
            v The earth’s surface undergoes a change by weathering and erosion.
            v Tectonic movements can be vertical or horizontal.

            v Human activity has greatly changed the earth’s surface and harmed the environment.
            v The faulting can be horizontal or vertical, or both types can occur simultaneously.








            A.   Tick (3) the right option :
                 1.   An exogenic force works ______________    the earth.
                      (a) within                       (b) outside                     (c) none of these

                                                                                    Changing Earth and Landforms
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