Page 108 - SST Class 07
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Changing Earth



                                                                      and Landforms                     15










             q   Volcanoes                                          q   Earthquakes
             q   Movement of water, ice and wind

            Introduction                                            atmosphere, it cools down quickly. A person can
                                                                    save himself from a volcano by running away.
            The earth keeps changing from place to place both
                                                                    After the lava cools down, it forms into rocks.
            inside and outside. Within the earth itself, there is a
            constant movement everywhere. These movements
            are divided on the basis of the forces which cause
            them. These two forces are called endogenic forces
            and exogenic forces . Endogenic forces work within
            the earth such as volcanoes and earthquakes.
            Exogenic forces work on earth’s surface, such as
            water, ice and wind.
                                                                                          A volcano
            Changes in the earth are called earth movements   .
                                                                    Volcanoes     can    be    classified  into    three
            These movements     can be sudden or gradual. The
            eruption    of  volcanoes    and   occurrence    of     types—active    volcanoes    which    erupt   often;
                                                                    dormant volcanoes    which erupt rarely; and extinct
            earthquakes are sudden movements, because they
                                                                    volcanoes  which have stopped erupting anymore.
            cause a sudden change in the earth; while the
            movement of water, ice and wind forms the gradual       Most of the volcanoes occur along the Ring of
            change. Volcanoes and earthquakes are so sudden         Fire , which runs along the edge of the Pacific
            that they can hardly be predicted. Scientists are       Ocean.
            making efforts to find ways to predict them.

                            VOLCANOES                                 G                            O

            A volcano is an opening or fissure in the              N                     F
            earth’s crust through which the magma                I        Kurile trench  Aleutian trench
            (molten material) erupts from the magma           R        Japan trench              F
            chamber. The magma is called lava     when        Ryukyu trench  Izu Bonin trench       I  R
                                                                 Philippine                                 Puerto Rico trench
            it comes out of the opening. The magma                trench                                  E
                                                                        Marianas trench
            may accompany with particles of rocks,                   Challenger Deep         Middle America
                                                                                               trench
            steam and gases. The eruption of a                                         Equator
            volcano may accompany with tremors           Java (Sunda)
                                                           trench
            and may lead to earthquakes.                                                         Peru-Chile trench
            Generally, the lava flows slowly, but its
            speed depends on the water content in it.                                                          South Sandwich
            When     it  comes     in   contact    with                                                           trench
                                                                                    Ring of Fire
                     Contemporary Social Science-7
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