Our Changing Earth Question Answers: NCERT Class 7 Social Science - Our Environment (Geography)

(i) The plates move because of the molten magma which is present inside the earth.

(ii) The forces that act in the interior of the earth are known as exogenic forces.

(iii) Erosion is the wearing away of the landscape by different agents like water, wind, insects and ice etc.

(iv) When rivers outflow their banks, they cause flood in the neighbourhood areas. The flood water takes away good soil, another material and deposits them along in the banks. This deposition leads to the formation of flood plains.

(v) Winds lift and carry sand from one place to the other. When they stop blowing, sand falls and gets deposited in low hill like structure which are known as sand dunes.

(vi) The sea waves deposit sediments along the shores which leads to the formation of beaches.

(vii) When a river enters the plain it forms a large bend which is cut off stream in due course of time. The cut of stream takes the form of a lake which is called as ox-bow lake.

(i) (a) cliff
(ii) (c) moraine
(iii) (a) volcano
(iv) (a) deserts
(v) (b) river valleys

(i) Glacier                                     (c) river of ice
(ii) Meanders                               (g) hard bed rock
(iii) Beach                                    (a) Sea shore
(iv) Sand dunes                          (h) deserts
(v) Waterfall                               (d) rivers
(vi) Earthquake                         (e) vibrations of earth

(i) In desert, wind is an active agent for soil erosion which erode the lower section of the rock more than the upper part of the rock. Therefore, some rocks have a shape of a mushroom which contain narrower base and wider top.

(ii) Flood plains are very fertile because floods deposit layers of fine soil and other material which is known as sediments which is ideal for cultivation along with its banks.

(iii) When cavities in sea caves become larger, only the roof of the caves remain forming sea arches. Further, erosion breaks the roof and only walls are left which forms the stacks.

(iv) During earthquakes, vibrations travel outwards from the epicenter as waves and propagate through the surface of the earth which produces sudden movements which leads to the collapse of buildings.

name of the Features                                    Type (erosional or Depositional or Both)
                                                                          
       Waterfall                                                                     both
       Meander                                                                     both

      Flood plain                                                            depositional