NCERT CLASS 7 SOCIAL SCIENCE GEOGRAPHY CHAPTER-3 Our Changing Earth

Important questions with answers.

1.      What are lithospheric plates?
 Answer: The earth's crust has several large and some small, rigid, irregularly shaped plates which carry continents and the ocean floor. These plates are called lithospheric plates. 

2.      What is the focus and epicentre of an earthquake?
 Answer: The place in the crust where the movement of the earthquake starts is called the focus and the place on the surface above the focus is called the epicentre.

3.      What are the three types of earthquake waves?
 Answer: The three types of earthquake waves are:
                  a. P waves or longitudinal waves.
                  b. S waves or transverse waves.
                  c. L waves or surface waves.

4.      Name the instrument used to measure earthquake.
 Answer: The instrument used to measure earthquake is seismograph.

5.      Name the highest waterfall in the world.
 Answer: The highest waterfall of the world is Angel Falls of Venezuela in South America.

6.      Define the terms:  weathering, erosion, meanders, ox-bow lake, floodplain, levees, delta, sea caves, sea arches, stacks, sea cliff, glacial moraines, mushroom rocks, and sand dunes.
 Answer: a.      Weathering: The breaking down of the exposed rocks on the earth by the action of different weather conditions like rain, snow, changes in temperature, wind, etc are called weathering.

               b.      Erosion: The geological process by which the surface particles of the earth are worn away and transported by factors like wind, water, and the air is called erosion.

               c.       Meanders: When a river enters a nearly plain area, the flow of water takes a curved path and forms a snake-like pattern. The curve so formed is called a meander.

               d.      Ox-bow Lake: Sometimes the meander loop gets cut away from the river due to the deposition of sediments. This cut off portion is called an ox-bow lake.

             e.       Flood plain: The flat land adjacent to a river which often gets flooded depositing sediments on it is called a flood plain.

                f.       Levees: The raised banks of a river formed by the deposition of the sediments by the river are called levees.

               g.      Delta: The river, before entering into the sea, splits up into different channels called distributaries. The speed of the flow of water this stage is slow resulting in the deposition of sediments. These sediments form a delta.

                h.      Sea caves: When sea waves continuously hit the surface of a rock, cracks appear on the surface of the rock. Over time, these cracks become larger leading to the formation of sea caves.

                i.        Stacks: Continuous erosion makes the sea arches bigger and bigger. Eventually, the roof of the sea arches breaks down and only the walls are left behind. These walls like structures are called stacks.

                  j.        Sea cliff: A large piece of a rock or a mountain which has a very steep side facing the sea or a river caused by erosion is called a sea cliff.

                   k.      Glacial moraines: When the glaciers move from the mountain top to the surface of the earth, it carries with it pieces of rocks of varying sizes as well as sand and silt. When the ice melts at the surface, the water moves away leaving the materials behind. These deposited materials form glacial moraines.

                    l.        Mushroom rocks: Mushroom rocks are rocks mostly found in the desert that looks like a mushroom as the lower part of the rock gets eroded by agents like the wind. Thus these rocks have a narrower base and wider top.

                  m.    Sand dunes: Sand dunes are hills of sand mostly created in the desert when the wind stops blowing leaving all the sand particles at one particular place.