Chapter 3 – Our Changing Earth

Chapter 3 – Our Changing Earth

 

1. Lithospheric Plates

• The Earth’s crust  is divided into many large and some smaller, hard, irregularly shaped plates, called  lithospheric plates.
• These plates rotate continuously slowly on the surface of the earth.
• This happens because of the movement of molten magma inside the earth. This molten magma rotates in a circular manner.

 

2. Forces and Earth Movements

The motions of the Earth are divided based on the forces that generate them:

1. Endogenic Forces:

• • These forces  originate in the interior  of the earth.
  •  Sudden Forces:
    • Earthquakes : When lithospheric plates move, vibrations occur on the earth’s surface. This vibration can travel around the Earth.
      •  Focus: The place from which the vibration originates.
      •  Epicentre: A place just above the focus on the earth’s crust. The places closest to the epicenter suffer the most damage.
      •  Seismograph: An instrument used to measure earthquakes.

 

1. Exogenic Forces:

• • These forces act on the surface of the  earth.
  •  Erosion: Breakdown and erosion of the landscape (e.g. by water, wind, ice).
  •  Deposition: Accumulation of materials brought after erosion elsewhere.
  • Examples: Rivers, wind, sea waves, glaciers.

 

3. Major Landforms

The  processes of erosion and deposition form different landforms on the surface of the earth:

1. Work of a River:

• •  Waterfalls: When the river falls from a hard rock on a steep slope.
  •  Meanders: When the river enters the plain, it takes large turns.
  •  Ox-bow Lakes: Loops of the snake cut and form a separate lake.
  •  Floodplain: When a river flows above its banks, it accumulates silt and other material with it, forming fertile floodplains.
  •  Levees: Natural embankments raised on river banks.
  •  Distributaries: When the river approaches the sea, it breaks into many smaller streams.
  • Delta : A collection of sediments deposited at the mouth of the distributaries.

1. Work of Sea Waves:

• •  Sea Caves: Caves formed in rocks by waves.
  • Coastal Arches: When the caves become so large that only the roof remains.
  •  Stacks: When the roof of the arch also collapses, only the steep rocks remain.
  •  Sea Cliffs: Steep rocky shores overlooking the sea.
  •  Beaches: Deposits of sand deposited by sea waves.

iii.  Work of Ice – Glaciers:

• •  Glaciers: Slow-moving ice rivers.
  • They carry stones and debris with them, forming deep, U-shaped valleys.
  •  Glacial Moraines:  Deposition of substances  (such as rocks, sand, and silt) brought by glaciers.

1. Work of Wind:

• •  Mushroom Rocks: The wind cuts the lower parts of the rocks more than the upper parts, forming mushroom-shaped rocks.
  •  Sand Dunes: When the wind picks up and deposits the sand, fewer hills are formed.
  •  Loess: When sand particles are very fine and light, wind can carry them long distances and accumulate over large areas. Large loess deposits are found in China.