The structure of the Earth. Image by BBC.

The structure of the Earth. Image by BBC.

ZIMSEC O Level Geography Notes: The Earth’s Crust

  • The earth is generally spherical in shape.
  • It’s surface however is made up of immeasurable valleys, mountains, rivers, hills etc of different shapes and sizes which in turn affect its shape.
  • These naturally occurring features are called landforms.
  • These landforms are constantly being created, changed and shaped by the earth’s internal and external forces.
  • We say the earth’s features are dynamic i.e. they are always changing.
  • Internal forces occur beneath the earth’s surface.
  • These forces include faulting and folding and can result in such landforms as fold mountains and rift valleys.
  • External forces occur above the earth’s surface and are often referred to as denudation processes.
  • They include such processes as wind and water action (erosion and deposition), weathering and mass wasting.
  • These forces transform and alter the original features and sometimes reduce their size.
  • In other instances completely new landforms are formed for example Yardangs and Kopjes.

External Forces

  1. Running water
  2. Wind
  3. Waves
  4. Ice
  5. Weathering
  6. Mass wasting

Internal Forces

  1. Folding
  2. Faulting
  3. Volcanic activity

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