Internal and External Forces in the Formation of Relief

Internal Forces in the Formation of Relief

• VOLCANOES: Cracks in the Earth's crust can be deep enough to reach areas where there is magma. The magma rises and passes through the volcano's crater to the surface in a volcanic eruption. Volcanic eruptions expel gases, ash, rocks, and lava. When these materials come into contact with the air, they cool down and form a volcanic cone.
• EARTHQUAKES: are the result of the movement of the Earth's tectonic plates. This movement travels in all directions in the form of seismic waves. Earthquakes usually last for only a few seconds, but they cause the ground to shake and can have devastating effects. Earthquakes can be of different magnitudes.

External Forces in the Formation of Relief

• THE ACTION OF WATER: Water is the main external force that changes relief. It can have various effects:
  • Rainwater runs downhill and erodes mountains. Rivers create ravines and valleys by carrying away soil and rocks. When running water slows down, it leaves materials, forming plains and deltas.
  • Water in the form of snow accumulates on mountains. Its weight can move soil and rocks, creating glacial valleys.
  • Water penetrates cracks in rocks. The pressure of the ice can break rocks.
  • Water reacts chemically with some components in rocks causing them to dissolve and form cracks.
  • Waves, ocean currents, and tides erode coastlines over time.
• THE ACTION OF WIND: The wind erodes rocks and transports small particles such as sand and dust. These effects are greater in dry places with little or no vegetation.
• THE ACTION OF VEGETATION: Vegetation can also change relief. Plant roots penetrate the ground and can break rocks.