FORCES AFFECTING THE EARTH'S CRUST
Forces beneath the Earth
In the Earth's crust there are different movements and tensions, which cause changes in the Earth's crust. Most of the landforms such as mountains, plateaus, plains and valleys are creation of internal process below the Earth's surface. The landforms on the surface are caused by the forces which are divided on the basis of their sources of origin into two categories ---
- Internal forces
- External forces
Endogenic forces or Internal force :
Forces operating beneath the Earth are called Endogenic forces. They are also called Tectonic movements.
The internal forces of the Earth are responsible for the formation of various types of landforms, hence they are called constructive forces. Folding and Faulting are internal forces.
The endogenic movements are devided into two types on the basis of their intensity -
Diastrophic forces -
It includes Vertical and Horizontal movements which are caused by the forces working beneath the Earth. These forces are slow and their effects are visible after a long time.
- These movements are also called epeirogenic or continent building movements. The word ' epeiros' means a continent.
- These movements are the result of internal forces acting radially from the centre of the Earth.
- These movements cause rise and fall of a portion of the Earth.
- The part which rises above the surrounding portion is known as Uplift and the part which sinks downward is called Subsidence.
- These movements are powerful as they could cause elevation of an extensive area such as a continent.
- They are also responsible for the formation of plateaus and valleys.
- These movements are also known as orogenic or mountain building movements.
- These movements are also a result of the internal forces but in these type of movements the forces acts horizontally to the Earth's surface and disturb the horizontal layers of the Earth's crust. Hence these movements are more complex than the vertical movements.
- They work in two ways - in opposite direction and towards each other. These are called compressional and tensional forces.
- Compressional forces lead to crumbling and folding of rocks.
- Tensional forces lead to fractures , cracks and faulting of rocks.
Sudden forces :
Such types of movements which are caused by sudden endogenic forces coming from deep within the Earth causes sudden and rapid events that cause massive destruction at and below the Earth's surfaces.
- Example of these events, like volcanic eruptions and earthquake are called Extreme Events and become disastrous hazards when they occur in densely populated localities. Geologically thesesudden forces are termed as " Constructive forces" because they create certain relief features on the earth's surface.
- For e.g : Volcanic eruption result in the formation of volcanic cones and mountain, while fissures flame of lava form extensive lava plateau and lava plains. Earthquake creates faults, fractures, lakes etc
The External or Exogenetic force -
Exogenetic Forces operate on or above the Earth's surface. Some major exogenetic forces are denudation, weathering, mass movements and erosion.
In the next article we will discuss Folding and Faulting