Endogenetic Forces

• The Earth crust is dynamic and is continuously changing.
• Internal forces which operates from inside the earth has built up the crust and acts continuously producing variations on the outer surface of the earth.
• Earth’s outer surface is continuously subjected to external forces which are basically induced from the energy of sun.
• Thus we can say that earth’s surface is continuously subjected to the external forces which are induced from the earth’s atmosphere and at the same time by the internal forces which are induced from inside the earth.
• The external forces are called exogenic forces and internal forces are called endogenic forces.
• Endogenic forces are constructive or land building forces whereas exogenic forces are destructive or land wearing forces.
• Geomorphic processes: The combination of endogenic and exogenic forces causes physical stresses and chemical action on the material of earth which brought changes in the configuration of the surface of the earth. This change in the configuration of the surface of the earth is known as geomorphic processes. Hence geomorphic processes are the result of action of two types of forces:
  1. Endogenetic Forces
  2. Exogenetic Forces

• Endogenetic forces or processes: The energy which comes out from inside of the earth are the main force behind endogenic processes. This energy which is generated inside the earth is mostly due to radioactive processes, rotational and tidal friction and primordial heat from the origin of the earth. This endogenic forces or processes induces diastrophism and volcanism in the lithosphere. Endogenic forces causes endogenic movements which can be classified into two categories:
  1. Sudden Movements (Quick movements).
  2. Diastrophic Movements (Slow movements).
• Sudden Movements: It includes earthquakes and volcanic eruptions etc. These sudden movements and their effects are very quick. However energy which drives these movements was built up in a long period. Geologically these sudden forces are also known as constructive forces because they construct or create new land forms on the earth’s surface. We will discuss Earthquake and volcanic eruption in the next chapter as it requires a detailed analysis. Please follow the hyperlink to read about “Earthquake and Volcanic Eruption”.
• Diastrophic Movement:
  1. There are a number of processes that causes movement, elevation or building of portions of the earth’s crust. Combination of all such processes is known as Diastrophism.
  2. These are the slow force which originates inside the earth and creates both horizontal and vertical movements.
  3. Changes brought by these forces are visible only after a very long period about thousands or millions of years.
  4. Diastrophic movements are the main reason for the formation of primary landforms e.g., Mountains, Plateau, Plains, Lakes etc.
  5. Diastrophic movements can be classified into three major classes:
     1. Tectonic Movements
     2. Isostatic Movements
     3. Eustatic Movements
  6. Tectonic Movements: It is the movements of plates of the earth crust. Tectonic movements can be classified into Epeirogenic and Orogenic movements.

Folding: When compressional forces act, rock strata bends in an arch like structure. This is called folding. Folds that     bends upward is called Anticlines and the folds that bends downward is called Synclines.

• Isostasy:
  1. In geology isostasy is defined as the state of gravitational equilibrium between lithosphere and asthenosphere.
  2. Isostatic movement is the vertical movement of the earth’s crust.
  3. Since the earth’s lithosphere and asthenosphere are in a gravitational equilibrium any extra weight put on earth’s lithosphere may result into its downward movement (Isostatic fall) and again when the weight is removed it results in rise of lithosphere (Isostatic rise).
  4. The last isostatic movement was happens during ice age. During ice age whole lithosphere was covered by a thick layer of ice. This large mass of ice put heavy pressure on lithosphere. Hence due to this:
     1. Sea level falls due to freezing of water on land.
     2. Lithosphere falls due to heavy pressure put by frozen ice on it.
  5. However when ice age finished, ice on lands melts and relieves the lithosphere from its weight and hence lithosphere moves upward (isostatic movement) and sea level also rises (Eustatic movement).
• Eustatic movement: It is the worldwide movement of sea level which happens due to change in the total volume of liquid sea water. It happens by formation of mid-oceanic ridges or enclosing of ocean basin due to movement of plates towards each other.
• It should be noted that the combination of orogeny, epeirogeny, earthquake and plate tectonics causes pressure, volume and temperature (PVT) changes and this PVT changes induces metamorphism of rocks.