The formation and deformation of landforms on the surface of the Earth is a continuous activity of two broad processes i.e. internal and external. These processes cause stress and deformation on Earth materials and finally bring changes on the surface of the Earth. These are referred as Geomorphic Processes.
The forces that act from the Earth’s interior towards the Earth’s surface are called Internal processess or Endogenetic processes. These forces build the landscape and create topographic relief.
The forces that act on the surface of the Earth due to natural agents like running water, glacier, wind, waves etc. are called External processes or Exogenetic processes. These external processes tear the landscape down into relatively low elevated plains.
The internal processes generate heat and eject materials from deep below the Earth’s crust. Internal radioactivity is the principal source of power for this process.
1. Plate Tectonics
The lithosphere is divided into a number of huge slabs of rocks called ‘Tectonic plates.’ These tectonic plates are divided into major and minor plates. These plates float independently over the mantle. Collisions of these plates produce mountain ranges and other irregular surface features, both on land and the ocean floor. This phenomenon is called ‘plate tectonics’. The movement of tectonic plates is due to thermal energy from the mantle. Now we have a better understanding about the plate movements and its relation to Earthquake and volcanic activities.
Types of Plate Boundaries:
Convergent Boundary – Here the plate moves toward each other and sometimes, a plate sinks under another. The location where the sinking of a plate occurs is called a subduction zone.
Divergent Boundary – Here the plates pull away from each other as magma pushes up from the mantle.
Transform Boundary – Here the plates slide horizontally past each other.
Movements of Continental Plates:
Due to lateral compressional forces, the plates are forced to move upwards and downwards. This is called ‘Folding’. Mountains formed by folding are called fold mountains. the Process of folding creates lofty mountain ranges such as the Himalayas and the Alps.
The movement of plates also create stress and tension in the rocks, causing them to stretch and crack. This is called ‘Faulting’. The great rift valley of East Africa is a notable example for the process of faulting. The process of folding and faulting together with volcanoes and Earthquakes continually reshape the continents and seafloor.
According to plate tectonics, the plates are in constant motion with an average rate of few centimetres per year. The movement might seem slow, but over millions of years, the plates and the continents riding on them move a long way. For example, about 250 million years ago, the Indian Plate was a part of the Gondwana land, which comprised of modern Africa, Australia, Antarctica, and South America.
Approximately 140 million years ago, the Indian plate broke away from the ancient super continent ‘Gondwana’ and began moving north and collided with Asia. The collision with the Eurasian Plate along the boundary between India and Nepal formed the Oro-genic belt that created the Tibetan Plateau and the mighty Himalayan Mountains.