Though the surface of earth appear to be static the interior of the earth is in a dynamic state and this dynamism of the earth results in endogenetic movements.
The Movements of the earth
- The surface of the earth is dynamic. It has been moving vertically and horizontally.
- Since the origin of the earth, there have been major changes in the distribution of continents and oceans.
- The earth has experienced innumerable earth movements which have brought about vast changes in its surface.
- The lithosphere is broken into a number of plates known as the Lithospheric plates.
- The movement and interaction of these plates cause changes on the surface of the earth.
- The forces which act in the interior of the earth are called as Endogenetic forces and the forces that work on the surface of the earth are called as Exogenetic forces.
- In general terms, the endogenetic forces are mainly land building forces and the exogenetic processes are mainly land wearing forces.
- The actions of exogenetic forces result in wearing down (degradation) of relief. But, the endogenetic forces continuously build up parts of the earth s surface and hence the exogenetic processes fail to even out the relief variations of the surface of the earth.
- So, variations remain as long as the opposing actions of exogenetic and endogenetic forces continue.
- The endogenetic and exogenetic forces that bring about changes in the configuration of the surface of the earth through physical and chemical actions on earth materials are known as geomorphic processes.
- Diastrophism and volcanism are endogenetic geomorphic processes.
- Weathering, mass wasting, erosion and deposition are exogenetic geomorphic processes.
Endogenetic geomorphic processes
- The energy emanating from within the earth is the main force behind endogenetic geomorphic processes.
- This energy is mostly generated by radioactivity, rotational and tidal friction and primordial heat from the origin of the earth.
- This energy due to geothermal gradients and heat flow from within induces diastrophism and volcanism in the lithosphere.
- Due to variations in geothermal gradients and heat flow from within, the action of endogenetic forces are not uniform and hence the tectonically controlled original crustal surface is uneven.
- As explained above, diastrophism, volcanism and earthquake are the endogenetic geomorphic processes
- Endogenetic forces sometimes produce sudden movements and at the other times produce slow movements.
- Sudden movements like earthquakes and volcanoes cause mass destruction over the surface of the earth.
- While diastrophic movements are rather slow. Diastrophism refers to deformation of the Earth's crust, and more especially to folding and faulting.
The movement which bring about changes in the Earth s crust gradually taking hundreds or thousands of years and which cover a period much longer than a human life span are called slow movements. These movements act on the earth s crust either vertically or horizontally.
Diastrophism is included within slow movements. All processes that move, elevate or build up portions of the earth s crust come under diastrophism. They include:
- Orogenic processes
- Epeirogenic processes
Through the processes of orogeny, epeirogeny, there can be folding, faulting and fracturing of the crust. All these processes cause pressure, volume and temperature (PVT) changes which in turn induce metamorphism of rocks.
- Epeirogeny is a continental building process.
- Due to epeirogeny, there may be mild deformations of the surface of the Earth.
- Epeirogenic processes involve uplift or warping of large parts of the earth s crust.
- Epeirogenic or continent forming movements act along the radius of the earth; therefore, they are also called radial movements.
- Their direction may be towards (subsidence) or away (uplift) from the centre.
- The results of such movements may be clearly defined in the relief.
- Orogeny is a mountain building process.
- Orogenic processes involve severe folding and affecting long and narrow belts of the earth s crust.
- In contrast to epeirogenic movement, orogenic movement is a more complicated deformation of the Earth's crust
- Orogenic processes are associated with crustal thickening, notably associated with the convergence of tectonic plates.
- Orogenic processes may push deeply buried rocks to the surface.
- If the orogeny is due to the colliding of the two continental plates, very high mountains can result. E.g. Himalayas.
Contrary to the slow movements, there are certain movements which bring about abrupt changes in the crust. The examples of such movements are volcanic eruptions and earthquakes.
- Earthquakes refer to trembling of the earth surface due to a sudden release of energy from within the earth s interior along a fault line or weak zone.
- Earthquake can occur at any time of the year, day or night. Its impact is very sudden.
- The place in the crust where the movement starts is called the focus. The place on the surface above the focus is called the epicentre.
- A sudden release of energy creates a vibration of the earth surface
- Vibrations travel outwards from the epicentre as earthquake waves.
- These earthquake waves create mass destruction on the earth surface.
- The greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.
- A volcano is a vent in the earth s crust through which molten material erupts suddenly toward the earth s surface.
- Volcanism is responsible for formation of many intrusive and extrusive volcanic forms.
- Volcanoes are classified on the basis of nature of eruption and the form developed at the surface. Major types of volcanoes include - Shield Volcanoes, Composite Volcanoes, Caldera, Flood Basalt Provinces and Mid-Ocean Ridge Volcanoes
Batholiths - A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes.
Laccoliths - These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below. These are located at deeper depths.
Lopolith is a saucer shape intrusive form, concave to the sky body.
Phacolith - These are lense shaped intrusive mass formed by the solidification of lava either on the crest of anticline or trough of the syncline.
SillsorSheets - These structures are formed by the solidification of lava in a surface parallel to the earth's surface. The thinner ones are called sheets whereas the thick ones are called sills.
Dykes - These are a wall-like structure formed by the solidification of lava perpendicular to the surface of the earth.