The interaction of matter and temperature generates these forces or movements inside the earth’s crust. The earth movements are mainly of two types: diastrophism and the sudden movements.
The energy emanating from within the earth is the main force behind endogenic 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.
Diastrophism
Diastrophism is the general term applied to slow bending, folding, warping and fracturing.
Wrap == make or become bent or twisted out of shape, typically from the action of heat or damp; make abnormal; distort.
All processes that move, elevate or build up portions of the earth’s crust come under diastrophism. They include:
orogenic processes involving mountain building through severe folding and affecting long and narrow belts of the earth’s crust;
epeirogenic processes involving uplift or warping of large parts of the earth’s crust;
earthquakes involving local relatively minor movements;
plate tectonics involving horizontal movements of crustal plates.
In the process of orogeny, the crust is severely deformed into folds. Due to epeirogeny, there may be simple deformation. Orogeny is a mountain building process whereas epeirogeny is continental building process.
Through the processes of orogeny, epeirogeny, earthquakes and plate tectonics, there can be faulting and fracturing of the crust. All these processes cause pressure, volume and temperature (PVT) changes which in turn induce metamorphism of rocks.
Epeirogenic or continent forming movements
In geology, Epeirogenic movement refers to upheavals or depressions of land exhibiting long wavelengths [undulations] and little folding.
The broad central parts of continents are called cratons, and are subject to epeirogeny.
The movement is caused by a set of forces acting along an Earth radius, such as those contributing to Isostacy and Faulting in the lithosphere
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 center. The results of such movements may be clearly defined in the relief.
Uplift
Raised beaches, elevated wave-cut terraces, sea caves and fossiliferous beds above sea level are evidences of uplift.
Raised beaches, some of them elevated as much as 15 m to 30 m above the present sea level, occur at several places along the Kathiawar, Nellore, and Thirunelveli coasts.
Several places which were on the sea some centuries ago are now a few miles inland. For example, Coringa near the mouth of the Godavari, Kaveripattinam in the Kaveri delta and Korkai on the coast of Thirunelveli, were all flourishing sea ports about 1,000 to 2,000 years ago.
Epeirogenic movement – uplift
Subsidence
Submerged forests and valleys as well as buildings are evidences of subsidence.
In 1819, a part of the Rann of Kachchh was submerged as a result of an earthquake.
Presence of peat and lignite beds below the sea level in Thirunelveli and the Sunderbans is an example of subsidence.
The Andamans and Nicobars have been isolated from the Arakan coast by submergence of the intervening land.
Epeirogenic movement – subsidence – arakan yomaEpeirogenic movement – subsidence – arakan yoma
On the east side of Bombay island, trees have been found embedded in mud about 4 m below low water mark. A similar submerged forest has also been noticed on the Thirunelveli coast in Tamil Nadu.
A large part of the Gulf of Mannar and Palk Strait is very shallow and has been submerged in geologically recent times. A part of the former town of Mahabalipuram near Chennai (Madras) is submerged in the sea.
