The endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in the configuration of the surface of the earth are known as geomorphic processes. Diastrophism and volcanism are endogenic geomorphic processes.
A process is a force applied on earth materials affecting the same. An agent is a mobile medium (like running water, moving ice masses, wind, waves and currents etc.) which removes, transports and deposits earth materials. Running water, groundwater, glaciers, wind, waves and currents, etc., can be called geomorphic agents.
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.