The term process applies to the many physical and chemical ways by which the earth surface undergoes modification. Some processes such as vulcanisim, diastrophism originate from the interior of the earth’s crust and some processes such as weathering, mass wasting and erosion exterior of the earth surface, are termed as endogenetic force and exogenetic force respectively. All these individual processes leave their stamp upon the earth’s surface is rather recent. Just as species of plants and animals have their diagnostics characteristics, so land forms have their individual distinguishing features dependent upon the geomorphic process responsible for their development. Floodplains, alluvial fans and deltas are products of stream actions; sinkholes and caverns are produced by groundwater; and end moraines and drumlins in a region attest to the former existence of glaciers in that area.
A proper appreciation of the significance of process in land form evolution not only gives a better picture of how individual land forms but also emphasizes the genetic relationships of land form assemblages. Land forms are not haphazardly developed with respect to one another but certain forms may expected to be associated with each other.
Landscape evolution is more complex than simplicity. Most of the topographic details have been produced during the current cycle of erosion, but, there may exist within an remnants of features produced during prior cycle and although there are many individual landform which can be said to the product of some single geomorphic process, it is a rare thing of find landscape assemblages which be attributed solely to one geomorphic process, even though commonly we are able to recognize the dominance of one. Thus, Horgberg(1952) did, in five major categories.
1) simple,2)compound,3)monocyclic,4)multi cyclic,5)exhumed or resurrected landscape.
These are those which are the product of a single dominant geomorphic process.
These are those in which two or more geomorphic processes have played major roles in the development of the existing topography, for example, if we take the case of a region having sedimentary rocks consisting of alternate bands of resistant and soft rock beds and river as agent of erosion, the differential fluvial erosion will give birth to stepped landscapes. Simple landscape is not the result of a single geomorphic process but for simplification and generalization the most dominant process is given due importance landscape development. Compound landscape is more common than simple landscape. Present example of compound landscape as glacial geomorphic features are found at higher altitude while fluvial landscape are found at lower levels. Several compound landscapes are seen in New Maxico, Arizona, Neveda, where volcanic cones and related volcanic landforms and lava flow related features have developed in fluvially originated river valleys.
These are those that bear the imprint of only one cycle of erosion. It is also less common in reality. It generally developed over volcanic cones, lava plains and lava plateaus, newly formed domes etc.
Produced during more than one erosion cycle. The landforms of older cycles are not found in their original forms because they are modified by succeeding phases of cycle of erosion and hence only relic features of older cycles are preserved. Multicyclic landscape can be identified on the basis of a few diagnostic and representative landforms e.g valley in valley, topography, rejuvenated river valley topography, uplifted peniplains etc. Appalachian highland of USA present fine example of multicyclic landscapes which have developed because of three successive cycle of erosion. The Damodar river valley in Hazaribagh and the Narmoda valley represent ideal example of rejuvenated valleys having terraces on either side.
These are those that were formed during same past period of geologic time, then buried some soft cover and then within more recent geologic time exposed through removal of the cover. For example; many of the landscapes were buried under lava sheet in Peninsular India during Cretaceous vulcanicity and a few of them have now been exhumed due to erosion of lava cover.
Read about Hypothesis related to Origin of the erth by Kant,