W D Thornbury Principles of Geomorphology

 Geomorphic processes leave their distinctive imprint upon landforms, and each geomorphic process develops its own characteristic assemblage of landforms.

• Process applies to the many physical and chemical ways by which the earth’s surface undergoes modification.

• Include endogenetic processes (diastrophism, volcanism etc.) and exogenetic processes (weathering, mass wasting, erosion etc.)

• Former tend to build up areas and latter tend to wear down.

• Individual distinctive features of landforms depend on the geomorphic process responsible for their development.

• Eg: Stream action (flood plains, alluvial fans, deltas etc.)

Ground water (sinkholes, poljes etc)

Glaciers (end moraines, drumlins etc.)

• Davis use this distinctiveness to genetically classify the landforms as Youth, Mature and Old.

• Davis models in Fluvial cycle, Glacial cycle, Arid cycle etc. upholds the above principles.

• However, Most of the landscapes are the products of a group of processes.

• Poly cyclic landforms like uplifted peneplains, valley in valley topography, which are most common in majority of the landscapes contradicts the above notions of single cycle

• Pleistocene glaciation left little evidences as erosional surfaces on the earth for denudation chronology.

• Similarly the structural school of geomorphic studies does not concur with the above views.

• Dynamic Theory proponents like J T Hack and Strahler rejects the concept of cyclical evolution.