The earth’s crust is constantly undergoing geological changes caused by Endogenic (internal) forces which create new relief features. Meanwhile Exogenic (external) forces are working vigorously to wear away the surface.

The various internal forces that help in formation of various landforms are Orogenesis, Folding and Faulting, volcanic disturbances.

Orogenesis  is the process of building new mountain ranges by the convergence of tectonic plates. This takes place by ocean-continent collision (e.g., the Andes), continent-continent collision (the Alps and the Himalayas), or island arc-continent collision (e.g., New Guinea). All these tectonic processes create sedimentary basins of various types.

Folding: A fold can be defined as a bend in rock that is the response to compressional forces. Folds are most visible in rocks that contain layering. It causes uplift of particular area. The simplest type of fold is called a monocline. This fold involves a slight bend in otherwise parallel layers of rock. An anticline is a convex up fold in rock that resembles an arch like structure with the rock beds (or limbs) dipping way from the center of the structure.

Faulting causes depression of particular areas. These faults are named according to the type of stress that acts on the rock and by the nature of the movement of the rock blocks either side of the fault plane. Normal faults occur when tensional forces act in opposite directions and cause one slab of the rock to be displaced up and the other slab down. Reverse faults develop when compressional forces exist. Compression causes one block to be pushed up and over the other block. A graben fault is produced when tensional stresses result in the subsidence of a block of rock. On a large scale these features are known as Rift Valleys. A horst fault is the development of two reverse faults causing a block of rock to be pushed up.

Volcanic disturbances also modify the landscape. It is release of hot magma from earth’s surface due to convectional cells operating underneath giving rise to features such as batholiths, phacoliths etc. underneath and volcanic mountains above earth’s surface.

The various external forces that working against constructive forces are weathering, erosion, transportation and depositing.

• Weathering: The gradual disintegration of rocks by atmospheric or weathering forces. They are of two kinds

1. Chemical Weathering: basic process by which denudation occurs. Extremely slow and gradual decomposition of rocks due to exposure to air and water. Solution, Oxidation and Decomposition by Organic Acids are few processes.
2. Physical or Mechanical weathering: physical disintegration of a rock by the actual prising apart of separate particles. Repeated temperature changes, Repeated wetting and drying, Frost action and Biotic factors are processes.

• Erosion: The active wearing away of the earth’s surface by moving agents like running water, wind, ice and waves. Example: formation of waterfalls, rapids, sea caves, sprayholes.
• Transportation: the removal of the eroded debris to new positions. Various types include mass movements like Soil Creep, Landslides. Example: Formation of Sand dunes in deserts, Barchans etc.
• Deposition: the dumping of the debris in certain parts of the earth, where it may accumulate to form new rocks. Example: Beaches

Anthropogenic activities, Climate change, global warming are further increase the pace of the external forces. Example: The deforestation helps in quickening the Erosion process leading to quicker denudation.

Conclusion: The interaction of these constructive and destructive forces gives rise to great diversity of present day landforms.