Processes that shape the earth: Part I – A presentation by ACWADAM

This presentation by ACWADAM on processes that shape the earth attempts to understand the irregularities of the surface of earth so as to consider the movement of groundwater. The earth’s surface is dotted with what is commonly perceived as high grounds or ‘hills’ and the low grounds or ‘valleys’. Hills and valleys result from movements in the earth and the long term processes of breaking-down the earth surface at some places and building it up at others, also called as diastrophism.  

The presentation deals with the formation of landforms. The primary irregularities of surface/relief are formed by tectonic movements in the area. The moment the surface is exposed to the atmosphere various agencies of diastrophism start operating. The strength of the agencies of wear and building depends on tectonics and climate. The processes that wear down the irregularities are weathering and erosion. They operate simultaneously and at times are difficult to differentiate.

There are two kinds of erosion and weathering – mechanical and chemical. In mechanical process, the rock destroyed does not change, other than getting broken into smaller size. In chemical process, the rock essentially breaks into different chemical units where some may go into solution. Mechanical process is common in extreme climates e.g. very cold or very hot and dry weather. Those rocks which are formed at high temperature and pressure are generally out of equilibrium at normal surface temperatures. So they tend to break up chemically faster than those that are formed at comparatively lower temperatures and pressures. 

Agents of weathering are mainly temperature and moisture/water. All the agents of weathering and erosion work simultaneously and it is difficult to separate them. Products of weathering and erosion indicate the comparative roles they have played. A combination of erosion and weathering along with the relief helps in understanding the development of landforms and surfaces. The agents, erosion and weathering, are also the agents of deposition. Thus, complex play of various agents, form and shape the earth’s surface.

This presentation is part of the training modules on planning, development and management of groundwater with special reference to watershed management programmes by ACWADAM. Please write to ACWADAM at acwadam@vsnl.net for sourcing these presentations.