Geomorphic Processes

The earth’s surface is uneven, and that unevenness is not a one-time accident of creation. It is the product of two opposing sets of forces that have been at work for hundreds and thousands of years and continue to operate today. The crust is dynamic — it has moved and still moves, both vertically and horizontally, though it moved faster in the past than it does now. The internal forces building up the crust from within the earth created the original variations in the outer surface. But the surface is also being continuously acted upon by external forces, driven basically by energy from sunlight. So the earth’s surface is subjected to two kinds of forces: external forces originating within the earth’s atmosphere, called exogenic forces, and internal forces from within the earth, called endogenic forces.

The actions of exogenic forces result in two broad effects: wearing down of relief and elevations (degradation) and filling up of basins and depressions (aggradation). The phenomenon of wearing down of relief variations of the earth’s surface through erosion is known as gradation. But the endogenic forces continuously elevate or build up parts of the earth’s surface, and because of this the exogenic processes fail to even out the relief variations completely. So variations remain as long as the opposing actions of exogenic and endogenic forces continue. In general terms, endogenic forces are mainly land-building forces, and exogenic processes are mainly land-wearing forces.

The surface of the earth is sensitive. Humans depend on it for sustenance and have been using it extensively and intensively. It is essential to understand its nature in order to use it effectively without disturbing its balance and diminishing its potential for the future. Almost all organisms contribute to sustaining the earth’s environment, but humans have caused extensive damage through overuse of resources. Use we must, but we must also leave it with enough potential to sustain life through the future. Most of the earth’s surface has been shaped over very long periods of time — hundreds and thousands of years — and because of its use and misuse by humans, its potential is being diminished at a fast rate. If the processes that shaped and are shaping the surface into varieties of forms, and the nature of the materials it is composed of, are understood, precautions can be taken to minimise the detrimental effects of human use and to preserve the surface for posterity.

Geomorphic Processes

The endogenic and exogenic forces cause physical stresses and chemical actions on earth materials, bringing about changes in the configuration of the surface of the earth. These are known as geomorphic processes.

• Diastrophism and volcanism are endogenic geomorphic processes. These were discussed in brief in the preceding unit.
• Weathering, mass wasting, erosion and deposition are exogenic geomorphic processes. These are dealt with in detail in this chapter.

Geomorphic Agents

Any exogenic element of nature — like water, ice, wind, etc. — capable of acquiring and transporting earth materials can be called a geomorphic agent. When these elements of nature become mobile due to gradients, they remove materials, transport them over slopes, and deposit them at lower levels.

Geomorphic processes and geomorphic agents, especially exogenic, are one and the same unless stated separately. But there is a useful distinction to make:

Running water, groundwater, glaciers, wind, waves and currents, etc., can all be called geomorphic agents.

The Role of Gravity …