Exogenic and Endogenic Forces: Gradation, Degradation and Aggradation
Geography › Geomorphic Processes and Landform Evolution · Topic 3.11
The surface of the Earth is shaped by two sets of forces. Endogenic forces arise inside the Earth, driven by its internal heat, and build up relief through folding, faulting, volcanism and earthquakes. Exogenic forces act at the surface, driven by solar energy and gravity through water, wind, ice and waves, and wear relief down. Gradation is the levelling of land by exogenic action; it includes degradation, the lowering of land by weathering and erosion, and aggradation, the raising of low areas by deposition.
5 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution
At a Glance
- Endogenic Internal heat; builds relief
- Exogenic Sun and gravity; wears relief down
- Gradation Levelling of the land
- Degradation Lowering by weathering and erosion
- Aggradation Raising by deposition
- Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution
Where Does It Fit?
This topic opens the second part of the macro, which turns from sudden events like earthquakes and volcanoes to the continuous forces that sculpt the land. It sets the framework used by every topic on landforms that follows. Previous topic: Tsunami: Mechanism, Properties and Effects. Next topic: Endogenic Processes: Diastrophism, Orogenic and Epeirogenic Processes.
What Are Endogenic Movements?
In short: endogenic movements are internal forces that raise, fold, break and shift the crust.
The surface of the Earth is shaped by two sets of forces. Endogenic forces originate inside the Earth and mostly build relief, creating mountains, plateaus and basins, while exogenic forces act at the surface and wear relief down. The endogenic forces are driven by heat in the interior, which comes mainly from the decay of radioactive elements and from the residual heat of the formation of the planet. Geomorphic movements are of two kinds. Sudden movements, such as earthquakes and volcanic eruptions, produce rapid changes. Slow movements, called diastrophism, work over thousands to millions of years. The structure of the interior that powers them is described in Internal Structure of the Earth: Crust, Mantle, Outer Core, Inner Core.
What Are Exogenic Processes and Denudation?
In short: exogenic processes are the surface forces that wear down what endogenic forces build.
Exogenic processes take their energy from the Sun and from gravity. The Sun provides heat that drives the atmosphere and the water cycle, and gravity pulls material downslope. The action of these forces in lowering and levelling the land is called denudation, which literally means stripping off. The aim of the processes is to bring the surface to a common level, called gradation. Denudation has four parts: weathering, mass movement or wasting, erosion and transportation. The agents of erosion and transport are running water, groundwater, glaciers, wind and waves. These processes are examined in Soil Erosion and Conservation and in the topics on landforms that follow in this subject.
How Do Endogenic and Exogenic Forces Compare?
| Feature | Endogenic forces | Exogenic forces |
|---|---|---|
| Energy source | Heat of the Earth’s interior: radioactivity and residual heat | Solar energy (insolation) and gravity |
| Direction of action | Build up relief | Wear down relief |
| Speed | Mostly slow; some sudden (earthquakes, eruptions) | Mostly slow; some sudden (landslides, floods) |
| Processes | Diastrophism (folding, faulting), volcanism, earthquakes | Weathering, mass movement, erosion, transport, deposition |
| Result | Mountains, plateaus, rifts, volcanoes | Valleys, plains, deltas, dunes, coasts |
| Scale | Large (continental) | Local to regional |
The endogenic forces are classed as sudden (volcanoes and earthquakes) and slow (diastrophism). The Earth is shaped by the long contest between the two: mountains rise by plate collision and are worn down by water and ice, and the debris builds plains and deltas.
What Are Gradation, Degradation and Aggradation?
- Gradation: the overall process by which exogenic forces level the land surface towards a base level, which is the lowest level to which a stream can erode, normally sea level.
- Degradation: the lowering of high ground by weathering, mass movement and erosion. Rivers cut valleys, glaciers scour troughs and winds hollow out basins.
- Aggradation: the raising of low ground by deposition of the eroded material, as in deltas, floodplains, dunes, moraines and beaches.
Erosion and deposition are two sides of the same coin: the sediment taken from the mountains is laid down as plains. The Ganga plain, for instance, is a thick aggradation of sediments from the Himalaya. The whole sequence is described in Exogenic Processes: Denudation, Weathering, Mass Movements, Erosion, Transportation, Deposition.
What Are the Geomorphic Agents?
| Agent | Mainly acts in | Typical landforms |
|---|---|---|
| Running water | Humid regions | Valleys, gorges, floodplains, deltas |
| Groundwater | Limestone regions | Caves, sinkholes, stalactites |
| Glaciers | Cold highlands and polar regions | Cirques, U-valleys, moraines |
| Wind | Deserts | Dunes, deflation hollows, mushroom rocks |
| Waves and currents | Coasts | Cliffs, stacks, beaches, spits |
An agent is any mobile medium that can pick up, carry and put down material. Each leaves a recognisable set of landforms, which are taken up in the topics from Wind (Aeolian) Erosional Landforms: Pediments, Pediplains, Playas, Deflation Hollows, Mushroom Rocks to Coastal Depositional Landforms: Beaches, Dunes, Bars, Barriers, Spits. The relief that results also depends on the rock, as in Relationship Between Rocks and Landforms.
As an analytical point, the present landscape records a balance between uplift and wear. Where uplift is faster, as in the young Himalaya, relief is high and steep. Where uplift stopped long ago, as in the Aravalli, relief is low and rounded.
Why Is This Topic Important?
- Framework Basis for all landform topics
- Terms Gradation terms are asked
- Balance Uplift versus wear
What Came Next?
The next topic looks at the endogenic processes in detail: diastrophism, and orogenic and epeirogenic movements. Next topic: Endogenic Processes: Diastrophism, Orogenic and Epeirogenic Processes.
Key People and Terms
- Endogenic force Force arising inside the Earth
- Exogenic force Force acting at the surface
- Gradation Levelling of land
- Degradation Lowering by erosion
- Aggradation Building up by deposition
- Base level Lowest level of stream erosion
Exam Corner
Points to Remember
- Endogenic forces build; exogenic forces wear down.
- Energy for exogenic forces: Sun and gravity.
- Gradation = degradation + aggradation.
- Base level is generally sea level.
- Volcanoes and earthquakes are sudden endogenic events.
Do Not Confuse With
- Degradation and aggradation Lowering versus raising of land
- Endogenic and exogenic Inside versus surface forces
- Gradation and gradient Levelling process versus slope
Memory Hook
Inside builds, outside wears; degrade takes down, aggrade lays down.
Mains Angle
Questions ask how the two sets of forces shape relief together. These points add depth.
- Balance Uplift versus wear
- Agents Water, wind, ice, waves
- Human role Dams, mining, urbanisation
A Question You May Face
An original practice question, not a past paper question.
“Distinguish between endogenic and exogenic forces and explain how they together shape the relief of the Earth.”
How to Answer
- Define Both sets of forces.
- Compare Energy and results.
- Gradation Degradation and aggradation.
- Example Himalaya and Ganga plain.
GS Relevance
Frequently Asked Questions
What are endogenic forces?
Endogenic forces are the forces that arise inside the Earth, driven by its internal heat. They build up relief by folding, faulting, volcanic eruptions and earthquakes. Some act suddenly, like earthquakes and eruptions, and others very slowly, like the uplift of mountains by plate collision.
What are exogenic forces?
Exogenic forces act at or near the surface of the Earth and are driven by solar energy and gravity. They include weathering, mass movement, erosion, transportation and deposition by running water, wind, glaciers, waves and groundwater, and they wear down the relief created by endogenic forces.
What is gradation?
Gradation is the overall levelling of the land surface by exogenic processes. It has two parts: degradation, which lowers high ground by weathering and erosion, and aggradation, which raises low ground by depositing eroded material, so that relief tends towards the base level of erosion.
What is the difference between degradation and aggradation?
Degradation is the lowering of the land by weathering, mass movement and erosion, as when a river cuts a valley. Aggradation is the building up of land by deposition of the eroded material, as in the formation of deltas, floodplains and dunes.
What is meant by base level?
Base level is the lowest level to which a river or other agent can erode the land. For most rivers it is sea level, which is the general base level, while lakes or resistant rock layers can serve as local base levels, above which the river cannot cut down.
PYQ Practice — Statement Analysis
1 Exogenic forces derive their energy mainly from the Sun and gravity.
Endogenic forces come from internal heat.
2 Aggradation is the lowering of land by erosion.
It is the raising of land by deposition.
3 Volcanism is an endogenic process.
It arises from the Earth's interior.
4 Gradation is the sum of degradation and aggradation.
Both level the land.
Past Mains Questions on This Topic
This topic comes under Geomorphic Processes and Landform Evolution. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
Related Topics
Browse the full Geography index