Hierarchy of Landforms - Salisbury's Classification
The search for geography as a systematic science resulted in simplification which in geomorphology was done by Salisbury. He classified landforms into a hierarchical order based on their scale and formation processes.
SALISBURY'S CLASSIFICATION OF LANDFORMS
Salisbury classified the landform into:
1. Relief Features of 1st Order
This includes two major features Continental Platforms and Ocean Basins. The first order relief features are stable in the geological history of the earth, though there are some small scale changes in their forms, boundaries and geographical location.
2. 2nd Order of Relief Feature
2nd order relief features are superimposed on the 1st order relief features. Some of the examples are Mountains, Plateau, Plains on the continental landmass and mid oceanic ridges, sea-mounts are present on the ocean basins.
The 2nd order relief features are mainly formed due to endogenetic forces specially diastrophism and volcanic activities. Though some 2nd order relief features such as plains may be caused due to exogenetic process.
3. 3rd Order Relief Feature
The smaller features which develop on 2nd order relief features due to exogenetic agents are known as 3rd order relief feature. The process of denudation which includes both weathering and erosion are responsible for such lesser features.
The 3rd order relief features are depositional or destructional landform or aggradational landforms. This landforms have been carved by external forces very slowly and it has taken millions of years for such landforms.
The most important scope of geomorphology lies in studying and analysing the 3rd order of relief features which was done by Davis, Penck and L.C.King.
2ND LAW OF GEOMORPHOLOGY is Landform in any area is an outcome of Structure, Process and Time
OR
The external agents of erosion act upon the earth to produce an orderly sequence of landforms.
This is a famous "Davisian" concept of geomorphic cycles in which landforms like living organisms pass through the stage of Youth, Mature and Old.
In the youthful stage the landforms are steep and hence erosion dominates resulting in formation of features such as deep and narrow V-shaped valleys such as gorges and canyons.
As the height of landform decreases the erosional capacity of external force decreases giving rise to a convexo-concave featureless surface, which Davis called as peneplain.
The formation of a featureless flat peneplain depends upon dynamic interaction of structure, process and time.
Structure
Structure includes arrangement of the rock, shape as well as mineral composition of rock, nature of the rock in the form whether the rock is compact or jointed. Structure also includes fold, fault etc.
Process
Process includes both endogenetic and exogenetic force. The external forces are regulated by the gravity which causes movement of the material on the surface of the earth in the form of rivers, glaciers, tides etc. This movement causes denudation and these sediments are then transported from higher height to lower height, which causes reduction of relief.
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| Note:-AI-generated diagram for educational purposes only |
The nature and intensity of the geomorphic processes is determined by climatic factors which include both present as well as past climatic condition.
Time or temporal factor
Time or temporal factor plays an important role because climate or process as well as the position of the continents and landforms change with time, but Davis over emphasized on the time as the most important factor, and hence was criticized by subsequent geomorphologists.
Because for the Davisian concept of time to be most important earth's crust has to be stable which is very far away from reality. In Geomorphology the law is the only thing that is permanent is change which shows that endogenetic and exogenetic processes will act continuously changing the landform and hence for Davis to be correct there has to be no change which is not possible in the dynamic Earth's surface.
Geological structure is a dominant control factor in the evolution of landform and is reflected in them.
This is a major criticism of Davisian school which over emphasized on stage or time. Numerous studies have proved the importance of process and structures in the development of landform.
The structure of rock is determined by endogenetic forces such as folds, fault, mineral composition as well as chemical properties of the rock.
Structure also includes presence or absence of joints, size of the rocks, slope of the rock as well as hardness present in the minerals of rocks.
Based on the structure rocks are classified into Hard/Resistant Rock and Soft/Non-Resistant Rocks.
The geomorphic processes will act differently on the rocks having different structures in a sense that resistant rock/hard rock will be weathered very slowly while a soft rock will be weathered quickly.
Which geomorphic processes act on rock is also determined by the structure for example limestone or calcium rich rocks is a hard rock in dry climatic condition while it is very weak rock in hot and humid climatic condition.
Examples Supporting Structural Control:
The peninsular plateau which is one of the oldest rock in the world, and hence termed as Shield, shows an evidence of dominance of metallic mineral which are highly resistant to erosion and hence rivers flow sluggishly through shallow valleys.
On the other hand the Himalayan rivers formed deep V-shaped valley carrying huge sediment load and forms numerous ox-bow lakes and meanders due to soft strata or rocks.
Thus structure and processes interact to give shape to the landforms, but even process dominating on the landform is determined by structure.
Geomorphic processes operate at different rates and therefore earth has different relief features
To a large degree earth surface possesses relief because the geomorphic processes operate at different rates.
The earth has different relief feature in the form of mountains, plateau, plains or the shape of rocks differ because the intensity and the type of geomorphic processes vary from region to region. This variation may be due to different climatic condition or due to structure.
The processes operate with varying intensity because lithology or rock structure changes. The hard rock is eroded easily if the speed of a river is greater which is observed in mountainous region. On the other hand the same hard rock will be more resistant to erosion in the plain dividing the river channel and hence the relief will be different.
The processes may also differ because of changes in the climatic conditions. Hot and humid climate cause more weathering and erosion of the rock and therefore the topography or relief is generally flat while the cold climate will have comparatively higher topography because of less weathering.
As the climatic condition changes which may be due to shifting of continent or due to height the processes operating may be different and therefore relief feature will be different.
Role of Endogenetic and Exogenetic Processes
The difference in the relief features on the earth surface is not due to processes alone but also due to the structure. But the entire landform on the earth surface is an outcome of either endogenetic process or exogenetic process.
The endogenetic processes such as volcanism will increase the height of landform to build up mountain valleys and the exogenetic process will destroy this landform to form featureless plain. Thus each geomorphic process develops its own characteristic on the landforms.
QUESTON:-COMPLEXITY OF GEOMORPHIC EVOLUTION IS MORE COMMON THAN SIMPLICITY
Most of the topography of the earth has been produced due to numerous cycle of erosion. There are very few landform which are an outcome of only a single cycle of erosion.
The landforms are classified into:
1. Simple landform
2. Compound landform
3. Monocyclic landform
4. Polycyclic/Multicyclic landform
5. Exhumed/Resurrected landform
1. Simple Landform
Simple landform are the product of only one geomorphic process.
2. Compound Landform
Compound landform are the product of two or more geomorphic processes. All the landforms in the world are compound landform because sometimes water act while during the dry season wind or glacier may act.
3. Monocyclic Landforms
Monocyclic landforms are those which are produced during a single cycle of erosion. Monocyclic landscape are extremely rare and very localised restricted to newly created landscape.
4. Polycyclic/Multicyclic Landform
Polycyclic/multicyclic landform are very common because majority of world has gone through more than one cycle of erosion. This is due to:
(a) Fluctuation in the climatic condition such as alternate warm period followed by period of glaciation.
(b) Many older landforms have more than one cycle of erosion because of change in the sea level and subsequent river rejuvenation i.e increase in the erosion capacity of a river or in other words old topography become young again.
- Incised/Entrenched meanders
- Valley in Valley Topography
- Knick point falls
- Uplifted peneplain
5. Exhumed/Resurrected Landform
These are ancient landforms that have been buried and later re-exposed by erosion.
Conclusion
Due to the dynamic nature of earth surface along with changes in the climate position of the continents have contributed to the complexity of geomorphic processes.
Why This Topic is Important for UPSC
The hierarchy of landforms and geomorphic cycles form a fundamental part of Physical Geography. Understanding Salisbury's classification and the structure-process-time framework is crucial for UPSC Prelims, Mains (GS-I) and State PCS examinations.
Prepared by Study Indepth | For UPSC and State PCS
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We hope these notes helped you understand the hierarchy of landforms and complexity of geomorphic evolution for UPSC and other competitive exams. Keep studying and stay consistent!
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