These geomorphic processes and plate tectonics notes for OPSC OAS cover Part 1 of the geomorphology chapter: endogenetic and exogenetic forces, Wegener's and Taylor's drift theories, sea-floor spreading, the seven major plates and their boundaries, and the fold, block, volcanic and residual types of mountains. Every sub-topic ends with the fact or example OPSC and UPSC actually test, and the page closes with previous year practice questions.
Geomorphic Processes: Endogenetic and Exogenetic Forces
Geomorphic processes are the physical and chemical processes that build and sculpture the Earth's surface. They are driven by two families of forces.
Endogenetic forces originate inside the Earth, in the crust and mantle, and build relief: diastrophism (folding, faulting, epeirogeny), volcanism and seismicity. Exogenetic forces originate outside the Earth, chiefly from solar energy, gravity and the atmosphere, and wear relief down: weathering, mass movement and erosion.
| Process | Force type | Example |
|---|---|---|
| Folding, faulting, epeirogeny | Endogenetic | Himalaya, Vosges, Tibetan Plateau |
| Volcanism, seismicity | Endogenetic | Barren Island, Bhuj 2001 |
| Weathering, mass movement, erosion | Exogenetic | Karst caves, landslides, deltas |
| Deposition | Exogenetic | Alluvial fans, moraines, loess |
OPSC 2018 asked what the processes that shape the Earth's surface are called — geomorphic processes.
Landforms are governed by what is usually called the structure–process–stage framework: the rock's composition and structure, the processes acting on it, and the time for which they have acted. Climate decides which process dominates.
- Geomorphic processes are not confined to plate boundaries; erosion and deposition operate across entire continents.
- Orogenesis is an endogenetic process, not a denudational one. Denudation is weathering + mass movement + erosion.
Continental Drift Theory: Wegener and Taylor
Alfred Wegener proposed the Continental Drift Theory in 1912 and elaborated it in his 1915 book The Origin of Continents and Oceans. He argued that all landmasses once formed a single supercontinent, Pangaea, surrounded by a single ocean, Panthalassa, which began splitting in the Carboniferous period and drifted apart.
F.B. Taylor had argued a similar case in 1910, attributing the drift to the tidal force of the Moon and Sun, and postulating two original landmasses, Lauratia in the north and Gondwana in the south.
| Feature | Wegener | F.B. Taylor |
|---|---|---|
| Year | 1912 (book 1915) | 1910 |
| Original landmasses | Pangaea, split into Laurasia and Gondwanaland | Lauratia and Gondwana |
| Driving force | Centrifugal force and tidal force | Tidal force |
| Ocean around the landmass | Panthalassa | — |
Evidence for continental drift
- Jigsaw fit: the facing coasts of South America and Africa match closely.
- Fossils: Glossopteris occurs in India, South Africa, South America, Australia and Antarctica; Cynognathus and Lystrosaurus are found across separated continents.
- Rocks of the same age and composition on opposite sides of the Atlantic, such as the Brazilian and West African Precambrian belts.
- Glacial tillites of Permo-Carboniferous age in present-day tropical regions.
- Placer deposits and coal seams of matching sequences.
- The rock evidence is of rocks of the same age, not of different ages. A statement claiming rocks of different ages is an evidence is false.
- Wegener could not explain the mechanism of drift, and his reconstructions of the pre-Carboniferous period and the drift sequence were later shown to be inaccurate.
IMAGE (Map): Break-up of Pangaea in four stages.
Labels: Pangaea (Permian, ~250 Ma), Laurasia and Gondwanaland with the Tethys Sea (Jurassic), opening of the Atlantic, present-day continents; mark the matching coastlines of South America and Africa and the Glossopteris fossil sites.
Caption: Stages in the break-up of Pangaea and drift of continents.
Find it: NCERT Class 11 Fundamentals of Physical Geography chapter on Distribution of Oceans and Continents, or Wikimedia Commons 'Pangaea break-up'.
Plate Tectonics and Sea-Floor Spreading
Arthur Holmes suggested in 1929 that convection currents in the mantle could move continents. Harry Hess proposed sea-floor spreading in 1960: new oceanic crust forms at mid-oceanic ridges, spreads laterally and is destroyed at trenches. Vine and Matthews confirmed it in 1963 through the symmetrical magnetic stripes on either side of the ridges.
- Symmetric magnetic stripes on either side of mid-oceanic ridges, recording reversals of Earth's magnetic field.
- Ocean floor is youngest at the ridges and oldest near subduction zones, and nowhere older than about 200 million years.
- Earthquake and volcano distribution follows plate margins.
- GPS measurements show plates moving a few centimetres a year.
- Palaeomagnetic and fossil evidence across continents.
The Indian Plate moves northward at roughly 5 cm per year, which continues to raise the Himalaya and makes India a seismically active region. The Pacific Plate is the largest, at about 103 million km², and moves fastest among the major plates.
| Major plates (7) | Minor plates (examples) |
|---|---|
| Pacific, North American, South American, Eurasian, African, Indo-Australian, Antarctic | Arabian, Cocos, Nazca, Philippine, Caribbean, Scotia, Juan de Fuca, Burma, Sunda |
NDA 2019 asked which is a major plate — the Pacific Plate. BPSC (Pre) 2018 asked where the Cocos Plate lies — between Central America and the Pacific Plate.
Types of plate boundaries
| Boundary | Motion | Landforms | Example |
|---|---|---|---|
| Divergent | Plates move apart; new crust forms | Mid-oceanic ridge, rift valley | Mid-Atlantic Ridge, East Pacific Rise, East African Rift |
| Convergent | Plates collide; ocean crust subducts | Trench, volcanic arc, fold mountains | Andes, Japan trench, Himalaya (continental collision) |
| Transform | Plates slide past each other; crust neither created nor destroyed | Fault line, offset streams | San Andreas Fault |
Volcanism occurs at all three settings and also at intra-plate hotspots such as Hawaii, Reunion and Iceland. The driving mechanism is now understood as a combination of mantle convection, slab pull (the sinking of cold subducting lithosphere) and ridge push. The heat itself comes mainly from radioactive decay in the mantle, not from the Sun.
Plate tectonics explains earthquakes, mountain belts and sea-floor features, but it does not explain ocean currents. Ocean currents are driven by winds, temperature, salinity and the Coriolis effect.
IMAGE (World map): Tectonic plates and their boundaries.
Labels: all seven major plates; Mid-Atlantic Ridge (divergent), East Pacific Rise, Peru-Chile Trench, Himalaya collision zone, San Andreas Fault (transform), Ring of Fire, Hawaii hotspot.
Caption: Major plates, their boundaries and the Ring of Fire.
Find it: USGS 'Tectonic plates map' or Wikimedia Commons 'Plate tectonics map'.
Mountains: Fold, Block, Volcanic and Residual
A geosyncline is a long, deep trough in which sediments accumulate; when compressed, the filled trough is uplifted into fold mountains. The concept is associated with James Hall and James Dana and was developed into the geosynclinal orogen theory by Kober.
| Type | How formed | Examples |
|---|---|---|
| Fold mountains | Compression buckles strata into anticlines and synclines | Himalaya, Alps, Andes, Rockies, Appalachians, Aravalli |
| Block mountains | Tension causes faulting; blocks are uplifted or subsided | Vosges, Black Forest, Sierra Nevada, Harz |
| Volcanic mountains | Accumulation of lava and ash around a vent | Fujiyama, Kilimanjaro, Vesuvius, Etna, Barren Island |
| Residual mountains | Dissection of an old upland by prolonged denudation | Vindhya, Satpura, Nilgiri, Rajmahal, Eastern Ghats |
Fold mountains are divided into young fold mountains, still rising and holding the highest peaks (Himalaya, Andes, Alps, Rockies), and old fold mountains, worn down by erosion (Aravalli, Appalachians, Pennines, Ural). The Aravalli is among the oldest fold mountain systems in the world.
BPSC (Pre) 2001 asked where the world's highest peaks are found — young fold mountains. BPSC (Pre) 2015 asked what the Pennines, Appalachians and Aravallis are — old mountains. UPPSC Mains 2015 called the Andes the 'Sea of Mountains'.
Major ranges: length and location facts
| Range | Fact |
|---|---|
| Andes | Longest continental range, about 7,000 km; South America; formed by subduction of the Nazca Plate; called the 'Sea of Mountains' |
| Rockies | About 4,800 km; North American 'backbone' |
| Great Dividing Range | About 3,700 km; eastern Australia |
| Himalaya | Highest range; about 2,500 km; continental collision of India and Eurasia |
| Caucasus | Lies between the Black Sea and the Caspian Sea |
| Darling Range | South-western coast of Australia, near Perth |
| Pamir Plateau | 'Roof of the World' |
The Himalaya is a fold mountain belt produced by continental collision, not by subduction volcanism. That is why the Himalaya has no active extrusive volcanoes, unlike the Andes or the Cascades, which sit above subducting plates.
IMAGE (Diagram): Formation of fold, block and volcanic mountains in three panels.
Labels: compression arrows, anticline and syncline, hanging wall and foot wall with graben and horst, lava cone with vent and crater.
Caption: Three ways in which mountains are built.
Find it: NCERT Class 11 Fundamentals of Physical Geography chapter on Geomorphic Processes, or Wikimedia Commons 'Types of mountains'.
Odisha Angle: Eastern Ghats and the Indian Plate
The Eastern Ghats run through Odisha as a discontinuous chain of ancient, residual hills of khondalite, charnockite and granite-gneiss, dissected by rivers such as the Mahanadi, Brahmani and Baitarani. Odisha's highest peak is Deomali (1,672 m) in Koraput district, followed by Mahendragiri (1,501 m) in Gajapati district. Similipal (1,168 m) in Mayurbhanj is a distinct horst-like upland of volcanic and sedimentary rocks.
Odisha lies mostly in seismic Zone III, with parts of the coastal belt in Zone II. The state's mineral wealth — the Sukinda chromite deposits of Jajpur district, hosted in ultramafic rocks of the Sukinda valley — is a direct product of ancient tectonic and magmatic processes in the Eastern Ghats belt.
Eastern Ghats = ancient residual hills, not young fold mountains. Deomali is Odisha's highest peak; Sukinda's chromite is associated with ultramafic rocks; the state sits mainly in Zone III.
Practice Questions
The processes that shape the Earth's surface are called:
- Geographical processes
- Hydrographic processes
- Tetra-hydro processes
- Geomorphic processes
Show answer
(d) – Endogenetic and exogenetic processes that build and sculpture landforms are geomorphic processes. OPSC 2018
Consider the following statements:
- Endogenetic forces originate inside the Earth and build relief.
- Orogenesis is a denudational process.
- Geomorphic processes operate only along plate boundaries.
How many of the statements given above are correct?
- Only one
- Only two
- All three
- None
Show answer
(a) – Only statement 1 is correct. Orogenesis is endogenetic, and geomorphic processes operate across whole continents, not just plate margins.
Which of the following are evidence for the Continental Drift Theory?
- Presence of similar fossils on distant continents
- Presence of rocks of different ages across continents
- Presence of glacial tillites
Select the correct answer using the code given below:
- Only I
- II and III
- I, II and III
- I and III
Show answer
(d) – Matching fossils and glacial tillites support drift; the rock evidence requires rocks of the same age, not different ages. Bank question
According to F.B. Taylor, the main driving force behind the drift of continents was:
- Gravitational pull
- Tidal force
- Electromagnetic force
- Geomagnetism
Show answer
(b) – Taylor (1910) attributed drift to the tidal force of the Moon and Sun; he postulated Lauratia and Gondwana as the two original landmasses. Bank question
Which one of the following is a major plate?
- Pacific Plate
- Cocos Plate
- Arabian Plate
- Philippine Plate
Show answer
(a) – The seven major plates are Pacific, North American, South American, Eurasian, African, Indo-Australian and Antarctic; the rest are minor plates. NDA 2019
The Cocos Plate lies between:
- Central America and the Pacific Plate
- South America and the Pacific Plate
- The Red Sea and the Persian Gulf
- The Asiatic Plate and the Pacific Plate
Show answer
(a) – The Cocos Plate lies off Central America and subducts beneath it, producing the Middle America Trench and its volcanic arc. BPSC (Pre) 2018
Highest peaks of the world are mostly found in which type of mountains?
- Old folded mountains
- Young folded mountains
- Residual mountains
- Block mountains
Show answer
(b) – Young fold mountains such as the Himalaya and the Andes are still rising and hold the highest peaks. BPSC (Pre) 2001
The Pennines (Europe), the Appalachians (America) and the Aravallis (India) are examples of:
- Young mountains
- Old mountains
- Block mountains
- Fold mountains
Show answer
(b) – All three are ancient, heavily eroded fold systems, hence called old mountains. BPSC (Pre) 2015
Place the following mountain ranges in descending order of their length:
- Andes
- Great Dividing Range
- The Himalaya
- The Rockies
Select the correct answer using the code given below:
- (i) (iii) (iv) (ii)
- (i) (iv) (ii) (iii)
- (iv) (i) (iii) (ii)
- (iv) (iii) (i) (ii)
Show answer
(b) – Andes (~7,000 km) > Rockies (~4,800 km) > Great Dividing Range (~3,700 km) > Himalaya (~2,500 km). UPPSC (Pre) 2008
Consider the following statements about Odisha's relief:
- Deomali is the highest peak of Odisha.
- The Eastern Ghats in Odisha are young fold mountains formed by the collision of India and Eurasia.
- The Sukinda valley's chromite deposits are associated with ultramafic rocks.
How many of the statements given above are correct?
- Only one
- Only two
- All three
- None
Show answer
(b) – Deomali (1,672 m, Koraput) is the highest peak and Sukinda's chromite occurs in ultramafic rocks. The Eastern Ghats are ancient residual hills, not young fold mountains.