GeographyISC Class 11 · Chapter 4

Plate Tectonics and Endogenous Processes: Drift, Sea Floor Spreading, Isostasy, Folding and Faulting, ISC Class 11

Updated 15 October 2026 · Fact-checked

Endogenous forces come from inside the earth. Wegener's continental drift, Hess's sea floor spreading and plate tectonics explain how rigid plates move over the mantle, driven by convection currents first proposed by Arthur Holmes. Isostasy explains how crust floats in balance. Horizontal and vertical forces fold and fault rocks into anticlines, synclines, rift valleys and block mountains.

What Plate Tectonics and Endogenous Processes is about

The syllabus covers four connected ideas.

1. Endogenetic forces: forces arising within the earth. They may be slow (diastrophic: epeirogenic vertical movements that raise or lower continents, and orogenic horizontal movements that build mountains) or sudden (earthquakes and volcanic eruptions). Vertical and horizontal forces have different effects.

2. Continental drift and sea floor spreading: Alfred Wegener's theory (1912) of a supercontinent Pangaea that broke apart; its evidence and weaknesses; Harry Hess's sea floor spreading (1961), supported by palaeomagnetic stripes and the young age of ocean floor.

3. Plate tectonics: seven major and several minor plates; divergent, convergent and transform boundaries; rates of movement; convection currents as the driving force (Arthur Holmes); the movement of the Indian plate.

4. Isostasy: the balance of the crust floating on the denser mantle; Pratt's view (columns of different density) and the role of Holmes's plastic, convecting mantle in isostatic adjustment.

5. Folding and faulting: types of folds (symmetrical, asymmetrical, monocline, isoclinal, overturned, recumbent, nappe) and faults (normal, reverse, thrust, tear), with landforms such as rift valleys and block mountains.

Weightage: CISCE gives no Class XI unit weightage for ISC Geography. Plate Tectonics and Endogenous Processes is topic 4 of the Class XI syllabus (Changing Face of the Earth) and can be asked anywhere in the 70-mark Paper I (Theory, 3 hours). Class XI is examined by the school, so your school sets the paper and decides how many marks each topic carries.Source: CISCE ISC Geography (853) syllabus, examination year 2028, Class XI

Key concepts

Endogenetic forces: slow and sudden, vertical and horizontal

Endogenetic (endogenous) forces originate inside the earth, driven mainly by its internal heat (from radioactive decay and heat left from its formation). They build up relief, while exogenetic forces (weathering and erosion) wear it down.

Slow (diastrophic) forces act over millions of years:
1. Epeirogenic movements (vertical): uplift or subsidence of large parts of continents, such as raised beaches, emerged coastal plains or drowned river valleys; they are continent-building.
2. Orogenic movements (horizontal or tangential): mountain building through:

compression (forces acting towards each other), which causes folding and thrust faults;
tension (forces pulling apart), which causes cracks and normal faults.

Sudden forces act within seconds or days: earthquakes and volcanic eruptions; they may cause destruction but also change landforms quickly.

Effects

Vertical forces produce uplift or subsidence, plateaus and block movements along faults.
Horizontal compressional forces produce folds, fold mountains and reverse or thrust faults.
Horizontal tensional forces produce normal faults, rift valleys and block mountains.

Worked example

[4] Distinguish between epeirogenic and orogenic movements. (Analysis)

Try it first, then show the solutionSolution

Both slow, diastrophic endogenetic forces - 1 mark.
Epeirogenic: vertical; uplift or subsidence of large areas; continent-building - 1 mark.
Orogenic: horizontal (compression or tension); mountain-building - 1 mark.
Effects: raised beaches/drowned valleys versus folds, faults, fold mountains - 1 mark.

Answer: Both are slow diastrophic movements caused by forces within the earth. Epeirogenic movements are vertical: they raise or lower large parts of continents, producing features such as raised beaches or drowned valleys. Orogenic movements are horizontal, by compression or tension, and build mountains through folding and faulting.

Continental drift and sea floor spreading

Continental drift (Alfred Wegener, 1912)

All continents once formed one supercontinent, Pangaea, surrounded by one ocean, Panthalassa. About 200 million years ago Pangaea split into Laurasia in the north and Gondwanaland in the south, which broke further into today's continents.
Evidence: the close fit of the coastlines of South America and Africa (shown accurately by Bullard in 1964 using the continental shelf edge); rocks of the same age and type on both sides of the Atlantic; glacial deposits (tillite) of the same age in India, Africa, South America, Antarctica and Australia; fossils of the same land reptile (Mesosaurus) and plant (Glossopteris) on continents now far apart; placer gold in Ghana whose source rock lies in Brazil.
Weakness: the forces he proposed (pole-fleeing force and tidal force) were far too weak to move continents, so the theory was rejected for decades.

Sea floor spreading (Harry Hess, 1961)

Magma rises along mid-ocean ridges, forms new ocean crust and pushes the older crust away on both sides; old crust sinks back into the mantle at ocean trenches.
Evidence: ocean floor rocks are youngest at the ridges and older away from them; no ocean floor is older than about 200 million years, whereas some continental rocks are over 3,000 million years old; stripes of normal and reversed magnetism lie symmetrically on both sides of ridges; sediments are thin near ridges and thicker away from them.
It provided the mechanism that Wegener lacked and led to plate tectonics.

Worked example

[4] State four pieces of evidence for continental drift. (Recall)

Try it first, then show the solutionSolution

Jigsaw fit of South America and Africa (Bullard, 1964) - 1 mark.
Rocks of the same age and type across the Atlantic - 1 mark.
Tillite of the same age on southern continents (Gondwana glaciation) - 1 mark.
Same fossils (Mesosaurus, Glossopteris) on separated continents; placer gold in Ghana - 1 mark.

Answer: The coastlines of South America and Africa fit closely, as Bullard showed in 1964; rocks of the same age and type occur on both sides of the Atlantic; glacial tillite of the same age is found in India, Africa, South America, Antarctica and Australia; and fossils of Mesosaurus and Glossopteris occur on continents now separated by oceans, all suggesting the continents were once joined.

Plate tectonics

The theory (developed from 1967 by McKenzie, Parker, Morgan and others) holds that the lithosphere is broken into rigid plates that move over the weaker asthenosphere. Continents are carried as parts of plates; it is the plates that move.

Plates: seven major plates (Antarctic, North American, South American, Pacific, Indo-Australian, African and Eurasian) and minor plates such as the Nazca, Cocos, Arabian, Philippine and Caroline plates.

Plate boundaries
1. Divergent (constructive): plates move apart; new crust forms; mid-ocean ridges such as the Mid-Atlantic Ridge, and rift valleys on land (East Africa).
2. Convergent (destructive): plates move towards each other; one is subducted at an ocean trench. Ocean-continent (Andes), ocean-ocean (island arcs such as Japan) and continent-continent (Himalayas).
3. Transform (conservative): plates slide past each other; crust neither created nor destroyed (San Andreas Fault).

Rates: measured from magnetic stripes; from less than 2.5 cm a year on the Arctic Ridge to more than 15 cm a year on the East Pacific Rise.

Driving force: convection currents in the mantle, an idea Arthur Holmes put forward in the 1930s: hot material rises, spreads beneath the plates, cools and sinks, dragging plates along.

Indian plate: it broke from Gondwanaland and moved north; about 140 million years ago it lay far south (about 50 degrees S); the Deccan Traps erupted as it moved; it collided with Asia about 40-50 million years ago, closing the Tethys Sea and raising the Himalayas, which are still rising.

Worked example

[4] Explain the three types of plate boundaries with examples. (Understanding)

Try it first, then show the solutionSolution

Divergent: plates move apart; new crust; Mid-Atlantic Ridge - 1 mark.
Convergent: one plate subducted; Andes, Japan; Himalayas (continent-continent) - 1 mark.
Transform: plates slide past; San Andreas Fault - 1 mark.
Crust created, destroyed or conserved respectively - 1 mark.

Answer: At divergent boundaries plates move apart and new crust forms, as along the Mid-Atlantic Ridge. At convergent boundaries plates move together and one sinks beneath the other, destroying crust, as in the Andes and Japan, while two continents collide to form ranges like the Himalayas. At transform boundaries plates slide past each other, conserving crust, as along the San Andreas Fault.

Isostasy: Pratt and Holmes

Meaning: isostasy (from Greek words meaning 'equal standing') is the state of balance in which blocks of the lighter crust float on the denser, plastic material below, rising or sinking until they are in equilibrium, just as blocks of wood float at different heights in water.

Background: during the survey of India in the nineteenth century, the plumb line near the Himalayas was deflected less than expected, suggesting that the mountains were not as massive as their size suggested. This led to theories of isostasy.

Pratt's view (J. H. Pratt, nineteenth century)
1. Crustal columns of different heights have different densities: higher mountains are made of lighter rock, lowlands and ocean floors of denser rock.
2. All columns end at a uniform depth, the level of compensation, where the pressure is equal.
3. So, the higher the column, the lower its density.

Airy's view (for comparison): rock density is roughly the same, but high mountains have deep 'roots' extending into the denser layer, like a thick iceberg.

Arthur Holmes's contribution

Holmes argued that the material beneath the crust, though solid, behaves plastically over long periods and moves in slow convection currents.
This plastic flow allows the crust to adjust isostatically: when ice sheets melt or mountains are eroded, the crust rises; when sediment or ice is added, it sinks. Holmes's convecting mantle also provided the force behind drifting continents.

Examples of isostatic adjustment: Scandinavia and Canada are still rising after the melting of Ice Age ice sheets; heavy delta sediments cause the crust to sink.

Worked example

[4] Explain Pratt's view of isostasy. (Understanding)

Try it first, then show the solutionSolution

Isostasy: balance of crustal blocks floating on denser material - 1 mark.
Columns of different heights have different densities - 1 mark.
Higher columns (mountains) are lighter; lower ones denser - 1 mark.
All columns end at a uniform level of compensation - 1 mark.

Answer: Isostasy is the balance in which crustal blocks float on denser material below. Pratt held that columns of crust of different heights have different densities: mountains stand high because they are made of lighter rock, while lowlands and ocean floors are of denser rock, and all columns end at the same depth, the level of compensation, where the pressure is equal.

Folding

Folding is the bending of rock layers into wave-like forms by horizontal compressional forces.

Parts: an anticline is an up-fold (arch); a syncline is a down-fold (trough); the limbs are the sides; the axial plane divides the fold.

Types of folds
1. Symmetrical (simple) fold: both limbs slope equally; formed by gentle, equal compression.
2. Asymmetrical fold: one limb steeper and shorter than the other.
3. Monocline: one limb is steep or vertical while the other is gently inclined or horizontal.
4. Isoclinal fold: both limbs are parallel, inclined in the same direction.
5. Overturned fold (overfold): one limb is pushed over the other.
6. Recumbent fold: the fold lies almost horizontally.
7. Nappe: when compression is so great that a recumbent fold breaks and its upper part is pushed forward over other rocks, sometimes for many kilometres (as in the Alps and Himalayas).

Landforms: fold mountains such as the Himalayas, Alps, Rockies and Andes; anticlinal ridges and synclinal valleys (as in the Jura).

Importance: folded sedimentary rocks often trap petroleum and natural gas in anticlines.

Worked example

[4] Describe four types of folds. (Recall)

Try it first, then show the solutionSolution

Symmetrical: limbs equally inclined - 1 mark.
Asymmetrical: one limb steeper than the other - 1 mark.
Overturned: one limb pushed over the other; recumbent: nearly horizontal - 1 mark.
Nappe: recumbent fold broken and thrust forward over other rocks - 1 mark.

Answer: In a symmetrical fold both limbs slope equally; in an asymmetrical fold one limb is steeper than the other; in an overturned fold one limb is pushed right over the other, and if the fold lies almost flat it is recumbent; when great pressure breaks a recumbent fold and pushes its upper part far forward over other rocks, a nappe forms, as in the Alps and Himalayas.

Faulting

A fault is a fracture in the crust along which rocks have moved. Faulting results from tension or compression when rocks are too rigid to fold.

Types of faults
1. Normal fault: caused by tension; one block slides down relative to the other along an inclined plane; the crust is extended.
2. Reverse fault: caused by compression; one block is pushed up over the other; the crust is shortened.
3. Thrust fault: a reverse fault with a low-angle plane, along which rocks move long distances (common in the Himalayas).
4. Tear (strike-slip or lateral) fault: blocks move horizontally past each other (the San Andreas Fault).

Landforms

Rift valley (graben): a long valley formed when a block sinks between two parallel normal faults, or when side blocks rise. Examples: the East African Rift Valley, the Rhine rift valley, and the Narmada and Tapi valleys in India.
Block mountain (horst): a block raised between faults, or left standing when the sides sink. Examples: the Vosges and Black Forest on either side of the Rhine valley.
Fault scarps: steep slopes along fault lines.

Effects: earthquakes along active faults; springs along fault lines; sometimes mineral deposits.

Worked example

[4] Explain how a rift valley and a block mountain are formed, with examples. (Understanding)

Try it first, then show the solutionSolution

Both formed by faulting, mainly tension and normal faults - 1 mark.
Rift valley: block sinks between parallel faults - 1 mark.
Block mountain: block rises or stands between faults - 1 mark.
Examples: East African Rift, Narmada valley; Vosges and Black Forest - 1 mark.

Answer: Both form by faulting. When tension creates parallel normal faults, a block may sink between them to form a rift valley, such as the East African Rift or the Narmada valley in India; a block that rises, or stands high when the land on either side sinks, forms a block mountain (horst), such as the Vosges and the Black Forest on either side of the Rhine rift valley.

Plate Tectonics and Endogenous Processes in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Isostasy

Suppose you float wooden blocks of different thickness in a tub of water. The thick blocks stand higher above the surface and also sink deeper below it, and when you remove a toy from a block it rises a little.

Which earth process does this model, and what is a real example?

Try it first, then show the solutionSolution

Blocks are crustal blocks floating on denser material.
Removing weight lets the block rise: isostatic adjustment.
Scandinavia is still rising after its ice sheet melted.

Answer: It models isostasy: crustal blocks float in balance on denser, plastic material and rise when load is removed, as Scandinavia and Canada are rising after the melting of Ice Age ice sheets.

Memory hook: Lighten the load, the crust floats up.

Spreading rate

Imagine a rock on the ocean floor 100 km from a mid-ocean ridge is found to be 4 million years old.

How fast has this side of the ocean floor moved?

Try it first, then show the solutionSolution

100 km = 10,000,000 cm.
Rate = 10,000,000 / 4,000,000 years.
= 2.5 cm a year.

Answer: About 2.5 cm a year, roughly the speed at which fingernails grow; such rates, measured from rock ages and magnetic stripes, support sea floor spreading.

Memory hook: Slow as fingernails, sure as time.

Compression and folding

Suppose you push a tablecloth from both ends across a smooth table. It rises into ridges and dips into troughs, and if you push harder, one ridge folds over another.

What does this show about the formation of fold mountains?

Try it first, then show the solutionSolution

Pushing from both ends is horizontal compression.
Ridges are anticlines, troughs synclines.
Greater pressure gives overturned and recumbent folds, as in the Himalayas.

Answer: It shows how horizontal compression bends rock layers into anticlines and synclines and, under greater pressure, into overturned and recumbent folds, building fold mountains like the Himalayas.

Memory hook: Push the cloth, raise the range.

Topics in this chapter

Plate Tectonics and Endogenous Processes: key facts

Spreading rate: $R a t e (c m / y r) = d i s t an ce (k m) x 100, 000/ t im e (y e a r s)$; 100 km in 4 million years = 2.5 cm/yr.
Age of ocean floor: $T im e = d i s t an ce / r a t e$; 500 km at 5 cm/yr = 10 million years.
Ocean widening: $W i d e nin g = 2 x ha l f - r a t e x t im e$; Half-rate 2 cm/yr for 1 million years = 40 km.
Drift and spreading: Wegener 1912 (Pangaea, Panthalassa); Hess 1961; plate tectonics 1967; Holmes: convection, 1930s.
Indian plate: About 50 degrees S 140 million years ago; collision with Asia 40-50 million years ago; Deccan Traps; Himalayas still rising.
Fold and fault types: $F o l d s : sy mm e t r i c a l, a sy mm e t r i c a l, m o n oc l in e, i soc l ina l, o v er t u r n e d, r ec u mb e n t, na pp e; F a u l t s : n or ma l, r e v er se, t h r u s t, t e a r$; Graben = rift valley; horst = block mountain.

How the school exam asks Plate Tectonics and Endogenous Processes

The question patterns to expect, and the method that works for each.

Question type	How it is asked	Method
Theory explanation	Explain continental drift and its evidence; sea floor spreading; plate tectonics.	Proponent, year, main idea, three pieces of evidence, weakness.
Diagram-based	Draw types of folds or faults; rift valley and block mountain; plate boundaries.	Neat labelled diagrams with arrows showing force direction.
Numerical	Spreading rate from distance and age; age of ocean floor; widening of an ocean.	Convert km to cm (x 100,000) and show units.

Tricks to remember Plate Tectonics and Endogenous Processes

Short memory aids. Say each one aloud once, then use it on a question the same day.

Drift evidence: 'Fit, Rocks, Ice, Fossils, Gold'
Jigsaw fit, same rocks, tillite, Mesosaurus and Glossopteris, placer gold.
Use it when: Evidence list.
Boundaries: 'Construct, Destroy, Conserve'
Divergent constructs, convergent destroys, transform conserves crust.
Use it when: Plate boundaries.
Faults by force
Tension: Normal (pull apart); Compression: Reverse and Thrust; Sideways: Tear.
Use it when: Fault types.

Plate Tectonics and Endogenous Processes: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Example 1: Who proposed sea floor spreading? · 1 mark · MCQExam level

The concept of sea floor spreading was proposed by:
(a) Alfred Wegener
(b) Harry Hess
(c) J. H. Pratt
(d) Arthur Holmes

Try it first, then show the solutionSolution

Wegener: continental drift; Pratt: isostasy; Holmes: convection currents.
Hess proposed sea floor spreading in 1961.

Answer: (b) Harry Hess.

Example 2: Assertion-reason: Wegener · 1 mark · Assertion-reasonHarder exam level

Assertion (A): Wegener's continental drift theory was rejected by most scientists for several decades.
Reason (R): Wegener could not suggest a force strong enough to move the continents.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Try it first, then show the solutionSolution

Pole-fleeing and tidal forces were far too weak.
This lack of mechanism was the main reason for rejection.

Answer: (a) Both A and R are true and R is the correct explanation of A.

Example 3: Age of the ocean floor · 4 marks · Short answerHarder exam level

[4] The sea floor on one side of a ridge moves at 5 cm per year. Find the age of the crust 500 km from the ridge, and the total widening of the ocean in 1 million years if both sides move at this rate. (Application)

Try it first, then show the solutionSolution

500 km = 50,000,000 cm.
Age = 50,000,000 / 5 = 10,000,000 years (10 million years).
Widening = 2 x 5 cm x 1,000,000 years = 10,000,000 cm.
= 100 km.

Answer: The crust 500 km from the ridge is 50,000,000 / 5 = 10 million years old; in 1 million years the ocean widens by 2 x 5 x 1,000,000 cm = 10,000,000 cm, which is 100 km.

Example 4: Why the Himalayas have no volcanoes · 4 marks · Short answerHOTS / competency

[4] Why do the Himalayas have many earthquakes but almost no active volcanoes, unlike the Andes? (Analysis)

Try it first, then show the solutionSolution

Himalayas: continent-continent convergence (India and Eurasia).
Both plates are light continental crust; neither sinks deep into the mantle.
Little subduction of oceanic crust, so little magma is generated.
Andes: oceanic Nazca plate subducts under South America, producing magma and volcanoes; both have earthquakes.

Answer: The Himalayas formed where two continental plates, India and Eurasia, collided; both are made of light continental crust, so neither sinks deep into the mantle and little magma is produced, though the stress causes frequent earthquakes. In the Andes, the dense oceanic Nazca plate is subducted beneath South America, melting at depth and feeding a chain of volcanoes.

Example 5: Drift to plate tectonics · 7 marks · Long answerHarder exam level

[7] (a) Explain the continental drift theory and its evidence. [4]
(b) Explain how sea floor spreading and convection currents led to the theory of plate tectonics. [3] (Understanding)

Try it first, then show the solutionSolution

(a) Wegener (1912): Pangaea, Panthalassa; break-up about 200 million years ago (1).
(a) Jigsaw fit; same rocks (1).
(a) Tillite; fossils; placer gold (1).
(a) Weakness: no adequate force (1).
(b) Hess (1961): new crust at ridges, destroyed at trenches (1).
(b) Evidence: ages, magnetic stripes; ocean floor under 200 million years (1).
(b) Holmes's convection currents as driving force; rigid plates move (1967) (1).

Answer: (a) Wegener proposed in 1912 that all continents once formed Pangaea, surrounded by Panthalassa, which broke apart about 200 million years ago. He cited the jigsaw fit of the Atlantic coasts, matching rocks on both sides, glacial tillite on the southern continents, the same fossils such as Mesosaurus and Glossopteris on separated continents and placer gold in Ghana from Brazilian sources. His weakness was the lack of a force strong enough to move continents. (b) Hess (1961) showed that new crust forms at mid-ocean ridges and is destroyed at trenches, supported by the increasing age of ocean floor away from ridges, symmetrical magnetic stripes and the absence of ocean floor older than about 200 million years. Holmes's convection currents provided the force, and from 1967 these ideas were combined into plate tectonics, in which rigid plates carrying continents move over the mantle.

Example 6: Isostasy in action · 4 marks · Short answerHarder exam level

[4] Using the idea of isostasy, explain why parts of Scandinavia are still rising today. (Analysis)

Try it first, then show the solutionSolution

During the Ice Age a thick ice sheet pressed the crust down.
Isostasy: crust floats in balance on denser plastic material.
When the ice melted, the load was removed.
The crust is slowly rising back to balance as the plastic material flows back (Holmes).

Answer: During the Ice Age a thick ice sheet loaded Scandinavia and pressed the crust down into the plastic material below. When the ice melted, the load was removed, so to restore isostatic balance the crust has been rising slowly, as the plastic mantle material flows back beneath it, a process that is still continuing.

Case-study practice (Section D style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 8-mark question split into 2 + 2 + 1 + 3 marks.

A geology field report (source-based)

Read the imaginary report and answer.

'Along the river we saw rock layers bent into arches and troughs. Upstream, the river flowed in a straight, steep-sided valley bounded by two parallel lines of cliffs, the land on either side standing higher. Older maps show that some coastal villages in the region are now farther from the sea than they were three centuries ago.'

(i) · 2 marks
Name the structures described as 'arches and troughs'. Which force formed them?
Answer
Answer: Anticlines (arches) and synclines (troughs); horizontal compressional force.
1 for names; 1 for force.
(ii) · 2 marks
What landform is the straight valley between parallel cliffs? Give an Indian example.
Answer
Answer: A rift valley (graben) formed between parallel faults; the Narmada valley (or Tapi).
1 each.
(iii) · 1 mark
What kind of movement could explain villages becoming farther from the sea?
Answer
Answer: Epeirogenic uplift of the coast (vertical movement), possibly isostatic rise.
1 mark.
(iv) · 3 marks
Classify the three observations as horizontal or vertical forces and explain one effect of each kind.
Answer
Answer: (1) Folds: horizontal compression, which builds fold mountains. (2) Rift valley: horizontal tension producing normal faults, with vertical movement of blocks. (3) Coastal uplift: vertical (epeirogenic) movement, which raises beaches and extends coastal plains.
1 mark each.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

[4] Age of ocean crust 500 km from a ridge at 5 cm/yr, and widening in 1 million years. (4 marks)

Step	Marks
Convert 500 km to 50,000,000 cm.	1
Age 10 million years.	1
Widening = 2 x 5 x 1,000,000 cm.	1
100 km with unit.	1

[7] Plate tectonics: plates, boundaries, driving force and the Indian plate. (7 marks)

Step	Marks
Lithosphere in rigid plates; seven major plates.	1
Divergent boundaries.	1
Convergent boundaries: three kinds.	1
Transform boundaries.	1
Rates of movement.	1
Convection currents (Holmes).	1
Indian plate's movement and Himalayas.	1

Where students lose marks in Plate Tectonics and Endogenous Processes

The slips examiners see most often, and what to write instead.

Mistake: Saying continents move by themselves
Plate tectonics replaced Wegener's idea.
Do this: Continents are carried as parts of moving plates.
Usually costs: 1 mark.
Mistake: Confusing graben and horst
Similar German terms.
Do this: Graben = sunken block (rift valley); horst = raised block (block mountain).
Usually costs: 1 mark.
Mistake: Forgetting to convert km to cm in spreading numericals
Units mixed.
Wrong working
100 km / 4,000,000 years = 0.000025 cm/yr.
Right working
100 km = 10,000,000 cm; 10,000,000 / 4,000,000 = 2.5 cm/yr.
Do this: Multiply km by 100,000 to get cm.
Usually costs: 2 marks.
Mistake: Describing isostasy without the level of compensation (Pratt)
The key idea is omitted.
Do this: Mention uniform depth where pressures are equal.
Usually costs: 1 mark.
Mistake: Fold types without force direction
A complete answer names the force that caused the fold.
Do this: State that all folds result from horizontal compression.
Usually costs: 1 mark.

Practice questions on Plate Tectonics and Endogenous Processes

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · Very short answerExam level
What was Pangaea?
Hint
Wegener.
Answer
The single supercontinent that, according to Wegener, included all landmasses.
Q2 · 1 mark · Very short answerExam level
What is a nappe?
Hint
Broken recumbent fold.
Answer
A recumbent fold broken and pushed forward over other rocks.
Q3 · 1 mark · MCQExam level
The San Andreas Fault is an example of a:
(a) Divergent boundary
(b) Convergent boundary
(c) Transform boundary
(d) Rift valley
Hint
Plates slide past.
Answer
(c) Transform boundary.
Q4 · 1 mark · Very short answerHarder exam level
Which fossil plant found on the southern continents supports continental drift?
Hint
A seed fern.
Answer
Glossopteris.
Q5 · 4 marks · Short answerHarder exam level
[4] Explain the evidence for sea floor spreading.
Hint
Age, magnetism, sediments, ridges.
Answer
(1) Rocks are youngest at mid-ocean ridges and become older away from them. (2) No ocean floor is older than about 200 million years. (3) Stripes of normal and reversed magnetism are symmetrical on both sides of ridges. (4) Sediments are thin near ridges and thicker farther away; volcanic activity occurs along ridge crests.
Q6 · 4 marks · Short answerHarder exam level
[4] Explain the movement of the Indian plate.
Hint
Gondwana, 140 million years, Deccan, collision.
Answer
(1) India was part of Gondwanaland and began moving north after Pangaea broke up. (2) About 140 million years ago it lay far south, near 50 degrees S. (3) As it moved, the Deccan Traps lava flows erupted. (4) It collided with Asia about 40-50 million years ago, closing the Tethys and raising the Himalayas, which are still rising.
Q7 · 4 marks · Short answerHarder exam level
[4] Distinguish between normal and reverse faults.
Hint
Force, movement, crust, landforms.
Answer
(1) Normal faults are caused by tension; reverse faults by compression. (2) In a normal fault one block slides down the fault plane; in a reverse fault one block is pushed up over the other. (3) Normal faults lengthen the crust; reverse faults shorten it. (4) Normal faults produce rift valleys and block mountains; reverse and thrust faults occur in fold mountains.
Q8 · 4 marks · Short answerHOTS / competency
[4] India moved about 6,000 km northward in roughly 50 million years. Calculate its average speed in cm per year and compare it with typical plate speeds.
Hint
km to cm.
Answer
(1) 6,000 km = 600,000,000 cm. (2) Speed = 600,000,000 / 50,000,000 = 12 cm per year. (3) Typical plates move about 2-10 cm a year (Arctic Ridge under 2.5 cm, East Pacific Rise over 15 cm). (4) So India moved fast, near the upper end of plate speeds.
Q9 · 4 marks · Short answerHOTS / competency
[4] Compare Pratt's and Airy's views of isostasy.
Hint
Density versus roots.
Answer
(1) Pratt: columns have different densities; higher columns are lighter. (2) Pratt: all columns end at a uniform level of compensation. (3) Airy: density is roughly uniform; higher mountains have deeper roots. (4) Both explain why mountains do not exert as much extra gravity as expected; modern evidence of mountain roots supports Airy's idea, while density differences also exist.
Q10 · 7 marks · Long answerHarder exam level
[7] (a) Explain endogenetic forces and their effects. [3]
(b) Explain the types of folds with diagrams in words. [4]
Hint
(a) slow/sudden, vertical/horizontal; (b) four types.
Answer
(a) (1) Internal forces from the earth's heat: slow (diastrophic) and sudden (earthquakes, volcanoes). (2) Epeirogenic vertical movements raise or lower continents. (3) Orogenic horizontal movements: compression folds rocks; tension faults them. (b) (1) Symmetrical: limbs equally inclined. (2) Asymmetrical: one limb steeper; monocline: one limb steep, other gentle. (3) Overturned: one limb pushed over; recumbent: nearly horizontal. (4) Nappe: recumbent fold broken and thrust forward.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Who proposed convection currents as the force behind drift?Show answer
Arthur Holmes (1930s).
2.What is the level of compensation?Show answer
The depth at which pressure is equal under all crustal columns (Pratt).
3.Name the slowest and fastest spreading ridges mentioned.Show answer
Arctic Ridge (under 2.5 cm/yr) and East Pacific Rise (over 15 cm/yr).
4.What is a monocline?Show answer
A fold with one steep limb and one gently inclined or horizontal limb.
5.Which fault moves blocks horizontally past each other?Show answer
A tear (strike-slip) fault.
6.When did India collide with Asia?Show answer
About 40-50 million years ago.

Best order to study it

Endogenetic forces: slow and sudden, vertical and horizontal.
Continental drift and evidence.
Sea floor spreading.
Plate tectonics and the Indian plate.
Isostasy (Pratt, Holmes).
Folding and faulting; numericals.

Quick revision checklist

The night before the exam: can you do each of these without looking?

Endogenetic: epeirogenic (vertical) and orogenic (horizontal: compression folds, tension faults); sudden: earthquakes, volcanoes.
Wegener 1912: Pangaea, Panthalassa; fit, rocks, tillite, fossils, placer gold; weak forces.
Hess 1961: new crust at ridges; magnetic stripes; ocean floor under 200 million years.
Plates: 7 major; divergent, convergent, transform; 2.5-15 cm/yr; Holmes's convection.
Isostasy: floating balance; Pratt: density varies, level of compensation; Holmes: plastic, convecting mantle allows adjustment.
Folds: symmetrical to nappe; faults: normal, reverse, thrust, tear; graben (rift valley), horst (block mountain).

Plate Tectonics and Endogenous Processes: frequently asked questions

Is plate tectonics proven?

It is supported by strong evidence: ocean floor ages, magnetic stripes, earthquake and volcano patterns and direct satellite measurements of plate motion.

Why does the syllabus mention Holmes with isostasy?

Holmes argued that the mantle flows slowly by convection, which both drives plates and allows the crust to adjust isostatically when loads are added or removed.

Are the Himalayas still rising?

Yes. India continues to push into Asia, and measurements show the Himalayas are still being uplifted, though erosion also wears them down.

Based on: CISCE ISC 2028 Geography (853) syllabus (Classes XI and XII); CISCE Regulations for the ISC Examination Year 2028 (Class XI internal examination)