What causes earthquakes?

Earthquakes are caused by the sudden release of energy stored in rocks along fault lines, usually due to tectonic plate movement. The point of origin inside the Earth is the focus (hypocentre), and the point on the surface directly above is the epicentre.

What is the difference between folding and faulting?

Folding is the bending of rock layers due to compressive forces, creating anticlines (upfolds) and synclines (downfolds). Faulting is the fracturing and displacement of rock layers due to tensional or compressive forces, creating normal faults, reverse faults, and transform faults.

Lithosphere Endogenic Processes Exercise Solutions | KalviGavani

Q: What is plate tectonics?

Plate tectonics is the theory that the Earth's lithosphere is divided into large plates that float on the semi-fluid asthenosphere. These plates move due to convection currents in the mantle, causing earthquakes, volcanism, and mountain building at plate boundaries.

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How to Use This Page

Solve each Samacheer Kalvi exercise question on your own first, then compare your answer with the solutions below. Endogenic processes are Earth's internal forces — understand how plate tectonics, earthquakes, and volcanism shape the landscape.

Key Concepts (Quick Recap)

Endogenic vs Exogenic Forces

Feature	Endogenic Forces	Exogenic Forces
Origin	Inside the Earth	Earth's surface (atmosphere, hydrosphere)
Effect	Build landforms (constructive)	Wear down landforms (destructive)
Examples	Earthquakes, volcanism, folding, faulting	Weathering, erosion, deposition
Energy source	Internal heat, radioactivity	Solar energy, gravity

Plate Tectonics

Lithosphere: Rigid outer shell (crust + upper mantle), divided into 7 major plates
Asthenosphere: Semi-fluid layer below lithosphere on which plates move
Convection currents in the mantle drive plate movement

Types of Plate Boundaries

Boundary	Movement	Feature	Example
Divergent (Constructive)	Plates move apart	Mid-oceanic ridges, rift valleys	Mid-Atlantic Ridge, East African Rift
Convergent (Destructive)	Plates collide	Mountains, trenches, volcanoes	Himalayas (continent-continent), Andes (ocean-continent)
Transform (Conservative)	Plates slide past	Faults, earthquakes	San Andreas Fault

Diastrophism (Mountain Building)

Folding: Compressive forces bend rock layers → anticlines (upfolds) and synclines (downfolds)
Faulting: Tensional or compressive forces fracture and displace rocks
Types of faults: Normal fault (tension), Reverse/Thrust fault (compression), Transform fault (lateral)

Types of Mountains

Type	Formation	Example
Fold mountains	Folding of rock layers by compressive forces	Himalayas, Alps, Andes, Rockies
Block mountains	Faulting — land between two faults rises	Vosges (France), Black Forest (Germany)
Volcanic mountains	Accumulation of volcanic material	Mt. Kilimanjaro, Mt. Fuji, Mt. St. Helens
Residual mountains	Erosion of surrounding land over millions of years	Aravalli Hills, Appalachian Mountains

Volcanism

Magma: Molten rock below the Earth's surface
Lava: Magma that reaches the surface
Active volcano: Has erupted recently and may erupt again (e.g., Mt. Etna, Mt. St. Helens)
Dormant volcano: Has not erupted recently but may erupt in the future (e.g., Mt. Fuji)
Extinct volcano: Has not erupted for thousands of years and is unlikely to erupt (e.g., Mt. Kilimanjaro)

Volcanic Landforms

Landform	Description
Shield volcano	Broad, gently sloping; formed by fluid basaltic lava (e.g., Mauna Loa, Hawaii)
Composite volcano	Steep, conical; formed by alternating layers of lava and ash (e.g., Mt. Fuji)
Caldera	Large depression formed by collapse of volcano summit (e.g., Crater Lake, Oregon)
Flood basalt	Extensive flat lava flows covering large areas (e.g., Deccan Traps, India)

Earthquakes

Term	Definition
Focus (Hypocentre)	Point of origin of earthquake inside the Earth
Epicentre	Point on the surface directly above the focus
Seismic waves	Energy waves released during an earthquake
P-waves (Primary)	Fastest, travel through solids and liquids, push-pull motion
S-waves (Secondary)	Slower, travel through solids only, perpendicular motion
L-waves (Surface)	Slowest, cause maximum damage, travel along surface
Richter scale	Measures earthquake magnitude (1-10)
Mercalli scale	Measures earthquake intensity (I-XII) based on damage

I. Choose the Best Answer (MCQs)

Q1. The theory of plate tectonics was proposed by (a) Alfred Wegener (b) Harry Hess (c) J. Tuzo Wilson (d) Arthur Holmes

Answer(a) Alfred Wegener — Alfred Wegener proposed the theory of continental drift (1912), which later evolved into plate tectonics. Harry Hess proposed seafloor spreading. The modern plate tectonic theory was developed by multiple scientists in the 1960s.

Q2. The point of origin of an earthquake inside the Earth is called (a) Epicentre (b) Focus (c) Seismograph (d) Crater

Answer(b) Focus — The focus (hypocentre) is the point inside the Earth where the earthquake originates. The epicentre is the point on the surface directly above the focus.

Q3. Fold mountains are formed by (a) Tensional forces (b) Compressive forces (c) Shearing forces (d) Volcanic activity

Answer(b) Compressive forces — Fold mountains are formed when compressive forces push rock layers together, causing them to buckle and fold. Examples: Himalayas, Alps, Andes.

Q4. The Himalayas were formed by the collision of (a) Pacific Plate and Eurasian Plate (b) Indian Plate and Eurasian Plate (c) African Plate and Eurasian Plate (d) Nazca Plate and South American Plate

Answer(b) Indian Plate and Eurasian Plate — The Himalayas were formed when the Indian Plate collided with the Eurasian Plate. This is an example of a continent-continent convergent boundary.

Q5. The Mid-Atlantic Ridge is an example of (a) Convergent boundary (b) Divergent boundary (c) Transform boundary (d) None of the above

Answer(b) Divergent boundary — The Mid-Atlantic Ridge is a divergent plate boundary where the North American Plate and Eurasian Plate are moving apart, creating new oceanic crust.

II. Fill in the Blanks

1. Endogenic forces originate from within the Earth. 2. Exogenic forces originate from the Earth's surface (atmosphere, hydrosphere). 3. The theory of continental drift was proposed by Alfred Wegener. 4. The Earth's lithosphere is divided into 7 major plates and several minor plates. 5. Plates move due to convection currents in the mantle. 6. When plates move apart, it is called a divergent boundary. 7. When plates collide, it is called a convergent boundary. 8. When plates slide past each other, it is a transform boundary. 9. The point of origin of an earthquake inside the Earth is the focus (hypocentre). 10. The point on the surface directly above the focus is the epicentre. 11. The Richter scale measures earthquake magnitude. 12. Fold mountains are formed by compressive forces. 13. Block mountains are formed by faulting. 14. The Deccan Traps in India are an example of flood basalts.

III. True or False (with corrections for false statements)

Q1. Endogenic forces are also called constructive forces.

AnswerTrue — Endogenic forces (earthquakes, volcanism, folding, faulting) build landforms like mountains, plateaus, and rift valleys. They are called constructive forces.

Q2. The focus is on the Earth's surface.

AnswerFalse — Correction: The focus (hypocentre) is inside the Earth — it is the point of origin of the earthquake. The epicentre is on the Earth's surface, directly above the focus.

Q3. S-waves can travel through both solids and liquids.

AnswerFalse — Correction: S-waves (secondary waves) can travel only through solids, not liquids. P-waves can travel through both solids and liquids.

Q4. The Himalayas are fold mountains.

AnswerTrue — The Himalayas are fold mountains formed by the collision of the Indian Plate and the Eurasian Plate. Compressive forces caused rock layers to fold, creating the world's highest mountain range.

Q5. A dormant volcano is one that has never erupted.

AnswerFalse — Correction: A dormant volcano is one that has not erupted recently but may erupt again in the future. An extinct volcano is one that has not erupted for thousands of years and is unlikely to erupt again.

IV. Match the Following

Column A	Column B	Answer
1. Fold mountains	(a) Faulting	(b) Compressive forces
2. Block mountains	(b) Compressive forces	(a) Faulting
3. Divergent boundary	(c) Plates collide	(d) Plates move apart
4. Convergent boundary	(d) Plates move apart	(c) Plates collide
5. Focus	(e) Surface point above focus	(f) Point inside Earth where quake starts
6. Epicentre	(f) Point inside Earth	(e) Surface point above focus

V. Answer Briefly (2-mark questions)

Q1. Distinguish between endogenic and exogenic forces.

Answer

| Feature | Endogenic Forces | Exogenic Forces | |---|---|---| | Origin | Inside the Earth | Earth's surface | | Nature | Constructive (build landforms) | Destructive (wear down landforms) | | Examples | Earthquakes, volcanism, folding | Weathering, erosion, deposition | | Energy source | Internal heat, radioactivity | Solar energy, gravity |

Q2. What is the focus and epicentre of an earthquake?

Answer

Focus (Hypocentre): The point inside the Earth where the earthquake originates. It can be shallow (0-70 km), intermediate (70-300 km), or deep (300-700 km). Epicentre: The point on the Earth's surface directly above the focus. It experiences the maximum intensity of the earthquake and the most damage.

Q3. Name three types of plate boundaries with one example each.

Answer

1. Divergent boundary (constructive): Plates move apart — e.g., Mid-Atlantic Ridge 2. Convergent boundary (destructive): Plates collide — e.g., Himalayas (Indian Plate + Eurasian Plate) 3. Transform boundary (conservative): Plates slide past — e.g., San Andreas Fault (Pacific Plate + North American Plate)

Q4. What are the types of volcanoes? Give one example of each.

Answer

1. Shield volcano: Broad, gently sloping, formed by fluid basaltic lava — e.g., Mauna Loa, Hawaii 2. Composite volcano (Stratovolcano): Steep, conical, alternating layers of lava and ash — e.g., Mt. Fuji, Japan 3. Caldera: Large depression formed by collapse of volcano summit — e.g., Crater Lake, Oregon

VI. Answer in Detail (5-mark questions)

Q1. Explain plate tectonics theory and describe the three types of plate boundaries.

Answer

Plate Tectonics Theory: The Earth's lithosphere is divided into large plates that float on the semi-fluid asthenosphere. These plates move due to convection currents in the mantle. The movement of plates causes earthquakes, volcanism, and mountain building at plate boundaries. Three Types of Plate Boundaries: 1. Divergent Boundary (Constructive): - Plates move apart from each other - Magma rises from the mantle to fill the gap, creating new crust - Features: Mid-oceanic ridges, rift valleys - Examples: Mid-Atlantic Ridge, East African Rift Valley 2. Convergent Boundary (Destructive): - Plates collide with each other - Three types: ocean-ocean, ocean-continent, continent-continent - Features: Mountains, trenches, volcanoes - Examples: Himalayas (continent-continent), Andes (ocean-continent), Mariana Trench (ocean-ocean) 3. Transform Boundary (Conservative): - Plates slide past each other horizontally - No crust is created or destroyed - Features: Faults, shallow earthquakes - Example: San Andreas Fault (Pacific Plate sliding past North American Plate)

Q2. Explain the causes and effects of earthquakes.

Answer

Causes of Earthquakes: 1. Tectonic activity: Movement of lithospheric plates causes stress to build up along fault lines. When the stress exceeds the strength of the rock, it ruptures, releasing energy as seismic waves. 2. Volcanic activity: Magma movement can cause tremors. 3. Human activities: Mining, reservoir construction, nuclear testing can trigger minor earthquakes. Types of Seismic Waves: - P-waves (Primary): Fastest, travel through solids and liquids, push-pull (longitudinal) motion - S-waves (Secondary): Slower than P-waves, travel through solids only, perpendicular (transverse) motion - L-waves (Surface): Slowest, travel along the surface, cause maximum damage Effects of Earthquakes: 1. Ground shaking: Causes buildings and infrastructure to collapse 2. Landslides: Earthquake-triggered landslides bury settlements 3. Tsunamis: Underwater earthquakes displace ocean water, creating destructive waves 4. Liquefaction: Water-saturated soil behaves like liquid, causing buildings to sink 5. Fires: Broken gas lines and electrical short circuits cause fires 6. Faulting: Ground rupture along fault lines Measurement: - Richter scale: Measures magnitude (energy released) on a logarithmic scale (1-10) - Mercalli scale: Measures intensity (damage caused) on a scale of I-XII

Q3. Distinguish between fold mountains and block mountains.

Answer

| Feature | Fold Mountains | Block Mountains | |---|---|---| | Formation | Compressive forces bend rock layers | Tensional forces fracture and displace blocks | | Process | Rocks fold into anticlines and synclines | Land between two faults rises or drops | | Shape | Long, narrow, with ridges and valleys | Flat top, steep sides | | Examples | Himalayas, Alps, Andes, Rockies | Vosges (France), Black Forest (Germany), Aravalli ranges | | Age | Generally young and tall | Generally old and eroded | | Associated with | Convergent plate boundaries | Tensional forces, faulting |

Common Mistakes to Avoid

Confusing focus and epicentre: Focus is INSIDE the Earth (where the earthquake starts). Epicentre is ON the surface (directly above the focus).
Confusing endogenic and exogenic forces: Endogenic = from WITHIN the Earth (constructive). Exogenic = from the surface (destructive).
Saying S-waves travel through liquids: S-waves travel through SOLIDS only. P-waves travel through both solids and liquids. This is how we know the outer core is liquid (S-waves don't pass through it).
Confusing fold mountains and block mountains: Fold mountains = compressive forces (folding). Block mountains = tensional forces (faulting).
Mixing up divergent and convergent boundaries: Divergent = plates move APART (new crust forms). Convergent = plates COLLIDE (crust destroyed).
Forgetting that dormant volcanoes can erupt again: Dormant = sleeping, may erupt. Extinct = dead, unlikely to erupt.

Exam Checklist

[ ] Can you distinguish between endogenic and exogenic forces?
[ ] Can you explain plate tectonics and name the three types of plate boundaries?
[ ] Can you describe divergent, convergent, and transform boundaries with examples?
[ ] Can you explain folding and faulting with examples?
[ ] Can you distinguish between fold mountains, block mountains, volcanic mountains, and residual mountains?
[ ] Can you explain the causes and types of volcanic eruptions?
[ ] Can you distinguish between active, dormant, and extinct volcanoes?
[ ] Can you explain earthquakes — causes, seismic waves, focus, epicentre?
[ ] Can you distinguish between P-waves, S-waves, and L-waves?
[ ] Can you describe the Richter and Mercalli scales?

Frequently Asked Questions

Endogenic processes are forces that originate from within the Earth. They include diastrophism (folding, faulting, mountain building) and volcanism (volcanic eruptions, earthquakes). These forces build landforms like mountains, plateaus, and rift valleys.