GeographyCBSE Class 11 · Interior of the Earth

Layers of the Earth, Types of Volcanoes and Volcanic Landforms (Class 11 Geography, Fundamentals of Physical Geography, Chapter 3)

Updated 17 October 2026 · Fact-checked

The earth has a brittle crust (oceanic about 5 km, continental about 30 km), a mantle to 2,900 km with the weak asthenosphere up to about 400 km, and a liquid outer core and solid inner core of nickel and iron. Volcanoes are shield, composite, caldera, flood basalt or mid-ocean ridge types; lava cooling in the crust forms batholiths, laccoliths, sills and dykes.

Notice that only the outer core is liquid, the asthenosphere is the weak upper mantle, and the crust is a very thin skin (5–70 km).

Illustration drawn for QuestionBuddy.

Understand Layers of the Earth, Volcanoes and Intrusive Landforms

Why this topic matters. Layers with thicknesses and the table of volcano types are favourite Board items.

1. Crust. The outermost brittle solid. Oceanic crust is thinner, mean 5 km; continental crust about 30 km, thicker under major mountains, up to 70 km in the Himalayan region.

2. Mantle. From the Moho discontinuity to 2,900 km. The upper part is the asthenosphere (astheno means weak), up to about 400 km, the main source of magma. The lithosphere is the crust plus the uppermost mantle, 10-200 km thick. The lower mantle is solid.

3. Core. The core-mantle boundary lies at 2,900 km. The outer core is liquid, the inner core solid. Made mostly of nickel and iron: the nife layer. Its existence is known from earthquake wave velocities.

4. Volcano. A place where gases, ash and molten rock escape. Molten material in the upper mantle is magma; on reaching the surface it is lava. Erupted material includes lava flows, pyroclastic debris, volcanic bombs, ash and gases.

5. Types.

Type	Features	Example
Shield	Very fluid basalt, low explosivity, largest, not steep	Hawaii
Composite	Cooler viscous lava, explosive, layers of pyroclastic material	-
Caldera	Most explosive, collapses to a depression	-
Flood basalt	Highly fluid lava over long distances, flows over 50 m thick	Deccan Traps
Mid-ocean ridge	Frequent eruptions along a ridge system over 70,000 km long	Oceans

6. Intrusive forms. Lava cooling in the crust forms intrusive forms. A batholith is a large body of magma cooled deep in the crust as a large dome, granitic, exposed only after denudation. A laccolith is a dome-shaped body with a level base connected to the source by a pipe-like conduit. Other forms include lapoliths, phacoliths, sills and sheets (horizontal) and dykes (vertical, cutting across rock).

7. Igneous rocks. Volcanic rocks cool at the surface, plutonic rocks in the crust.

Layers of the Earth, Volcanoes and Intrusive Landforms: key facts

Layers and thickness: Oceanic crust about 5 km
Continental crust about 30 km, up to 70 km under Himalaya
Mantle to 2,900 km
Asthenosphere up to about 400 km
Lithosphere 10-200 km; Numbers.
Core: Boundary at 2,900 km
Outer core liquid
Inner core solid
Material nickel and iron (nife); Core facts.
Volcano types: Shield Hawaii
Composite explosive, layered
Caldera most explosive
Flood basalt Deccan Traps
Mid-ocean ridge over 70,000 km; Five types.
Magma and lava: Magma: molten material in the upper mantle | Lava: on reaching the surface; Definition.

Oceanic crust	about 5 km
Continental crust	about 30 km, up to 70 km under Himalaya
Mantle	to 2,900 km
Asthenosphere	up to about 400 km
Lithosphere	10-200 km

	Boundary at 2,900 km
Outer core	liquid
Inner core	solid
Material	nickel and iron (nife)

Shield	Hawaii
Composite	explosive, layered
Caldera	most explosive
Flood basalt	Deccan Traps
Mid-ocean ridge	over 70,000 km

How to answer Layers of the Earth, Volcanoes and Intrusive Landforms questions

Layer and volcano questions rely on tables.

1Give each layer with depth and state.
2Mention the asthenosphere as magma source.
3Describe the volcano types in a table.
4Add one Indian example: Deccan Traps.
5Draw intrusive forms.

Layers of the Earth, Volcanoes and Intrusive Landforms in real life

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

Thick and thin skin

Suppose an apple has a thin skin and a boiled egg has a thicker shell relative to the white.

What does the comparison suggest about the earth's crust?

Try it first, then show the solutionSolution

The crust is thin compared with the earth's radius.
Oceanic crust is about 5 km and continental about 30 km.

Answer: The crust is a thin brittle outer layer, much thinner than the mantle and core.

Memory hook: Thin crust.

Runny and thick lava

Suppose honey flows easily across a plate while thick paste piles up in a heap.

Which volcano types do they resemble?

Try it first, then show the solutionSolution

Fluid basalt spreads, as in shield volcanoes and flood basalts.
Viscous lava piles up and erupts explosively, as in composite volcanoes.

Answer: Runny honey resembles shield or flood basalt eruptions; paste resembles composite volcanoes.

Memory hook: Runny spreads, thick piles.

Tricks to remember Layers of the Earth, Volcanoes and Intrusive Landforms

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

5-30-70
Oceanic, continental, Himalayan crust
Use it when: Crust thickness.
2,900
Core-mantle boundary depth
Use it when: Key number.
Dyke = Down, Sill = Spread
Vertical dyke, horizontal sill
Use it when: Intrusive forms.

Layers of the Earth, Volcanoes and Intrusive Landforms: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Asthenosphere · 1 mark · MCQBoard level

The main source of magma is the:
(A) crust
(B) asthenosphere
(C) inner core
(D) lithosphere

Try it first, then show the solutionSolution

The asthenosphere up to 400 km is the main source of magma (1 mark).

Answer: (B)

Example 2: Lithosphere · 2 marks · Very short answerBoard level

Define the lithosphere and give its thickness. (2 marks)

Try it first, then show the solutionSolution

Crust plus the uppermost part of the mantle (1 mark).
10-200 km thick (1 mark).

Answer: The lithosphere is the crust together with the uppermost mantle and is 10-200 km thick.

Example 3: Shield versus composite · 3 marks · Short answerHarder board level

Compare shield and composite volcanoes. (3 marks)

Try it first, then show the solutionSolution

Shield: very fluid basalt, low explosivity, not steep (1 mark).
Composite: cooler, more viscous lava, explosive, layers of ash and debris (1 mark).
Example: Hawaii for shield (1 mark).

Answer: Shield volcanoes erupt very fluid basalt with low explosivity and have gentle slopes, as in Hawaii. Composite volcanoes erupt cooler, more viscous lava explosively, and layers of pyroclastic material and ash build up near the vent.

Example 4: Assertion and reason: Deccan · 1 mark · Assertion-reasonHarder board level

Assertion (A): The Deccan Traps cover a large part of the Maharashtra plateau.
Reason (R): Highly fluid basaltic lava can flow over long distances and cover thousands of square kilometres.
(A) Both true, R explains A
(B) Both true, R does not explain A
(C) A true, R false
(D) A false, R true

Try it first, then show the solutionSolution

Flood basalt provinces are the Deccan Traps example (1 mark).

Answer: (A)

Example 5: HOTS: why the core is liquid outside · 5 marks · Long answerHOTS / competency

How do we know the outer core is liquid even though nobody has reached it? (5 marks)

Try it first, then show the solutionSolution

Information comes from earthquake waves (1 mark).
S-waves cannot pass through liquid (1 mark).
They are absent beyond 105 degrees from the epicentre (1 mark).
P-waves are refracted giving a shadow zone between 105 and 145 degrees (1 mark).
So a liquid outer core with an inner solid core is inferred (1 mark).

Answer: Direct observation is impossible, so scientists use seismic waves. S-waves cannot travel through liquids, and they are not recorded beyond 105 degrees from an epicentre. P-waves are refracted at the core boundary, producing a shadow zone between 105 and 145 degrees. These observations show a liquid outer core around a solid inner core made of nickel and iron.

Where students lose marks in Layers of the Earth, Volcanoes and Intrusive Landforms

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

Mistake: Calling the core solid throughout
Inner core is solid.
Wrong working
Both cores are solid.
Right working
Outer core liquid; inner core solid.
Do this: Write both states.
Usually costs: 1 mark.
Mistake: Confusing lithosphere with crust
Both are outer layers.
Wrong working
Lithosphere is the crust.
Right working
Lithosphere = crust plus uppermost mantle.
Do this: Add "plus uppermost mantle".
Usually costs: 1 mark.
Mistake: Wrong example for shield volcano
Several famous volcanoes.
Wrong working
Deccan is a shield volcano.
Right working
Hawaii is shield; Deccan Traps are flood basalt.
Do this: Pair type and example.
Usually costs: 1 mark.

Exam tips

Draw a layered circle with depths marked.
Use the table for volcano types.
Say "nife" for nickel and iron.

Practice questions on Layers of the Earth, Volcanoes and Intrusive Landforms

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 · MCQBoard level
Which is the thickest crust?
(A) Oceanic crust
(B) Continental crust under the Himalayas
(C) Crust under the Deccan
(D) Crust at mid-ocean ridges
Hint
Up to 70 km.
Answer
(B).
Q2 · 2 marks · Very short answerBoard level
Continental crust is about 30 km thick and up to 70 km in the Himalayan region. How many times thicker is the Himalayan crust than the mean oceanic crust of 5 km? (2 marks)
Hint
Divide.
Answer
70 / 5 = 14 times.
Q3 · 3 marks · Short answerHarder board level
What are intrusive forms? Name and describe any three. (3 marks)
Hint
Batholith, laccolith, dyke.
Answer
Intrusive forms are bodies of lava that cool inside the crust. A batholith is a large granitic dome cooled deep; a laccolith is a dome with a level base joined to the source by a conduit; a dyke is a vertical sheet cutting across rocks. Sills are horizontal sheets.
Q4 · 3 marks · Short answerHarder board level
Distinguish magma from lava and explain how the nature of lava shapes a volcano, using shield and composite types. (3 marks)
Hint
Fluid versus viscous.
Answer
Magma is molten material in the upper mantle or moving towards the crust; lava is magma that reaches the surface. Very fluid basaltic lava spreads to build broad, gently sloping shield volcanoes, while cooler, more viscous lava erupts explosively with ash and debris and builds layered composite cones.
Q5 · 4 marks · Short answerHOTS / competency
Imagine a volcano that is the most explosive and collapses leaving a depression. Identify the type, and compare it with a shield volcano. (4 marks)
Hint
Caldera vs shield.
Answer
It is a caldera. A caldera volcano is the most explosive, with a huge magma chamber close below, and collapses on itself, leaving a depression. A shield volcano erupts fluid basalt with low explosivity and builds a broad, gently sloped, large cone, as in Hawaii.

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.What is the Moho?Show answer
The boundary between crust and mantle.
2.Which are granitic intrusive bodies?Show answer
Batholiths.
3.What is the mid-ocean ridge length?Show answer
Over 70,000 km.
4.How thick can a flood basalt flow be?Show answer
Over 50 m.

Layers of the Earth, Volcanoes and Intrusive Landforms: frequently asked questions

What does astheno mean?

Weak.

What is a dyke?

A vertical sheet of igneous rock cutting across layers.

Why is the continental crust thicker under mountains?

NCERT gives the fact that it is thicker under major mountains, up to 70 km in the Himalayas.