Volcanoes ICSE Class 9: Types, Effects and Volcanic Zones of the World

What Volcanoes is about

Weightage: CISCE publishes no chapter weightage and no question-paper layout for ICSE Class 9 Geography. Class IX is examined by your school: one 80-mark paper of 2 hours plus 20 marks of internal assessment (a record file and one project). Volcanoes is topic 2(d), Structure of the Earth, of the 2028 syllabus.Source: CISCE ICSE 2028 Geography syllabus, Class IX

Key concepts

Meaning of a volcano and why eruptions happen

A volcano is a vent or opening in the earth's crust through which magma, gases, steam, ash and rock fragments are thrown out on to the surface. The term also covers the conical hill or mountain built up around the vent by the erupted material.

Magma and lava: molten rock below the surface is magma; once it reaches the surface it is called lava.

Why eruptions happen:

• Temperature rises with depth, so rock in the upper mantle can partly melt, especially where pressure is reduced or water is added.
• Molten rock is lighter than the solid rock around it, so it rises and collects in a magma chamber.
• Gases (mainly steam, with carbon dioxide and sulphur gases) dissolved in the magma expand as it rises; their pressure finally breaks through weak zones in the crust.
• Weak zones are found mainly along plate boundaries: where plates move apart (divergent) and where one plate sinks under another (convergent). Some volcanoes, such as those of Hawaii, lie over 'hot spots' far from plate edges.

Materials ejected: lava; pyroclasts (fragments such as volcanic bombs, lapilli and ash); gases and steam.

Worked example

(2 marks) What is a volcano? Distinguish between magma and lava.

Try it first, then show the solutionSolution

1. Volcano: an opening in the crust through which molten material, gases and ash erupt - 1 mark.
2. Magma is molten rock below the surface; lava is the same material after it reaches the surface - 1 mark.

Answer: A volcano is an opening in the earth's crust through which magma, gases, ash and rock fragments erupt on to the surface. Molten rock beneath the surface is magma; when it pours out on the surface it is called lava.

Parts of a volcano (diagram checklist)

Draw a cross-section and label these parts:
1. Magma chamber: the reservoir of molten rock beneath the volcano.
2. Pipe (conduit): the passage through which magma rises.
3. Vent: the opening at the surface through which material escapes.
4. Crater: the funnel-shaped depression at the top of the cone, around the vent.
5. Volcanic cone: the hill built of layers of lava and ash (draw alternating layers).
6. Secondary (parasitic) cone: a smaller cone on the side, fed by a branch pipe.
7. Lava flow down the slope, and an ash and gas cloud above the crater.

Caldera: a very large basin-shaped depression formed when the top of a volcano collapses or is blown away after a huge eruption. It is much wider than a crater and may later fill with water to form a lake.

Where students lose marks: labelling the crater as the 'vent', drawing the magma chamber at the surface, or leaving out the pipe that joins chamber and vent.

Worked example

(2 marks) Distinguish between a crater and a caldera.

Try it first, then show the solutionSolution

1. Crater: the small funnel-shaped hollow at the top of the cone around the vent - 1 mark.
2. Caldera: a much larger basin formed by collapse or explosion of the volcano's summit; may hold a lake - 1 mark.

Answer: A crater is the funnel-shaped depression at the top of a volcanic cone around the vent. A caldera is a far larger basin formed when the summit collapses or is blown off in a violent eruption; it may later fill with water to form a lake.

Types of volcanoes by activity

Volcanoes are classified by how recently and how often they erupt.

1. Active volcanoes erupt frequently or have erupted in recent times and show signs of activity (gases, tremors).
Examples: Mount Etna and Stromboli (Italy), Mauna Loa and Kilauea (Hawaii), Barren Island in the Andaman Sea (India's only confirmed active volcano). Stromboli erupts so regularly that it is called the 'Lighthouse of the Mediterranean'.

2. Dormant (sleeping) volcanoes have not erupted for a long time but may erupt again; they still show signs such as hot springs or gas.
Examples: Mount Vesuvius (Italy), whose eruption of 79 CE buried Pompeii, last erupted in 1944; Mount Fuji (Japan) last erupted in 1707; Narcondam Island (India).
A dormant volcano can become active suddenly: Krakatoa (Indonesia) exploded violently in 1883 after a long quiet period.

3. Extinct (dead) volcanoes have not erupted in recorded history and are not expected to erupt again; their craters are often worn down or filled with water.
Examples: Mount Kenya (Kenya); Arthur's Seat in Edinburgh (Scotland).

The line between dormant and extinct is not sharp: some volcanoes thought extinct have erupted again, so geologists classify them with caution.

Worked example

(3 marks) Distinguish between active, dormant and extinct volcanoes, with one example of each.

Try it first, then show the solutionSolution

1. Active: erupts frequently or recently, e.g. Mount Etna or Barren Island - 1 mark.
2. Dormant: quiet for a long time but may erupt again, e.g. Vesuvius or Fuji - 1 mark.
3. Extinct: no eruption in recorded history and not expected to erupt, e.g. Mount Kenya - 1 mark.

Answer: An active volcano erupts often or has erupted recently (Mount Etna). A dormant volcano has been quiet for a long time but may erupt again (Mount Vesuvius). An extinct volcano has not erupted in recorded history and is not expected to erupt again (Mount Kenya).

Constructive effects of volcanoes

Volcanoes are not only destructive; they also build and enrich.

• Fertile soils: weathered lava and ash form rich soils. The black (regur) soil of the Deccan, formed from basalt, is ideal for cotton; volcanic soils on the slopes of Etna and in Java support dense farming.
• New landforms: lava builds mountains, lava plateaus (the Deccan Plateau, formed by fissure eruptions) and even new islands (the Hawaiian Islands, Iceland).
• Minerals: magma brings valuable minerals such as copper, gold, sulphur and diamonds (in kimberlite pipes) closer to the surface.
• Geothermal energy: heat from volcanic areas generates electricity and heats homes, as in Iceland and New Zealand.
• Hot springs and geysers: these attract tourists and are used for bathing and heating; Old Faithful geyser in Yellowstone (USA) is famous.
• Building materials: basalt is used for roads and buildings; pumice is used as a light abrasive.
• Tourism: volcanic landscapes and national parks attract visitors.
• Over geological time, volcanic gases helped form the early atmosphere and oceans.

Worked example

(3 marks) State three constructive effects of volcanic activity.

Try it first, then show the solutionSolution

1. Weathered lava forms fertile soil, e.g. black soil of the Deccan - 1 mark.
2. Lava builds new land, plateaus and islands, e.g. Deccan Plateau, Hawaii - 1 mark.
3. Volcanic areas provide minerals or geothermal energy, e.g. Iceland - 1 mark.

Answer: (1) Lava weathers into very fertile soil, such as the black soil of the Deccan used for cotton. (2) Lava builds new landforms: plateaus like the Deccan and islands like Hawaii. (3) Volcanic areas supply minerals and geothermal energy, as in Iceland.

Destructive effects of volcanoes

• Loss of life and property: lava flows, falling ash and rocks destroy towns and farms. Pompeii and Herculaneum were buried by Vesuvius in 79 CE.
• Pyroclastic flows: fast-moving avalanches of hot gas, ash and rock rush down the slopes and kill everything in their path.
• Ash fall: thick ash collapses roofs, buries crops and pollutes water; fine ash in the sky endangers aircraft. Ash from Eyjafjallajökull in Iceland closed much of European airspace in April 2010.
• Mudflows (lahars): ash mixes with rain or melted snow to form fast mudflows that bury valleys.
• Tsunamis and earthquakes: violent eruptions near or under the sea can set off huge waves, as Krakatoa did in 1883.
• Poisonous gases and acid rain: sulphur gases form acid rain and harm people and animals.
• Climate effects: fine dust and sulphur droplets in the stratosphere block sunlight and can cool the earth for a year or two, as after the eruption of Mount Pinatubo (Philippines) in 1991.
• Disruption of life: people must be evacuated; transport, power and water supplies are cut.

Worked example

(2 marks) How can a volcanic eruption affect air travel far from the volcano?

Try it first, then show the solutionSolution

1. Fine ash is carried high and far by winds - 1 mark.
2. It can damage jet engines and reduce visibility, so airspace is closed (e.g. Iceland, 2010) - 1 mark.

Answer: Fine volcanic ash is carried high into the atmosphere and spread over long distances by winds. Because it can damage aircraft engines and reduce visibility, airspace is closed and flights cancelled, as happened over Europe after the Icelandic eruption of 2010.

Important volcanic zones of the world

Volcanoes are not scattered at random; most lie along plate boundaries.

1. Circum-Pacific belt (Pacific Ring of Fire): a horseshoe-shaped belt round the Pacific Ocean, along the Andes and Rockies in the Americas, through the Aleutian Islands, Kamchatka, Japan, the Philippines and Indonesia to New Zealand. It has the majority of the world's active volcanoes. Examples: Cotopaxi (Ecuador), Mount St Helens (USA), Popocatépetl (Mexico), Fuji (Japan), Pinatubo (Philippines), Krakatoa (Indonesia). Cause: oceanic plates sinking under other plates (subduction).

2. Mid-continental (Alpine-Himalayan / Mediterranean) belt: along the young fold mountains from the Alps through the Mediterranean region to Asia Minor (Turkey). Examples: Vesuvius, Etna and Stromboli (Italy), Mount Ararat (Turkey). The Himalayas themselves have no active volcanoes.

3. Mid-Atlantic Ridge: an underwater mountain range down the middle of the Atlantic where plates move apart. Iceland lies on it and has many active volcanoes, such as Hekla. The Azores and Tristan da Cunha are also volcanic islands of the ridge.

4. East African Rift Valley: Kilimanjaro, Mount Kenya and the active Nyiragongo (Democratic Republic of the Congo).

5. Intra-plate hot spots: Hawaii in the middle of the Pacific (Mauna Loa, Kilauea).

India: Barren Island (active) and Narcondam (dormant) lie in the Andaman Sea, part of the arc that continues into Indonesia.

Worked example

(3 marks) What is the 'Ring of Fire'? Why does it have so many volcanoes? Name two volcanoes in it.

Try it first, then show the solutionSolution

1. The belt of volcanoes encircling the Pacific Ocean - 1 mark.
2. Oceanic plates sink beneath other plates; the melting produces magma along these weak boundaries - 1 mark.
3. Examples: Fuji, Pinatubo, Cotopaxi, Mount St Helens (any two) - 1 mark.

Answer: The Ring of Fire is the horseshoe-shaped belt of volcanoes around the edges of the Pacific Ocean. It has so many volcanoes because oceanic plates sink under neighbouring plates there; the descending plate melts, producing magma that rises through the weak crust. Examples: Mount Fuji (Japan) and Cotopaxi (Ecuador).

Volcanoes 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.

Topics in this chapter

• Volcanoes: Parts, Types, Effects and Volcanic Zones

Volcanoes: key facts

Magma vs lava

$Magma=moltenrockbelowthesurface;lava=moltenrockonthesurface$

Same material, different position.

Types by activity

Active (Etna, Stromboli, Barren Island); dormant (Vesuvius, Fuji, Narcondam); extinct (Mount Kenya, Arthur's Seat)

Always give one example per type.

Parts

1. 1.Magma chamber
2. 2.pipe
3. 3.vent
4. 4.crater; cone; secondary cone; caldera

Caldera much larger than a crater.

Constructive effects

Soil, new land, minerals, geothermal energy, hot springs and geysers, building stone, tourism

Deccan black soil; Iceland geothermal.

Destructive effects

Lava, pyroclastic flows, ash fall, lahars, tsunamis, gases and acid rain, cooling of climate

Pompeii 79 CE; Krakatoa 1883; Pinatubo 1991.

Zones

Ring of Fire; Mid-continental (Mediterranean) belt; Mid-Atlantic Ridge; East African Rift; hot spots (Hawaii)

Most volcanoes lie on plate boundaries.

How the school exam asks Volcanoes

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

Tricks to remember Volcanoes

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

• A-D-E

  Active = Awake (Etna); Dormant = Dozing (Vesuvius); Extinct = Ended (Mount Kenya).

  Use it when: Three types with examples.

• Ma-Pi-Ve-Cr

  Magma chamber, Pipe, Vent, Crater: the path of the magma from bottom to top.

  Use it when: Labelling the diagram in order.

• SNOW-GH

  Constructive effects: Soil, New land, Ores (minerals), Warmth (geothermal), Geysers, Hot springs.

  Use it when: Constructive effects.

Volcanoes: exam-level solved questions

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

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 7-mark question split into 2 + 3 + 2 marks.

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.

Where students lose marks in Volcanoes

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

• ✗Mistake: Calling Vesuvius extinct

  Students remember Pompeii as ancient history.

  Wrong working

  Vesuvius is an extinct volcano that destroyed Pompeii.

  Right working

  Vesuvius is dormant: it erupted in 79 CE and again in 1944 and may erupt again.

  ✓Do this: Extinct means no eruption in recorded history.

  Usually costs: 1 mark.

• ✗Mistake: Using magma and lava interchangeably

  Same material, different names.

  ✓Do this: Below the surface: magma; on the surface: lava.

  Usually costs: 1 mark in definitions.

• ✗Mistake: Writing only destructive effects

  Volcanoes are seen as disasters.

  ✓Do this: When asked for 'effects', give constructive and destructive points with examples.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Unlabelled or wrongly labelled diagram

  Crater and vent confused; chamber drawn at the surface.

  ✓Do this: Vent = opening; crater = depression around it; chamber below the ground line, joined by a pipe.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Naming zones without examples or causes

  Lists learnt without understanding.

  ✓Do this: Pair each zone with a volcano and a plate-boundary reason.

  Usually costs: 1 mark.

Practice questions on Volcanoes

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

1. Q1 · 1 mark · MCQExam level

   Which volcano is called the 'Lighthouse of the Mediterranean'?
   (a) Vesuvius
   (b) Etna
   (c) Stromboli
   (d) Hekla

   Hint

   Erupts regularly, small island.

   Answer

   (c) Stromboli.

2. Q2 · 1 mark · MCQExam level

   A large basin formed by the collapse of a volcano's summit is a:
   (a) crater
   (b) vent
   (c) caldera
   (d) geyser

   Hint

   Bigger than a crater.

   Answer

   (c) caldera.

3. Q3 · 2 marks · Very short answerExam level

   Name one volcano each from Japan and Ecuador and the zone they belong to.

   Hint

   Pacific.

   Answer

   Mount Fuji (Japan) and Cotopaxi (Ecuador); both lie in the circum-Pacific belt (Ring of Fire).

4. Q4 · 2 marks · Short answerHOTS / competency

   Why are there no active volcanoes in the Himalayas, though they lie in the mid-continental belt of young fold mountains?

   Hint

   Two continental plates.

   Answer

   The Himalayas were formed by the collision of two continental plates (Indian and Eurasian). Neither plate sinks deep enough into the mantle to melt and produce magma, unlike an oceanic plate at a subduction zone, so there is no active volcanism there.

5. Q5 · 2 marks · Very short answerHarder exam level

   What are lahars? Why are they dangerous?

   Hint

   Ash and water.

   Answer

   Lahars are mudflows of volcanic ash and debris mixed with rain or melted snow. They move fast down valleys and can bury villages far from the crater.

6. Q6 · 2 marks · Very short answerHarder exam level

   How does a volcano help in the formation of minerals and geothermal energy?

   Hint

   Magma brings up; heat stays.

   Answer

   Rising magma brings minerals such as copper, gold and sulphur near the surface; and the hot rock beneath volcanic areas heats groundwater, whose steam can drive turbines or heat homes (Iceland, New Zealand).

7. Q7 · 2 marks · Very short answerHarder exam level

   Explain why the black soil of the Deccan is linked to volcanic activity.

   Hint

   Fissure eruptions, basalt.

   Answer

   The Deccan Plateau was built by vast flows of basaltic lava from fissure eruptions. Weathering of this basalt over millions of years produced the fertile black (regur) soil.

8. Q8 · 3 marks · Short answerHarder exam level

   Name the five volcanic zones of the world and give one example of a volcano in each.

   Hint

   Pacific, Mediterranean, Atlantic, Africa, hot spot.

   Answer

   Circum-Pacific belt: Fuji. Mid-continental (Mediterranean) belt: Vesuvius. Mid-Atlantic Ridge: Hekla (Iceland). East African Rift: Nyiragongo. Hot spot: Mauna Loa (Hawaii).

9. Q9 · 3 marks · Short answerHOTS / competency

   A dormant volcano is often more dangerous to people than an active one. Give two reasons.

   Hint

   Complacency and pressure build-up.

   Answer

   (1) People settle close to a long-quiet volcano and farm its slopes, forgetting the danger, so more lives are at risk. (2) Gas pressure may build up for a long time behind a blocked vent, so when it finally erupts the explosion can be very violent, as at Krakatoa in 1883 and Vesuvius in 79 CE.

10. Q10 · 3 marks · Short answerHarder exam level

    Describe three destructive effects of volcanic eruptions with an example of each.

    Hint

    Burial, waves, climate.

    Answer

    (1) Burial of towns by ash and pyroclastic flows: Pompeii, 79 CE. (2) Tsunamis set off by eruptions near the sea: Krakatoa, 1883. (3) Ash in the upper atmosphere disrupting flights and cooling climate: Iceland, 2010; Pinatubo, 1991.

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. 1.Molten rock below the surface is called?Show answer

   Magma.

2. 2.Which volcano buried Pompeii?Show answer

   Mount Vesuvius, in 79 CE.

3. 3.India's only confirmed active volcano?Show answer

   Barren Island, Andaman Sea.

4. 4.Which belt has most of the world's active volcanoes?Show answer

   The circum-Pacific belt (Ring of Fire).

5. 5.On which ridge does Iceland lie?Show answer

   The Mid-Atlantic Ridge.

6. 6.Example of an extinct volcano?Show answer

   Mount Kenya (or Arthur's Seat, Edinburgh).

Quick revision checklist

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

• ☐Volcano: vent in the crust through which magma, gases and ash erupt; magma below, lava above.
• ☐Parts: magma chamber, pipe, vent, crater, cone, secondary cone; caldera = large collapsed basin.
• ☐Active: Etna, Stromboli, Mauna Loa, Barren Island. Dormant: Vesuvius, Fuji, Narcondam. Extinct: Mount Kenya.
• ☐Constructive: fertile soil, new land, minerals, geothermal energy, geysers, tourism.
• ☐Destructive: lava, pyroclastic flows, ash, lahars, tsunamis, gases, climate cooling.
• ☐Zones: Ring of Fire, Mediterranean belt, Mid-Atlantic Ridge, East African Rift, hot spots.

Volcanoes: frequently asked questions