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Chapter 7

Volcanoes

Class 9 - Total Geography Morning Star


Match the following

Question 1

Column AColumn B
VentAn active volcano
Extinct VolcanoHot water fountain
GeyserDead volcano
Mt. StromboliAn opening in the earth's crust through which lava flows.

Answer

Column AColumn B
VentAn opening in the earth's crust through which lava flows.
Extinct VolcanoDead volcano
GeyserHot water fountain
Mt. StromboliAn active volcano

Short Answer Questions

Question 1

What is a volcano? Give one example.

Answer

A volcano is a vent in the earth's crust from which fiery hot magma erupts from the earth's interior. For example, Mt. Stromboli in Italy.

Question 2

What is the difference between magma and lava?

Answer

MagmaLava
The molten rock material inside the earth is known as magma.When magma reaches the surface of the earth, it is known as lava.

Question 3

Give one example each of an active volcano and a dormant volcano.

Answer

Active volcano - Mt. Etna in Italy
Dormant volcano - Mt. Kilimanjaro in Africa

Question 4

What is the difference between dormant volcano and an extinct volcano?

Answer

Dormant volcanoExtinct volcano
These volcanoes have not erupted in recent historical period.These volcanoes have not erupted in the present geological period.
They may become active at any time.They are not likely to become active again.
For example- Mt. Kilimanjaro in AfricaFor example- Mt. Kenya in Africa

Question 5

What is the magma chamber of a volcano? State the products erupted by a volcano.

Answer

The molten material while still under the earth's surface, melts weak rocks and creates a huge chamber for itself. Fresh magma continues to pour inside the chamber. This is known as magma chamber.

A volcano erupts a number of products like steam, gases, molten rock, dust, ashes and other liquid and solid matter.

Question 6

Name two types of landforms made by volcanoes. Give an example of each type.

Answer

Two types of landforms made by volcanoes are-

1. Volcanic Plateaus — For example, Plateau of Peninsular India
2. Volcanic mountains — For example, Mauna Loa in Hawaii

Question 7

What is the Pacific Ring of Fire? Why is it so called?

Answer

The Pacific Ring of Fire is near the earthquake belt around the young fold mountains. It is called so because over 80% of the total number of active volcanoes are concentrated in this region. Among these are included 40 active volcanoes in Andes, over 100 in the Philippines, 70 in Indonesia and 40 in Japan.

Structured Questions

Question 1(a)

Describe the two causes of volcanic eruptions.

Answer

The two causes of volcanic eruptions are-

1. Heat and Pressure inside the Earth — Temperature and pressure both increase from the surface towards the centre of the earth. Rocks are bad conductors of heat. So the earth’s heat does not escape on its own. Instead it melts the rocks and builds up great pressure. The pressure forces the heat to find an escape route through fissures and cracks in the rocks.

2. Plate Tectonics — Most volcanic eruptions take place near plate margins. When these plates slide past each other or collide against each other due to intense heat inside the earth's core, their edges produce faults along the lines of weakness. It is along these plate boundaries that the crust is weakened and through which the hot magma gushes out leading to volcanic eruptions.

Question 1(b)

Describe the two types of volcanoes, giving an example of each type.

Answer

The two types of volcanoes are-

1. Active volcanoes — These are the volcanoes which are presently in active state and which have erupted in the recent past. For example, Mt. Etna in Italy.

2. Dormant volcanoes — These volcanoes have not erupted in recent historical period. They may become active at any time. For example, Mt. Kilimanjaro in Africa.

Question 1(c)

Give a geographical reason for each of the following:

(i) Many volcanoes are found along plate boundaries.
(ii) Volcanic mountains are the most diverse mountains in the world.
(iii) Hot springs have medicinal properties to cure skin diseases.

Answer

(i) Many volcanoes are found along plate boundaries because when tectonic plates slide past each other or collide against each other due to intense heat inside the earth's core, their edges produce faults along the lines of weakness. It is along these plate boundaries that the crust is weakened and through which the hot magma gushes out leading to volcanic eruptions.

(ii) Volcanic mountains are the most diverse mountains in the world because there are great differences in volcanic eruptions as well as materials they throw up.

(iii) Hot springs have medicinal properties to cure skin diseases since they are a rich source of sulphur.

Question 1(d)

Draw a well labelled diagram showing the different parts of a volcano and the products erupted by it.

Answer

Draw a well labelled diagram showing the different parts of a volcano and the products erupted by it. Volcanoes, Total Geography ICSE Class 9.

Question 2(a)

Explain briefly the landforms created by volcanoes on the surface of the earth.

Answer

The landforms created by volcanoes on the surface of the earth are-

1. Volcanic Plateaus — These are derived from lava which flows from volcanic eruptions. For example, Columbian Plateau.

2. Volcanic Mountains — These mountains are built from material ejected from the fissures of the earth's crust. For example, Mauna Loa in Hawaii.

3. Volcanic Plains — These plains are formed by extensive volcanic flooding from volcanic centres. For example, Victorian Plains in Victoria.

4. Caldera Lake — A large depression at the summit of a volcano is called a caldera. When this depression gets filled with water, it forms a lake known as caldera lake. For example, Crater Lake in USA.

5. Hot springs — The movement of magma in the interior of the earth heats up underground water particularly around magma chambers. When water turns into steam, it gushes up to the surface. Hot springs are a rich source of sulphur. For example, hot springs at Manikaran in Kullu Valley, Himachal Predesh.

6. Geysers — It is a fountain of hot water and steam that escapes when underground water comes into contact with hot volcanic rocks. For example, the Old Faithful geyser in Wyoming, USA.

Question 2(b)

Write any three destructive effects of volcanoes.

Answer

Three destructive effects of volcanoes are-

  1. When the volcanoes erupt they destroy life and property. The hot lava together with ash and dust destroy not only human beings but also animals as well as plant life.
  2. Agricultural fields are covered with layers of volcanic ash and dust making them unsuitable for cultivation.
  3. Huge clouds are formed after the eruption of volcanoes causing heavy rains which result in floods and landslides.

Question 2(c)

Explain the following terms:

(i) Volcanic Cone
(ii) Caldera
(iii) Geyser

Answer

(i) Volcanic Cone — The erupted fluid material being hot collects around the vent and begins to cool gradually and solidifies. The accumulation of material around the vent gives to the volcano its typical cone-like shape known as a volcanic cone.

(ii) Caldera — A large depression at the summit of a volcano is called a caldera.

(iii) Geyser — It is a fountain of hot water and steam that escapes when underground water comes into contact with hot volcanic rocks. For example, the Old Faithful geyser in Wyoming, USA.

Question 2(d)

Describe world distribution of volcanoes.

Answer

Volcanoes are found along the weak zones of the earth’s crust where due to continuous tussle by tectonic forces maximum active volcanoes have created. The important volcanic zones of the world are-

1. Circum-Pacific Belt — The volcanoes occur near the earthquake belts around the young fold mountains. It is also known as 'Pacific Ring of Fire' because over 80% of the total number of active volcanoes are concentrated in this region. Among these are included 40 active volcanoes in Andes, over 100 in the Philippines, 70 in Indonesia and 40 in Japan.

2. Mid-World Mountain Belt — Mt. Stromboli, Mt. Vesuvius and Mt. Etna are located in the Midworld Mountain Belt. The only active volcano in India, in Andaman and Nicobar Islands is also located in this belt. The Hawaiian Islands, Canary Islands, Mt. Kenya are all in the Midworld Mountain belt.

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