WBBSE Solutions For Class 8 Geography Chapter 2 Unstable Earth Topic B Volcanism

Chapter 2 Topic B Volcanism Analytical Type Questions

Question 1. What are the causes of volcanism? Or, How does volcanism take place?
Answer:

Causes Of Volcanism:-

There are various causes of volcanism.

These are

1. Presence of cracks in the earth’s crust:

At the time of the formation of the earth’s crust, there might have been some cracks, joints or any weak parts which help in the eruption of lava and induced volcanism.

2. Presence of molten rocks:

With increase in depth, the temperature and pressure of the rock layer increase. Naturally, rocks are supposed to melt at 2000°C temperature in the mantle. Due to high pressure, the rocks show elasticity.

WBBSE Class 8 Geography Chapter 8 Question Answer

But, with the unloading of pressure due to some reasons, the elasticity of the rocks is destroyed and the rocks begin to melt. This molten rock is more voluminous. As a result, it tries to gush out immediately through cracks.

Read and Learn More WBBSE Solutions For Class 8 Geography

3. Occurence of water into the earth’s interior:

Water from the oceans reaches the earth’s interior through cracks, joints, etc. It turns into vapour due to proximity with hot rocks and this helps in the upwelling of magma.

4. Plate tectonics:

There are 6 major and 20 minor plates in the world. Volcanism occurs along the boundaries of these plates.

Question 2. Classify volcanoes on the basis of their nature and duration.
Answer:

Classification Volcanoes On The Basis Of Their Nature And Duration:-

The volcanoes may be classified into three categories on the basis of their nature and duration.

1. Active volcano:

Active volcanoes are volcanoes which have been erupting continuously or frequently since their origin.

They are of two types

Incessant volcano:

Lava erupts continuously from this type of volcano.

Example-Vesuvius in Italy.

WBBSE Class 8 Geography Chapter 8 Question Answer

Intermittent volcano:

Lava erupts from this volcano after certain intervals.

Example-Etna in Sicily Island, Mauna Loa in Hawaii Islands, and Barren in India. Volcanic activities were recorded last in Barren in 2017.

2. Dormant volcano:

The volcanoes which remain inactive for a long period, but suddenly erupt violently and cause much damage are called dormant volcanoes.

Example-Fujiyama in Japan, Krakatau in Indonesia, and Narcondam in India.

3. Extinct volcano:

Volcanoes are considered to be extinct when there are no indications of future eruptions. The crater is filled up with water and lakes are formed.

Examples- are Mt. Popa in Myanmar, and Mauna Kea in Hawaii Island. (It may be pointed out that no volcano can be declared permanently dead, as what is happening below the earth’s surface, is still unknown to us).

 

 

Question 3. What are the effects of volcanic eruptions on the earth’s surface?
Answer:

Effects Of Volcanic Eruptions On The Earth’s Surface

The effects of volcanic eruptions on the earth’s surface can be discussed under two broad categories

Destructive effects:

The destructive effects of volcanic eruptions are

1. Earthquakes:

Volcanic eruptions are accompanied by earthquakes, which cause the destruction of life and property.

WBBSE Class 8 Geography Chapter 8 Question Answer

2. Tsunamis:

Volcanic activities in the seabed give rise to tsunamis, which causes widespread destruction.

3. Pollution:

Volcanic eruptions often emit poisonous gases, which cause air pollution. Forest fires: When lava flows through. forests, it causes forest fires.

Constructive effects:

The constructive effects of volcanic eruptions are

1. Formation of soil:

Black soil is formed by the rock particles ejected during volcanic eruptions. This soil is suitable for cultivating crops like cotton.

2. Minerals:

Volcanic activities often cause minerals to rise up near the surface of the earth.

3. Formation of landforms:

The lava that comes out from volcanoes solidifies on the earth’s surface, giving rise to plateaus, plains and even mountains.

4. Formation of islands:

Lava solidifies on the seabed, forming islands, for example, Barren Island.

5. Others:

Hot springs, geysers, etc., are also formed due to volcanic eruptions.

Chapter 2 Topic B Volcanism Short Analytical Type Questions

Question 1. What is a volcano? How does an igneous mountain form?
Answer:

Volcano:-

During volcanism, the lava flows around the crater, cools and solidifies in the shape of a conical hill. Then it is called a volcano.

Formation of Igneous Mountain:

According to the scientist McDonald, this mountain is formed due to the upwelling of magma in the following ways- along a convergent plate boundary, along the weak part along a divergent plate boundary, from the hotspots by convection currents.

 

Question 2. The atmospheric temperature of the earth is controlled by volcanism.— Explain.
Answer:

The Atmospheric Temperature Of The Earth Is Controlled By Volcanism:-

The surface temperature of the earth decreases in course of time due to radiation. Later on, ash, cinder, volcanic dust, and various gases mix with the atmosphere due to volcanic activities.

This helps to increase the temperature of the earth by trapping insolation in the long run. In this way, the temperature is indirectly regulated by volcanism. Greater incidences of volcanism in recent times is one of the primary causes of global warming.

WBBSE Class 8 Geography Chapter 8 Question Answer

Question 3. What is a Fissure Eruption?
Answer:

Fissure Eruption:-

When the magma from the earth’s interior oozes out through some small or big cracks on the earth’s surface without any explosion, it is called a fissure eruption. Example-Deccan Trap of South India.

Fissure Eruption Characteristics:

1. No craters are formed in this type of eruption.
2. The cracks are long.
3. Lava flows out without any explosion.
4. It is basic (non-acidic) and liquid in nature.

Question 4. Does volcanism occur along all types of plate boundaries?
Answer:

Most of the plate boundaries have volcanoes located on them, but there may not be any volcanism due to the variance of the speed of plate movement and thickness of the plates. For example, The Himalayan mountain region has no volcanoes.

About 80% volcanoes of the world are located along convergent plate boundaries while divergent and neutral plate boundaries have only 15% and 5% of volcanoes located on there respectively.

Question 5. Is there any relationship between volcanism and plate boundaries?
Answer:

Relationship Between Volcanism And Plate Boundaries:-

There is a close relationship between volcanism and plate boundaries because most of the active volcanoes are located along the plate boundaries.

Divergent plate boundaries:

Divergent movement causes the plates to move away from each other. As a result, the upwelling magma coming out through the intra-plate crack develops new landforms along this boundary, for example, mid-oceanic ridges.

Convergent plate boundaries:

Convergent movement causes the plates to move towards each other and collide. The heavier plate margin is subducted beneath the lighter plate margin. The subducted plate, after reaching the mantle, melts and the magma is forced to ascend as a volcanic eruption.

Example-Circum- Pacific Belt and Mid-Continental Belt.

Neutral plate boundaries:

Two plates slide past each other without any collision and result in faults and volcanoes.

Question 6. Why are dormant volcanoes extremely dangerous?
Answer:

dormant volcanoes extremely dangerous:-

The volcanoes which remain inactive for longer period of time but suddenly erupt violently, causing enormous damage, are known as dormant volcanoes. It is quite impossible to understand whether these volcanoes are dormant or extinct.

At any time, these volcanoes can erupt again and cause severe damage.

WBBSE Class 8 Geography Chapter 8 Question Answer

Example-Pinatubo volcano in the Philippines caused severe damage in 1991. Krakatau volcano in Indonesia suddenly became active after 200 years and destroyed three cities in the recent past.

Question 7. What is the Pacific Ring of Fire?
Answer:

Pacific Ring Of Fire:-

Around 70% of the active volcanoes of the world encircle the Pacific Ocean. There are about 106 active volcanoes on the east of the Pacific Ocean from Cape Horn in South America to Andes, Rocky and Alaska to the north.

The volcanoes include Popocatepetl, St. Helens, Cotopaxi, Aconcagua, etc. Again there are about 340 volcanoes from Bering Strait, Aleutian Islands, Kamchatka, Japan, Philippines in the east to the Indian archipelago in the west.

These include Fujiyama, Krakatau, Pinatubo, etc. Together they form a ring around the Pacific Ocean, known as the Pacific Ring of Fire.

Question 8. What are the disastrous effects of volcanoes?
Answer:

Disastrous Effects Of Volcanoes:-

Volcanoes have many disastrous effects such as- They can destroy settlements, forests and even civilisation. The ash, cinder and poisonous gases lead to the formation of smog, which can adversely affect our respiratory system.

These gases reach the atmosphere and damage the ozone layer of the stratosphere. The ash, smog and cinder create an atmospheric barrier that prevents sunlight from reaching us and consequently the temperature decreases in short term.

They can also cause massive destruction of life and property, for example, the destruction of the city of Pompeii due to the eruption of Mt. Vesuvius.

Class 8 Geography Solution WBBSE

Question 9. Point out the differences between magma and lava.
Answer:

The differences between magma and lava are as follows-

 

Question 10. What are the differences between acidic lava and basic lava?
Answer:

The following differences can be found between acidic lava and basic lava-

 

Question 11. Write down the differences between A’a lava and Pahoehoe lava.
Answer:

The differences between A’a lava and Pahoehoe lava are as follows-

 

Question 12. What do you mean by a hot spring?
Answer:

Hot Spring:-

The natural spring whose water is substantially warmer than the air temperature of the surrounding region is known as hot spring. When the groundwater reaches the hotter regions below the earth’s crust, the temperature of the water increases due to the contact with the hot magma.

Class 8 Geography Solution WBBSE

This water comes out through the cracks on the earth’s surface. As this discharges warm or hot water, we call it a hot spring. Examples-the hot springs of Bakreshwar in West Bengal, Rajgir in Bihar and Manikaran in Himachal Pradesh.

Question 13. Write a short note on the geyser.
Answer:

Geyser:-

A Geyser is a hot spring that spouts hot water and steam from the interior of the earth at fixed intervals of time.

Example-The Old Faithful Geyser at Yellowstone National Park in the USA spouts hot water at regular intervals.

Geyser Origin:

When groundwater comes into contact with hot magma, it begins to boil and produces steam, which then erupts along with the hot water.

Due to the upwelling of hot water and steam, the pressure of the water vapour in the outlet of the geyser decreases and the cool water enters there and warms up again.

Question 14. What are hotspots?
Answer:

Hotspots:-

Radioactivity in the earth’s interior leads to an increase in temperature at some places and from here, magma comes out because of the upward movement of the convection current in the asthenosphere. These are known as hotspots.

Example-Tibesti, Hogger, and Jebel Marra of mid-Sahara are examples of hotspots along the continental plate boundary.

Hotspots Characteristics:

1. Volcanoes may be located on hotspots.
2. The relative movements of the hotspot volcanoes are equal to the spreading of the sea floor.
3. There are 21 officially recorded hotspots in the world.

Chapter 2 Topic B Volcanism Short Answer Type Questions

Question 1. Define volcanism.
Answer:

Volcanism:-

Volcanism defined as the may be a combination of the processes of upwelling of magma from the interior of the earth to the surface through cracks, joints or weak parts of the crust and the solidification of lava on the earth’s surface.

Question 2. Why is volcanism called a geo-tectonic process?
Answer:

Volcanism Called A Geo-Tectonic Process:-

Eruption of magma due to volcanism causes fragmentation, displacement and folding of rocks. Solidified lava also forms new landforms on the surface of the earth. Thus volcanism is also called a geo-tectonic process. Caldera is a result of tectonic activities.

Question 3. What do you mean by extinct or dead volcano?
Answer:

Extinct Or Dead Volcano:-

Volcanoes are considered to be extinct when there are no indications of future eruptions. The craters of such volcanoes are filled with water forming lakes. Example- Mt. Popa in Myanmar.

Question 4. What is A’a lava?
Answer:

A’a Lava:-

The dense, sticky and viscous lava ejected from volcanoes is known as A’a lava in Hawaiian language.
This lava spreads over a distance slowly. It has thick layers fragmented into jagged blocks.

Class 8 Geography Solution WBBSE

Question 5. What is Pahoehoe lava?
Answer:

Pahoehoe Lava:-

Comparatively less viscous or highly fluid lava which spreads like sheets, is called Pahoehoe lava. It looks like twisted ropes due to rapid solidification.

Question 6. Why is volcanic eruption described as a land-building process?
Answer:

Volcanic Eruption Described As A Land-Building Process:-

Although volcanoes can cause catastrophic damage, they are also important for the formation of land. Volcanic eruptions cause fragmentation and disintegration of rocks, give rise to folds on the earth’s crust and thus create different landforms. They also give us new fertile soil.

Example-Caldera

which is a huge basin-like crater is formed as a result of volcanic activities.

Question 7. What is plume?
Answer:

Plume:-

If the temperature of the convergent boundary is higher than that of the neighbouring places, then that intra-plate region is called a hotspot. The upwelling of hot and molten magma through the asthenosphere to the hotspot is known as a plume.

Chapter 2 Topic B Volcanism Multiple Choice Questions Choose The Correct Option

Question 1. The force that causes volcanism is

1. Sudden endogenic
2. Slow endogenic
3. Sudden exogenic
4. Slow exogenic

Answer: 1. Sudden endogenic

Question 2. Fissure eruption is found at plate boundaries that are

1. Convergent
2. Neutral
3. Indefinite
4. None of these

Answer: 2. Neutral

Class 8 Geography Solution WBBSE

Question 3. Stromboli in Lipari is a volcano that is-

1. Active
2. Extinct
3. Dormant
4. Super active

Answer: 1. Active

Question 4. The only active volcano in India is the-

1. Barren
2. Aravallis
3. Narcondam
4. Nilgiris

Answer: 1. Barren

Question 5. Mt. Popa in Myanmar is a volcano that is-

1. Dormant
2. Extinct
3. Active
4. Super active

Answer: 2. Extinct

Question 6. In the Hawaiian language, the dense viscous materials that erupt from the volcanoes of Indonesia are called-

1. Pahoehoe
2. Poe Pa
3. A’a
4. Hoe-hoe-ah-ah

Answer: 3. A’a

Question 7. The predominant mineral in acidic lava is-

1. Silica
2. Aluminium
3. Iron
4. Gold

Answer: 1. Silica

Question 8. The state of basic lava is-

1. Liquid
2. Solid
3. Semi-Solid
4. Gaseous

Answer: 1. Liquid

Class 8 Geography Solution WBBSE

Question 9. Hotspots are formed in the-

1. Earth’s Crust
2. Core
3. Mantle
4. sea floor

Answer: 3. Mantle

Question 10. A highly explosive volcano is called-

1. Hawaiian type
2. Etna type
3. Plinian type
4. Iceland type

Answer: 3. Plinian type

Chapter 2 Topic B Volcanism Very Short Answer Type Questions Fill In The Blanks

Question 1. Rocks begin to melt at  ______________ °C in the mantle.
Answer: 2000

Question 2. With the upward rising of magma, the pressure and melting point ______________.
Answer: Decreases

Question 3. The eruption of the ______________  volcano destroyed the city of Pompeii in ancient Rome.
Answer: Vesuvius

Question 4. Acidic lava is more ______________ than basic lava.
Answer: Viscous

Question 5. Old Faithful of Yellowstone National Park in USA is an example of a ______________.
Answer: Geyser

Chapter 2 Topic B Volcanism Chapter 2 Topic B Volcanism Write True or False

Question 1. Krakatau is an active volcano.
Answer: False

Question 2. Volcanism is a type of geo-tectonic process.
Answer: True

Question 3. There is no indication of future eruption from a dormant volcano.
Answer: False

Question 4. The peak of an igneous mountain is flat.
Answer: False

Question 5. There is a hot spring in Sandeshkhali in the Sundarbans.
Answer: False

Chapter 2 Topic B Volcanism Match The Columns

1.

Answer: 1. C, 2. B, 3. D, 4. A

Chapter 2 Topic B Volcanism Answer In One Or Two Words

Question 1. Name one volcano of Europe.
Answer: Stromboli in Lipari island, Italy.

Question 2. What is volcanism along long cracks known as?
Answer: Fissure eruption.

Class 8 Geography WBBSE

Question 3. Which plateau in India is a result of a fissure eruption?
Answer: Deccan Plateau or Deccan Trap.

Question 4. Name an igneous mountain.
Answer: Kilauea in the Hawaiian Islands.

Question 5. Name a dormant volcano.
Answer: Fujiyama in Japan.

Question 6. Name an extinct volcano.
Answer: Paricutin in Mexico.

Question 7. Which type of lava is responsible for the formation of a conical volcano?
Answer: Acidic lava.

Question 8. Where does most of the volcanic activity of the world take place?
Answer: Pacific Ring of Fire.