Question 1

Question 2How are volcanoes caused?

Accepted Answer

The main causes of volcanism can be summarised as follows:The temperature inside the earth's crust increases with increase in depth at the rate of 1°C per 32 metres. The high temperature and pressure inside the earth crust, which increases with increase in depth is responsible for instability. Molten magma under great pressure has the capacity to liquefy great volume of gases.The surface water that percolates through the cracks and crevices, turns into steam due to hot rocks. The steam being very powerful, forces itself through the weak points of the earth crust along with molten material.The plate tectonics or the movement and splitting of the major and minor plates of the earth cause cracks, crevices and fissures in the earth's crust through which the magma is poured out.

Question 2

Question 9State three beneficial effects of volcanoes.

Accepted Answer

Three beneficial effects of volcanoes are:They lead to formation of geysers and springs. These are important from health and medical point of view.The crater lakes serve as great source of perennial rivers. For example, Lake Nyos in South Africa.Precious stones are found in volcanoes. For example, diamonds in South Africa.

Question 3

Question 10Mention three adverse effects of volcanoes.

Accepted Answer

Three adverse effects of volcanoes are:They cause extreme destruction of forests, cities and lives in large area.Volcanoes eject poisonous gases that cause pollution and health problems.The volcanic area becomes inhabitable by man. The rain water is immediately percolated due to high porosity.

Question 4

Question 11Describe the distribution of volcanoes.

Accepted Answer

Volcanoes generally occur in the weaker zone of the earth crust and are characterized by young fold mountains. The following are the three belts of volcanic eruptions:The Circum-Pacific Belt (Ring of Fire) — It extends through the Andes of South America, Central America, Mexico, the mountains of western U.S.A, the Aleutian Islands, Kamchatka, the Kurile Islands, Sakhalin, Japan, Philippines, Celebes, New guinea, the Solomon Islands, New Caladonia and New Zealand.Mid-Atlantic— This belt includes the volcanoes of Mid-Atlantic ridge. It also includes the volcanoes of Lesser Antilles, Southern Antilles, Azores, St. Helena, etc.Mid-Continental— This belt includes the Volcanoes of Alps Mountains, Mediterranean Sea (Stromboli, Vesuvius, Etna, etc.) and volcanoes of Aegean Sea, Mt. Ararat (Turkey), Elbrus, Hindukush and the Himalayas.

Question 5

Question 12Explain in brief, how a volcanic eruption is caused.

Accepted Answer

The temperature inside the Earth increases at the rate of 1° per 32 metres of descent. It results in very high temperature as well as extreme pressure deep inside the Earth. The molten lava inside the Earth, turns surface water (which percolates through the cracks and crevices to the interior) into steam. This steam and other compressed gases put pressure on the Earth's crust. The movement of Tectonic plates cause cracks, crevices and fissures in the Earth's crust through which the magma is poured out.

Question 6

Question 13Classify volcanoes on the basis of their intensity of eruption.

Accepted Answer

On the basis of intensity of eruption, volcanoes are of three types:Active volcanoes — They constantly eject lava, gases and ash. For example- Sabancaya in Peru.Dormant volcanoes — They remain dormant but can suddenly erupt and again go dormant. For example- The Vesuvius volcano in Italy.Extinct volcanoes — They are volcanoes where there has been no volcanic activity since long. Their crater usually developes into a lake. For example- For example- Arthur's seat at Edinburgh in Scotland.

Question 7

Question 15Give one example of an active volcano.

Accepted Answer

Sabancaya in Peru in South America is an example of an active volcano.

Question 8

Question 14Assertion (A): The lava and ash deposited during an eruption breaks down to provide valuable nutrients for the soil and thus create fertile soil.Reason (R): Agricultural fields are covered with layers of volcanic ash and dust making them unsuitable for cultivation.Both A and R are true and R is the correct explanation of A.Both A and R are true but R does not explain A.A is true but R is false.A is false but R is true.

Accepted Answer

Both A and R are true and R is the correct explanation of A.Explanation — Agricultural fields are covered with layers of volcanic ash and dust making them unsuitable for cultivation, but only temporarily. In fact, once weathered and broken down the lava and ash deposited during an eruption provides valuable nutrients to the soil making it fertile.

Question 9

Question 4Volcanos have constructive effects in favour of man.

Accepted Answer

Volcanos have constructive effects in favour of man because:Lava from plains are very fertile. For example- plains in Java, Malwa region in Deccan plateau and parts of Brazil.Lava activity also provides us precious stones.Geyser and springs are formed that provide water with health benefits.Crater lakes are formed which serve as source of water to perennial rivers. For example-Lake Nyos.Sometimes remnants of volcanoes after erosion helps in preserving traces of old civilization.

Question 10

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.

Accepted 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 11

Question 2(a)Explain briefly the landforms created by volcanoes on the surface of the earth.

Accepted 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 12

Question 2(b)Write any three destructive effects of volcanoes.

Accepted Answer

Three destructive effects of volcanoes are-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.Agricultural fields are covered with layers of volcanic ash and dust making them unsuitable for cultivation.Huge clouds are formed after the eruption of volcanoes causing heavy rains which result in floods and landslides.

Question 13

Question 2(c)Explain the following terms:(i) Volcanic Cone(ii) Caldera(iii) Geyser

Accepted 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 14

Question 2(d)Describe world distribution of volcanoes.

Accepted 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.

Question 15

Question 1Imagine that you had gone for a holiday and an extinct volcano erupted. List the consequences.

Accepted Answer

If an extinct volcano erupted during a holiday, it could have significant consequences. Here are some of the potential outcomes:Lava flows — The eruption could produce fast-moving lava flows, which could endanger the lives of the people and cause damage to properties.Ash clouds — The volcanic ash cloud could disrupt flights, causing travel chaos for tourists. It could also cause respiratory problems for people with pre-existing health conditions.Landslides and mudflows — The eruption could trigger landslides and mudflows in the surrounding areas.Environmental damage — The eruption could have long-term environmental effects, such as damage to vegetation, wildlife habitats, and ecosystems. Climate changes could also result from the eruption.Economic impact — The eruption could cause significant economic losses for the tourism industry in the region.Emergency response — The eruption would require an emergency response to evacuate people from the area and provide them with basic necessities such as food, water, and medical supplies.

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