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The formation of the highest mountains of Himalayas and Alps have been created by the bucking up of the geo synclines of tethys sea between Angaraland and Gondwanaland which pushed towards each other and forced the geosynclines to be lifted up forming the mountains. The Mid-Atlantic Ridge is the proof of the edge raised at the joint of continental plates which gives birth to several volcanic islands.

Basic – type lava sheet weather into fertile soil e.g.Deccan trap soil. Other useful feature of volcanicity is that the precious minerals come out with the magma near the land surface e.g. diamond and gold etc.

The molten rocks of vulcanicity is of considerable environmental significance other than soil fertility since it is the direct or indirect cause of several classes of landforms. Basic lava weather into more fertile soils.

There are three types of volcanoes e.g. active volcano which is still active in erupting magma dormant volcano which erupts in uncertain intervals and extinct volcano which has stopped eruption permanently it is also called dead volcano.

There are 80% active volcanoes around the Pacific ocean which is called the Ring of Fire.

(a) Some times the volcanic eruption takes place through several small holes which is known as fissure type volcanoes. 

(b) The volcanic cone made by the quick solidification of viscous lava and having steep slopes is known as spine or plug. 

(c) Caldera is the spacious crater of a volcano created by tremendous eruption. Crater lake in Oregon U.S.A occupies a caldera about 9 kilometre in diameter. 

(d) Mud Volcanoes — A volcanic cone made of the mud due to the eruption of muddy water is called a mud volcano. 

(e) Epicentre — It is the place of surface position immediately above the origin or focus of an earthquake. 

(f) ‘Ring of Fire’ — It is the belt around the pacific ocean where due to the weak crust 75% of active volcanoes exist forming a huge ‘ring of fire’ phenomenon.

(g) Cinder Cone — The volcanic cone built of small pieces and fragments of solidified lava and ash is called ‘Cinder Cone’.

The effects of volcanoes on human life are both positive and negative :

  Destructive influences : The deposition of lava makes the area very porous which creates water problem. The major flow of hot lava of Etna destroyed the whole area and property in Sicily. Mt. Vesuvius destroyed the city of Pompeii seven times since 79 AD. and the city of Herculaneum. 

Constructive Influences : Volcanoes have provided some fertile lands e.g. Java and Deccan plateau and areas of South Brazil. Various precious minerals come out on the upper part of the earth’s crust through eruption e.g. Diamonds of Kimberley and gold of Johannesburg in South Africa nickel deposits of Sudbury in Canada.

The materials thrown out of a volcano due to eruptions are of three types : 

1. Solid Materials : The solid materials include large fragments of rocks known as volcanic bombs. The finest particles include cinder volcanic ash and dust. 

2. Liquid Materials : The liquid materials include Basic lava and Acid lava. Acid lava has more of silica while Basic lava has low content of silica. 

3. Gaseous materials : The gaseous material is mainly composed of steam. The other gases include Oxygen Hydrogen Sulphuric acid Carbon dioxide etc.

Describe any three advantages of volcanoes. 

1. Many minerals from the interior of the Earth come on to the surface. 

2. Fertile soils like Black soil are made by breaking up of lava. 

3. Electricity is generated from gases emitted out during volcanic eruptions.

1. Hot interior of the Earth  

2. Steam and gases 

3. Faults and fissures.

Molten material moving under the earth’s crust is called magma. When magma comes to the surface of the earth it is known as lava.

Obviously volcanoes will be found in those regions where the crust of the earth is weak because lava can easily be discharged from such places. These are found in areas of Fold mountains. 

There are three main belts of volcanoes : 

1. Circum-Pacific Belt : This belt runs round the Pacific Ocean in Asia and the America. It starts from Cape Horn goes along the Andes and the Rockies to Alaska. From their it turns westwards and passing through Aleutian Islands Japan and Formosa goes to the Philippine Island. Here one branch goes to East Indies that is Java Sumatra and Bameo and other branch goes to New-Zealand. Some of the well known Volcanoes are Karakatoa (on a hilly island between Sumatra and Java) Mayon (N. Philippines) Fujiyama (Japan) Chimborezo and Cotopaxi (Equador S. America). 

2. Mid World Mountain Belts : This belt starts from the West Indies and passing through the Canavy Islands. The Mediterranean sea Caucasus mountains and Turkey reaches the Himalayas. Mt. Vesuvius (Italy) Mt Stromboli (Sicily) Etna (the Mediterranean sea) and Mt. Pelee (West Indies) are the important Volcanoes of this belt. 

3. African Belts : This belt follows the Great African Rift Valley. This belt running through Red Sea extends upto Africa. Important Volcanoes are Kilimanjaro Kenya Canary Islands St. Helena (Atlantic ocean).

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. 

These are : 

1. Cirum-Pacific Belt— It is also known as ‘ring of fire due to consisting 75% active volcanoes of the world. 

2. Mid-World Mountain Belt or Mid Continental Belt— It extends along the fold mountain zone of Alpine-Himalayan Region. Although this belt is noted for drastic earthquake but these are some of the very destructive volcanoes e.g. Stromboli Vesuvius Mt. Etna Mt. Pelee (West Indies). Out of these belts there are also various volcanoes scattered here and there.

There are about 500 active volcanoes. Most of them are confined to Circum-Pacific Belt and Mid World Mountain Belt.

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. 

These are :--

1. Cirum-Pacific Belt : It is also known as ‘ring of fire due to consisting 75 % active volcanoes of the world. 

2. Mid-World Mountain Belt or Mid Continental Belt : It extends along the fold mountain zone of Alpine-Himalayan Region. Although this belt is noted for drastic earthquake but these are some of the very destructive volcanoes e.g. Stromboli Vesuvius Mt. Etna Mt. Pelee (West Indies). Out of these belts there are also various volcanoes scattered here and there.

The landforms created on earth’s surface are called Extrusive Landforms. These include volcanic plateaus volcanic mountains and volcanic plains.

(a) Volcanic Plateaus : These are derived from lava which flows from volcanic eruptions. The Plateau of Peninsular India especially the north western Deccan is an example of lava plateau. Other examples are South African plateau Columbian Plateau and Ethiopian plateau. 

(b) Volcanic Mountains : These mountains are built from material ejected from the fissures in the earth’s crust. Volcanic mountains are the most diverse because there are great differences in volcanic eruptions as well as the materials they throw up. 

(c) Volcanic Plains : These plains are vast and smooth formed by extensive volcanic flooding from volcanic centres. The Western Victorian Plains in Victoria Australia are the finest examples of Volcanic Plains.

1. Seismology and Volcanology : Seismology is the science of study of earthquake and Volcanology is the science of study of volcanic phenomena.

2. Volcanic Dust and Volcanic Ash : The finely pulverised fragments of rock are called volcanic ash and very fine particles which blow into air are called volcanic dust.

Distinguish between Tilted Block mountains and Lifted Block mountains :-

1.  Active Volcano – Mt. Stromboli and Mt. Etna in Italy   

2. Dormant Volcano – Mt. Kilimanjaro of Africa.

‘Magma’ is the one word of several matters erupting out of a volcano e.g. lava, steam, cinderellas, stones, cinder, smoke etc.

Volcanoes are formed by the eruption of magma from the interior and deposited on the land surface and after cooling down take the shape of volcanoes.

(i) Magma and Lava : 

Magma : 

1. Magma is hot sticky molten material. 

2. It contains solutions of water and gases. 

3. It comes out during volcanic eruptions. 

Lava : 

1. Lava is solidified magma.

2. Gases and water disappear after evaporataion. 

3. It cools down as it comes into contact with atmosphere. 

(ii) Acidic Lava and Basic lava 

Acidic Lava :

1. It is highly viscous lava. 

2. It is light coloured like granite. 

3. It has low density. 

4. It has a high percentage of silica. 

5. It flows slowly and results in steepsided cones or lava domes.

Basic Lava : 

1. It is highly fine and thin. 

2. It is dark coloured like Basalt. 

3. It has high density. 

4. It is poor in silica. 

5. It flows rapidly as thin sheets resulting in shield cones.

  (iii) Cinder Cone : Volcanic cones are called Cinder cones when the material erupted consists of cinder and other solid particles. These cones have steep slopes because they consist of particles of large size. 

Composite Cone : The volcanoes which start as cinder cone and grown into large volcanic hills with alternating layers of lava and ash are called Composite cones. These cones are formed due to an explosive eruption followed by eruption of lava. Explosive eruption leads to the formation of a layer of ash while lava solidifies as a sheet on the layer of ash. This is followed by a quiet period and then the process gets repeated. 

(iv) Fissure type of volcanoes : A volcano is a vent in the earth’s crust out of which hot molten rocks (lava) flow. The hot rocks may also eject violently in the form of solid pieces. If the vent is in the form of a long crack then it is known as a Fissure Type Volcano. In this type volcanic activity occurs quietly the lava upwells silently and spreads over a large area giving rise to volcanic plateaux and extensive lava sheets. 

Central-type Volcanoes : If the vent in the earth’s crust is of such type that the rock materials come out and mounds hills or cones are formed than the volcanoes formed are known as Volcanoes of the Central type. Vesuvius and Fuji Yama are the best examples of this type. 

(v) Crater and Caldera : Crater forms the summit and Caldera the enlarged mouth or the sunken crater at the centre of a volcano. When water accumulates in a crater it forms a crater lake and in a caldera a lake like Taba lake of Sumatra. A crater is formed as a result of overflow of lava and calera as a result of subsidence. 

(vi) Laccoliths : Laccoliths are large lens-shaped intrusions which assume a dome shape. They vary in thickness and extent. When laccoliths are exposed on the surface they form low hills. 

Lapoliths : Lapoliths are saucer-shaped intrusive layer of solidified magma and sinks as shallow basins in rock-beds. 

(vii) Hot Springs : 

1. It is a stream of hot water issuing from the ground. The hot water flows unobstructed quietly and continuously. 

2. Hot springs are common where joints fissures and porous beds allow the free exit of water to the surface. The water becomes hot when it comes into contact with the heated rocks or upper heated steam lying deep into the earth’s crust.

Geysers : 

1. It is a hot spring which at regular or irregular intervals throws a jet of hot water and steam into the air. 

2. In the case of geyser the fissure or vent connecting the source of hot water to the surface is very narrow which greatly increases the pressure and temperature of the hot water and so when water comes out it rise high into the air.

Two types of landforms are :

1. Extrusive landforms : 

Extrusive landforms include crater composite cones caldere lava platforms. 

2. Intrusive landforms : 

Intrusive landforms include dykes batholiths laccoliths volcanic hill etc.

Two main types of volcanic eruptions are :

(a) Explosive and  

(b)Quiet or Hawaiian. 

1. The Explosive eruption are the most violent and destructive Explosion of pent up gases mainly steam cause enormous quantities of magma to be thrown into the air to form great clouds. Example Krakatoa volcano in Sunda Strait in Indonesia erupt in 1883. 

2. The Quiet eruption cause and other gases to escape. There is no violent explosion. Lava flows the creaters and flows down the sides of the cone. 

Example : Hawaiian volcanoes and Maupa Loa.

Tectonic movements are changes through earth’s natural activities which are known as ‘diastrophism’. These movements are of two types e.g. vertical movement and horizontal movement.

The magma chamber is created by the molten magma itself by melting the surrounding rocks in the form of a huge chamber.

1. Movements of the earth’s crust along lines of weakness produces great tremors. 

2. During volcanic activity movement of lava beneath the crust also causes tremors inside the earth.

1. Earth movements like Continental Drift theory changed the whole face of the earth into distinct continents and oceans of today with highest mountains plateaus plains drainage system and so on. 

2. Internal processes are associated with tectonic forces resulting in drastic changes e.g. earthquakes volcanoes etc. External processes are carried on by natural agents of change e.g. water wind and ice which produce gradual changes. 

3. Folding and Faulting frequently go together because the stress on folding exceeds more than enough then folds break through fault line to two pieces slipping one upon another which is called faulting. 

4. Inspite of various changes occurring within the earth it does not expand as it is affected by the centripital force of gravity working towards the centre of the earth.

1. The forces arising from the interior of the earth are called endogenic forces. 

2. The molten rock that reaches the surface of the earth is called magma. 

3. A lava shield is made up of basic lava flows solidified away from the vent. 

4. Vents are intrusions of igneous rock that are vertical in shape. 

5. The Circum-Paciflc Belt is also called Pacific Ring of Fire.

Dormant volcano can erupt at any interval but extinct volcano can never erupt again.

Crater of a volcano is the mouth of volcano in its vertex in the form of a circular hole.

Mauna Loa (Hawaii islands).

Stromboli  is light house of the Mediterranean .

Crater, ash, dyke, domes.

1. The volcanoes and earthquakes are associated with each other as every volcanic activity takes place by shaking and breaking the weak crust which naturally creates tremors and earthquakes within the earth’s crust. 

2. Basic lava cones are formed by liquid lava which expands and covers a large area while the Acid cones are formed by solid material e.g. ash cinders etc which heap up but do not cover large area and form a high conical hill as compared to broad and low volcanic deposits on the surface. 

3. The circum-pacific belt is truly known as “The Belt of Fire” or “The Ring of Fire” as 75% active volcanoes erupting fire are located in this belt.

Destructive Effects : 

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. 

4. Volcanoes also emit poisonous gases which pollute the environment and cause health problems. 

5. Explosive volcanoes in ocean islands are followed ‘by high Tsunami waves. They flood the area and destroy property people animals and crops.

Most of the active volcanoes are formed along the fold mountains such as the Himalayas, The Alps, The Andes etc. Fold mountains have been formed by mountain building movements. These involve intense folding and faulting which mark lines of weakness on the surface. Most of the eruptions take place along these lines of weak.

Circum Pacific Belt.

The materials thrown out of a volcano due to eruptions are of three types : 

1. Solid materials :- The solid materials include large fragments of rocks known as volcanic Bombs. The finest particles include cinder volcanic ash dust. 

2. Liquid materials :- The liquid materials include basic lava and Acid lava. Acid lava has more silica while Basic lava has low content of Silica.

3. Gaseous materials :- The gaseous material is mainly composed of steam. The other gases include Oxygen Hydrogen Sulphuric acid Carbon dioxide etc.

It causes the pressure to build up which results in violent explosion.

Karakatoa island is situated between the islands of Java and Sumatra in the Sunda strait. It suddenly erupted in 1883. The top of the mountain was blown away by the explosion 16 metres high tidal waves were caused killing 36,000 persons in west Java. Volcanic dust rose to a height of about 27 kilometres. This dust encircled the globe for 3 years. Its effect caused strange sunrise and sunset conditions.

A volcanoes erupting with plentiful lava spreading over the surface into several kilometres with huge circumference and taking a shape of shield are called as shield volcanoes.

Adverse effects of volcanoes 

1. Most of the recently formed volcanic areas are barren and forbidding to man. 

2. The sudden flow of basic lava from an eruptive volcano may cause the total destruction of human life property and crops in the neighbouring areas. 

3. The Karakatoa volcanic eruption (in 1883) caused such high sea waves that Karakatoa and several other neighbouring islands were completely destroyed. 

4. Volcanoes eruption of Vesuvius in 79 A.D. buried and destroyed completely the two Roman towns of Pompeii and Herculaneum. 

Beneficial effects of Volcanoes : 

1. The soil made up of lava is very fertile. 

2. Lakes are formed when the craters are filled up with waters. 

3. Several minerals which are found deep down come up near the surface of the earth. 

4. Lava flows have preserved many fossils which throw much light on the past life.

The main causes of volcanic eruptions are the following : 

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. The same forces that cause earthquakes also cause volcanic eruptions.

3. Magma Chamber : The molten material while still under the earth’s crust melts weak rocks and creates a huge chamber for itself. Fresh magma continues to pour inside the chamber. Since magma contains silicate materials gases and water vapours the pressure always acts vertically upwards. Once a route is found it rises to the surface

Volcanoes are the vents in the earth’s crust erupting hot magma from the interior core motivated by endogenic forces.