In simple words, volcanoes are formed due to volcanic eruptions.
Due to the decay of radioactive substances beneath the surface of the earth or in the earth’s mantle, a large amount of heat produced below the earth's surface, which melts the rocks slowly and forms a thick flowing layer of substance is called magma (consisting of the mixer of minerals, water vapor, different kinds of dissolved gases like carbon dioxide, sulfur, carbon monoxide, etc. Magma continuously exerts pressure on the earth's surface to escape from the earth's mantle. As a result, the surface of the earth becomes weaker at a point day by day and finally, a fault is formed at the weakest point of the earth surface through which magma come out the surface with the help of volcanic vent and form a conical like structure after a long period of time which is known as a volcano and the process, through which the volcanoes are formed is called volcanos.
2) Draw a figure and show their components
Answer:
Volcanic pipe: Due to Endogenetic forces, the magma comes out of the surface of the earth with the help of a channel or pipe, which is known as volcanic pipe or conduit.
Volcanic cone: When magma comes out of the surface of the earth with the help of a volcanic pipe, they become cool and settle down near the volcanic pipe. They continuously settle down and after a long period of time, the lavas form a conical or dome-like structure, which is known as a volcanic cone.
Volcanic vent: The chimney-like opening in the volcanic pipe of a volcano, from which lavas are emitted and spread all the directions, such chimney-like opening is called the volcanic vent.
Crater: crater is a circular depression area around the volcanic vent, which is found at the top of a volcano.
Sometimes, the mouth or vent of a volcano is closed due to cool and hard lava covering its mouth. When rainwater covers the crater, then the crater is called Crater Lake.
3) What are the products released during a volcanic eruption?
Answer: During a volcanic eruption, three types of products are thrown out from a Volcano.
1) Gaseous product: The most important constituent of volcanic gases is steam. A large amount of carbon dioxide, nitrogen, carbon monoxide, chlorine, with a small amount of Sulphur, water vapor, etc. are mainly present in a volcano. The density of magma is reduced due to the presence of dissolved gases.
2) Liquid product: Liquid emission from a volcano is called lava. Chemically lavas are consisting mainly of silica, oxygen, iron, a mixer of minerals, melted rock, etc.
On the basis of the presence of silica, the lavas can be dividing into two types-
Acidic Lava: In Acidic lava, the percentage of silica is greater than the basic lava. Since the percentage of silica is greater in acidic lava so they are yellow in color. They are more viscous and have less mobility than the basic lava. Acidic lava erupts from the central type volcanic eruption.
Basic Lava: In basic lava, the percentage of silica is less, but the percentage of magnesium is greater than the acidic lava. Hence, the basic lavas are black in color. They are highly fluid in nature due to the presence of dissolved gases.
3) Solid product: Besides gases and liquids, volcanoes are also ejected solid particles like rock fragments during a volcanic eruption, which are known as pyroclasts.
Depending on the size of rock fragments, the pyroclasts are divided into the following types
a) Volcanic Block: Bigger angular shaped rock fragments called volcanic block
b) Volcanic Bomb: Bigger rounded shaped rock fragments are called volcanic bomb
c) Lapilli: The rock fragments which size may be equal in gravel size are called Lapilli. Normally, their size ranges from 4 to 32 millimeters.
d) Ash: particles ranges between 0.25 and 4 millimeters are called ash.
e) Dust: particles size is less than 0.25 millimeters called dust.
f) Pumice: In viscous acidic lava, the vesicles may be so abundant that the rock takes the form of a light spongy mass, which is called Pumice. They are so light that they can float on water.
g) Scoriae: Scoriae are those bomb and Lapilli, which are spongy like Pumice, but they are more rugged and have a knife-sharp edge.
h) Tuff: It is a light, porous rock formed by the consolidation of volcanic ash and dust particles.
4) Write about its types.
Answer: Volcanoes are classified on the following basis-
a) On the basis of variation in the frequency of volcanic activity, the volcanoes are classified into three types-
• Active Volcano: Active volcanoes are those volcanoes, which erupt volcanic material continuously.
The volcanoes that occur along a great arc of The Pacific Ocean from chili to the East Indies are good examples of it.
• Dormant Volcano: The Volcanoes, which show volcanic eruption after a long period of time then volcanoes are called dormant volcanoes.
Mount Kilimanjaro, Tanzania, etc. are good examples of it.
• Extinct Volcano: The volcanoes, which are not showing any volcanic activity after a long period of time such volcanoes are called extinct volcanoes.
Mount Thieves in Oregon in the US and the mount Slemish in Co. Antrim is a good example of it.
b) On the basis of mode of eruption, the volcanoes are classified into two types-
• Central Type: It is a type of volcano, in which the products of volcanoes escape through a pipe.
• Fissure Type: It is a type of volcano, in which the products of volcanoes escape through a long or group of parallel fissures or closed fissures.
c) On the basis of the nature of the eruption, volcanoes are classified into two types-
• Explosive Type: It is a type of volcano, which contains Felsic magma, which is more viscous and less mobility so, they produce an explosive volcanic eruption.
• Quiet Type: It is a type of volcano, which contains mafic magma, which is highly fluid in nature so, they produce quiet volcanic eruptions.
The other types of Volcanoes are-
A) Hawaiian Type.
B) Vesuvian Type
C) Vulcanian Type
D) Stromboli Type
E) Plinian Type
F) Pelean Type
5) Write about the distribution of volcanoes over the world.
Answer: Like earthquakes, the distribution of volcanoes over the world is well marked and well understood because the volcanoes are found in a specific zone or belt. If we observe the globe map, then we are found that the volcanoes occur in the weaker zone of the earth’s crust.
There is three major belts or zone, in which most of the volcanoes are found.
a) The Circum pacific belt: The Circum Pacific Belt is also known as the volcanic zone of convergent plate margin. It is also known as rings of fire due to the presence of 420 active volcanoes in this belt.
This belt includes the volcanoes of western and eastern coastal areas of the Pacific Ocean or western coastal margin of North and South America and the eastern coastal margin of Asia.
Here, volcanic eruption takes place due to the collision between the American plates and the pacific plates or subduction of the Pacific plate below the Asiatic plate.
b) The mid-continental belt: The mid-continental belt is also known as the volcanic zone of a convergent continental plate margin.
This belt includes the volcanoes of The Alpine Mountain chain and the volcanoes of fault zones of East Africa.
Here, the volcanic eruption takes place due to the collision of the Eurasian plate, African plate, and Indian plate.
c) The mid-oceanic-ridge belt: The mid-oceanic-ridge belt is also known as the volcanic zone of divergent oceanic plate margin.
This belt includes the volcanoes of mainly of the mid-Atlantic-ridge.
Due to the movement of The American Plate and the Eurasian plate away from each other, a fault is formed at the weaker zone of the earth’s crust, through which the magma comes out the surface of the earth and form a mid-oceanic-ridge.
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