The activities which are related to the movement of lava flowing from the interior of the earth to the earth’s surface are called volcanic eruptions. On this basis, they are divided into two classes.
1. In penetrating action, the lava of the underground does not reach the surface, but stays below the surface and cools down, and becomes solid. As a result of this action, different forms are formed from the earth’s surface, in which Mahasangh, Chhatrak, Samur Shale, Newtubz Shale, wing and circle wing, lava plate, etc. are prominent.
2. In the extrusion process, the substances of the earth’s womb come out on the surface and form cones. The ejection of various substances from the earth’s womb brings about volcanic eruptions. Under this process, hot springs, tropospheres, evaporators, and cracks come.
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There are usually three types of substances emanating from a Volcano
1. Vapor and Gases- Water vapor is the main in the gases that come out of the volcano. Its quantity is 90 percent. The gaseous forms of sulfur and carbon also come out. There are many flammable gases in them. Carbon dioxide and sulfur oxides are the main ones in combustible gases.
When the pressure decreases, the state of the gases changes. Due to the intense heat and pressure underground, the gases remain dissolved in the lava, but as the heat and pressure decrease, the gases separate from the lava.
2. Fragmented material – Small and large boulders are formed when the gases are separated from the lava with the explosion. These boulders jump hundreds of meters high in the eruption. They have different sizes and types, some are round, some are oval, some are long and some are cylindrical. These solids are formed in three ways
(a) due to the breaking of the walls of the volcano, and
(b) the destruction of the lava stopper of the volcano,
(c) Due to the cooling of lava bodies.
Volcanic dust and ash, nodules, bombs, embers or cinders, pumice, volcanic ash, and volcanic mud are notable among the solids from the above three methods. These solid bodies range from fine-particle dust to tons of heavy boulders. The finest particles are called volcanic dust. Particles equal to millet or peas are called volcanic ash.
The betel nut-shaped pieces are called lapilli. Large angular rock fragments ranging from one inch to several meters in diameter are called volcanic bodies. When a piece of molten lava spins and goes into the air. So it assumes circular and elliptical forms with rotation.
At the same time, it also becomes tough. When they fall to the ground, they are called volcanic bombs. They have round, oval, long, and different types of distinctive shapes. These are also from a few centimeters to 1 meter in diameter. They are often hollow.
The rough, angular, and red material thrown out of the volcano is called an ember. It is a light and porous material. Sometimes after the eruption of a volcano, there is heavy rain, due to which volcanic dust and ash start flowing in the form of mud. This is called volcanic punk. The city of Herculaneum was destroyed by the eruption of Vesuvius.
3. Erupted Lava – Lava comes out of the volcano in liquid form. This is called magma. Various gases and minerals are found in it. Based on density, there are two classes of supersilicic lava and semisilicic lava. Supersilicic lava is yellow. Its weight is light. It melts at high temperatures. It is thick and flows very slowly. A light pink-colored rock called rhyolite is formed by the cooling of super silica magma. The quantity of can in it is 77 percent.
Alpasilic lava is dark in color. It is relatively heavy and black. It melts at low temperatures. Being thin, it flows faster. Gases are also mixed in it, but after cooling on the surface, it starts solidifying soon. When solidified, this lava solidifies in layers like glass, but the best example of supersilicic lava is basalt rock.
The flow speed of lava depends on the slope of the surface and the mobility of the lava. This speed is usually less than 16 kilometers per hour.
Volcanic Eruption causes the following consequences
1. Generation of heat: The increase of heat in the earth’s atmosphere increases the volume of substances from which they try to escape. The basis of the origin of this heat is geothermal and chemical reactions and disintegration. The interior of the Earth itself is warm. The loss of this primitiveness occurs in the melting of the rocks of the earth. Chemical changes occurring in the interior, such as the dissolution of flammable substances, also give rise to a huge amount of heat.
2. Liquid Lava – Due to the pressure of the rocks of the upper crust, the rocks of the Earth’s interior cannot remain in a liquid state. Whenever the upper crust pressure is reduced due to fracture and erosion. So the melting point of the rocks decreases. As a result, the rocks of the earth’s womb become liquid due to intense heat. As they become liquid, their volume increases and they try to come out, which leads to the eruption of the volcano.
3. Elevation of Lava – The lava rises due to two reasons, first, the movement in the surface and second, the pressure of gases and vapors on the lava. Due to the movement of the crust, the pressure decreases and the vapors and gases present in the lava also expand and the lava Throws it up.
4. Gas and Vapor- A large amount of vapor is produced from underground water flow. Its action is more near the sea. Volcanoes erupt due to these gases. At the same time, due to the decrease in the pressure of the upper rock, there is a flow of liquid basalt, which is a by-product of the force of attraction.
For the above-mentioned reasons, lava, wherever it finds the crust of vapors and gases weak, tries to break out from there. The crust is often weak in areas of the fold, fracture and movement.
Type of Volcano
There are many types of volcanoes. They are classified based on the method of extraction and the substances released. Many scholars have given their distinctions based on volcanic cones. With the help of all the above-mentioned bases, the following distinctions of volcanoes are told.
1. Volcanoes based on eruptions
(a) Active Volcano – Eruption often takes place in this volcano. Their mouth is always open and there is a lack of vegetation near the mouth. Cone is formed by newly cooled lava.
(b) Evacuated Volcanoes – They do not have to erupt action. The deposits of lava and other earthy substances in their tube get closed and the mouth is closed. Over time, the mouth turns into a lake, on which trees and plants grow.
(c) Dormant Volcanoes – These have not erupted for a long time, but there are possibilities of it. Gases and vapors come out from their mouth.
(d) Explosive Volcano- This type of volcano erupts with eruption and the broken boulders and gases come out from the mouth. (e) Ejected Volcano – Lava and gases come out from this type of volcano without any kind of sound. There is no banging sound in them.
(f) Mixed Volcanoes: These are dependent forms of erupting and erupting volcanoes. In these, sometimes the lava erupts peacefully, and sometimes due to eruption, Vesuvius, Etna, Kenya, and Rainier are all mixed volcanoes.
2. Volcanoes based on size, type, and composition of cones
(a) Cinder Cone Volcano – Cones are formed by the cooling of lava at their mouth. Similarly, ash cones are found at the mouth of the volcano.
(b) Mixed Cone Volcanoes: In this category are those volcanoes in which lava and ash deposits have been alternately deposited. In these, the deposition of cones is the deposition of rock fragments and ash layers from the eruptive eruption. In this way, compound cones are formed by the accumulation of several layers one after the other.
(c) Slope Volcano – Hair cones are formed by the spread of more liquid lava over a wide area. In these, the lava keeps on accumulating in parallel.
(d) Kund Volcano – There are also some such volcanoes whose mouth is wide on the base of the wide cauldron square crater of ‘La Caldera’. New volcanoes of small size are also found within its walls, which are formed due to the small amount of re-eruption after the formation of the volcano.
When a submerged volcano is formed by a very severe eruption that breaks the upper parts of the volcano’s cones, it is called an explosive submerged volcano. In these, the explosion and the blown material spread around the volcano in the form of volcanic or concentrated dust or tuff. When the eruption is very severe, the rocks break so much that they turn into fine dust or ash. Dust particles are carried by the wind to great heights, as in the 1883 eruption in Krakatoa.
Formation of Erupted Volcanoes Submerged volcanic troughs are formed when the cistern is pacified. These are mostly in the form of lakes. The Weaver Lake in the United States of America’s Ogan state is of this type. Its diameter is 8 kilometers and its depth is 600 meters. It is surrounded by steep sloping mountains which are just the remains of tall cones.