Volcanic eruptions are activities that involve the movement of lava from the interior of the Earth to the Earth’s surface. They are divided into two categories:
- Intrusive: In this process, the underground lava does not reach the surface but cools below the surface, forming different structures such as dikes, sills, laccoliths, and volcanic necks.
- Extrusive: In this process, the materials from the Earth’s interior come out on the surface and form cones. Various substances like ash, lava, and gases are ejected during volcanic eruptions, leading to the formation of features like hot springs, geysers, fumaroles, and vents.
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Volcanic Eruptions
There are typically three types of substances that emanate from a volcano:
- Vapor and Gases – Water vapor makes up the majority of the gases emitted from a volcano, at 90 percent. Other gaseous forms, such as sulfur and carbon, are also released, many of which are flammable. Carbon dioxide and sulfur oxides are the main combustible gases.
As pressure decreases, the state of the gases changes. Due to intense heat and pressure underground, the gases remain dissolved in the lava, but as heat and pressure decrease, the gases separate from the lava.
- Fragmented Material – Small and large boulders are formed when gases separate from the lava through an explosion. These boulders can jump hundreds of meters high during an eruption and come in different sizes and shapes, some round, some oval, some long, and some cylindrical. These solids are formed in three ways:
(a) due to the breaking of the volcano’s walls,
(b) destruction of the lava stopper of the volcano, and
(c) due to the cooling of lava bodies.
Notable among the solids from the above three methods are volcanic dust and ash, nodules, bombs, embers or cinders, pumice, volcanic ash, and volcanic mud. These solid bodies range from fine-particle dust to tons of heavy boulders. The finest particles are called volcanic dust. Particles the size of millet or peas are called volcanic ash.
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, 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 distinctive shapes, including round, oval, long, and others, and range 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 a volcano eruption, heavy rain causes volcanic dust and ash to flow as mud, which is called volcanic punk. The city of Herculaneum was destroyed by the eruption of Vesuvius.
- Erupted Lava – Lava comes out of the volcano in liquid form, called magma. It contains various gases and minerals. Based on density, there are two classes of lava: super silicic lava and semi silicic lava. Supersilicic lava is yellow, light in weight, and 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 silicic magma, which contains 77 percent can.
Alpasilic lava is dark in color, relatively heavy and black, and 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 super silicic lava is basalt rock.
The speed of lava flow depends on the slope of the surface and the mobility of the lava. This speed is usually less than 16 kilometers per hour.
Volcanic eruptions can cause various consequences, including:
- Generation of Heat: Geothermal and chemical reactions cause an increase in heat in the Earth’s atmosphere, which increases the volume of substances that try to escape. The interior of the Earth is warm, and the melting of rocks in the Earth’s interior can lead to a huge amount of heat.
- Liquid Lava: Pressure from the rocks of the upper crust can cause the rocks in the Earth’s interior to become liquid due to intense heat. The liquid volume increases and tries to come out, leading to the eruption of the volcano.
- Elevation of Lava: The lava rises due to movement in the surface and the pressure of gases and vapors on the lava. As the pressure decreases, the vapors and gases present in the lava expand, leading to the eruption of the volcano.
- Gas and Vapor: A large amount of vapor is produced from underground water flow, especially near the sea. Volcanoes can erupt due to these gases. The decrease in the pressure of the upper rock can also cause the flow of liquid basalt, which is a by-product of the force of attraction.
Lava tries to break out from areas of the fold, fracture, and movement where the crust is often weak.
Volcano Types
There are various types of volcanoes categorized based on their eruption type, substances released, and volcanic cones. Below are the types of volcanoes based on these categories:
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Volcanoes Based on Eruptions
(a) Active Volcano – This type of volcano frequently erupts, and its mouth is always open. Vegetation is lacking around the mouth, and the cone is formed by newly cooled lava.
(b) Extinct Volcanoes – These volcanoes do not erupt and are closed due to the deposits of lava and other substances in their tubes. Over time, the closed mouth turns into a lake, and trees and plants grow on it.
(c) Dormant Volcanoes – This type of volcano has not erupted for a long time, but there is a possibility of an eruption. Gases and vapors come out of their mouths.
(d) Explosive Volcano – This type of volcano erupts explosively, and broken boulders and gases come out of its mouth.
(e) Effusive Volcano – Lava and gases come out of this type of volcano without any sound or explosion.
(f) Mixed Volcanoes – These are a combination of the above types of volcanoes and have both explosive and effusive eruptions. For example, Vesuvius, Etna, Kenya, and Rainier are all mixed volcanoes.
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Volcanoes Based on Cone Size, Type, and Composition
(a) Cinder Cone Volcano – These cones are formed by the cooling of lava at the mouth of the volcano. Ash cones are also found at the mouth of the volcano.
(b) Composite Cone Volcano – These volcanoes have alternating layers of lava and ash deposits, forming rock fragments and ash layers from the eruptive eruption. They are formed by the accumulation of several layers one after the other.
(c) Shield Volcano – These volcanoes are formed by the spread of more liquid lava over a wide area, forming hair cones. The lava keeps accumulating in parallel.
(d) Caldera Volcano – These are large, wide volcanoes with a wide cauldron square crater of ‘La Caldera’ at their base. Small new volcanoes are also found within its walls, formed by the small amount of re-eruption after the formation of the volcano.
Explosive submerged volcanoes are formed when the upper parts of the volcano’s cones are broken by a severe eruption. The explosion and the blown material spread around the volcano in the form of volcanic or concentrated dust or tuff. The rocks break into fine dust or ash during a severe eruption. Dust particles are carried by the wind to great heights, as in the 1883 eruption in Krakatoa.
Erupted volcanoes form submerged volcanic troughs, mostly in the form of lakes. For example, Weaver Lake in the United States of America Oregon state. Its diameter is 8 kilometers, and its depth is 600 meters. It is surrounded by steep sloping mountains that are the remains of tall cones.