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Volcanoes – Formation, Factors and Types

Grade 7
Jun 5, 2023

In this article, we’ll learn about Volcanoes and their formation, factors and types. Let’s begin


The earth’s structure is divided into four major components: the crust, mantle, outer core, and inner core. Each layer has its own chemical composition and physical state, and it can have an impact on life on Earth’s surface.

Plates shift as a result of movement in the mantle caused by variations in heat from the core, which can result in earthquakes and volcanic eruptions. These natural disasters then alter our landscape and, in some cases, endanger lives and property.


The Crust

The crust is composed of light elements such as silica, aluminum, and oxygen. Its thickness is also highly variable.


The crust, like the upper zone of the mantle, is broken into large pieces, much like a giant jigsaw puzzle. These are referred to as tectonic plates. This move slowly, gaining only 3 to 5 centimeters (1.2 to 2 inches) per year.

What drives the movement of tectonic plates is still unknown. It could be related to heat-driven convection currents in the lower mantle. Some scientists believe it is caused by the tug of different densities of crust slabs, a phenomenon known as “slab pull.” These plates will eventually converge, pull apart, or slide past each other. Most earthquakes and volcanoes are caused by these actions.


It is the second layer, which is divided into two parts, upper and lower. The thick layer is made of extremely hot, semisolid rock that is beneath the crust and is approximately 2,900 km thick and is composed of iron and magnesium.


When compared to the mantle, the core is twice as thick. The only liquid layer is the outer core, which is mostly iron and nickel alloy. It is approximately 2,300 km thick.

The liquid outer core controls the majority of the Earth’s magnetic field, allowing for spinning action as the Earth rotates. Because the core is extremely hot and under extremely high pressure, the iron and nickel are in liquid form. The inner core is mainly molten iron.



This layer, which is made up of the crust and a small amount of the upper mantle, is divided into several very slowly moving plates of solid rock that hold the continents and oceans.


The upper mantle causes the lithosphere’s plates to move on this hot, liquid magma just beneath the lithosphere.

Plate Tectonics

According to the plate tectonics theory, the earth’s outer layer, or lithosphere, is divided into several large pieces known as plates.

These are the tectonic plates that support the continents and oceans and move slowly but steadily across the Earth’s surface. The movement of the plates demonstrates that the continents are not fixed and have moved over time, as well as describes how and why earthquakes, volcanoes, and other natural events occur.

Plate Boundaries

A plate boundary is formed when these tectonic plates collide. These are classified according to the movement they make.

Convergent plate boundaries – Plates colliding with each other.

Divergent plate boundaries – Plates moving away from each other.

Plate boundary transformation – Plates slide against each other.




A volcano is an opening in the Earth’s crust through which hot liquid rock called magma from deep within the Earth erupts to the surface.

Volcanoes with the highest activity Kilauea is the world’s most active volcano, located in Hawaii. This volcano has been erupting for centuries, but not explosively. A major part of Kalpana Gardens was destroyed in May 1990, but no one was hurt as the lava moved slowly and people could escape.

Kilauea’s most recent series of eruptions began in January 1983 and is still ongoing. Iceland’s active volcanoes are another reason for the country’s fame. It is known as the Land of Fire and Ice because it is located where the Earth’s plates are moving apart.


Formation of Volcanoes

Volcanoes are formed by powerful internal forces on Earth. The rock in the mantle and lower crust melts and becomes magma as one crustal plate moves beneath another. Melting rock generates gases that combine with the magma.

Because the gas-filled magma is less dense than the solid rock surrounding it, it rises over time. Rising magma can form a magma chamber when it accumulates in a weak spot in the overlying rock. Magma chambers serve as reservoirs for volcanic materials.

Magma that reaches the surface erupts through a central opening known as a vent. When magma reaches the surface, it is described as lava. Lava cools and hardens after eruptions, forming a mound. This mound can grow after many eruptions. A crater is an area surrounding a volcano’s vent.

Some volcanoes are found in the center of a plate. Scientists believe these volcanoes form over a hot spot in the mantle. Rising plumes of magma break through as a plate moves over a hot spot. As the Pacific plate moved over a hot spot, the Hawaiian Islands formed.

formation of volcanoes

Occurrence of Volcano

Volcanoes frequently form in areas where plates are moving apart, and plates are moving together and in areas known as hot spots.

Figure 6, depicts the locations of active volcanoes at plate boundaries and hot spots. Many examples of volcanoes that form in these three types of environments can be found all over the world. Volcanoes will be explored in Iceland, on the island of Montserrat, and in Hawaii.

Occurrence of Volcano

Divergent Plate Boundaries

Iceland is a big North Atlantic Ocean island. Since it is close to the Arctic Circle, it has some glaciers. Because Iceland is part of the Mid-Atlantic Ridge, it has volcanic activity.

The Mid-Atlantic Ridge is a divergent plate boundary, which means that the plates of the Earth are moving apart. When plates separate, long, deep cracks known as rifts form. Lava flows from these rifts and is quickly cooled by seawater.

Figure 7, depicts the process by which magma rises at rifts to form new volcanic rock. More lava flows and hardens, accumulating on the seafloor. Volcanoes and rift eruptions can occasionally rise above sea level, forming islands such as Iceland. Surtsey, a new island, was formed during a volcanic eruption in 1963.

Divergent Plate Boundaries

Convergent Plate Boundary

Convergent plate boundaries are areas where the Earth’s plates move together. They include areas where an oceanic plate slides beneath a continental plate, and areas where one oceanic plate slides beneath another.

The South American Andes began to form when an oceanic plate began to slide beneath a continental plate. Volcanoes that form along the convergent plate boundaries erupt more violently than other types of volcanoes.

Magma forms when a plate sliding beneath another plate becomes deep enough and hot enough to partially melt. The magma is then forced to the surface, forming volcanoes such as the Soufrière Hills on Montserrat.

Convergent Plate Boundary

Hot Spots

Some areas at the Earth’s mantle-core boundary are thought to be unusually hot. Hot rock is forced toward the crust in these areas, where it partially melts to form a hot spot.

The Hawaiian Islands are located on top of a hotspot beneath the Pacific Plate. Several volcanoes have formed as a result of magma breaking through the crust. Figure 9, depicts the Hawaiian Islands, which are formed by volcanoes that rise above the water.

Hot Spots

Factors Affecting the Volcanic Eruption

Some volcanic eruptions, such as those from Soufrière Hills volcano, Mount Pinatubo, and Mount St. Helens, are explosive. In others, such as the Kilauea eruptions, lava flows quietly from a vent. What causes these variations?

Two major factors influence whether an eruption is explosive or quiet. The amount of water vapor and other gases trapped in the magma is one factor. The second factor is the extent of silica in the magma. Silica is a chemical compound made up of the elements silicon and oxygen.

Trapped Gases

When you shake a soft-drink container and then quickly open it, the gas in the drink suddenly releases pressure, spraying the drink all over. Gases such as water vapor and carbon dioxide are similarly trapped in magma by the pressure of the surrounding magma and rock.

As magma approaches the surface, its pressure decreases. This allows the magma’s gas to escape. During quiet eruptions, gas easily escapes from some magma. High-pressure gas, on the other hand, eventually causes explosive eruptions. For example, Mount St. Helens volcano.

Water Vapor

Water vapor is abundant in the magma at some convergent plate boundaries. This is because at some convergent plate boundaries, oceanic plate material and some of its water slide beneath other plate material. Explosive eruptions can result from trapped water vapor in magma.


Composition of Magma

The composition of the magma is the second most important factor influencing the nature of the eruption. Magma is classified into two types: silica poor and silica-rich.

Quiet Eruptions

Basaltic magma is characterized by a low silica content. It is fluid in nature and causes quiet, non-explosive eruptions like those seen at Kilauea.

This lava flows from volcanic vents and down the sides of volcanoes. This pahoehoe lava forms a rope-like structure as it cools. When the same lava flows at a lower temperature, it forms a stiff, slow-moving aa (AH-ah) lava. On Kilauea, you can even walk right up to some aa lava flows.

Quiet Eruptions

Explosive Magma

Explosive eruptions like those at Soufrière Hills volcano are caused by silica-rich, or granitic, magma. This magma can form when the Earth’s plates collide and one plate slides beneath another. Some rock is melted as the plate sliding beneath the other gets deeper.

The magma is forced upward by denser surrounding rock, comes into contact with the crust, and becomes silica-enriched. Because silica-rich granitic magma is thick, gas becomes trapped within it, causing pressure to build up. When an explosive eruption occurs, the gases expand rapidly, often carrying lava fragments with them.

Explosive Magma

Types of Volcanic Eruption

The shape of a volcano is determined by whether it was formed by a quiet or explosive eruption, as well as the type of lava used—basaltic, granitic, or andesitic (intermediate). Shield volcanoes, cinder cone volcanoes, and composite volcanoes are the three basic types of volcanoes.

Volcanic eruptions produce three distinct types of landforms.

Cinder Cone Volcano (Scoria Cones)

When a volcano erupts, it releases a large number of rock fragments. These rock fragments are known as pyroclastic fragments, and they are classified as volcano composites that differ from ordinary rocks due to their composition.

Cinder cone volcanoes are formed by pyroclastic fragments. This volcano is cylindrical in shape and is responsible for lava eruptions. The top of a volcano usually has a deep bowl-like crater that has grown outward from the force.

The way this works is fascinating: after each eruption, rocks form their own tunnel and shape the inside of the volcano. Cinder cone volcanoes have beautiful interiors because the stones are made of lava fragments and can have a pretty, glassy appearance.

Examples of Cinder cones are as follows:

CERRO NEGRO: Cerro Negro is a Nicaraguan active cinder cone. It is the newest in Central America, having first appeared in 1850.

PARICUTIN VOLCANO: The Paricutin volcano in Mexico is a cinder cone that erupted unexpectedly in a corn field. The eruption created a 420-meter-high cone that never erupted again.

Shield Volcano

Shield volcanoes got their name because they resemble a shield. The Hawaiian volcanoes are classic shield volcanoes.

Shield volcanoes are known for erupting fluid basalt lava. Explosions with lethal consequences are possible. They are, however, less common in shield volcanoes.

Because basalt has a low viscosity (is more watery), it can flow more easily on the surface. When these volcanoes erupt, lava flows for long distances.


MAUNA LOA: Mauna Loa is the world’s largest active shield volcano, located in Hawaii. It is also the tallest mountain in the world, from its base below sea level to its summit.

FERNANDINA ISLAND: In the Galapagos Islands, Fernandina Island is an active shield volcano.

Composite Volcano (Stratovolcanoes Volcano)

A composite volcano is a volcanic landform composed of layers of thick lava flows alternated with layers of ash, cinders, and rocks. These layers form a symmetrical cone with steep concave sides that curve inward.

MOUNT FUJI: A inactive composite volcano that last erupted in the early 1700s.

MOUNT TOBA: It is in Sumatra 100 kilometers long and 30 kilometers wide long volcanic crater (caldera).




Effect of Volcanoes

When volcanoes erupt, they frequently have immediate and dramatic effects on people’s lives and property. Lava flows annihilate everything in their path. Volcanic ash can collapse buildings, block roads, and cause lung disease in humans and animals in some cases.

Volcanic ash and debris can sometimes cascade down the volcano’s side. This is known as a pyroclastic flow. The temperatures inside the flow can reach temperatures high enough to ignite the wood.

People are frequently forced to abandon their land and homes when large eruptions occur. People who live farther away from volcanoes are more likely to survive, but falling debris can damage cities, towns, crops, and buildings in the area.

Human and Environmental Impacts of Volcanoes

The eruption of Montserrat’s Soufrière Hills volcano, which began in July 1995, was one of the largest recent volcanic eruptions close to North America.

People who lived nearby were evacuated because geologists predicted it would erupt. Large pyroclastic flows swept down the volcano on June 25, 1997. Cities and towns in their path were buried. The eruption killed 20 people who refused to evacuate.

Acid rain is formed when sulfurous gases emitted by volcanoes combine with water vapor in the atmosphere. Acid rain had a significant impact on the vegetation, lakes, and streams surrounding the Soufrière Hills volcano. The organisms that lived in the forest were forced to leave or died as the vegetation died.



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