The Origin of Volcanoes

Introduction

Volcanoes originate from the deep mantle beneath the Earth’s surface. Solid rocks melt to form magma due to the movement of tectonic plates and a gradual increase in the temperature. The magma level rises with the increasing pressure until it erupts out of the opening on the Earth’s surface. Therefore, tectonic plates play a remarkable role in volcanism, along with other factors such as magma viscosity and temperature.

A volcano is an opening in the Earth’s crust that allows an abrupt eruption of gas, molten rocks, and ash. In contrast, volcanism involves the explosive movement of molten material from the chambers to the ground. A volcanic eruption is an endogenic process. The energy required for this process originates within the Earth. Volcanoes develop when pressure builds in the Earth’s crust, specifically where the tectonic plates diverge or converge.

Origin of a Volcano

Due to a gradual increase in temperature, some rocks melt and get converted into a molten material called magma. As magma is lighter than its surrounding rocks, it emerges through the opening in the Earth’s crust. The magma that flows out and accumulates on the ground is called lava and appears as a mountain or plateau formation, causing volcano formation.

Magma

Magma is a hot liquid or molten rock material found beneath the Earth’s surface and is rich in minerals. Therefore, several volcano-affected areas comprise ores for stones like opals and metals like aluminium. Magma contains dissolved gases like sulphur, nitrogen compounds, traces of argon and hydrogen, and water vapour. There are three types of magma, namely, basaltic, andesitic, and rhyolitic, each differentiated by their chemical composition.

Origin of Magma

Several layers comprising the inner and outer cores, mantle, and crust form the Earth’s structure. Magma is formed beneath the Earth’s crust. The Earth’s mantle, specifically the asthenosphere, acts as an essential magma source. When sufficient magma is accumulated in the magma chambers, it pushes its way up to the opening due to a shift in temperature, pressure, or tectonic plates, leading to a volcano. 

Magma Viscosity

A highly viscous and thick magma leads to more explosive volcanic eruptions. The gases remain trapped in the thick magma and are pushed forward under excessive pressure; however, these gases and vapours do not require a higher force to escape in less viscous magma. Therefore, the volcanic eruption is less explosive in this case. The viscosity of magma is directly proportional to its silica content and inversely proportional to its temperature.

Types of Volcanoes

We can categorise volcanoes into three types based on the frequency of eruption:

1. Active volcano: An active volcano is a type of volcano that has recently erupted and has a possibility of re-eruption.
2. Dormant volcano: This type of volcano has not erupted for several years; however, it may erupt soon.
3. Extinct volcano: This volcano may have erupted a long time ago and has no possibility of re-eruption in the future.

Role of Tectonic Plates

Most of the volcanoes are formed at the boundaries of the Earth’s tectonic plates. These plates move continuously at a glacial pace. Often, these plates either collide with each other or drift apart. Volcanic eruptions commonly occur in these active boundaries, specifically in divergent and convergent plate boundaries.

Divergent Plate Boundaries

The tectonic plates drift apart at a divergent boundary, but they do not separate as the magma continuously moves upwards from the asthenosphere into this boundary. The East Pacific Rise and the Mid-Atlantic Ridge are home to several submarine volcanoes and have divergent plate boundaries.

Convergent Plate Boundaries

The tectonic plates move towards each other at a convergent plate boundary and collide. Often, this causes the plate edge with high density to sink beneath that with low density. The consistent shifting and sinking of plate edges create subduction zones leading to deep trenches. Consequently, there is an increase in the pressure and temperature surrounding these plate edges. Therefore, the molten rock or magma rises above the plate and erupts through the surface, leading to a volcano. The Ring of Fire is a strip of 425 Pacific Ocean volcanoes that lead to aluminium eruptions due to convergent plate boundaries.

Conclusion 

The volcanoes originate from divergent or convergent movement of the tectonic plates, change in temperature and pressure beneath the Earth’s crust and the mantle, and subsequent eruption of molten rock material or magma from the magma to the Earth’s surface. Once the magma reaches the Earth’s surface, it is called lava. The mountains and plateaus in volcanoes are solidified lava and volcanic debris.