What Causes Volcanic Eruptions?

We learn about the Earth’s different layers from a very early period of our schooling. It is composed of the inner core, the outer core, the mantle and the crust. Knowing this, we have to wonder, from where does the volcanic eruption we hear of arise from and what actually composes these eruptions. Well, let’s find out shall we?

Firstly let’s talk about what actually emerges from the vents of a volcano during a volcanic eruption. It’s Magma. Magma refers to molten rocks that form from the melting of the upper mantle or the lower regions of the crust. This level of magma forming melting occurs in these layers due to the movement of tectonic plates whether they’re pulling apart (divergent boundary) to create a rift zone or one plate is being pushed by another (convergent boundary). A volcano is essentially a vent, an orifice or an opening through which the molten magma and other dissolved gases in it can be released due to growing pressure from the magma. The molten magma is stored deep within the layers of the earth between the layers of the mantle and the lower crust in a region called the magma chamber. This chamber leads up the vent that is visible outside through which the major eruption occurs. The chamber can also have other branch points of magma release called sills or dykes or other side vents depending on their position from the crust and the magma chamber. There are three crucial factors that predominate and predetermine the eruption of a volcano and they are:

  • Buoyancy of the magma
  • Pressure from the gases formed from the magma
  • Injection of more magma into the already full magma chamber

The molten magma that formed from the melting of rocks is lighter than rocks, therefore they gain buoyancy and are pushed further up. If the magma formed is thick, the gases contained within them cannot readily escape, thus building up within the magma making them buoyant and increasing the pressure to be released. These readily volatile dissolved gases include water(H2O), Sulphur dioxide (SO2) and carbon dioxide(CO2). Magma that is deeper within the volcano, kilometers away from the vent has water content within it. However, as the pressure increases and the magma rises up, this water content ex-solves from the magma in the form of bubbles and is released.

Therefore, when the magma moves up, it’s water content is very diminished thus making the magma/gas composition very high. The ex-solving of water bubbles reaches about 75%, the magma now mostly composed of solid and molten fragments called pyroclasts erupts from the vent of the volcano.

Yet another means by which eruption can occur is due to the further melting of rocks, leading to formation of new magma which results in the overfilling of the magma chamber, forcing the magma to the top, leading to an explosive eruption. In case of underwater volcanoes, interaction of molten hot magma with water results in steam production which might apply enough pressure from the steam resulting in eruptions.

Volcanoes are classified into three states depending on their activities,

  • Extinct- These volcanoes have not erupted in recorded history and therefore are unlikely to erupt again.
  • Dormant- Currently not prone to eruption however they may erupt.
  • Active- Shows near future eruptive volcanic activity, these include volcanoes that produce ash falls, flows and or volcanic mudflows which are also known as lahars.

Scientists cannot fully predict the activities of volcanoes or their eruptions properly as of yet, however their history, previous eruptions and other details can provide clues as to when a possible eruption might occur. Towns and cities built near volcanoes and volcanic activities must be diligent and take note of any unusual weather activities or seismic occurrences. Currently monitoring earthquakes, it’s seismic activity’s frequency and depth along with gaseous patterns of sulphur dioxide emissions near volcanic regions provide information about any possible events. Such knowledge and predictability are truly what stands between disasters like that of eruption of Mount Vesuvius in ancient Pompeii and triumphant saving of people in the Philippines during the 1991 volcanic eruption of Pinatubo volcano. Such information is vital in carrying out timely evacuations and rescue missions to ensure the lack of casualties from such volcanic activities. Therefore knowledge, curiosity and further study of volcanic activity can truly help save civilizations and its people!

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