Why do Volcanoes Erupt?

You may have heard about the eruptions of volcanoes like Mount Vesuvius and Mount Tambora that devastated the land surrounding them and killed thousands of people living in their vicinity. However, not many of us stop to question why or how a volcano erupts in the first place. It is indeed not only an interesting, but also a useful bit of knowledge to have about one of the most fascinating natural phenomena that occur in our world.

What is the process?

We know that deep within the earth, the temperatures are extremely high. In fact, it is so hot that some rocks gradually start melting and become a thick flowing substance called magma. This melting takes place in the layer of the earth’s interior called the ‘mantle’. The mantle is the layer between the dense, superheated core and thin outer crust of the earth. The immense heat from the core melts the earth’s mantle and this melted rock (magma) begins its journey to the surface. The melting may happen where tectonic plates are pulling apart or when one plate is pushed down under another.

Magma being a lighter and more viscous substance than the rock surrounding it, starts rising to the top and collecting in areas known as magma chambers. As the magma rises, bubbles of gas also form inside it. Eventually, some of the runnier magma charges through any vents or fissures in the earth’s crust and gets released onto the surface as lava. Hence, magma that is released through volcanoes are then called lava, which flow in every direction away from the volcano to surrounding areas.

For the magma that is thicker in nature, the gas bubbles are not able to escape easily and the pressure starts building as the magma rises. When the pressure that is building reaches a point where it is too high for the earth’s surface to handle, an explosive eruption happens from the volcano. Such eruptions may also occur suddenly if the rocky surface above the magma has eroded over time, allowing the pressurized magma to easily burst through. Explosive eruptions are what often cause mass death and destruction, as the lava flows with much greater force and heat intensity. It can melt anything in its path, and most human creations will succumb to its natural power. The aforementioned bubbles, which are of undissolved water and sulphur, then burst with the intensity of a gunshot and release plumes of ash into the atmosphere. This ash can suffocate plants, animals and humans.

Another way eruptions happen is when water underneath the earth’s surface happens to come in contact with hot magma and creates steam. This may happen when ocean water is able to slip into the earth’s mantle and mingle with the magma. Over time, the rock strength of earth’s surface decreases as the pressure builds, and the steam can gradually build enough pressure to cause an explosion through the volcano.

It is important to highlight that some volcanic eruptions are explosive while others are not. As explained, it depends on the composition of the magma. If it is runny and gas is able to escape easily, lava will simply flow out. This is easy for people to avoid as it flows slowly and gives them time to move away. However, if magma is thick and gas cannot escape easily, pressure builds up until there is a violent explosion for it to escape. Magma blasts into the air, and lava flows at a greater speed for a greater distance. This is often unexpected and harder to escape from.

What is the role of Climate Change?

Geological studies have shown that human-induced climate change will most likely cause an increase in volcanic activity around the world. This is primarily because climate change has caused melting of glaciers in the earth’s crust. These glaciers have an impact on the flow of magma to the surface, and so melting glaciers may cause more magma eruptions. Basically, after glaciers are removed, the surface pressure decreases and the magma can more easily propagate to the surface and thereby erupt.

A team of researchers in the UK found that with the advancement of glaciers over time, there was diminishing volcanic activity. In turn, the team found that as the climate warmed up due to global warming and glaciers melted, there were more frequent and bigger eruptions. It has been found that even relatively minor climate changes may have an influence on this. Hence, it can be concluded that today’s global warming could mean more frequent, and even greater volcanic eruptions.