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Why Do Volcanoes Erupt

Sheetal Mandora Oct 21, 2018
A volcano erupts through a rupture in planet's surface, allowing hot magma, ashes, and gases to escape. Get to know the reason for eruption.
It has taken four and a half billion years to create our planet, a world of extraordinary landscapes and a home to life. There are four powerful forces that have come together to create our world: the oceans, the atmosphere, ice, and volcanoes.
Volcanoes are terrifyingly destructive but are one of the most fundamental forces on the planet. They are part of a global system that continuously reshape our world, and play a major role in the formation of Earth's atmosphere and oceans. And they've formed an alliance that keeps our planet habitable.

Volcano Eruptions

225 million years ago, all the continents were joined together into a supercontinent, called Pangaea. As the plates moved, the supercontinent broke up into seven plates. This process occurred due to Earth's inner heat. The continents are moving at the rate of 2 centimeters a year, which means that in 1000 years, it will move 20 meters.
This number may not seem so big right now, but if we start thinking in terms of millions of years, just imagine how big the number can get. It happened because hot rock rises, heated by the Earth's core. Near the surface, the rock spreads in two directions, goes sideways, and begins to lose heat.
Through this process, the Earth's crust is slowly dragged apart and forces the continents to move. Ultimately, the much cooler rock sinks back down. This is the basis for all volcanic eruptions where an opening in the Earth's surface allows gases and molten rock to escape. The magma pushes itself through the cracks and forces the volcano to erupt.

Are Every Eruptions Different from One Another?

We know that majority of volcanoes take place on plate boundaries (Earth's surface shifting apart or meeting). Volcanoes develop on convergent (colliding) plates, divergent (separating) plates, and over hotspots. Let's go through the details and understand this concept clearly.

Colliding Plates

- 2 plates collide violently and 1 plate descends beneath the other, melting it and causing magma to rise
- Stratovolcanoes: large, cone-shaped volcanoes
- Mt. St. Helens in U.S., Mayon Volcano in Philippines, and Popocatepetl in Mexico

Separating Plates

- 2 plates move apart and stretch (mostly undersea), which forces hot rock to the surface
- Shield volcanoes: long undersea rifts filled with magma
- Mid-Atlantic Ridge, East Pacific Rise, and East African Great Rift Valley


- Plates move over hotspots, volcanoes spring up and die down
- Hotspot volcanoes: slow moving tectonic plate beneath the Earth's surface
- Hawaii hotspot, Galapagos hotspot, and St. Helena hotspot
The thickness of the lava or magma, the temperature, the gas contents, and the silica (crystalline rock material) also play an important role in the different kinds of volcanic eruptions. Combine all the aspects and you will know why do volcanoes erupt in certain places.
To understand this concept more clearly, imagine shaking a coke bottle vigorously and immediately opening the tab. The intense pressure built due to the trapped gas, results into a destructive volcanic eruption.