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Why Do Volcanoes Erupt

Sheetal Mandora
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.

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Over four and a half billion years, Earth has formed into a diverse planet, shaped by four major forces: oceans, 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.

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Volcano Eruptions

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225 million years ago, Pangaea, a supercontinent, comprised all continents. Plate movements due to Earth's inner heat caused Pangaea to split into seven plates. Continents currently move at 2 centimeters yearly, projecting a 20-meter shift in 1000 years.

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This number may not seem significant now, but over millions of years, it can become immense. Hot rock rises from the Earth's core, spreads near the surface, and begins to lose heat as it moves sideways.
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.

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Are Every Eruptions Different from One Another?

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Most volcanoes occur at plate boundaries, where the Earth's surface shifts apart or collides. They form on convergent, divergent, and hotspot plates. 

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

Hotspots

- 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 lava or magma, temperature, gas content, and silica all influence various types of volcanic eruptions. Understanding these aspects reveals why volcanoes erupt in specific locations.

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To understand this concept, imagine shaking a Coke bottle vigorously and then immediately opening the tab. The intense pressure from the trapped gas leads to a destructive volcanic eruption.