Everything you need to know about the two great bands and more

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Besides the continuous bands of volcanoes on the ocean floor in large regions like the Mid-Atlantic Ridge, there are about 1,350 potentially active volcanoes on Earth. In fact, between 50 and 70 volcanoes erupt each year.

Yet each volcano is somewhat unique. From the formation and classification of volcanoes to the most explosive on Earth, THAT’S TO SAY sums up everything you need to know about these eye-catching geological structures. We’ll of course provide some (very cool) images along the way.

What is a volcano?

Simply put, a volcano is a break in the crust of a planet, like Earth’s, that allows hot lava, volcanic ash, and gases to escape from an underground magma chamber. During many eruptions, layers of these materials can build up, forming a volcano.

How are volcanoes formed?

Volcanoes can arise in different ways, but they always do so when there is magma, or partially molten rock, beneath the Earth’s surface. Then this magma rises through natural cracks in the crust or becomes trapped underground, where pressure builds until it violently explodes.

In the case of Earth, volcanoes occur because our planet’s lithosphere is broken up into plates of solid rock called tectonic plates. These float on a warmer, softer, partially molten layer known as the asthenosphere.

We must first understand both types of plate tectonic scenarios to understand how “certain” volcanoes form.

Converging Plate Boundaries

Convergent plate boundaries are areas where lithospheric plates are moving towards each other. When these plates collide, the thinner, denser plate is replaced by the thicker, less dense plate. The subduction plate is heated as it is forced deeper into the mantle, until it finally begins to melt. This produces magma chambers. Since magma has a lower density than the surrounding rock material, it melts and fractures through the overlying rock material to the surface.

Divergent Plate Boundaries

When tectonic plates move away from each other, they are called divergent plate boundaries. A crack forms when they separate, releasing the pressure. This pressure drop decreases the melting temperature of the mantle rocks. Then this newly molten magma explodes to the surface. This most often happens under the sea.


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