Earth measures more than 12,000 km in diameter, but our direct knowledge of our planet extends only to its outer layer. In fact – up to now – no drilling has penetrated more than fifteen km into the ground.
With indirect observations, such as the study of earthquakes, scientists have been able to establish a model of the interior of the planet.
The outer layer of Earth - composed of solid rock – is called “the crust”. At a depth of 10 to 70 km the curst is very thin on the scale of Earth as a whole.
The crust sits on “the mantle”, which takes up 80% of the planet’s volume. The upper part of the mantle is rigid, while at greater depths, the rock is partially melted at temperatures as high as 3,000 ° C.
Finally, the centre of Earth is called “the core”: it is an extremely dense area composed mainly of metals, where the temperature is above 6,000 °C.
Part of this heat, carried by the slow movement of the molten matter, rises toward the surface and warms Earth’s crust.
Volcanoes are the most explosive land forms, able to eject molten rock, clouds of thick ash high into the atmosphere with devastating consequences.
Volcanoes mostly occur along destructive and constructive boundaries, where plates are pushed together or dragged apart.
Cracks, or weaknesses, allow magma to rise up from below the Earth’s crust. Pressure builds up, which then releases suddenly, causing the magma to explode: a volcanic eruption.
Magma that reaches the Earth’s surface is called lava.
This molten lava eventually cools, to form new rock.
After more eruptions over time, the amount of rock builds up, forming a cone-shaped volcano.
Volcanoes all have the same key structure; a collection of magma underneath the volcano forms a hot bubbling furnace, called the “magma chamber”. The main vent allows this magma to escape, and secondary vents are smaller outlets where magma can travel through. The caved-in surface is called “the crater”. It’s created after an eruption blows the top of the volcano.
Eruptions occur when pressure forces magma from the chamber up the main vent towards the crater.
If the ashy mud mix with rain water or snow it creates fast-moving mud flows. The hot lava and overwhelming mud flows can destroy huge areas.
However volcanoes are also essential for life on our planet.
Scientists believe that volcanoes formed first Earth’s atmosphere by spewing water vapor, sulphur dioxide nitrogen, and carbon dioxide into the air, and volcanic eruptions continue to contribute to the carbon cycle, crucial to life, by releasing carbon dioxide.
They can go through long periods of being very active, but they may also become dormant, not erupting for hundreds or thousands of years. And eventually they can become extinct – just leaving a cone-shaped hill that never erupts again.