- A volcano is an opening in the Earth’s crust through which molten rock or magma from within the Earth’s upper mantle escapes. At the surface, it erupts to form lava flows and ash deposits.
- The Earth’s crust is made up of huge slabs called tectonic plates, which fit together like a big jigsaw puzzle. These plates constantly move, interacting with one another in three ways – moving away from one another, colliding with each other, or slide past one another. This movement puts pressure on the magma beneath the surface and causes volcanic eruptions.
- Volcanoes are typically found at the fault lines between these plates. There can be active volcanoes, which regularly erupt, dormant volcanoes, which are capable of erupting but haven’t recently, and extinct volcanoes, which will never erupt again. There are more than 1500 active volcanoes on the Earth. (We currently know of 80 or more under the oceans. An underwater volcanic eruption can lead to a tsunami, which is a large ocean wave that can turn destructive.)
- When an oceanic plate collides with a continental plate, the denser oceanic plate sub ducts under the lighter continental plate. The oceanic plate sinks further into the Earth’s mantle. High temperature and pressure causes the rocky mantle to melt and become liquid rock or magma. The magma rises up towards the Earth’s surface, and builds up in magma chambers. The magma in such a chamber is under great pressure. Pressure building up over months and years can gradually fracture the rock around it, creating a way for the magma to move upward to the surface, resulting in a volcanic eruption. When magma reaches the Earth’s surface, it is called lava. When the lava cools, it turns into rock.
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