What Causes a Volcanic Eruption?

The Reason Why Volcanoes Erupt

• Volcanoes can be found all over the world; some are dormant, some active and others extinct. The reason why these volcanoes exist or have existed is because molten rock, called magma, underneath the crust of the Earth has found its way up to the Earth's surface. When magma emerges into the Earth's atmosphere it is called lava, and this constitutes a volcanic eruption. Volcanic eruptions can be explosive and violent at one end of the scale or calm and slow at the other, depending on certain contributing factors.

Movement of Tectonic Plates

• Many volcanoes are found where the Earth's tectonic plates are pushing together or pulling apart. Movement of tectonic plates can push magma towards the Earth's crust. When tectonic plates slide past each other, magma can be pushed towards the surface of the Earth and out through a volcano. Alternatively, when plates pull apart magma will move through the gap and travel towards the surface. Lava flowing out of a volcano is a sign that magma has finished its journey up through the Earth's crust.

Pressure of Magma Trying to Reach the Earth's Surface

• Volcanoes have been erupting around the world since the Earth was created, and they are the exit points for magma traveling towards the Earth's surface. When it reaches the surface, the lava may flow gently out of the volcano, but this not always the case. If a volcano has not erupted for a long time the conduit within the volcano may have become blocked with hardened lava. If the volcano has been plugged, the pressure of magma being pushed upon it will increase until it is strong enough to push the plug out of the volcano conduit. When this happens the result is an explosive and violent volcanic eruption.

Areas Where the Earth's Crust has Become Thin

• Another factor that can cause a volcanic eruption is places where the Earth's crust has become thin or stretched. The pressure of magma, which would normally be withheld by the thickness of the Earth's crust, can weaken thin patches. The magma slowly pushes up through the area of crustal thinning and can create volcanic fields where lava flows out of multiple points within a close proximity of each other. The Wells Grey-Clearwater volcanic field is a example of volcanic eruptions occurring because of a thin area of the Earth's crust.