Provider of one of nature’s most awe inspiring displays and a force capable of destroying entire civilisations. Volcanoes are essentially a rupture in the earth’s crust, allowing magma to reach the surface of the earth.Magma is a hot fluid or semi-fluid material below or within the earth's crust, from which lava and other igneous rock is formed, it is made up of a combination of liquid, solids and gaseous material, which when reaching the surface becomes lava, cooling to then form igneous rocks.
To understand the origins of magma, we need to delve into the structure of planet Earth. Our planet is composed of a number of layers a little bit like an onion, the main two we need to be concerned about for this are the outer crust and the mantle.
We live on the outer crust, which is 3-6 miles thick under the oceans and 20-44 miles thick under the land, which compared to the rest of the planet is very thin.
Directly under the outer crust we can find the mantle, which is the largest layer of the earth. Although it’s extremely hot, it remains mostly as a solid, owing to the pressure being so intense the mantle is mostly unable to melt. However, in certain circumstances the mantle material can melt forming magma, making its way out through the outer crust.
Magma is most commonly produced around plate boundaries (we will touch on these in a future post) and is less dense than the rock surrounding it, if this is produced at ocean ridges it just hardens to form new crust material, however if this surfaces on land the magma will push up with great vengeance and furious anger, its intense heat melting more rock, adding to the melted mixture.
As it moves through the crust, magma collects in magma chambers below the surface of the earth, once the pressure reaches a high enough level, or a crack opens in the crust magma (now termed as lava) is discharged at the earth’s surface.
Volcanoes differ massively in terms of their destructive prowess. Some will explode violently destroying everything around it within minutes, whilst others seep lava out slowly, the severity mostly depends on the composition of the magma.
Generally, the most explosive eruptions are resulting from magma which has high levels of gas and viscosity, with subdued eruptions coming from the opposite end of this scale.
Although there are several typical eruption types the most destructive are termed as Plinian Eruptions, producing powerful upward thrusts of expanding gases, projecting pyroclastic material as high as 30 miles in the air. They can also produce fast moving lava flows destroying everything in their path. This type of eruption is accompanied with a sustained eruption plume and has been the type attributed to destroying and burying Pompeii in in the eruption of Mount Vesuvius in 79 AD.
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