The Earth has numerous geological processes that are happening within and upon it continuously. Heat from the accretion of the planet is continually lost and so this ongoing loss of heat is what drives these processes.
Why is this important?
The Earth’s crust is made up of giant “plates”. They are generated and destroyed by this heat we just discussed. New plates are created at the divergent (constructive) plate boundary. This is where the hot rock that is heated at the Earth’s core rises up. The tectonic plates are pushed apart and rising magma (the melted rock) from the mantle reaches the surface.
Fissure volcanoes with low viscosity melt will appear at the divergent plate boundary as tensional forces pull the plates apart. As the magma rises up through the crust it will generate a fissure eruption.
At the other side of the plates is the destructive plate boundary, this is where one plate is pushed beneath another (in the subduction zone). As the rock is forced deeper into the Earth the layer of rock becomes heated and so melts.
This continues the cycle where the melted rock moves and starts to rise again at the divergent plate boundary.
Volcanoes & Mountains
Okay so now I’m going to talk about Volcanoes and other mountains…don’t worry I will pull this stuff all together later.
Mountains are considered mountains if they are at least 2000 ft high and have an incline greater than 2 degrees. There are also different types of mountains.
For example, some mountains are created at the plate boundaries where the plates collide and one plate sinks below its neighbour (destructive boundary, remember J). The crust folds and buckles creating what are known as Fold Mountains.
Volcanic mountains are formed when liquid magma is forced upwards, then cools and hardens forming volcanoes. Volcanoes are mostly formed around plate boundaries as the pressure and friction creates enough energy to melt rock (as mentioned above, yes I will sometimes repeat myself).
Dome Mountains are also caused by magma. Pressure beneath causes the Earth’s crust to swell and “dome” but unlike volcanoes the magma does not break through so creates a dome rather than a cone shape.
Pressure along fault lines can cause slabs of rock to tilt creating what are known as Block mountains.
Wow all these fun facts about mountains, let’s move to volcanoes – stay with me people!!
Spreading Centre Volcanism is when volcanoes occur along the divergent plate boundary. The plates move apart, the hot magma rises up and spills out of the surface. This lava constantly accreted at the edges of the plate produces new oceanic crust.
Intraplate Volcanism is where volcanoes are produced within the plate rather than at its boundaries (like most volcanoes). Thermal plumes of heat from within the Earth rise up. This high temperature mixed with lower pressure at the bottom of the tectonic plate assists the melting of rock. Magma rises through the fractures and erupts.
The Hawaiian Islands are a great example of land formed by hot spots. They were formed in the middle of the Pacific plate and though the hot spot is a fixed form, the plate itself is still moving so over the many many thousands upon thousands of years as the plate moved the hot spot created more islands until there is a chain of them.
Subduction Zone Volcanism is where volcanoes are created at the destructive plate boundary (one plate is forced beneath another). So as one plate goes into the depths of the Earth it contains a lot of surface water and minerals from the seabed. The further down it goes the greater the heat and the pressure. Water is released and lowers the melting temperature of the mantle. The magma flows upwards forming stratovolcanoes in a linear belt (think Ring of Fire around the Pacific Ocean).
OMG so much science!!!
So what have we learnt?
We learnt that the planet has this massive active system that creates and destroys rock. We see that this immense process forms mountains by tearing apart the landscape. Volcanoes are made from these cycles of creation and destruction which run on heat and pressure. Islands can be formed by volcanoes.
Let’s throw in a little more information. At one time many of Earth’s current continents were connected as one super-continent known as Pangaea. It broke into pieces around 175 million years ago, not all at once but in three phases. This left us with continents spread across the globe that had once been connected.
The movement of these continents away from each other is often referred to as the Continental Drift and is caused by plate tectonics.
AN IDEA ABOUT LANDSCAPE
Now how do we apply this awesome science to world building?
Several ways, the better understanding you have for geological processes the better your world building can be.
Will you need all the science? Probably not, but knowing it can help. Think of the basics of description – if you have a long line of mountains, you don’t want to be describing them as dome shaped!
This kind of information about land formation can give you some great ideas for your story. For example – many cultures created divinity around such processes. The Fire Goddess Pele is from Hawaiian religion and is seen as the being who formed the Hawaiian islands.
Imagine if you are writing a sci-fi and you have a world on the brink of disaster. Top scientists are struggling to find ways to reduce this sudden increase of volcanic activity that has spread around your world. Why could it be happening? Knowing some of the science can help you build up plausible (as much as possible for fantasy/sci-fi) ideas that can pull the reader along for the ride.
Now I know this can sometimes be a little science lesson-y, and I will always try not to overdo it, but this is meant to make you think about the world you are creating and why some things have happened or could happen or will happen.
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