There is a super hot mixture of molten and semi-molten rocks that flows deep beneath the Earth's surface and it is called magma. But what exactly is magma and how and where does it come from? In today's video we'll learn what magma is, what types of magma there are and how magma is formed.
And if you stay until the end, I will explain what is the difference between magma and lava. First, let's learn about the composition of magma. Magma is a hot, viscous material that consists of inorganic components such as minerals and rocks, as well as dissolved gases, all embedded in the melt, which is the hot liquid base of the magma. The composition of the magma depends on the type of magma that we're talking about. Depending on the chemical composition of the magma, we can classify magma in three different categories.
These categories are basaltic magma, andesitic magma, and rhyolitic magma. Let's start with basaltic magma. Basaltic magma has the lowest concentration of silica, about 45 to 55 weight percentage, and it is high in iron, magnesium, and calcium, and low in potassium and sodium. Basaltic magma also has the lowest gas content and the lowest viscosity of the three types of magma. It's also the magma with the highest temperatures.
The second type of magma is endocytic magma. This one has a higher weight percentage of silica than the basaltic magma, about 55 to 65 in weight percentage, and it has moderate amounts of iron, magnesium, calcium, potassium, and sodium, as well as moderate amounts of gases. Andesitic magma has a lower temperature and a higher viscosity than basaltic magma. Finally, we have the rhyolitic magma, which has the highest weight percentage of silica of around 65 to 75 and it is low in iron, magnesium and calcium, and high in potassium and sodium, and it also has a higher gas content. Rhyolitic magma has the lowest temperature of all the different magma types, and it has the highest viscosity.
There you have it, the different types of magma and their characteristics. One of their characteristics was the viscosity of the magma, which is a property that describes a fluid. So how come magma stays fluid?
To find out the answer to this question, let's first have a look at the earth's layers. Earth consists of four main layers, the inner core, the outer core, the mantle, and the crust. This brief view of Earth's layers is enough for now, but if you're interested in learning more about these layers, I'll discuss them in more details in a future video.
Now, going back to the magma, it originates deep beneath the Earth's surface, in the lower crust and the upper mantle. At those depths, the magma experiences high pressures and temperatures, and it is fluid because of the different combinations of temperature, pressure, and some other factors we'll discuss in the next section where we learn how magma is formed. There are different mechanisms through which magma is formed.
Thus, magma can form through partial melting, decompression melting, or flux-induced melting. Let's now discuss each of these mechanisms and see the differences between the different magma formation processes. First, we'll talk about partial melting.
Magma forms through the heat-induced melting of the rocks that are present in the upper mantle or the crust. In the case of partial melting, only some of the minerals in the rock's composition are melting. But why is it that only some of the minerals melt? We know that rocks contain different minerals in their composition, each made up of various combinations of chemical elements.
These minerals have different melting temperatures, and those with higher melting temperatures will remain solid, while those with lower melting temperatures will start melting. This magma then moves upward from the mantle and can go all the way through the crust. On its way up, as it encounters other rocks through the mantle and crust layers, it transfers some of its heat to those rocks. The components of those rocks with lower melting temperatures than the temperature of the magma will also start melting and join the magma flow. Before discussing the next magma formation process, I need to introduce a new term called a phase diagram.
A phase diagram is a graphical representation of the physical state of a material as a function of different temperature and pressure conditions. Here you can see an example of a phase diagram of a material showing the temperature and pressure ranges where the material is a solid, a liquid, or a gas. This is just a simple representation of a phase diagram, but if you would like to learn more about phase diagrams and how materials change from one physical state to another, under different temperature and pressure conditions, let me know in the comments below and I will be happy to create a more detailed video about phase diagrams. Now we are ready to discuss the decompression melting process for magma formation. Going back to this phase diagram example, if we look at the blue star, at those temperature and pressure conditions, the material is a solid.
If we kept the pressure constant as we increase the temperature, The solid melts, shown here by the red star. But we don't need to increase the temperature to go from a solid to a liquid. Another way the solid could melt is by decreasing the pressure that's acting on that solid. And you see here that even though the temperature hasn't changed, by reducing the pressure we moved from a solid state to a liquid state. This is what happens in decompression melting.
The temperature in the earth's mantle is very high, but so is the pressure. And under those high pressures, the mantle rocks are solid. But if the rocks move upward where the pressure is lower, or in the regions where the crust is thinner, such as in rift zones, those rocks will experience a smaller pressure, and this reduction in pressure will lead to a decompression melting of the rocks.
Before talking about the third magma formation mechanism, if you're enjoying this video, please give it a thumbs up and subscribe to my channel for more stories about the wonders of our planet. Now, let's see what other factors, other than temperature and pressure, can influence magma formation. The third mechanism we're talking about is flux-induced melting. When a rock is hot, close to its melting point, but not quite there yet, there are certain facts that could lower its melting point.
A flux that can lower the melting temperature of the rocks is water. But carbon dioxide and other gases can have the same effect. When some water reaches the rock, it lowers the melting temperature and once the rock starts melting, we're back to the first process and from here the partial melting takes over. And now that we know what magma is, what types of magma there are and how magma is formed, we still have an important question to answer.
What is the difference between magma and lava? Sometimes the magma breaks through the Earth's surface, either during a volcano eruption or through another vent. The magma that's ejected and reaches the Earth's surface is now called lava, and when this lava then cools, it forms volcanic rocks and volcanic glass.
We'll be discussing volcanic rocks in other videos, But for now, that's all I wanted to share with you about magma. And if you want to see what magma can bring with it to the surface, you might enjoy this other video I created about diamonds and how magma transports them upwards to the Earth's crust. Thank you for watching and I hope to see you back here next time. Bye!