When we contemplate a volcanic eruption, the most normal thing is to use the terms lava and magma. However, many people do not know what is magma from volcanoes and the differences they have with lava.
For this reason, we are going to dedicate this article to telling you what the magma of volcanoes is, how it originates and what its characteristics are.
What is the magma of volcanoes
The word magma comes from the Greek and can be translated as "paste". Volcanic magma is a mixture of molten rock and volatile solid compounds that forms within the Earth. The substance is very unstable and may contain air bubbles and suspended crystals. Lava is easily found in volcanic chambers and can also be found in nearby rocks. Once the magma cools and crystallizes, it forms igneous rocks.
The compounds that form the magma oscillate between 700 ºC and 1.300 ºC. These high temperatures can only be reached in the Earth's subduction zones, that is, in the mid-ocean ridges, continental regions and other hot spots on Earth. The process of magma formation is quite complicated, which we will explain later.
magma types
Quite a few types of magma can be defined. However, the most common are three:
basalt magma
Basaltic magmas arise from the amalgamation of ultrabasic rocks, although their composition varies depending on the region of formation. They are low in silica (-50%) if they come from oceanic ridges, and more alkaline and rich in sodium and potassium if they come from inside tectonic plates. They are the most common.
andesite magma
Andesite magma forms in subduction zones of the continental and oceanic crust and contains up to 60% silica and hydrated minerals such as hornblende or biotite. Andesite magma is the richest in water, but when it erupts, it evaporates as steam. When this magma crystallized at depth, it formed diorite and the water became part of the hornblende.
granite magma
This magma has the lowest melting point and can crystallize into large chunks of plutonic rock. They form in orogenic belts such as andesite, but from andesitic or basaltic magma that managed to penetrate and melt the sedimentary or igneous rocks of the earth's crust. These rocks change the composition of the magma as they dissolve in it.
Where is it located
Magma originates in those regions of the Earth's crust and upper mantle where temperatures reach temperatures at which the rock-forming minerals begin to melt. However, the melting temperature also depends on other factors such as pressure or the presence/absence of water.
Therefore, the increase in pressure coupled with the lack of water makes it difficult to melt, as it happens in the depths of the Earth, for example. Conversely, the presence of water lowers the melting point of the rock. Therefore, magma only forms and remains (unless magma escapes) where it is conducive to its formation, such as the crust and upper mantle.
When a volcano erupts, the magma manages to spew out in the form of lava. Because lava crystallizes quickly, chunks of volcanic glass, such as obsidian or pumice, are formed instead of large crystals.
How does magma form in volcanoes?
Magma gradually forms when the rocky material that makes up our planet melts. The rocks of our planet are made up of minerals with different melting points and different physical and chemical properties, which condition the formation of different types of magma. The high pressure inside the Earth determines the softening of the solid components.
As we have already pointed out, in liquid magma complexes the temperature is very high, between 700ºC and 1.300ºC. In general, the composition of the different types of magma is related to the environment in which it formed, usually subduction zones such as mid-ocean ridges, continental regions and other hotspots on Earth.
There are two reasons why magma ceases to exist, one is the evolution to crystallization, and the other is that it is exported as lava during volcanic eruptions. In both cases, when solidifying, it produces igneous rocks such as diorite, basalt or granite.
Differences between magma and lava
The difference between magma and lava is location. When geologists talk about magma, they mean lava that is still trapped in the ground. If this molten rock reaches the surface and continues to flow as a liquid, it is called lava.
As it rises up the volcano, the magma or molten rock breaks the rock around it, creating small waves that are measured by seismographs and, depending on their strength, earthquakes can be felt on Earth. In the case of Cumbre Vieja, more than 25.000 earthquakes formed a more active swarm than usual, heralding a possible eruption. Subsequently, the National Geographic Institute reported more than 2.600 earthquakes in the region since the volcano woke up.
Magmas or lavas vary in their chemical composition, which gives them and the volcanoes that contain them, different properties. In the case of Cumbre Vieja, its alternation between the Strombolian and Hawaiian phases determines the development of its flow. The first lava fields to form were of the Malpas type, where the lava fragmented and cooled rapidly.
These lavas do not form tubes, to form tubes you need hot lava flowing at a constant and very smooth speed, melting and eroding the ground inside, making these tubes drains that reactivate the flow front.
As you can see, these confusions often occur when talking about volcanic eruptions and the news is booming. However, it is quite simple to know the terms and what are the differences between them. I hope that with this information you can learn more about what the magma of volcanoes is, its characteristics, origin and differences with lava.