Volcanic eruptions reveal some of the great force and heat that move the Earth’s bowels, but what is the temperature of a volcano’s lava? Generally speaking, it varies between 700 °C and 1,200 °C — enough to melt most rocks.
The temperature of a volcano’s lava also gives volcanologists some valuable information, such as its viscosity (whether it’s “thick” or “thin”) and how it can travel across the landscape after an eruption. Furthermore, the color of the volcanic fluid can also roughly tell how hot it is.
Finding the temperature of a volcano’s lava
Beneath the earth’s crust, the molten geological material is called magma. When it reaches the surface, either through a volcanic eruption or through the separation of tectonic plates, it is called lava — but these names only serve to locate the same thing.
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When lava reaches the surface, it can have temperatures ranging from 700 °C to 1,200 °C. Its viscositythat is, how easily it can flowdepends solely on the fluid’s composition and not on temperature.
It is the minerals molten in lava that determine whether it will be “thick” or “thin”. When thick, the fluid is unlikely to travel long distances with speed, as its high viscosity encounters a lot of resistance along the way. But when it is thinner, lava can travel several kilometers before solidifying.
Once in contact with the air and the ground, the lava flow begins to lose heat to them and an outer crust begins to form. Still, as the “shell” cools and thickens even more, it acts as a thermal insulator, and inside, the flux remains super-heated.
Types of volcano lava
If a volcano’s lava is nothing more than molten rock, that means it’s filled with minerals and metals that have passed their melting point — going from solid to liquid — at the high temperatures below the Earth’s crust.
However, the lava of a volcano does not always have the same composition, as this varies from region to region of the planet and which elements are predominant in the geological structure that will be melted in the Earth’s mantle.
Among the different types of volcano lava, the three below stand out:
- felsica: the felsic lava is the coldest, whose temperature is around 600 °C to 800 °C and it has a reddish color, being rich in light elements such as silicon, oxygen, aluminum, sodium and potassium — and they are responsible for its high viscosity;
- Andesitic: this type of lava reaches the surface with temperatures ranging from 800 °C to 1,000 °C, with an orange color. Its composition is basically molten rocky material from the lower part of the earth’s crust. For this reason, more than 63% of it is made of silica (the most abundant material in the crust), which gives it its intermediate viscosity;
- Basalt: this is the most common type of lava, including the one most often depicted in eruption images. Yellowish in color, this is the volcanic fluid with the highest temperature of all: from 1,000 °C to 1,200 °C. Basalt lava is rich in iron and magnesium, but low in silica.
It is worth noting that, although high temperatures are indispensable to melt materials as hard as minerals and metals, the formation of magma (the lava still inside the Earth) will also depend on the pressure conditions that occur below the crust.
Why doesn’t lava melt the volcano?
Any element that has a melting point below 700 °C is melted and becomes part of the lava. At this temperature, any construction material for houses, roads and crops along the way is easily melted by the volcanic fluid.
But if lava is so hot that it melts iron, then why doesn’t it melt the volcanic structure itself? The main reason is the temperature of the lava, which, although high, is not enough to melt the rock that forms the volcanic cone.
In addition, the rock that forms the volcano has a different composition from lava because it is older and, therefore, has a higher melting point than the temperature of the lava when it reaches the surface — remembering that it loses heat very quickly as it reaches the surface. once expelled.
Pressure also has an important influence on this process: the rock that makes up the volcano’s structure is under much greater pressure than the surface, which only suffers from atmospheric pressure. In this case, the volcanic rock is also subject to lithostatic pressure — which is caused by the pressure exerted by the upper layers. In this way, the greater the pressure, the greater the melting point of the rock, which is precisely why the lava does not have enough heat to melt it.
