Why Lava is Red And What Other Colors It Can Take

In this article we analyze what determines the color of lava and the (rare) cases in which it can appear blue or white!

Why Lava is Red And What Other Colors It Can Take

Emitted as an incandescent fluid by active volcanoes , lava  certainly remains one of the most fascinating and, at the same time, feared volcanic products . But why does it usually have colors that tend towards red/orange ? In this article we analyze what the color of the lava depends on and we tell you about some cases in which the lava takes on colors that are very different from those we are used to!

What does the color of objects depend on?

To understand the different colors that lava can assume, we need to briefly introduce the concept of thermal radiation .

Every body with temperatures above absolute 0 (-273.15 °C) emits its own radiation also known as electromagnetic radiation or thermal radiation . The electromagnetic radiation emitted by a body varies significantly with the variation of its temperature according to the so-called Wien's law. At room temperature (which refers to the value of the temperature in the surrounding air, usually around 20°C) the emission occurs through infrared wavelengths that our eyes cannot perceive. In this case, the color of the body depends on its interaction with light, in particular on the wavelengths it manages to reflect.

When the temperature emitted by an object reaches hundreds of degrees Celsius , the energy emitted by radiation is greater than the energy reflected. In such cases, the light emitted by the body has wavelengths ranging between approximately 400 and 700 nm , i.e. in the visible portion of the electromagnetic spectrum and therefore the radiation emitted by that object determines the color we perceive.

The pattern of the color of lava

Depending on the chemical composition , the surface temperature of the lava varies between 500°C and 1200°C and the resulting colors are: dark red (500 or -740 o C), light red (740 or -900 o C), orange ( 950 or -1,000 o C), yellowish (~1,000 or -1,200 o C) to even white (~1,300 o C). Thus, regardless of the initial temperature, the surface color of the lava darkens as it cools to gray or black once ambient temperature is reached.

Some unusual colors that lava can take

We currently know of two volcanoes that can give life to lava with different colors from the table above: Kawah Ijen in Indonesia and Ol Doinyo Lengai in Tanzania.

The blue lava of Kawah Ijen

Kawah Ijen is a stratovolcano located east of the island of Java and is part of a system of many stratovolcanoes that have developed inside an ancient caldera. Kawah Ijen crater contains the largest natural hyperacid lake in the world with a turquoise-blue color due to the high acidity of the water and the presence of dissolved metals.

It needs to be clarified: most of the material recently emitted by Kawah Ijen  corresponds to gas and ash. The presence of gas at high temperature (up to 600 o C), high pressure and high concentration of sulfur causes it to immediately catch fire as soon as it emerges from the fractures of the volcano through the so-called fumaroles. The color of the flame, electric blue, is similar to what we observe in the flames of the gas ovens we have in our homes. In the case of the Kawah Ijen, part of this very hot gas condenses into a blue colored fluid in contact with the cooler air. At this point the result that we can observe (especially at night) is the presence of a blue fluid flowing, like lava, on the sides of the volcano above the lava which in fact has a very normal dark gray colour.

The white lava of Ol Doinyo Lengai

Ol Doinyo Lengai, on the other hand, is located in the southern portion of the African Rift Valley , i.e. a large elongated depression that splits the African continent. This place is famous for being the only volcano in the world to produce "carbonatitic" lava and not rich in silica like all other volcanoes. Suffice it to say that most of the lava contains a quantity of silicates between 40-80% of the total weight . This value at Ol Doinyo Lengai drops to around 10% . Precisely the composition means that the lava can remain liquid even at low temperatures, of 'only' 500 o C on average. The abundant presence of calcium carbonates (such as calcite, CaCO ₃), sodium and potassium, which are not very resistant to erosion when exposed to a humid environment, means that the black lava can easily and quickly turn white due to the interaction with atmospheric water.

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