What is volcanic ash and why is it important?

Figure 1. The poster of Apocalypse: Pompeii with active Mount Vesuvius in the background Source: IMDb 2023

Have you ever experienced a volcanic eruption? For most people, the answer is no. However, you might have watched films about famous volcanoes, such as Apocalypse: Pompeii, in which Mount Vesuvius ejected massive burning ash (see Figure 1) almost destroying the city of Pompeii.

Volcanic ash is not something that you can only find in cinemas, but also in real life. In the past decade, countries such as Japan (see the following video), Guatemala and Tonga all experienced dramatic volcanic eruptions.

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In the video, tourists fled in fear with moving ash clouds chasing them in the back. They could neither breathe nor open their eyes. Under the circumstances, ‘dangerous’ became the only word that haunted them.

So why does volcanic ash have such destructive power? I will introduce you to its physical and chemical features to answer this question.

Traditionally, volcanic ash consists of pyroclasts with a diameter of less than 2mm, and can even go below 64 μm. It can be formed during three volcanic processes: explosive volcanic eruption (ashes transform from expanding bubbles created by lava fragmentation), phreatomagmatic eruption (ashes start to form when hot magma meets cold liquids) and the movement of pyroclastic density current (create fine ash). During the formation of volcanic ash, various physical components with different levels of SiO2 are included (see Table 1), accompanied by sulfur and halogen gases on the surface of the ash.

Table 1. Volcanic ash composition in some famous eruptions Source: adapted from Rose and Durant 2009

These physical and chemical characteristics of volcanic ash matter because they allow the ash to exert a detrimental impact on the environment. From table 1, it is clear that volcanic ash is composed of rocks that are difficult to dissolve in water. This can worsen freshwater ecology by increasing water turbidity, which can limit the amount of light reaching lower depths, impede aquatic plant growth, and ultimately influence creatures that rely on those plants. Moreover, small particles ejected from volcanoes can also cause acidification and fluoride contamination, either reducing water pH or increasing water toxicity.

Apart from damaging the freshwater system, ash accumulation might also pose a threat to the life of animals. Studies have shown that Ruapehu Volcano (in New Zealand) in 1995/1996 ejected tons of tephra, burying meadows that local livestock relied on. As a result, a number of them starved to death. Even if they did not die due to starvation, fluorosis could also kill them. Furthermore, ingesting volcanic ash is likely to cause blockages in the stomach and intestines among animals.

Such environmental destruction caused by volcanic ash should be acknowledged by more people as one can find volcanoes on almost every continent across the world (see Figure 2).

Figure 2. The distribution of Earth’s major volcanoes Source: National Geographic 2023

After reading this post, hopefully you have understood what volcanic ash is and its significance to our environment. Now, you might start to think about the social relevance of those small pyroclasts. Please note down any thoughts that pop up in your mind to see whether we get similar ideas in the next post.