Indonesia’s Mount Anak Krakatau has erupted again this week, sending plumes of volcanic ash high into the sky and disrupting hundreds of flights. More than 300,000 passengers have been affected.

Anak Krakatau, meaning “child of Krakatau” in Indonesian, has erupted on and off for almost a hundred years. This volcano emerged from the devastation caused when its predecessor, Krakatau (also known as Krakatoa), famously erupted between May and August in 1883.

It’s hard to overstate just how big the 1883 eruption was, and the catastrophic and often strange impacts that followed.

The Moon went blue, sunsets went green and global temperatures fell. Around 35,000 people lost their lives, almost all in tsunamis caused by the eruptions. The sound of one of the 1883 explosions is still the loudest sound in recorded history; it could be heard “like the distant roar of heavy guns” near Mauritius, almost 5,000 kilometres away.

So what caused the 1883 eruptions – and could they happen again?

What caused the 1883 eruption?

Most volcanoes sit at the edges of the Earth’s tectonic plates.

Krakatau sits above what’s called a subduction zone, where the Indo-Australian plate is forced beneath the Eurasian plate. This produces molten rock (or magma) with a lot of gas dissolved in it, which helps explain why Indonesian volcanoes can erupt so explosively.

There is still some debate about the main triggers at various stages of the eruption.

It was once thought the 1883 eruption was caused by seawater entering the volcanic system and interacting with the magma, leading to an explosive........

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