Krakatau: It ain’t no Anak!


What's left of Krakatau today

Krakatau, for those who survived it’s August 27th 1883 eruption had to have seemed exactly to have been the very end of the world, even of the cosmos. Over 36,400 people died that day in a disaster they had no way of anticipating, and could not possibly have comprehended.

The cataclysm of that eruption can by no measure be overstated as it has no equal in documented human experience. All the universe was turned against the inhabitants of the Sunda Strait on that day, August 27th, 1883.

These days we tend to measure such events relative to the atomic bomb that devastated Hiroshima. There’s no specific name for this unit of measure, so I’ll call it the Hiro. In terms of explosive devastation Krakatau was 13,000 Hiros. The blast has been variously estimated to be equivalent to 200 megatons. That’s four times greater than the biggest nuke ever detonated, and yet the blast was hardly the worst of it for those living around the Sunda Strait. The tsunamis and pyroclastic floes wiped out 165 towns and villages.

After the cataclysm all seemed quiet for a few decades, and the disaster faded into the past, until…

In 1927 the sea boiled in the Sunda Strait, right where Krakatau had been, and it was not long before the new cone emerged from the waters, spewing ash and smoke, rising out of the sea as it rebuilt itself. The monster was reborn, refusing to die it was arising again out of the same magma chamber and vent and reminding of it’s past while threatening the same in the future.

While it cannot have come near equaling the six times greater eruption of Tambora, decades earlier, we have a far better record of it’s effects on humanity owing to the greater presence of Europeans and their technology in the region during the disaster that took place on that day, which was recorded and transmitted to the astonished world via telegraph as it happened.

It should be remembered forever that what happened in the Sunda Strait that day was far from being the greatest of what our planet is capable of in the way of volcanic cataclysms, and yet it remains the greatest of what we have witnessed and documented.

Indonesians have dubbed the new cone Anak Krakatau, meaning child of Krakatau, but lets be clear about it, that’s not the child of Krakatau at all. It’s Krakatau! Same vent, same magma chamber, new cone. It’s not the first incarnation of Krakatau either, or the first cone it’s built.

Krakatau is known to have performed the same act in the past as it did in 1883. In 416 AD it did pretty much the same thing, blowing itself to bits in a cataclysmic eruption and collapsing into the Sunda Strait. There is evidence of a similar event in 535 AD, and a history of lesser eruptive event since then. These have been tentatively dated as 850, 950, 1050, 1150, 1320, and 1530 (all AD).

Today's Krakatau, rebirth of a monster

What has always made Krakatau so very dangerous and so cataclysmically eruptive is it’s location on a bend in the axis of the Indonesian arc subduction zone. Krakatau is directly above the subduction zone of the Eurasian Plate and the Indo-Australian Plate where the plate boundaries make a sharp change of direction, possibly resulting in an unusually weak crust in the region as well as a forced mixing of felsic and mafic magma types. This mixing of magma types is thought to be responsible for the magnitude and violence of Krakatau’s past eruptions.

Krakatau has blown itself apart repeatedly in the past, and if it’s past is any indication the new cone is just a start on a repeat performance at some future date. I very much wish there were a web accessible seismograph on Krakatau, but there is not, and the one they have there is usually down, perhaps because of frequent eruptions as the new cone is built.

At any rate I would not want to be living anywhere around the Sunda Strait the next time Krakatau does it’s thing. Thankfully that’s likely to be some time off, after it has built itself up to it’s previous size or something close to it. It will take some time for that, but I’m betting that the 1883 eruption will be repeated, perhaps with even greater force than then.

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About Martina Vaslovik

Volcano nerd and seismogeek
This entry was posted in Uncategorized, Volcanology. Bookmark the permalink.

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