Satellite Images Show Krakatau Eruption, Landslide Triggered Tsunami

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Even if you don’t know much about volcanoes, chances are you’ve heard of Krakatau (often westernized as Krakatoa). New satellite footage shows that the volcano of Anak Krakatau (child of Krakatau) has partially collapsed following an explosive eruption. Both the eruption and the landslide are thought to be responsible for the Sunda Strait tsunami of December 22 2018, which killed 429 people and injured 1459 as of this writing.

Anak Krakatau is the reformed remnant of the original Krakatau, which famously exploded on December 27, 1883. The explosion — a VEI 6 event, and one of the most powerful volcanic eruption in modern times (it fell short of the 1815 “Year Without a Summer,” which ranked as a VEI 7)– had cataclysmic effects on the nearby Indonesian islands and, to a lesser extent, the entire global climate. Explosions were heard 1,930 miles away, with the pressure wave from the final blast recorded seven separate times as it reverberated around the world.


The Scream, Edvard Munch

The original 1883 blast blew so much material into the atmosphere, it allowed us to make the first observations of the jet stream. Volcanic activity tends to create beautiful (and unusual) sunsets; it’s been suggested that the Edvard Munch painting “The Scream” and its highly unusual blood-red sky may have been the result of the Krakatau eruption. The total eruption force is estimated at 200 megatons of TNT.

It was initially thought that most of the island of Krakatau exploded in the final eruption, but we now know this to be unlikely based on samples of the debris. It’s now believed that the island of Krakatau — the original one — collapsed into the empty magma chamber following the eruption. Krakatau never truly became dormant; the first signs of what we now call Anak Krakatau were detected as early as 1919. The new island poked its head above water in 1927 and has been growing ever since. Anak Krakatau has grown by an average of 5.1 inches per week (22 feet per year) since the 1950s.

The landslide that caused the Sunda Strait tsunami last week was likely the result of a flank collapse. A 2012 paper “Tsunami hazard related to a flank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia” notes that Anak Krakatau is built on the northeast side of the caldera created by the explosion of Krakatau and is most active on its own southwest flank. In human terms, this is known as a very, very bad place to build a house.

That paper notes that a collapse-caused tsunami has ample opportunity to inflict damage across the islands in the Sunda Strait, which we now know is precisely what happened. The images show that the landslide occurred on the SW side of Anak Krakatau, as predicted in 2012.

There is no danger of a second Krakatau-sized explosion of the sort we experienced in 1883 — the island of Anak Krakatau isn’t nearly large enough to produce that kind of blast, and not nearly enough time has passed relative to the last eruption. But even relatively quiescent volcanoes can produce cataclysmic effects, particularly when the impact of underwater landslides is taken into account.

Feature image by Wikipedia

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