Little story of the Krakatoa volcano… and its son!

A tsunami devastated the coasts of Banten (west of Java) and South Sumatra last Saturday, December 22, 2018. This natural event, due to the subsidence of part (64 ha!) of the flanks of the Anak Krakatau volcano (which means "the child of Krakatoa" in Indonesian), unfortunately caused the death of more than 400 people who were gathered on the region's superb beaches to celebrate the weekend and the start of the end-of-year holidays. Anak Krakatau is an island volcano located in the middle of the Sunda Strait, which separates the islands of Java & Sumatra, and emerged in 1927 from the remains of the famous eruption of Mt Krakatoa in 1883. The volcano is in an increasing eruptive phase since July 2018 and the recent tsunami actually raises fears of new disasters in the more or less near future. Geomorphic changes after the eruption of December 22, 2018, which caused a tsunami

In 2012, the Geological Society of London modeled the effects of subsidence of the unstable flanks of Anak Krakatau (see http://sp.lyellcollection.org/content/361/1/79#F1). The result was that a collapse of even 300 m3 of volcano surface could potentially cause a wave of 43 m, which would reach the neighboring islands of Serting, Panjang & Rakata in 1 minute. It would then propagate radially, in 35-45 minutes and at a speed of 80-110 km/h, towards the west coast of Java, with an amplitude measured between 1.5 m and 3.4 m. The problem therefore lies in the speed of detection of this type of incident by local scientific authorities, combined with an effective alert system on the coasts, which unfortunately does not seem to have been the case on December 22, 2018.

 However, the tsunami of December 2018 must be put into perspective.

Flashback: Kakatoa eruption

Between August 26 and 28, 1883, the eruption of the Krakatoa volcano and the numerous tsunamis that followed caused the death of more than 35,000 indigenous people along the coasts of the Sunda Strait. This cataclysm was one of the most powerful and devastating in recent volcanological history. One of the numerous tsunamis, which were the consequence of the volcano's eruption, created a wave of around 15 m, which reached the coast of Java in no less than 35-40 minutes. Nearly 200 villages were wiped off the map and many ships were thrown several kilometers inland. This eruption remained anchored in collective memory, because it changed the course of humanity. Volcanic ash from Krakatoa swirled around the Earth and caused temperatures to drop on a global scale. The effects of the eruption were in fact felt as far away as Europe and its detonation heard as far away as Australia, India, etc. It was also the explosion of Krakatoa which helped trigger the first revolt of fundamentalist Muslims against the Dutch colonists.

45 years later, “the Child of Krakatau” was born on the ruins of his mother and grew to his current size of just over 330 m. This “child” has continued to show worrying signs ever since, and it was not until the early 1980s that an observatory was built in Pasauran (on the west coast of Java), located about 50 km east of the volcano. It is therefore thanks to seismic surveys and other visual observations that local scientific authorities can decide on preventive measures, but Man nevertheless remains powerless in the face of the force of nature. After the series of disasters experienced by Indonesia in 2018 (earthquakes in Lombok, tsunamis in the Palu region and in the Sunda Strait), let us hope that the Gods will calm down in the coming months, so that a large number of travelers can explore the wonders that this gigantic archipelago has in store! See you next Thursday for a new article concerning the history of Krakatoa and its eruption on August 27, 1883. Note: if the history of the eruption of Krakatoa of 1883 fascinates you, we invite you to read Simon's story Winchester, “Krakatoa: August 27, 1883, the day the Earth exploded” (Editions JC Lattès).