How Was Krakatoa Volcano Created?
Krakatoa, known as Krakatau in Indonesian, is a volcano on Rakata Island in the Krakatoa archipelago comprised of Rakata, Lang, Verlaten and the younger peak Anak Krakatoa. The islands lie in the Sunda Strait between the larger Indonesian islands of Java and Sumatra.
Rakata is all that remains of the original Krakatoa Island. Seventy percent of the island was decimated during the catastrophic August 1883 eruptions. Krakatoa sits at the point of two converging tectonic plates, sections of the Earth's crust and mantle often referred to as the lithosphere.
The interaction of the Eurasian and Indo-Australian plates caused an 1800m high (above sea level) volcano to form at an unknown point during the last million years.
An escalation of seismic activity led to the volcano's significant eruptions in summer 1883.
Krakatoa's Volcanic Eruption: The Build-Up
The eruptions on Krakatoa Island started four months before the zenith of the activity. On 20th May 1883, steam was released from the summit of Perboewatan volcano, one of three volcanoes on the island. The others were named Danan and Krakatoa. Within a short time, ash clouds were fired up to 6km into the air, and the volcanic eruptions could be heard 160km away in Jakarta, the capital of Indonesia.
The Krakatoa volcano became active almost one month later, on 16th June 1883. A thick black plume of smoke and ash caused an eerie darkness for five days until an east wind blew the smothering cloud away. Two ash columns still rose from the volcano.
As the tectonic plates continued to shift, an air vent formed between Perboewatan and Danan. Danan began to emit ash. Steam and ash clouds, earthquakes, large pumice deposits in the Indian Ocean, and unusually high tides were widely reported for the next few months.
26th August 1883: Multiple Volcanic Explosions
A Dutch topographical engineer named Hendrik Fersenaar travelled to Krakatoa to study the eruptions in early August 1883. He advised people to stay away from the island, which was fortunately uninhabited. At the time of his visit, the ash carpet was half a metre thick across the island, and all vegetation had been destroyed except for a few languishing tree trunks.
By the 26th August, the eruptions had notably increased in intensity. Using the Volcanic Explosivity Index (V.E.I.) established in 1982, the eruption was now entering its paroxysmal phase at level 3, and it peaked at 6, a classification of colossal. The V.E.I. peaks at 8, a mega-colossal eruption.
Krakatoa's eruption at 1 p.m. on the 26th August expelled smoke and ash clouds that reached up to 30km within an hour. Explosions were heard every ten minutes before the activity became constant. Lumps of pumice and airborne ash landed on ships sailing approximately 20km away. That evening, a small tsunami affected Sumatra and Java 40km from the island.
The Loudest Sound Ever Heard on Earth
On the morning of 27th August 1883, the eruptions on Krakatoa Island reached a climax.
At 5:30 a.m., Perboewatan exploded, triggering a tsunami along the south coast of Sumatra. Krakatoa exploded at 6:44 a.m., creating another tsunami.
10:02 a.m. delivered the largest explosion from Krakatoa. The noise was heard over 3100km away in Perth, Australia, and it was believed to be gunshots. Inhabitants of islands close to Mauritius in the Indian Ocean, approximately 4800km away, thought they heard cannon fire.
The third explosion that morning still holds the record for the loudest sound ever heard on earth. Achieving a total of 310 decibels, the Krakatoa explosion was audible 5000km away.
160km from Krakatoa, the noise was estimated at 180 decibels. For comparison, a gunshot can reach 140db and a fighter jet 150db. A rocket launch is 180db.
Krakatoa Island Blown Apart, Thousands Dead
Sailors at a distance of 40km from the blast suffered from ruptured eardrums, and the captain of one ship believed that it was the day of judgement. Pressure at the Batavia gasworks on Java literally went off the scale.
Total darkness fell over a large geographic area as the gaseous ash clouds of more than 1000 degrees Celsius rose to 80km. Several tsunamis of over 30m followed.
At 10:41 a.m., Krakatoa Island was torn apart. The Danan and Perboewatan volcanoes were shattered, and a shallow sea was created. The remaining 30% of the land mass was subsequently renamed Rakata.
By the early morning of 28th August 1883, Krakatoa was silent.
Official reports stated that 36417 lives were lost during eruptions or the resulting tsunamis. Unofficial estimates soared to over 120000.
Global Shock Waves and Arak Krakatoa
For five days, global barographs measuring barometric pressure (atmospheric pressure) recorded seven significant waves, four moving away from Krakatoa and three headed toward Krakatoa. The pressure wave travelled around the globe three and a half times. Mirroring the pressure's progress, the oceans swelled to unforeseen levels.
The tons of ash in the atmosphere resulted in a global temperature decrease of 1.2 degrees Celsius that lasted for several years.
Smaller eruptions, largely consisting of mud, occurred between October 1883 and February 1884.
On 11th August 1930, Arak Krakatoa, or "Child of Krakatoa", emerged from the sea, and it did not sink as a previous island had done in 1927. The island expanded for the rest of the century and into this one. On 22nd December 2018, the Sunda Strait Tsumani occurred as a result of the partial collapse of Anak Krakatoa.
This volcano erupted over 20 times in the first four months of 2022, with the 24th April eruption resulting in ash clouds 3157m high. Let's hope that the horrifying records set in 1883 are never beaten.
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