The eruption of Krakatoa, August 27, 1883

Krakatoa was dormant until May 20, 1883, when it erupted catastrophically. By August 11, three vents were regularly erupting on the volcano. During this time tides were unusually high, and phenonema such as windows suddenly shattering were commonplace. Ships at anchor were sometimes tied down with chains as a result.

The August 26 eruptions occurred at 5:30 am, 6:42 am, 8:20 am and 10:02 am local time. The last of these eruptions opened fissures in the walls of the volcano, allowing sea water to pour into the magma chamber. The resulting explosion of superheated steam destroyed most of the island. The sound of the explosion was heard as far away as Australia 3500 km away, and the island of Rodrigues near Mauritius 4800 km away. It is the loudest-ever sound in recorded history. (A possibly louder sound is believed to have been generated during the 1815 eruption of Mount Tambora, also in the Indonesian archipelago).

Although no one is known to have been killed as a result of the initial explosion, the tsunamis it generated had disastrous results, killing some 36,000 people and wiping out a number of settlements, including Telok Batong in Sumatra, and Sirik and Semarang in Java. An additional 1,000 or so people died from superheated volcanic ash which literally rushed across the surface of the ocean. Ships as far away as South Africa rocked as tsunamis hit them, and the bodies of victims were found floating in the ocean for weeks after the event. There are even numerous documented reports of groups of human skeletons floating across the Indian Ocean on rafts of volcanic pumice and washing up on the east coast of Africa up to a year after the eruption.

The 1883 eruption was amongst the most severe volcanic explosions in modern times (VEI of 6, equivalent to 200 megatons of TNT - by way of comparison, the biggest bomb ever made by man, Tsar Bomba, is around 50 megatons). Concussive air waves from the explosions travelled seven times around the world, and the sky was darkened for days afterwards. The island of Rakata itself largely ceased to exist as over two thirds of its exposed land area was blown to dust, and its surrounding ocean floor was drastically altered. Two nearby islands, Verlaten and Lang, had their land masses increased. Volcanic ash continues to be a significant part of the geological composition of these islands.

The eruption produced spectacular sunsets throughout the world for many months afterwards, as a result of sunlight reflected from suspended dust particles ejected by the volcano high into Earth's atmosphere. Interestingly, researchers in 2004 proposed the idea that the blood-red sky shown in Edvard Munch's famous 1893 painting The Scream is an accurate depiction of the sky over Norway after the 1883 eruption of Krakatoa.

It has been suggested that an eruption of Krakatoa may have been responsible for the global climate changes of 535-536. Additionally, in recent times, it has been argued that it was this eruption which created the islands of Verlaten and Lang (remnants of the original) and the beginnings of Rakata - all indicators of that early Krakatoa's caldera size, and not the long-believed eruption of c. 416, for which conclusive evidence does not exist.

Since the 1883 eruption, a new island volcano, called Anak Krakatau ("Child of Krakatoa"), has formed in the caldera. Of considerable interest to volcanologists, this has been the subject of extensive study since 1960. Additionally, it has also been studied as a case study of island biogeography and founder populations in an ecosystem being built from the ground up, virtually sterilized, certainly with no macroscopic life surviving the explosion. However, the island is still active, growing at the rate of 13 cm per week.