 An early 19th century image of Krakatoa. Krakatoa (Indonesian name: Krakatau) is a volcano on the Indonesian island of Rakata in the Sunda Strait. It has erupted repeatedly, massively and with disastrous consequences throughout recorded history, but the most well known of these events occurred in August 1883.
The 1883 eruption ejected more than six cubic miles (25 cubic kilometres) of rock, ash and pumice, and generated the loudest sound ever recorded by human beings - the cataclysmic explosion was distinctly heard as far away as Alice Springs in Australia, and Rodriguez near Mauritius. 165 villages were devastated, 36,417 people died and uncountable thousands were injured by the eruption, mostly in the tsunami which followed the biggest explosion.
The 1883 eruption destroyed two-thirds of the pre-existing island of Krakatoa. New eruptions at the volcano since 1927 have built a new island, called Anak Krakatau (son of Krakatoa).
1883 eruption Krakatoa had been dormant for two centuries before it began erupting on 20 May 1883. The eruption had been preceded by several years of noticeable earthquakes, some felt as far away as Australia. The eruption began with small steam eruptions on 20 May, and these continued for the next three months.
By 11 August, 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. 11 August saw the onset of larger eruptions, with ash-laden eruption columns being emitted by up to eleven eruption vents. 24 August saw a further intensification of the eruption, and the cataclysmic phase began on Sunday 26 August at about midday. Ash clouds from the eruption reached a height of 36km, and the first tsunamis were generated.
The August 27 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 (2200 miles), and the island of Rodrigues near Mauritius 4800 km away (3000 miles). 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).
 Krakatoa before and after the explosion 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 the effects of volcanic fumes and ashes. 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.
There is some evidence that the final colossal explosion may not have been caused by the ingress of sea water. The magma chamber below the volcano was composed of light coloured, relatively cool material. Following the May 20th eruption hotter, darker coloured material entered the chamber from below. The new material heated the original molten rock, releasing dissolved gases, and increasing the pressure. The early eruptions on August 25th and 26th cleared the throat of the volcano, releasing the pressure in the cataclysmic explosion that destroyed most of the island. Pumice stone from the eruption shows a mixture of dark and light materiel.
Long-term effects 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 five inches (12.7 cm) per week.
Media The volcano has inspired several books and films. - Krakatoa is the name of a short 1933 movie about the volcano that won the Academy Award for Best Short Subject, Novelty for its producer Joe Rock. This movie was notable for overwhelming the sound systems of the cinemas of the time. In Australia, the distributors insisted on a power output of 10 watts RMS as a minimum for cinemas wishing to show the movie. This was then considered a large system, and forced many cinemas to upgrade.
- Simon Winchester explores the eruption of Krakatoa in his book Krakatoa: The Day the World Exploded, August 27, 1883. (2003, ISBN 0066212855). The book examines the history of the region, the early spice trade, the growth of colonial governments, explains the geology of volcanos and describes in detail the series of eruptions and tsunamis and their effects around the globe.
- The novel Krakatit (1924, ISBN 0685513386) by Czech writer Karel Čapek, dealing with lethal menace of a fictional explosive, was inspired by the name of the volcano.
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