Krakatoa
Krakatoa, or Krakatau (Indonesian: Krakatau), is a caldera[2] in the Sunda Strait between the islands of Java and Sumatra in the Indonesian province of Lampung. The caldera is part of a volcanic island group (Krakatoa Archipelago) comprising four islands: two of which, Lang and Verlaten, are remnants of a previous volcanic edifice destroyed in eruptions long before the famous 1883 eruption; another, Rakata, is the remnant of a much larger island destroyed in the 1883 eruption.
In 1927, a fourth island, Anak Krakatau, or "Child of Krakatoa", emerged from the caldera formed in 1883. There has been new eruptive activity since the late 20th century, with a large collapse causing a deadly tsunami in December 2018.
The most notable eruptions of Krakatoa culminated in a series of massive explosions over 26–27 August 1883, which were among the most violent volcanic events in recorded history.
With an estimated Volcanic Explosivity Index (VEI) of 6,[3] the eruption was equivalent to 200 megatons of TNT (840 PJ)—about 13,000 times the nuclear yield of the Little Boy bomb (13 to 16 kt) that devastated Hiroshima, Japan, during World War II, and four times the yield of Tsar Bomba, the most powerful nuclear device ever detonated at 50 Mt.
The 1883 eruption ejected approximately 25 km3 (6 cubic miles) of rock.[4] The cataclysmic explosion was heard 3,600 km (2,200 mi) away in Alice Springs, Australia, and on the island of Rodrigues near Mauritius, 4,780 km (2,970 mi) to the west.[5]
According to the official records of the Dutch East Indies colony, 165 villages and towns were destroyed near Krakatoa, and 132 were seriously damaged. At least 36,417 people died, and many more thousands were injured, mostly from the tsunamis that followed the explosion. The eruption destroyed two-thirds of the island of Krakatoa.
Eruptions in the area since 1927 have built a new island at the same location, named Anak Krakatau (which is Indonesian for "Child of Krakatoa"). Periodic eruptions have continued since, with recent eruptions in 2009, 2010, 2011, and 2012, and a major collapse in 2018. In late 2011, this island had a radius of roughly 2 kilometres (1.2 mi), and a highest point of about 324 metres (1,063 ft) above sea level,[6] growing five metres (16 ft) each year.[7] In 2017, the height of Anak Krakatau was reported as over 400 m (1,300 ft) above sea level;[8] following a collapse in December 2018, the height was reduced to 110 meters (361 ft).[9][6]
Etymology
Although there are earlier descriptions of an island in the Sunda Strait with a "pointed mountain," the earliest mention of Krakatoa by name in the western world was on a 1611 map by Lucas Janszoon Waghenaer, who labelled the island "Pulo Carcata" (pulo is the Sundanese word for "island"). About two dozen variants have been found, including Crackatouw, Cracatoa, and Krakatao (in an older Portuguese-based spelling). The first known appearance of the spelling Krakatau was by Wouter Schouten, who passed by "the high tree-covered island of Krakatau" in October 1658.[10]
The origin of the Indonesian name Krakatau is uncertain.[11]
The Smithsonian Institution's Global Volcanism Program cites the Indonesian name, Krakatau, as the correct name, but says that Krakatoa is often employed.[7][12][13]
Geographical setting
Indonesia has over 130 active volcanoes,[14] the most of any nation. They make up the axis of the Indonesian island arc system produced by northeastward subduction of the Indo-Australian Plate. A majority of these volcanoes lie along Indonesia's two largest islands, Java and Sumatra. These two islands are separated by the Sunda Strait located at a bend in the axis of the island arc. Krakatau is directly above the subduction zone of the Eurasian Plate and the Indo-Australian Plate where the plate boundaries make a sharp change of direction, possibly resulting in an unusually weak crust in the region.
Pre-1883 history
At some point in prehistory, an earlier caldera-forming eruption had occurred, leaving as remnants Verlaten (or Sertung); Lang (also known as Rakata Kecil, or Panjang); Poolsche Hoed ("Polish Hat");[15] and the base of Rakata. Later, at least two more cones (Perboewatan and Danan) formed and eventually joined with Rakata, forming the main island of Krakatoa.[16] At the time of the 1883 eruption, the Krakatoa group comprised Lang, Verlaten, and Krakatoa itself, an island 9 km (5.6 mi) long by 5 km (3.1 mi) wide. There were also the tree-covered islet near Lang (Poolsche Hoed) and several small rocky islets or banks between Krakatoa and Verlaten.
There were three volcanic cones on Krakatoa island: Rakata, (820 m or 2,690 ft) to the south; Danan, (450 m or 1,480 ft) near the center; and Perboewatan, (120 m or 390 ft) to the north.
416 AD event
The Javanese Book of Kings (Pustaka Raja) records that in the year 338 Saka (416 AD):
A thundering sound was heard from the mountain Batuwara [now called Pulosari, an extinct volcano in Bantam, the nearest to the Sunda Strait] which was answered by a similar noise from Kapi, lying westward of the modern Bantam [(Banten) is the westernmost province in Java, so this seems to indicate that Krakatoa is meant]. A great glowing fire, which reached the sky, came out of the last-named mountain; the whole world was greatly shaken and violent thundering, accompanied by heavy rain and storms took place, but not only did not this heavy rain extinguish the eruption of the fire of the mountain Kapi, but augmented the fire; the noise was fearful, at last the mountain Kapi with a tremendous roar burst into pieces and sank into the deepest of the earth. The water of the sea rose and inundated the land, the country to the east of the mountain Batuwara, to the mountain Rajabasa [the most southerly volcano in Sumatra], was inundated by the sea; the inhabitants of the northern part of the Sunda country to the mountain Rajabasa were drowned and swept away with all property[17] ... The water subsided but the land on which Kapi stood became sea, and Java and Sumatra were divided into two parts.
There is no geological evidence of a Krakatoa eruption of this size around that time; it may describe loss of land which previously joined Java to Sumatra across what is now the narrow east end of the Sunda Strait; or it may be a mistaken date, referring to a later eruption in 535 AD, for which there is some corroborating historical evidence.[18]
535 AD event
David Keys, Ken Wohletz, and others have postulated that a violent volcanic eruption, possibly of Krakatoa, in 535 may have been responsible for the global climate changes of 535–536.[18] Keys explores what he believes to be the radical and far-ranging global effects of just such a putative 6th-century eruption in his book Catastrophe: An Investigation into the Origins of the Modern World. This eruption was believed to have been even more violent than Krakatoa's 1883 eruption, and also the one that created Krakatoa's original caldera, which resulted in the creation of Verlaten Island and Lang Island.[19] However, there are other explanations for the climate change, including an eruption of Ilopango in El Salvador, in Central America.
Thornton mentions that Krakatoa was known as "The Fire Mountain" during Java's Sailendra dynasty, with records of seven eruptive events between the 9th and 16th centuries.[20] These have been tentatively dated as having occurred in 850, 950, 1050, 1150, 1320, and 1530.
1680
In February 1681, Johann Wilhelm Vogel, a Dutch mining engineer at Salida, Sumatra (near Padang), on his way to Batavia (now Jakarta) passed through the Sunda Strait. In his diary he wrote:
...I saw with amazement that the island of Krakatoa, on my first trip to Sumatra [June 1679] completely green and healthy with trees, lay completely burnt and barren in front of our eyes and that at four locations was throwing up large chunks of fire. And when I asked the ship's Captain when the aforementioned island had erupted, he told me that this had happened in May 1680 ... He showed me a piece of pumice as big as his fist.
Vogel spent several months in Batavia, returning to Sumatra in November 1681. On the same ship were several other Dutch travellers, including Elias Hesse, a writer. Hesse's journal reports:
...on the 19th [of November 1681] we again lifted anchor and proceeded first to the north of us to the island of Sleepzie (Sebesi), uninhabited, ... and then still north of the island of Krakatou, which erupted about a year ago and also is uninhabited. The rising smoke column of this island can be seen from miles away; we were with our ship very close to shore and we could see the trees sticking out high on the mountain, and which looked completely burned, but we could not see the fire itself.[21]
The eruption was also reported by a Bengali sea captain, who wrote of the event later, but had not recorded it at the time in the ship's log.[22] Neither Vogel nor Hesse mention Krakatoa in any real detail in their other passages, and no other travellers at the time mention an eruption or evidence of one. (In November 1681, a pepper crop was being offered for sale by inhabitants.)[23] In 1880, Verbeek investigated a fresh unweathered lava flow at the northern coast of Perboewatan, which could not have been more than two centuries old.
