Krakatoa ( / ˌ k r ɑː k ə ˈ t oʊ ə , ˌ k r æ k -/ ), also spelled Krakatau ( /- ˈ t aʊ / ), is a caldera located 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 called the Krakatoa archipelago, which includes four islands. Two of these islands are named Lang and Verlaten. Another island, Rakata, is the only remaining part of an island once called Krakatoa, which was mostly destroyed by an eruption in 1883. This eruption created the caldera.

In 1927, a fourth island, Anak Krakatoa, or "Child of Krakatoa," formed from the caldera created in 1883. New volcanic activity has occurred since the late 20th century, including a large collapse that caused the 2018 Sunda Strait tsunami. A new cinder cone eventually grew from the area where the collapse happened due to eruptions in the 2020s.

Historical significance

The most famous eruptions of Krakatoa happened on August 26 and 27, 1883. These eruptions were among the most powerful volcanic events ever recorded.

The eruption had a volcanic explosivity index of 6. This means it was as strong as 200 million tons of TNT, which is about 13,000 times the power of the bomb dropped on Hiroshima, Japan, during World War II. It was also four times as strong as the largest nuclear bomb ever tested, called the Tsar Bomba.

During the 1883 eruption, Krakatoa sent about 25 kilometers of rock into the air. The explosion was so loud that people could hear it 3,600 kilometers away in Alice Springs, Australia, and 4,780 kilometers away on Rodrigues Island near Mauritius.

According to records from the Dutch East Indies colony, 165 villages and towns near Krakatoa were destroyed, and 132 were badly damaged. At least 36,417 people died, and many more were injured, mostly because of huge waves called tsunamis that followed the eruption. The eruption also destroyed two-thirds of the island of Krakatoa.

Since 1927, eruptions in the area have created a new island at the same location. This island is called Anak Krakatau, which means "Child of Krakatoa" in Indonesian. Volcanic activity has continued there, with eruptions in 2009, 2010, 2011, and 2012. In 2018, a major collapse happened on the island.

In late 2011, Anak Krakatau had a radius of about 2 kilometers and reached a height of 324 meters above sea level. The island grew about 5 meters each year. By 2017, its height was over 400 meters. However, after a collapse in December 2018, the island’s height dropped to 110 meters.

Etymology

The name Krakatoa first appears in an Old Sundanese text called Bujangga Manik. This text was likely written in western Java around the late 15th century. In this text, the island is called "the island of Rakata, a mountain in the middle of the sea" (pulo Rakata gunung ti tengah sagara, f. 27v). Earlier European writings describe an island in the Sunda Strait with a "pointed mountain." However, the first known use of the name Krakatoa in the Western world was on a 1611 map by Lucas Janszoon Waghenaer. He labeled the island "Pulo Carcata," where "pulo" means "island" in Sundanese. Many different spellings of the name have been found, such as Crackatouw, Cracatoa, and Krakatao (which uses an older Portuguese spelling). The first use of the spelling "Krakatau" was by Wouter Schouten. He passed by "the high tree-covered island of Krakatau" in October 1658. The origin of the Indonesian name Krakatau is not known for sure. Some theories suggest possible explanations. The Smithsonian Institution's Global Volcanism Program says that "Krakatau" is the correct name. However, "Krakatoa" is also commonly used.

Geographical setting

Indonesia has more than 130 active volcanoes, the highest number of any country. These volcanoes form the central part of the Indonesian island chain system, created by the movement of the Indo-Australian Plate pushing under another plate to the northeast. Most of these volcanoes are found along Indonesia's two largest islands, Java and Sumatra. These islands are separated by the Sunda Strait, which is located where the island chain bends. Krakatau is positioned directly above the area where the Eurasian Plate and the Indo-Australian Plate meet, and where the direction of the plate boundaries changes sharply. This change in direction may cause the crust in that region to be weaker than usual.

Pre-1883 history

Before the 1883 eruption, Krakatoa was shaped by earlier volcanic events. These events left behind islands such as Verlaten (or Sertung), Lang (also called Rakata Kecil or Panjang), Poolsche Hoed ("Polish Hat"), and the base of Rakata. Later, two other volcanic cones, Perboewatan and Danan, formed and eventually merged with Rakata to create the main island of Krakatoa. In 1883, the Krakatoa group included Lang, Verlaten, and Krakatoa itself, which was 9 km (5.6 mi) long and 5 km (3.1 mi) wide. Nearby were Poolsche Hoed, a tree-covered islet, and several small rocky islets or banks between Krakatoa and Verlaten.

Three volcanic cones existed on Krakatoa: Rakata, which was 820 m (2,690 ft) tall and located in the south; Danan, 450 m (1,480 ft) tall and near the center; and Perboewatan, 120 m (390 ft) tall and in the north.

The Pustaka Raja, a 19th-century collection of historical stories from Central Java, describes an event in 338 Śaka (416 AD). It claims that a loud noise came from a mountain called Batuwara (now Pulosari, an extinct volcano in Banten) and another from a mountain called Kapi, near Banten. A glowing fire erupted from Kapi, shaking the land and causing storms. The fire did not stop, and the mountain eventually collapsed, causing the sea to rise and flood the area. This event is said to have divided Java and Sumatra. However, no geological evidence supports this story, and its accuracy is uncertain.

Some scientists, like David Keys and Ken Wohletz, have suggested that a volcanic eruption, possibly from Krakatoa, in 535 AD caused global climate changes. However, drilling projects in the Sunda Strait found no evidence of an eruption in 535 AD.

During Java’s Sailendra dynasty, Krakatoa was called "The Fire Mountain." Records mention seven eruptions between the 9th and 16th centuries, tentatively dated to 850, 950, 1050, 1150, 1320, and 1530.

In 1680, an eruption occurred on Krakatoa. Johann Wilhelm Vogel, a Dutch engineer, saw the island in 1681 and described it as burned and barren, with fire erupting from four locations. He noted that the eruption happened in May 1680 and showed a piece of pumice as large as a fist. Another traveler, Elias Hesse, wrote that the island, which had erupted about a year earlier, had a visible smoke column and burned trees but no visible fire. A Bengali sea captain also later wrote about the eruption, though it was not recorded in the ship’s log at the time.

Simon Winchester, in his 2003 book, says that an 18th-century drawing by Dutch cartographer Jan van Schley, titled Het Brandende Eiland ("The Burning Island"), likely depicted the 1680 eruption.

In 1880, Rogier Verbeek studied a fresh lava flow on Perboewatan and estimated it was no more than 200 years old.

In 1780, the crews of HMS Resolution and HMS Discovery visited Krakatoa and found a freshwater spring and a hot spring. They described the island’s inhabitants as "friendly" and made sketches of the area. Edmund Roberts, in 1832, visited Krakatoa and Lang Island, noting the difficulty of landing due to strong waves and coral. He observed hot springs and a beautiful underwater garden near Krakatoa.

In 1620, the Dutch established a naval station on the islands and later built a shipyard. A pepper plantation was attempted in the late 17th century, but the islands were largely ignored by the Dutch East India Company. A penal colony was briefly established in 1809 but closed after a decade. By the 1880s, the islands had no permanent residents, with the nearest settlement being Sebesi, about 12 km (7.5 mi) away, which had a population of 3,000.

Maps of the islands were made in 1854 and 1874, showing differences in their details. In 1880, Rogier Verbeek conducted an official survey of the islands, collecting samples that later helped scientists understand the 1883 eruption.

1883 eruption

Before the huge 1883 eruption, the volcano had strong shaking activity for many years. Smaller eruptions began on May 20, 1883, and the volcano sent out large clouds of steam and ash that lasted until late August.

On August 27, the volcano had four very large explosions that nearly destroyed the island. These explosions were so loud that people in Perth, Western Australia, and Rodrigues, near Mauritius, could hear them. The third and loudest explosion sent a pressure wave that was recorded by instruments called barographs around the world. These instruments showed the wave traveled around the globe three and a half times. The wave went away from the volcano to the opposite side of the Earth and then returned three times. Ash from the eruption reached a height of 80 kilometers (260,000 feet). People living within 160 kilometers (100 miles) of the volcano reported hearing pain and permanent hearing loss. The sound was measured at 172 decibels, similar to the noise of a Space Shuttle’s rockets during takeoff. A ship about 64 kilometers (40 miles) from the island experienced a pressure wave of about 190 decibels, which broke the eardrums of more than half the crew.

The eruption caused serious damage from fast-moving hot gas and ash, volcanic ash, and giant ocean waves. Dutch officials recorded 36,417 deaths, but other sources suggest the number may have been over 120,000. Many reports describe human skeletons floating on rafts of volcanic rock in the Indian Ocean and washing up on Africa’s east coast up to a year after the eruption. In the year following the eruption, summer temperatures in the northern hemisphere dropped by an average of 0.4°C (0.72°F).

Aftermath

Verbeek, in his report about the eruption, predicted that any new activity would happen in the area between Perboewatan and Danan. This prediction happened on 29 December 1927, when a submarine lava dome near Perboewatan showed signs of eruptions (a similar event had been reported in June 1927). A few days later, a new island volcano rose above the water. At first, eruptions produced pumice and ash, and the island and the two islands that followed were quickly worn away by the sea. Later, a fourth island, named Anak Krakatau (meaning "child of Krakatoa" in Indonesian), emerged above the water in August 1930. This island produced lava flows faster than the waves could erode them. Anak Krakatoa had multiple eruptions throughout the next century.

On 22 December 2018, an eruption of Anak Krakatoa caused the main volcanic cone and the southwestern side of the volcano to collapse, leading to a deadly tsunami with waves up to five meters high. On 10 January 2019, eruptions began again, and a phreatomagmatic eruption was observed near the newly formed crater in May 2019. Eruptions continued periodically into 2023.

On 2 October 1883, five weeks after the eruption, a Dutch soldier was repeatedly stabbed by a bearded man wearing white robes while buying tobacco in the town of Serang. The attacker was never caught, but a similarly dressed man attacked a guard at the garrison six weeks later, blaming the Dutch for causing divine punishment in the area. The man’s strong religious beliefs were noted by interrogators, and historians believe these feelings were used by Muslim conservatives and anticolonial leaders, such as Abdul Karim Amrullah, to support the Banten Peasant’s Revolt in 1888. These leaders also took advantage of the Dutch public’s guilt over reports of abuse, such as those in Max Havelaar.

The explosion was the first natural disaster in history whose effects were clearly felt worldwide, and its cause was known, thanks to transoceanic communication cables. Winchester suggests this disaster marked the beginning of an era where people globally became more aware of events happening far away.

Biological research

The islands have become an important example for studying how life returns to an area after being almost completely destroyed. Scientists use them to learn about how new ecosystems form from nothing, especially after a major event like a volcanic eruption.

Before the 1883 eruption, very little was known about the islands' plants and animals. Only two collections of biological samples from before 1883 are recorded: one with plant samples and another with part of a shell collection. Drawings and descriptions from the HMS Discovery suggest the islands had a type of forest common to Java. However, very little is known about the animals that lived there before 1883, though they were likely similar to those on nearby small islands.

A major scientific question, called the "Krakatau problem," asks whether the 1883 eruption completely destroyed all life on the islands or if some plants or animals survived. When scientists first visited the islands in May 1884, they found only one living spider in a crevice on Rakata. Soon after, life began to return. By October 1884, grass was already growing. Over time, trees and shrubs covered parts of the island, likely brought by ocean currents, birds, or people. However, the plant life on Rakata remains fragile and has suffered damage from recent eruptions at Anak Krakatau.

In 1914, plans were made to protect Rakata as a natural reserve. In 1916, a man named Johann Handl, a German pumice collector, received permission to mine pumice on the island despite public opposition, possibly to avoid the effects of World War I. His permit allowed him to mine 8.7 square kilometers (3.4 square miles)—about half the island—for 30 years. Handl lived on the south coast of Rakata, built a house, and brought four European families and about 30 workers with him. He discovered wood that was not burned by the 1883 eruption and found fresh water below 5.5 meters (18 feet). His group stayed for four years but left after breaking the terms of their lease. It is believed that his group accidentally brought black rats to the island, which quickly multiplied and spread.

Conservation

Krakatoa was made a nature reserve in 1921, classified under IUCN management category Ia (strict nature reserve). In 1980, it was suggested as part of a national park along with other nature reserves. In 1991, "Ujung Kulon National Park and Krakatau Nature Reserve" was added to the UNESCO World Heritage List, meeting Natural criteria vii and x. Ujung Kulon National Park was officially created in 1992, including Krakatoa within its boundaries.