Krakatoa, also spelled Krakatau, 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 group of volcanic islands 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 also 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. Eruptive activity has occurred again since the late 20th century, including a large collapse that caused the 2018 Sunda Strait tsunami. A new cinder cone formed in the area where the collapse happened during eruptions in the 2020s.

Historical significance

The most important eruptions of Krakatoa happened during a series of large explosions on August 26–27, 1883. These eruptions were among the most powerful volcanic events ever recorded.

The eruption had a volcanic explosivity index of 6, which means it was as strong as 200 million tons of TNT (840 petajoules). This is about 13,000 times stronger than the atomic bomb dropped on Hiroshima, Japan, during World War II, and four times as strong as the Tsar Bomba, the largest nuclear bomb ever tested.

The eruption sent about 25 kilometers (6 cubic miles) of rock into the air. The loud explosion was heard 3,600 kilometers (2,200 miles) away in Alice Springs, Australia, and 4,780 kilometers (2,970 miles) 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 seriously damaged. At least 36,417 people died, and many more were injured, mostly because of 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, named Anak Krakatau, which means "Child of Krakatoa" in Indonesian. Eruptions have happened regularly since then, including in 2009, 2010, 2011, and 2012. In late 2011, the island had a radius of about 2 kilometers (1.2 miles) and reached a height of about 324 meters (1,063 feet) above sea level. It grew about 5 meters (16 feet) each year. By 2017, the island’s height was over 400 meters (1,300 feet). However, a major collapse in December 2018 reduced its height to 110 meters (361 feet).

Etymology

One of the earliest known references to the name Krakatoa appears in the Old Sundanese text Bujangga Manik, which was likely written in western Java during the late 15th century. In this text, Krakatoa is described as "the island of Rakata, a mountain in the middle of the sea" (pulo Rakata gunung ti tengah sagara, f. 27v). Earlier European records mention an island in the Sunda Strait with a "pointed mountain," but the first known use of the name Krakatoa in the Western world appears on a map created in 1611 by Lucas Janszoon Waghenaer. On this map, the island is labeled "Pulo Carcata" (pulo means "island" in Sundanese).

Many different spellings of the name have been recorded, including Crackatouw, Cracatoa, and Krakatao (an older Portuguese-based version). The first known use of the spelling "Krakatau" was by Wouter Schouten, who described "the high tree-covered island of Krakatau" during a voyage in October 1658.

The origin of the Indonesian name Krakatau is unclear. The Smithsonian Institution’s Global Volcanism Program states that Krakatau is the correct name, though Krakatoa is also commonly used.

Geographical setting

Indonesia has more than 130 active volcanoes, the highest number of any country. These volcanoes form the main line of the Indonesian island arc system, which is created by the movement of the Indo-Australian Plate under another plate. Most of these volcanoes are found on Indonesia's two largest islands, Java and Sumatra. These islands are separated by the Sunda Strait, which is located at a bend in the main line of the island arc. Krakatau is positioned directly above the area where the Eurasian Plate and the Indo-Australian Plate meet. At this location, the edges of the plates change direction suddenly, which may cause the Earth's crust in the region to be unusually weak.

Pre-1883 history

Long ago, before recorded history, an earlier volcanic eruption formed a caldera, leaving behind parts of the islands Verlaten (or Sertung), Lang (also called Rakata Kecil or Panjang), Poolsche Hoed ("Polish Hat"), and the base of Rakata. Later, two more volcanic cones, Perboewatan and Danan, formed and eventually joined with Rakata to create the main island of Krakatoa. In 1883, the Krakatoa group included Lang, Verlaten, and Krakatoa itself, an island 9 km (5.6 mi) long and 5 km (3.1 mi) wide. Nearby were Poolsche Hoed, a tree-covered islet near Lang, and several small rocky islets or banks between Krakatoa and Verlaten.

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

The Javanese Book of Kings (Pustaka Raja), a 19th-century collection of historical traditions from Central Java, describes an event in 338 Śaka (416 AD). It claims that a loud sound was heard from Mount Batuwara (now called Pulosari, an extinct volcano in Bantam), followed by a similar noise from Mount Kapi, located west of modern Bantam (Banten, the westernmost province of Java). A glowing fire erupted from Mount Kapi, shaking the world and causing thunder, rain, and storms. The fire did not stop; instead, it grew stronger. Eventually, Mount Kapi exploded and sank into the earth. The sea rose, flooding the land east of Mount Batuwara and the area near Mount Rajabasa (the southernmost volcano in Sumatra). People in the northern part of the Sunda region were drowned, and their property was lost. After the event, the land where Mount Kapi stood became sea, and Java and Sumatra were divided into two parts.

The Pustaka Raja does not use primary sources for this description, and its accuracy is uncertain. No geological evidence supports the eruption described in the text. Some scientists, like David Keys and Ken Wohletz, have suggested that a volcanic eruption, possibly from Krakatoa, in 535 AD caused global climate changes in 535–536. 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 eruptive events between the 9th and 16th centuries, tentatively dated to 850, 950, 1050, 1150, 1320, and 1530.

In February 1681, Johann Wilhelm Vogel, a Dutch mining engineer, passed through the Sunda Strait. In his diary, he wrote that Krakatoa, which he had seen in 1679 as a green and healthy island, was now completely burned and barren. He saw fire erupting from four locations on the island and noted that the eruption occurred in May 1680. Vogel showed a piece of pumice as large as his fist.

Vogel returned to Sumatra in November 1681. On the same ship were other Dutch travelers, including Elias Hesse. Hesse’s journal described Krakatoa as an island that had erupted about a year earlier. He wrote that the island was uninhabited, with smoke rising from it. From a distance, the smoke column was visible, and trees on the mountain appeared burned, though no fire was seen.

A Bengali sea captain later wrote about the 1680 eruption but did not record it in the ship’s log at the time. Neither Vogel nor Hesse provided detailed descriptions of the eruption in their other writings. No other travelers mentioned the event. In November 1681, a pepper crop was being sold by local inhabitants.

Simon Winchester, in his 2003 book Krakatoa: The Day the World Exploded: August 27, 1883, wrote that an 18th-century etching by Dutch cartographer Jan van Schley, titled Het Brandende Eiland ("The Burning Island"), likely depicted the 1680 eruption.

In 1880, Verbeek studied a fresh, unweathered lava flow on the northern coast of Perboewatan. He estimated it was no more than 200 years old.

In February 1780, the crews of HMS Resolution (1771) and HMS Discovery (1774) stopped at Krakatoa during their return journey after Captain James Cook’s death in Hawaii. They found a freshwater spring and a hot spring on the island. They described the island’s inhabitants as "friendly" and made several sketches. John Ledyard, in his journal, called the island "Cocoterra."

Edmund Roberts referred to the island as "Crokatoa" in his journal. In 1832, the US sloop-of-war Peacock anchored near the north end of Krakatoa and visited Lang Island. Landing was difficult due to heavy waves and coral extending far from the shore. Hot springs were found on the eastern side of Krakatoa, 150 feet (46 m) from the shore. Roberts, Captain Geisinger, and marine lieutenant Fowler visited Forsaken Island, mistaking the sound of locusts for running water. They observed a beautiful underwater garden with colorful corals and tropical plants, but found no water or food.

In 1620, the Dutch established a naval station on the islands and later built a shipyard. In the late 17th century, an attempt to grow pepper on Krakatoa failed, and the islands were largely ignored by the Dutch East India Company. A penal colony was established in 1809 but operated for only about a decade. By the 1880s, the islands had no permanent residents; the nearest settlement was Sebesi, about 12 km (7.5 mi) away, with a population of 3,000.

Several maps and mariners’ charts were made of the islands, but they were not widely explored. An 1854 map was used in an English chart, which differed from a Dutch map made in

1883 eruption

Before the powerful 1883 eruption, the volcano had frequent earthquake activity. On 20 May 1883, smaller eruptions began, sending large clouds of steam and ash into the sky. These eruptions continued until late August.

On 27 August, the volcano erupted violently four times, causing widespread destruction. The explosions were so loud that people in Perth, Western Australia, and Rodrigues Island, near Mauritius, could hear them even though these places were 3,110 km (1,930 mi) and 4,800 km (3,000 mi) away, respectively. The third and most powerful explosion created a pressure wave that was recorded worldwide. Barographs, which measure air pressure, recorded the wave seven times over five days. Four times, the wave traveled from the volcano to the opposite side of the Earth, and three times, it returned to the volcano. The wave circled the globe more than three and a half times. Ash from the eruption reached a height of 80 km (260,000 ft). People living within 160 km (100 mi) of the volcano experienced severe ear pain and permanent hearing loss. The sound intensity at this distance was 172 dB, similar to the noise of the Space Shuttle’s rockets during launch. A ship 64 km (40 mi) away from the island recorded a pressure wave of 190 dB, which caused damage to the eardrums of more than half the crew.

The eruption’s effects, including fast-moving lava flows, volcanic ash, and tsunamis, caused major destruction in the region and globally. Dutch officials reported 36,417 deaths, but other sources suggest the death toll may have been over 120,000. Many accounts describe human skeletons floating on rafts of volcanic rock across 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 predicted that any new volcanic activity would occur in the area between Perboewatan and Danan. This prediction was correct on 29 December 1927, when a submarine lava dome near Perboewatan showed signs of eruptions (an earlier event in the same area had been reported in June 1927). A few days later, a new island volcano rose above the water. The eruptions began with pumice and ash, and the island along with two others that formed later were quickly worn away by the sea. Eventually, a fourth island, named Anak Krakatau (meaning "child of Krakatoa" in Indonesian), appeared 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 regularly into 2023.

On 2 October 1883, five weeks after the eruption, a Dutch soldier was stabbed many times by a bearded man wearing white robes while buying tobacco in Serang. The attacker was never caught, but a similar 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 those who questioned him. Historians believe these beliefs were used by Muslim conservatives and anticolonial leaders, such as Abdul Karim Amrullah, to help cause the Banten Peasant’s Revolt in 1888 and to take advantage of the Dutch feeling guilty about reports of abuse.

The explosion was the first natural disaster in history whose effects were clearly felt worldwide, and its cause was known, after the development of cables that connected across oceans. Winchester suggests this disaster marked the beginning of an era when people around the world became more aware of global events.

Biological research

The islands are an important example for studying how life returns to an area after a major event. Before the 1883 eruption, scientists had studied the islands very little. Only two biological collections from before 1883 are known: one with plant samples and another with part of a shell collection. Descriptions and drawings from the HMS Discovery suggest that the island’s plants were similar to those in a mature tropical forest found in Java. Little is known about the island’s animals before 1883, but they were likely similar to those on nearby smaller islands.

A key question in biology, called the "Krakatau problem," is whether the eruption completely destroyed all life on the islands or if some native life survived. When scientists first visited the islands in May 1884, they found only a spider in a crevice on Rakata. However, life returned quickly. By October 1884, grass was already growing. Over time, trees and shrubs covered parts of the island, likely brought by seeds carried by ocean currents, birds, or people. The plant life on Rakata is fragile and has suffered from recent eruptions at Anak Krakatau.

In 1914, plans were made to protect Rakata as a nature reserve. In 1916, a German man named Johann Handl received permission to mine pumice from the island, despite local opposition, possibly to avoid World War I. His permit covered 8.7 square kilometers (3.4 square miles), mostly the eastern part of the island, for 30 years. Handl lived on the southern coast of Rakata, built a house, and brought four European families and about 30 workers. He discovered wood and fresh water below the 1883 eruption layers. He and his group stayed for four years but left because they broke the lease rules. It is believed that his group accidentally brought black rats to the island, which then spread quickly.

Conservation

Krakatoa was designated as a nature reserve in 1921. It was classified under IUCN management category Ia, which is a strict nature reserve. Along with several other nature reserves, it was proposed as a national park in 1980. In 1991, "Ujung Kulon National Park and Krakatau Nature Reserve" was added to the UNESCO World Heritage Site list. It met Natural criteria (vii) and (x). Ujung Kulon National Park was officially created in 1992, and it includes Krakatoa.