Anak Krakatoa

About

Anak Krakatoa, or Anak Krakatau (Indonesian for 'child of Krakatoa'), is a volcanic island and an active volcano in Indonesia. On 29 December 1927, Anak Krakatoa first emerged from the caldera formed by the explosive volcanic 1883 eruption of Krakatoa that destroyed the island of Krakatoa (Krakatau). Sporadic eruptive activity has occurred at the site since the late 20th century. A large sector collapse of the volcano occurred on 22 December 2018, causing a deadly tsunami—the 2018 Sunda Strait tsunami. There has been subsequent activity since then in the 2020s. Anak Krakatoa's 4–6 September 2026 eruption caused a fog of ash in the nearby islands of Java, Sumatra, and other surrounding areas. Owing to its young age, the island of Anak Krakatoa is one of several in the area which are of interest to, and the subject of extensive study by, volcanologists.

After the cataclysmic eruption of Krakatoa in 1883, Krakatoa Island lost approximately two-thirds of its mass on the northwest side, obliterating the peaks of Perboewatan and Danan, and leaving only the southern half of the island, including the Rakata Volcano, as the last remnant of the original island. The lost area became a shallow sea.

In early 1927, visible volcanic activity began to occur at the point located between where the former peaks of Mount Perboewatan and Mount Danan had been. This was a short-lived appearance of a small island that was sunk by sea waves within a week. Several months later, volcanic activity began to create a more permanent land formation which, owing to rain and waves, once again collapsed under the sea after its volcanic activity stopped. This process reoccurred several times during the next three years.

On 11 August 1930, the volcanic island permanently rose above sea level and was locally named Anak Krakatau ('child of Krakatoa'). It has been the site of repeated eruptive episodes ever since. Anak Krakatoa's highest point increased at an average rate of 7–9 meters per year through September 2018.

Anak Krakatoa is located in the Sunda Strait—between the islands of Java and Sumatra—in the Indonesian province of Lampung. The volcano is contained within the Ujung Kulon National Park, and is part of the Pacific Ring of Fire. The island is surrounded by three other nearby islands: Sertung Island (Verlaten Island) to the west, Krakatau Kecil Island (Lang Island, Panjang Island, or Rakata Kecil) to the east, and Rakata Island to the south; they are all in what is now the Krakatoa archipelago.

The island is situated approximately 700 km (430 mi) north of the Sunda Trench marking the subduction zone separating the Australian Plate and the fixed Sunda Plate, atop an oceanic crust less than 25 km (16 mi) thick. In geological terms, it has recently formed within the caldera of the Krakatoa volcanic eruption. The entire island comprises a Somma-stratovolcano system of the late Holocene epoch, and features a pyroclastic cone. The major rock-type components of Anak Krakatoa include andesite, dacite and basalt, with minor indications of trachyte. The island had reached a maximum elevation of 338 m (1,109 ft) before its collapse during the 2018 eruptive event.

The volcano's most recent eruptive episode began in 1994. Quiet periods lasting a few days have alternated with almost continuous Strombolian eruptions since then. Hot gases, rocks, and lava were released in an eruption in April 2008. Scientists monitoring the volcano warned people to stay out of a 3 km (1.9 mi) zone around the island. On 6 May 2009, the Volcanological Survey of Indonesia raised the eruption alert status of Anak Krakatoa to Level III (Siaga; 'alert'). An expedition to the volcano revealed that a 100 m (330 ft) wide lava dome was growing in its crater. In January 2012, volcanologists at the University of Oregon warned that a tsunami caused by flank collapse of Anak Krakatoa was likely, as it had formed on the steep eastern slope of the large caldera formed by the 1883 explosive eruption.

Adapted from Wikipedia (CC BY-SA). Photography via Wikimedia Commons.