Anak Krakatoa in the context of Volcanologist

Krakatoa (/ˌkrɑːkəˈtoʊə, ˌkræk-/), also transcribed Krakatau (/-ˈtaʊ/), is now a caldera 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 them are known as Lang and Verlaten; another, Rakata, is the only remnant of an island, also called Krakatoa, mostly destroyed by an eruption in 1883 which created the caldera.

In 1927, a fourth island, Anak Krakatoa, 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 the 2018 Sunda Strait tsunami.

The Krakatoa Archipelago is a small uninhabited archipelago of volcanic islands formed by the Krakatoa stratovolcano located in the Sunda Strait, nestled between the much larger islands of Java and Sumatra. As of 2018, the archipelago consists of four main islands: Verlaten (a.k.a. Sertung) to the northwest, Lang (a.k.a. Rakata Kecil, or Panjang) to the northeast, Rakata (what remains the main island) to the south, and the currently volcanically active Anak Krakatoa in the north-centre. Together, the islands are a part of the Indonesian island arc system, created by the northeastward subduction of the Indo-Australian Plate. As part of a dynamic volcanic system, the islands have been continuously reshaped throughout recorded history, most notably in the 1883 eruption of Krakatoa.

Administratively, the Krakatoa Archipelago lies entirely within Lampung, Indonesia and forms a part of Ujung Kulon National Park.

The 2018 Sunda Strait tsunami (Indonesian: Tsunami Selat Sunda 2018) occurred on 22 December 2018 at around 21:38 local time after large parts of the southwestern side of Anak Krakatoa collapsed onto its caldera. The landslide spawned a tsunami wave that struck multiple coastal regions in Banten and Lampung, including the tourist destination of Anyer.

Lack of warnings on the arrival of the tsunami, coinciding with the Christmas and New Year holiday season in the nation and the tsunami occurring at nighttime, contributed to the large loss of life. With 426 deaths, the tsunami was the deadliest volcanic tsunami in Indonesia since the 1883 Krakatoa tsunami, which originated from the same island.