Anak Krakatau

Anak Krakatau
Adhari Arief · CC BY-SA 4.0 · source
Name	Anak Krakatau
Photo caption	Anak Krakatau in 2019
Elevation m	338
Location	Sunda Strait, Indonesia
Coordinates	6°7′S 105°24′E
Type	Stratovolcano
Range	Sunda Arc
Last eruption	Ongoing (2020s)

Anak Krakatau is a volcanic island formed in the caldera of the historic Krakatoa eruption of 1883. It emerged in 1927 and has produced frequent Strombolian and Vulcanian activity, rebuilding and modifying the remnant caldera in the Sunda Strait between the islands of Java and Sumatra. The edifice is part of the Sunda Arc subduction system and is closely monitored by regional and international scientific organizations.

Geography and geology

Anak Krakatau occupies a central position within the horseshoe-shaped caldera created by the 1883 eruption associated with the Krakatoa eruption (1883), and lies in the maritime corridor between Banten (western Java) and Lampung (southern Sumatra). The island’s morphology is controlled by repeated eruptive construction and frequent flank collapse, influenced by subduction of the Australian Plate beneath the Eurasian Plate along the Sunda Arc. Rock types are dominantly andesitic to basaltic-andesitic, similar to other arc volcanoes such as Merapi, Tambora, and Rinjani. The bathymetry of the surrounding sea floor, mapped by surveys from institutions including the National Oceanic and Atmospheric Administration and Indonesia’s Center for Volcanology and Geological Hazard Mitigation, shows steep submarine slopes and talus deposits typical of collapse-prone volcanic islands. Volcanological classification places the cone among stratovolcanoes that exhibit both explosive and effusive behavior, comparable in style to Stromboli and Mount Etna in certain phases.

Eruptive history

Initial emergence in 1927 followed decades of episodic eruptions, with constructional phases interspersed with collapses documented by the United States Geological Survey, Dutch colonial observers, and Indonesian volcanologists from the Volcanological Survey of Indonesia. Notable eruptive episodes occurred in the 1930s, 1950s, 1980s, and the early 21st century, with documented explosive events recorded by institutions such as the Global Volcanism Program and research groups at University of Cambridge, University of Washington, and Institut Teknologi Bandung. Petrological studies link magma evolution to crustal assimilation and magma mixing processes observed in other Sunda Arc volcanoes, including Semeru and Sangay. Monitoring has recorded Strombolian bombs, ash plumes, lava flows, and periodic pyroclastic density currents; these phenomena have parallels with historical eruptions at Mount St. Helens and Nevado del Ruiz regarding collapse and flank failure triggers.

2018 eruption and tsunami

On 22 December 2018 a major eruption and partial flank collapse generated a deadly tsunami that affected the coasts of Banten and Lampung provinces, producing casualties and infrastructure damage recorded by the Indonesian National Board for Disaster Management and international relief agencies including the International Federation of Red Cross and Red Crescent Societies. The event’s timing and mechanism were examined by researchers from British Geological Survey, Stockholm University, Caltech, and Monash University, who used seismic records, satellite imagery from Landsat and Sentinel-2, and eyewitness reports from local ports such as Merak and Krakatau National Park rangers. The tsunami differed from tectonic tsunamis associated with the 2004 Indian Ocean earthquake and tsunami by being generated by subaerial flank collapse and rapid landslide entry into shallow water, similar in mechanism to prehistoric events inferred at Santorini and documented at Fogo. Post-event investigations highlighted challenges in early warning integration between seismic, tide, and tsunami-monitoring systems managed by agencies including BMKG and regional maritime authorities.

Volcanic monitoring and hazards

Monitoring of the volcano is conducted by the Center for Volcanology and Geological Hazard Mitigation (PVMBG/BPPTKG), academic partners such as Universitas Gadjah Mada and Bogor Agricultural University, and international collaborators including UNESCO-affiliated programs and the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI). Instrumentation includes seismographs, GPS, infrasound sensors, SO2 spectrometers, satellite-based thermal and radar remote sensing from MODIS and Sentinel-1, and periodic field surveys. Primary hazards are explosive ash emissions affecting aviation corridors near Soekarno–Hatta International Airport, pyroclastic density currents threatening nearby islands such as Sertung and Rakata, tsunamigenic flank collapse, and lahars in coastal catchments impacted by heavy tropical rainfall influenced by Indian Ocean Dipole and La Niña/El Niño cycles. Risk mitigation measures involve exclusion zones, early warning bulletins, public education led by provincial administrations, and coordination with maritime agencies like the Indonesian Navy and BASARNAS for search-and-rescue preparedness.

Ecology and human impact

The island and surrounding marine ecosystem host pioneering successional habitats studied by ecologists from University of Cambridge, National University of Singapore, and Universitas Indonesia, showing colonization by seabirds, pioneer plants, and reef-building corals similar to ecological recovery documented after eruptions at Surtsey and Krakatoa (post-1883) studies by Alfred Russel Wallace and subsequent naturalists. The 2018 event had acute human impacts on fishing communities in coastal towns such as Anyer and Tanjung Lesung, tourism operators linked to Krakatoa National Park, and energy and port facilities serving the Sunda Strait shipping lanes. Socioeconomic research by World Bank, Asian Development Bank, and Indonesian universities highlights recovery needs, livelihood diversification, and resilience-building in affected districts, while conservation initiatives by Ministry of Environment and Forestry (Indonesia) and NGOs aim to balance biodiversity protection with disaster risk reduction.

Category:Volcanoes of Indonesia