Krakatoa (Indonesian: Krakatau) is a volcanic complex in the Sunda Strait between the Indonesian islands of Java and Sumatra. Its eruption in August 1883 was one of the most destructive volcanic events in recorded history: it destroyed most of the original island, generated tsunamis that killed more than 36,000 people, and sent volcanic material high into the atmosphere, where it affected weather and sunsets around the world. Since the 1920s, a new volcano, Anak Krakatau, has grown inside the collapsed remnant of the old edifice and remains active.
Geography and geology
Krakatoa lies in the Sunda Strait, part of the volcanic arc associated with the subduction of the Indian Ocean crust beneath the Eurasian and Sunda plates, a setting shared with much of the Pacific Ring of Fire. The volcano is a caldera-forming system. Before 1883 the island group consisted of a large composite edifice with several cones, including the peaks known as Rakata, Danan and Perbuwatan. Geologists generally consider that an earlier collapse, probably in the fifth or sixth century CE, produced a caldera of roughly 7 km width, and that the islands of Lang and Verlatan are remnants of that structure.
The island's surroundings are shallow and volcanically active, and the regional tectonic setting is described under plate tectonics.
Eruptions before 1883
Krakatoa was considered dormant for much of the period before 1883, and European colonial authorities in the region paid little attention to its potential for eruption. Local populations, however, had long regarded it as a dangerous "fire mountain." The only confirmed eruption before 1883 was a moderate one around 1680. Earlier catastrophic activity, possibly in the sixth century, is inferred mainly from geological evidence and not from written records.
The 1883 eruption
Activity began in May 1883, when ash and steam were reported rising from the island and vessels in the strait recorded thunderous noises and glowing clouds. The eruption built to a climax on 26–27 August. The first major blast on 26 August sent an ash column roughly 27 km into the air, and the paroxysm of the following morning produced the loudest sounds in recorded history; they were reported as far away as Australia and the Indian Ocean region, with some sources giving distances of more than 4,600 km. Pyroclastic flows ran across the water, and the eruption ended with the collapse of most of the island into the sea. Roughly two-thirds of the island, about 23 km², sank, leaving a submarine caldera whose summit lay about 250 m below sea level.
The main hazard was the tsunami. Collapse and displacement of material into the strait generated waves that reached heights of up to about 40 m along the coasts of Java and Sumatra, and according to commonly cited figures they destroyed around 300 villages. Most deaths were caused by these waves or by heat and burns from pyroclastic flows. The total death toll is estimated at about 36,417, although the figure is an estimate and records from the region are incomplete. Because the eruption occurred in the Dutch East Indies and the telegraph station at Anjer, Java, relayed eyewitness reports, it became one of the first events to be covered as an international news story in near real time.
Global effects
The eruption injected large quantities of sulfur dioxide and fine ash into the atmosphere, and the aerosols spread around the globe. Estimates of the resulting cooling vary between sources: some report a drop of about 0.3 °C in summer temperatures in the Northern Hemisphere, others about 0.4 °C in the year that followed, and the value of 1.2 °C often cited for a five-year average lacks a firm reference. Aerosol-driven cooling of this kind is an early example of the link between volcanic emissions and global temperature change that later studies of climate would examine in greater detail.
Observers in the following months also recorded unusually vivid twilight "afterglows," first reported from Hawaii in September 1883 and seen as far as northern Europe by December. These were understood to result from the scattering of sunlight by fine particles high in the atmosphere. Unusual rainfall patterns were also reported in some regions.
The Royal Society in London established a Krakatoa Committee under the meteorologist George Symons to collect accounts of the eruption and its atmospheric effects. The resulting report, published in 1888, became a foundational work in the study of volcanic aerosols and was widely read in the decades that followed.
Anak Krakatau
Submarine eruptions began again in December 1927 along the same fissure line as the earlier cones. A new cone reached the sea surface in 1928 and became a small island named Anak Krakatau ("Child of Krakatoa"). It has grown since then, with eruptions recorded frequently, and it has repeatedly altered its own shape through explosions, lava flows and flank failures.
On 22 December 2018, the southwestern flank of Anak Krakatau collapsed into the sea during an eruption. The resulting tsunami struck the coasts of Java and Sumatra within about 24 minutes and killed several hundred people. The island's height was reduced from over 400 m to around 110 m. Subsequent eruptions have partially rebuilt the cone. A further eruption began in September 2026.
Scientific significance
The 1883 eruption shaped the development of volcanology. It drew attention to the atmospheric consequences of large eruptions and to the mechanisms by which tsunamis can be generated by volcanic collapse. The Volcanic Explosivity Index rates it at the high end of the scale (VEI 6), and the event is commonly referenced in discussions of Plinian eruptions and caldera formation. Anak Krakatau has also become a natural laboratory for studying how an ecosystem develops on newly formed volcanic land, because the island was created from bare rock and recolonized by plants and animals over decades.
Hazard and monitoring
The Krakatoa region remains hazardous. The 2018 collapse demonstrated that flank failure can generate destructive waves with little warning, and the surrounding coasts of Java and Sumatra are densely populated. Monitoring of the volcanic complex is carried out by Indonesian authorities and by international volcano-observation programs, which track seismicity, ash emissions and changes in the island's form.
Legacy
Krakatoa has been the subject of popular and scholarly works, and its story is often used to illustrate how a local geological event can have global consequences. The 1883 eruption remains one of the most cited examples in discussions of volcanic risk.
References
- Krakatoa Volcano: Facts About Deadly Eruptionlivescience.com
- 1883 eruption of Krakatoaen.wikipedia.org
- 10 Facts About the Eruption of Krakatoahistoryhit.com
- Krakatoa Volcano Eruptsebsco.com
- The 1883 Eruption of Krakatoa — Google Arts & Cultureartsandculture.google.com
- Krakatoabritannica.com
- Krakatoa 1883: West of Java!courses.ems.psu.edu
- Krakatoa - Eruption, Causes & Impacthistory.com
- Krakatoaen.wikipedia.org
- Krakatauebsco.com
- Anak Krakatoa: The dark history of volcano emerging from the seaaljazeera.com
- Global Volcanism Programvolcano.si.edu
- Anak Krakatau - NASA Sciencescience.nasa.gov
- Krakatau Volcano, Sunda Strait, Indonesia: Facts & Informationvolcanodiscovery.com
- Krakatau (Krakatoa) — Eruption History, Height, Type & Factsvolcanoatlas.vercel.app