Krakatoa: a deep dive into the volcano that shook the world
Krakatoa is the volcano that turned global news, for the first time, into a near-real-time event. Its 1883 eruption in the Sunda Strait between Java and Sumatra produced the loudest sound in modern history, tsunamis that killed more than 36,000 people, and an aerosol veil that reddened sunsets in Europe for years.
A caldera in the Sunda Strait
Before 1883 Krakatoa was a small archipelago of three volcanic islands in the Sunda Strait. Beneath them sat a much older caldera, formed in an enormous prehistoric eruption. The 1883 event hollowed most of the central edifice out, and what remained — Rakata — collapsed into a new submarine caldera some 250 metres deep.
The 1883 cataclysm
The eruption climaxed on 26–27 August 1883 with a series of four enormous explosions. The fourth was so loud it was heard 4,800 kilometres away in Rodrigues Island, near Mauritius. Pyroclastic flows raced across the sea on cushions of steam. Tsunamis up to 30 metres high struck the Java and Sumatra coasts.
The death toll and the tsunamis
Most of the dead were not killed by lava or ash, but by the tsunamis. Whole villages on Java's west coast and Sumatra's south coast were swept away. Western Anyer lost its lighthouse. Two thousand kilometres away, tidal gauges in South Africa registered the wave; across the Pacific, harbours rocked for days.
Global climate effects
About 20 cubic kilometres of material reached the stratosphere. The aerosol layer cooled global average temperatures by roughly half a degree Celsius for several years. Sunsets in Europe and North America turned a strange luminous red — the colour Edvard Munch later captured in "The Scream," whose sky may have been a Krakatoa sky.
The birth of Anak Krakatau
In 1927 a new vent broke the surface of the 1883 caldera. The cone that grew from it — "Child of Krakatoa," Anak Krakatau — became one of Indonesia's most active volcanoes. By 2018 it was about 400 metres high. In December 2018, the southwest flank collapsed into the sea, generating a tsunami that killed hundreds along the Sunda Strait.
What is left of the cone
After the 2018 collapse, Anak Krakatau lost about two-thirds of its height in minutes. It is now rebuilding, with frequent strombolian eruptions visible from the Java and Sumatra coasts on clear nights. Tour operators in Carita and Anyer run boats out to the caldera.
Monitoring and warning systems
The 2018 tsunami exposed a weakness in Indonesia's warning system: flank-collapse tsunamis can occur without an earthquake, and the seismic-trigger logic of standard tsunami buoys may not catch them. Improved coastal sea-level sensors and continuous SAR satellite monitoring of the volcano have since been deployed.
Why Krakatoa matters
Krakatoa is the eruption that taught the modern world that a single volcano can change the climate. It is the eruption that shaped how we think about giant explosions. And Anak Krakatau is a reminder that the system is not finished — only paused between acts.
On the map
Open the map and find Anak Krakatau in the Sunda Strait between Java and Sumatra. The Indonesian arc continues east through Tambora and Rinjani, and west into the great Sumatran chain.