At four minutes past ten on the morning of Monday, 27 August 1883, the chief of police on the island of Rodrigues, in the western Indian Ocean, made a note in his daily report. He had heard, he wrote, “the distant roar of heavy guns” coming from the east-northeast. He guessed a naval engagement, perhaps near Mauritius. He sent a messenger to the harbor to find out which ship was in trouble.
There was no ship in trouble. The sound he had heard was the fourth and final detonation of the volcano Krakatoa, in the Sunda Strait, between the islands of Java and Sumatra. It had traveled across open ocean for four hours and four minutes. Rodrigues is 4,800 kilometers from Krakatoa. The chief of police was on the opposite side of the Indian Ocean from the volcano. He still heard the explosion.
It is, by every measurement we have, the loudest sound in recorded human history.
What had happened in the strait
Krakatoa had been showing signs of restlessness for three months. Ships passing through the strait had reported smoke and ash from its three peaks since May. Steamers heading for Batavia (now Jakarta) had photographed it. The Dutch colonial authorities, who governed the East Indies, considered the activity routine.
The activity was not routine. Beneath the island, a vast pocket of seawater had been working its way into the magma chamber. By the morning of 26 August, the volcano had begun a sustained eruption. Ash columns rose 25 kilometers into the atmosphere. Pumice fell on ships forty kilometers away, thick enough that crews had to clear it from the decks with shovels. Captain Lindemann of the German bark Berbice, anchored in the strait, recorded in his log that the air “rained stones” and the rigging was on fire from falling embers.
The four climactic explosions came on the morning of 27 August. At 5:30 a.m., 6:44 a.m., 10:02 a.m., and 10:41 a.m., the island tore itself apart in successive paroxysms. The third was the largest. Two-thirds of the island simply ceased to exist — roughly twenty cubic kilometers of rock, ejected, vaporized, collapsed into the empty magma chamber, or thrown into the sky. Where the cone of the volcano had been, there was now a submarine caldera six kilometers across and 250 meters deep.
The energy released in that ten-thirty explosion has been estimated at the equivalent of 200 megatons of TNT — roughly ten thousand times the force of the bomb that destroyed Hiroshima.
The pressure wave from the fourth explosion was so violent that it circled the planet. Barographs in Greenwich, in Vienna, in Washington, and in Tokyo all recorded the same sudden, sharp deflection of atmospheric pressure. Over the next five days, the wave passed each location seven times — three times traveling east from Krakatoa, four times traveling west. Investigators tracking the data later that decade calculated that the wave had circled the Earth, at least at the speed of sound, three and a half times.
The wave that did the killing
The sound did not kill anyone. The eruption itself, despite its violence, killed almost no one directly. The cone of Krakatoa had been uninhabited.
What killed people was the water.
When the central column of rock collapsed into the emptied magma chamber, the sea fell in after it — and was thrown back out as a series of tsunamis. The largest of them reached more than thirty meters in height as they crossed the shallow coastal shelves on either side of the strait. In some places the wave was higher than the tallest coconut palms.
It hit the coastal villages of Java and Sumatra without warning. The Dutch lighthouse at Anyer, on the Javanese coast, was destroyed; its keeper, a man named Schuit, was killed along with his family. The town of Telok Betong, in southern Sumatra, was scoured down to its foundations. A Dutch gunboat, the Berouw, was carried inland nearly three kilometers and deposited in a tree, where the wreck remained as a tourist attraction for several decades.
The official Dutch colonial death toll was 36,417. Modern estimates run higher, sometimes considerably higher, because many of the coastal villages were never censused and were entirely erased. The Royal Society’s report of 1888, edited by G. J. Symons, accepted the lower official number while noting that the actual figure was probably “much greater.”
Most of those who died had no warning. The first they knew of the eruption was the wave.
The world changed colour
The atmospheric effects of the eruption lasted for years.
Krakatoa had injected roughly twenty million tons of sulfur dioxide into the stratosphere. This combined with water vapor to form a fine veil of sulfuric acid aerosol that wrapped the upper atmosphere and refracted sunlight in unfamiliar ways. For the rest of 1883 and well into 1884, sunsets across Europe and North America turned brilliant and strange — pink, copper, blood-red, with a green flash sometimes appearing at the horizon after the sun went down.
In London, the unusual sunsets became a public sensation. The painter William Ashcroft made hundreds of pastels of the western sky from Chelsea, dated and annotated, between October 1883 and February 1884. They are now in the Royal Society’s archive and are some of the most detailed visual records of an atmospheric event ever made. The poet Gerard Manley Hopkins, who saw the sunsets from the Welsh coast, described them in a long letter to the journal Nature in January 1884:
“The sunsets were not only of unusual beauty, but were almost frightful. They were strangely lurid and prolonged.”
The cooling effect was measurable. The average temperature of the Northern Hemisphere dropped by about half a degree Celsius in 1884. Monsoons failed; crop yields declined. The El Niño of 1884 was the strongest of the nineteenth century, and is now believed to have been triggered, or at least amplified, by the eruption.
It would be another century and a quarter before scientists would understand the chain of causation in detail. The sequence — eruption, stratospheric aerosols, global cooling, displaced weather patterns — had been suggested by individual scientists in the years after Krakatoa, but no one had the global temperature data to confirm it. The Krakatoa veil cleared from the upper atmosphere by 1888. The mechanism it had revealed waited for the data to catch up.
The cable did the news
There is one detail of Krakatoa’s story that often gets left out. It is the first natural disaster of the modern age — not in the sense of scale, which had been matched by other historical eruptions, but in the sense of speed of communication.
The submarine telegraph cable linking Europe to East Asia had been completed in 1872. By 1883, dispatches from Batavia could reach London within a day. The first reports of the eruption appeared in The Times of London on 28 August, the day after the climactic explosion. By the first week of September, English newspapers were running detailed maps of the strait, with depth soundings and the location of the destroyed villages.
This was new. For previous eruptions on this scale — Tambora in 1815, Laki in 1783 — news had taken months to reach Europe, and then arrived as fragments. Krakatoa arrived as a continuous story. The Royal Society’s exhaustive report, published in 1888, was the first international scientific investigation of a volcanic event to draw on data from every continent. It included tide records from South America, barograph traces from Tokyo, photographs from London, and eyewitness accounts collected by mail from Australian and Indian readers of Nature.
A volcano that had been geographically remote became, for several months, the most discussed event in the world.
The island that came back
On 29 December 1927, fishermen working near the destroyed site of Krakatoa noticed bubbles in the water and a faint plume of steam. Over the following two years, a new cone built itself up, eruption by eruption, in the same place the original island had been. By 1930, it had broken the surface. The Dutch authorities named it Anak Krakatau: “Child of Krakatoa.”
It is still growing. As of the most recent measurements, in 2023, it stands roughly 150 meters above sea level. In December 2018 it lost most of its summit in a flank collapse, which triggered a tsunami that killed at least 437 people on the coasts of Java and Sumatra — many of them in towns that had been rebuilt after 1883, on the same beaches.
The cone is rebuilding itself again. Each year it adds a few meters of height. It will eventually be as large as the original Krakatoa, and then it will tear itself apart, and then a new island will surface in the strait and begin growing, and the cycle will run again.
The chief of police on Rodrigues filed his report and waited for news of a battle that had never been fought.