The eruption did not begin with the great explosion. It began with a cough. On May 20, 1883, Strombolian eruptions started from Perboewatan, the northernmost of Krakatoa's three volcanic cones. Steam and ash reached an estimated 6,000 meters. Explosions echoed in Batavia -- modern-day Jakarta -- 160 kilometers away, rattling windows and doors. Six days later, an excursion party landed on the island and found everything coated in fine white dust, with bursts erupting from Perboewatan every five to ten minutes. By June, Danan, the middle cone, had joined in. The summit of Perboewatan was already gone. On August 11, a Dutch engineer named Captain Ferzaneer mapped the erupting vents and found activity concentrated around Danan, while Rakata, the largest cone to the south, sat quiet. The island was tearing itself apart from north to south, and for three months the world barely noticed.

August 26 brought the overture: a volcanic blast around 1 PM sent a column of gas and debris 24 kilometers into the sky. But the catastrophe proper came the next morning. At 5:30 AM, Perboewatan exploded, sending a tsunami racing toward Telok Betong on the Sumatran coast. At 6:44, Danan detonated, generating waves that propagated east and west through the strait. Then, at 10:02 AM, the third explosion obliterated the island. Its force has been estimated at VEI-6, ejecting roughly 25 cubic kilometers of rock and ash into the atmosphere. The sound reached Perth to the southeast and Rodrigues to the west. It remains the farthest distance a natural sound has ever been reliably documented. A fourth major explosion followed at 10:52. By midday, two-thirds of Krakatoa had collapsed into the emptied magma chamber beneath it, creating a submarine caldera 250 meters deep where the island had stood just hours before.

The tsunamis killed more people than the eruption itself. Of the estimated 36,417 dead, more than 34,000 drowned. Massive waves swept through the Sunda Strait, entirely submerging some smaller islands. The largest recorded wave in the Indonesian province of Banten reached an estimated 41 meters -- taller than a twelve-story building. Across 165 coastal villages, nothing remained. Pyroclastic flows added a horror of their own: superheated clouds of gas, ash, and rock that raced across the surface of the strait at terrifying speed, reaching the coast of southern Sumatra. Roughly 2,000 people there were burned to death. Ships at sea were hit by hot winds and falling tephra. The steamer Loudon and the sailing vessel W.H. Besse survived only because they were far enough from shore that the pyroclastic flows had cooled by the time they reached them. Closer to the volcano, the destruction was total.

In the weeks and months that followed, the world changed color. Volcanic aerosols -- tiny sulfur dioxide particles lofted into the stratosphere -- scattered sunlight in ways no one alive had seen before. Sunsets across the globe turned vivid, unearthly shades of red, orange, and purple. In New York, Poughkeepsie, and New Haven, the skies glowed so intensely that fire engines were dispatched to fight what citizens assumed were distant conflagrations. Green suns were reported. Blue moons appeared. Average global temperatures dropped by as much as 1.2 degrees Celsius over the following five years, as stratospheric sulfuric acid haze reflected sunlight back into space. Northern Hemisphere summer temperatures fell 0.4 degrees in the year after the eruption. In Norway, the blood-red twilights persisted from late November 1883 through mid-February 1884 -- a period that some scholars have linked to the eerie, anguished sky in Edvard Munch's 1893 painting The Scream, though other researchers attribute Munch's inspiration to rare nacreous clouds.

Krakatoa was not the largest volcanic eruption in history -- Tambora in 1815 was far greater. But it was the first to unfold in the age of global telecommunications. Undersea telegraph cables, laid in the decades before, connected the colonial outposts of the Dutch East Indies to Europe and the rest of the world. Within hours, news of the eruption was being relayed from Batavia to Amsterdam, from London to New York. Newspapers published eyewitness accounts within days. The Royal Society in London organized a systematic collection of atmospheric observations from around the world, producing one of the first truly global scientific datasets. Rogier Verbeek, a Dutch geologist who had surveyed Krakatoa just years before, produced a 550-page report that set new standards for eruption documentation. The eruption became, in a sense, the first shared global disaster -- a catastrophe that the world experienced not in retrospect, months or years later, but almost in real time. The sunsets everyone saw were proof: the atmosphere had no borders, and what happened in the Sunda Strait belonged to everyone.