Months of warning before the climax
Krakatoa’s eruption unfolded over several months rather than arriving without warning. Activity began around 20 May 1883 with Strombolian-style venting of steam from Perboewatan, the northernmost of the volcanic cones on the island, a relatively mild opening phase that nonetheless signalled renewed volcanic activity in the Sunda Strait between Java and Sumatra. Through June, explosive activity intensified and new vents opened between Perboewatan and a second cone called Danan, evidence that pressure building beneath the island was finding multiple outlets rather than remaining confined to a single point. This extended build-up gave observers months of increasingly dramatic activity to document before the eruption reached its devastating climax at the end of August.
Eleven explosions in two days
The eruption’s most violent phase struck on 26 and 27 August 1883, when a sequence of eleven major explosions tore through the island in rapid succession. The most powerful of these, and the eruption’s overall climax, occurred at 10:02 in the morning on 27 August, an explosion so severe that the island subsequently collapsed into a submarine caldera, physically removing most of the landmass that had produced the eruption in the first place. This two-day climactic sequence compressed months of gradually building volcanic pressure into a catastrophically short window, and it was this final, largest explosion, rather than the preceding months of activity, that generated the eruption’s most devastating and far-reaching effects.
Waves up to forty-six metres high
The collapse of the island generated tsunamis that struck coastal communities around the Sunda Strait with tremendous force. The town of Merak was destroyed by a wave reaching forty-six metres in height, while wave heights elsewhere ranged up to twenty-four metres along Sumatra’s southern coast and forty-two metres along the western coast of Java; even the low-lying Thousand Islands, well removed from the immediate blast zone, were submerged under some two metres of seawater, forcing residents to climb into trees to survive. The official death toll from the disaster stands at 36,417, broken down by region as 21,565 in Banten, 12,466 in Lampung, 2,350 in Batavia, and smaller numbers elsewhere; every one of the roughly three thousand inhabitants of Sebesi island is recorded as having died.
A sound that circled the world’s instruments
The scale of the climactic explosion registered far beyond the immediate disaster zone. It has been described as the loudest sound ever measured by instruments, audible as far away as Perth, Western Australia, and Rodrigues island near Mauritius, distances of roughly 3,110 and 4,800 kilometres respectively from the eruption site. The pressure wave generated by the blast was detected circling the entire globe more than three times over the following five days, recorded by barographs at weather stations worldwide that had no direct knowledge of the eruption’s cause but registered its atmospheric signature regardless, giving scientists an unprecedented instrumental record of a single volcanic event’s global physical reach.
A cooler summer, and skies that stayed red for months
Beyond its immediate and acoustic effects, the eruption altered global climate patterns measurably for more than a year afterward. Sulfur dioxide injected high into the stratosphere increased sulfuric acid concentrations in cirrus clouds, reflecting incoming solar radiation and contributing to a roughly 0.4 degree Celsius drop in Northern Hemisphere summer temperatures the following year. The same atmospheric particles produced strikingly vivid red sunsets around the world for months, phenomena dramatic enough that fire departments in New York, Poughkeepsie, and New Haven received emergency calls from residents who mistook the glowing sky for a distant fire. Southern California also recorded exceptional rainfall during the 1883 to 1884 season, a pattern some researchers connect to the eruption’s broader atmospheric disruption.
A volcano studied like never before
Krakatoa’s effects were documented with a degree of scientific rigour unusual for a disaster of this period. The Dutch investigator Rogier Verbeek led a systematic study of the eruption, establishing that volcanic activity had effectively ceased by mid-October 1883 and producing what became an influential early model for studying large explosive eruptions. The English artist William Ascroft separately created thousands of colour sketches attempting to capture the eruption’s distinctive red sunsets as accurately as possible, a visual record that, combined with the worldwide barograph data tracking the pressure wave, made Krakatoa one of the first volcanic disasters for which contemporary observers assembled genuinely global, cross-referenced physical evidence rather than relying solely on scattered eyewitness testimony.