Prior to Krakatoa's massive eruption of 1883, the volcano lay dormant for two centuries. In the years preceding the event, seismic activity around the volcano was intense, with some earthquakes felt as far distant as Australia. Beginning 20 May 1883, three months before the final explosion, steam venting began to occur on a regular basis.

By early August, three vents were regularly erupting on Krakatoa; tides in the vicinity were unusually high, and ships at anchor were moored with chains as a result. 11 August saw the onset of larger eruptions, with ashy plumes being emitted from as many as eleven vents. On 24 August, eruptions further intensified, and the cataclysmic phase began on Sunday 26 August, near midday. Ash clouds from the eruption reached a height of 36 km, and the first tsunamis were generated.

The 27 August eruptions occurred at 5:30 A.M., 6:44 A.M., 8:20 A.M., and 10:02 A.M. local time. The last of these eruptions opened fissures in the walls of the volcano, allowing sea water to flood the subterranean magma chamber. The resulting phreatic eruption of superheated steam all but annihilated Krakatoa, leaving only the southern tip (Rakata.) The blast was heard as far distant as the island of Rodrigues, near Mauritius, 4,800 km away; the sound of Krakatoa's destruction is believed to be the loudest sound in recorded history. After the largest explosion, there were several smaller ones through the day (some which nevertheless were heard as far as Sri Lanka) but generally declining in volume. By 28 August, Krakatoa was quiet again. Ash cloads caused by eruption blocked sunlight for couple of days within the area.

The 1883 eruption of Krakatoa is among the most violent volcanic events in modern times (a VEI of 6, equivalent to 200 megatons of TNT. In contrast, the biggest bomb ever made by man, the Tsar Bomba, had an explosive power of around 50 megatons.) Concussive air waves from the explosions travelled seven times around the world, and the sky was darkened for days afterwards. The surrounding ocean floor was drastically altered. The land masses of Verlaten and Lang were increased, and volcanic ash continues to be a significant part of the geological composition of these islands. Polish Hat disappeared. A new rock islet called Bootsmansrots was left: it is a fragment of Danan. Two nearby sandbanks (called Steers and Calmeyer) were built up into islands by ashfall, but the sea later washed them away.

Explosions like a battery of guns are heard across in Telok  Betong. Lightning strikes the lighthouse at Vlakke Hoek in southern Sumatra. The lighthouse at Fourth Point, just to the south of Anjer, is hit by a vast wave and destroyed, ripped off at its base, leaving only an amputated stump of jagged masonry. An immense wave then leaves Krakatoa at almost exactly 10 a.m. -- and then two minutes later, according to all the instruments that record it, came the fourth and greatest explosion of them all, a detonation heard thousands of miles away. It was said to have been the most violent explosion heard and experienced by man. The cloud of gas and white-hot pumice is said and fire and smoke is said to have risen -- been hurled, more probably, blasted as though from a gigantic cannon -- as many as twenty-four miles into the air!

' A fearful explosion.' ' A frightful sound.' Captain Sampson of the British vessel Norham Castle wrote simply in his log: ' I am writing this blind in pitch darkness. We are under continual rain of pumice-stone and dust. So violent are the explosions that the ear-drums of over half my crew have been shattered. My last thoughts are with my dear wife. I am convinced that the Day of Judgement has come.'

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