The eruption of Krakatau, located in the Sunda straits between the islands of Java and Sumatra in what is now Indonesia, is probably the most famous volcanic eruption in history. A large part of this notoriety derives from the destructive tsunami associated with the climactic phase of the eruption on 26 and 27 August 1883. These tsunami claimed around 33 000 lives, more than 90% of the total death toll from the eruption. Most of these deaths occurred in coastal towns around the Sunda straits, in particular Anjer on Java and Kalimbang and Teluk Betong on Sumatra. The death toll in the inundated areas approached 100%, in large part because the tsunami formed fast moving turbulent bores as they impacted the coastline.

From the accounts of survivors and records from the tide gauge at Tandjung Priok, 100 km outside the straits to the east, at least four main waves were generated in a period of around six hours on the morning of 27 August. Wave runups of 30 to 40 m above normal sea level occurred on steep coastlines, and in flat-lying areas the water swept up to 8 km inland, in many parts through dense jungle: this is particularly remarkable in view of the fact that standing trees offer the greatest resistance to the advance of tsunami onto land (see Physics - Impact). The waves were sufficiently energetic to carry small ships at anchor in the ports, including a Dutch colonial gunboat, the Berouw, kilometres inland where they were stranded. Conversely, ships at sea within the straits were unaffected as the waves passed beneath them in relatively deep water where wave amplitudes would have been small (see Physics - Propagation). The tsunami, on exiting the straits, also caused significant damage along the coast of Java to the north and east and minor damage in NE Australia to the south; they were recorded on tide gauges as far away as the Atlantic coast of France.

The 1883 eruption of Krakatau is, as befits the destruction that it caused, one of the most intensively studied in history. Nevertheless, the precise mechanism (or mechanisms) by which the several tsunami associated with it were generated have remained controversial. Reconstruction of the eruption from the historical accounts and from geological evidence collected since has identified several tsunamigenic processes which operated at different stages of the eruption. The climactic eruption involved the ejection of huge volumes of magma, primarily as dense pyroclastic flows. These flows were initially erupted from vents in the north of the island of Krakatau itself and these could have generated tsunami as they entered the sea, by physically pushing water out of the way. Some of the pyroclastic flows travelled as far as the coast of Sumatra, where they killed around 3000 people in areas not affected by the tsunami. Later in the eruption, most of the island of Krakatau subsided as the emptying magma chamber collapsed, producing a giant crater or caldera, around 5 km across and several hundred metres deep. Further eruption of magma into this crater would have produced giant steam explosions which could also have produced tsunami. Finally, the high stratovolcano of Rakata,in the south of the pre-eruption island, collapsed into the newly formed caldera as a debris avalanche. Different stages of the Krakatau eruption could therefore have involved generation of tsunami by entry of pyroclastic flows into the sea, caldera collapse, submarine explosive eruption, and stratovolcano lateral collapse.