The 1883 eruption of Krakatoa in the Dutch East Indies (nowIndonesia) began on August 26,
1883(with origins as early as May of that year) and culminated with several destructive eruptions of the remaining caldera. On August 27, two thirds of Krakatoa collapsed in a chain of titanic explosions,destroying most of the island and its surrounding archipelago. Additional alleged seismic activity continued to be reported until February 1884, though reports of those after October 1883 were later dismissed by Rogier Verbeek's investigation. It was one of the deadliest and most destructive volcanic events in recorded history, with at least 36,417 deaths being attributed to the eruption itself and the tsunamis it created. Significant additional effects were also felt around the world.
Early phase
In the years before the 1883 eruption, seismic activity around the volcano was intense, with earthquakes felt as far away as Australia. Beginning 20 May 1883, steam venting began to occur regularly from Perboewatan, the northernmost of the island's three cones. Eruptions of ash reached an estimated altitude of 6 km (20,000 ft) and explosions could be heard in New Batavia (Jakarta) 160 km (99 mi) away. Activity died down by the end of May, and there was no further recorded activity for several weeks.
Eruptions started again around 16 June, featuring loud explosions and covering the islands with a thick black cloud for five days. On 24 June, a prevailing east wind cleared the cloud, and two ash columns were seen issuing from Krakatoa. The seat of the eruption is believed to have been a new vent or vents which formed between Perboewatan and Danan. The violence of the ongoing eruptions caused tides in the vicinity to be unusually high, and ships at anchor had to be moored with chains as a result. Earthquake shocks began to be felt atAnyer, West Java, and ships began to report large pumice masses appearing in the Indian Ocean to the west.
On 11 August, a Dutch topographical engineer, Captain H. J. G. Ferzenaar, investigated the islands. He noted three major ash columns (the newer from Danan), which obscured the western part of the island, and steam plumes from at least eleven other vents, mostly between Danan and Rakata. When he landed, he noted an ash layer about 0.5 m (1 ft 8 in) thick, and the destruction of all vegetation, leaving only tree stumps. He advised against any further landings. The next day, a ship passing to the north reported a new vent "only a few meters above sea level." (This may be the most northerly spot indicated on Ferzenaar's map.) Activity continued through mid-August.
Climactic
By 25 August, eruptions further intensified. At about 13:00 (local time) on 26 August, the volcano went into its paroxysmal phase. By 14:00 observers could see a black cloud of ash 27 km (17 mi) high. At this point, the eruption was virtually continuous and explosions could be heard every ten minutes or so. Ships within 20 km (12 mi) of the volcano reported heavy ash fall, with pieces of hot pumice up to 10 cm (3.9 in) in diameter landing on their decks. A small tsunami hit the shores of Java and Sumatra, some 40 km (25 mi) away, between the time of 18:00 and 19:00 hours.
On 27 August four enormous explosions took place at 05:30, 06:44, 10:02, and 10:41 local time. At 5:30 A.M, the first explosion was at Perboewatan volcano, triggering a tsunami heading straight to Telok Betong. At 6:44 A.M, Krakatoa exploded again on Danan volcano, with the resulting tsunami stretching eastward and westward. The largest explosion, at 10:02A.M, was so violent that it was heard 3,110 km (1,930 mi) away in Perth, Western Australia, and the Indian Ocean island of Rodrigues near Mauritius (4,800 km (3,000 mi) away), where they were thought to be cannon fire from a nearby ship. Each explosion was accompanied by large tsunamis, which are believed to have been over 30 meters (98 feet) high in places. A large area of the Sunda Strait and a number of places on the Sumatran coast were affected by pyroclastic flows from the volcano. The energy released from the explosion has been estimated to be equal to about 200 megatons of TNT, roughly four times as powerful as the Tsar Bomba (the most powerful thermonuclear weapon ever detonated). At 10:41 A.M, a landslide tore off half of Rakata volcano, causing the final explosion.
Final explosive eruption
The pressure wave generated by the colossal fourth and final explosion radiated out from Krakatoa at 1,086 km/h (675 mph).[5]:248 It was so powerful that it ruptured the eardrums of sailors on ships in the Sunda Strait,[5]:235 and caused a spike of more than 2½ inches of mercury (ca 85 hPa) in pressure gauges attached to gasometers in the Batavia gasworks, sending them off the scale.[note 1] The pressure wave radiated across the globe and was recorded on barographs all over the world, which continued to register it up to 5 days after the explosion. Barographic recordings show that the shock wave from the final explosion reverberated around the globe 7 times in total.[3] Ash was propelled to an estimated height of 80 km (50 mi).
The eruptions diminished rapidly after that point, and by the morning of 28 August, Krakatoa was silent. Small eruptions, mostly of mud, continued into October 1883.
"The Burning Ashes of Ketimbang"
Around noon on 27 August 1883, a rain of hot ash fell around Ketimbang (now Katibung inLampung Province) in Sumatra. Approximately 1,000 people were killed, the only large number of victims killed by Krakatoa itself, and not by the waves or after effects.[5] Verbeek, and later writers, believe this unique event was a lateral blast, or pyroclastic surge (similar to the catastrophic 1980 eruption of Mount St. Helens), which crossed the water. The region of the ash fall ended to the northeast of Ketimbang,[6] where the bulk of Sebesi Island offered protection from any horizontal surges.
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