1883 eruption of Krakatoa - Wikipedia

On August 26, 1883, the Indonesian island of Krakatoa erupts in the largest explosion recorded in history, heard 2,200 miles away in Madagascar. From the article:

"Early phase
In the years before the 1883 eruption, seismic activity around the Krakatoa 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 at Krakatoa started again around 16 June with loud explosions and a thick black cloud covering the islands for five days. On 24 June, a prevailing east wind cleared the cloud, and two ash columns could be seen issuing from Krakatoa. The seat of the eruption is believed to have been a new vent or vents that 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. Earthquakes were felt at Anyer, Banten, and ships began to report large pumice masses to the west in the Indian Ocean.[citation needed]

On 11 August, a Dutch topographical engineer, Captain H. J. G. Ferzenaar, investigated the Krakatoa islands.[1] 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.[citation needed]

Climactic phase
By August 25, the Krakatoa eruptions intensified. At about 13:00 (local time) on 26 August, the volcano went into its paroxysmal phase. By 14:00, a black cloud of ash could be seen 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 (4 in) in diameter landing on their decks. Between 18:00 and 19:00 hours, a small tsunami hit the shores of Java and Sumatra, some 40 km (25 mi) away.

On August 27, four enormous explosions occurred. At 5:30 am, the first explosion was at Perboewatan, triggering a tsunami heading straight to Telok Betong, now known as Bandar Lampung. At 6:44 am, Krakatoa exploded again at Danan, with the resulting tsunami stretching eastward and westward. The largest explosion, at 10:02 am, 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. The third explosion has been reported as the loudest sound heard in historic times.[2][3]:79 The loudness of the blast heard 160 km (100 mi) from the volcano has been calculated to have been 180 dB.[4] Each explosion was accompanied by tsunamis estimated 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,[5] roughly four times as powerful as the Tsar Bomba, the most powerful thermonuclear weapon ever detonated. At 10:41 am, 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). The eruption is estimated to have reached 310 dB, loud enough to be heard clearly 5,000 kilometres (3,100 mi) away.[6]:248 It was so powerful that it ruptured the eardrums of sailors 64 km (40 miles) away on ships in the Sunda Strait,[6]:235 and caused a spike of more than 2.5 inches of mercury (8.5 kPa) in pressure gauges 160 km (100 miles) away, attached to gasometers in the Batavia gasworks, sending them off the scale.[note 1]

The pressure wave was recorded on barographs all over the world. Several barographs recorded the wave seven times over the course of five days: four times with the wave travelling away from the volcano to its antipodal point, and three times travelling back to the volcano.[3]:63 Hence, the wave rounded the globe three and a half times. 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. By then, less than 30% of the original island remained."