The 1883 eruption of Krakatoa in the Dutch East Indies (now Indonesia) began in the afternoon of Sunday, 26 August 1883 (with origins as early as May of that year), and peaked in the late morning of Monday, 27 August when over 70% of the island and its surrounding archipelago were destroyed as it collapsed into a caldera. Additional seismic activity was reported to have continued until February 1884, though reports of seismic activity after October 1883 were later dismissed by Rogier Verbeek‘s investigation into the eruption. The 1883 eruption was one of the deadliest and most destructive volcanic events in recorded history. At least 36,417 deaths are attributed to the eruption and the tsunamis it created. Significant additional effects were also felt around the world in the days and weeks after the volcano’s eruption.
Climactic phase
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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.
Global optical effects
The 1883 Krakatoa eruption darkened the sky worldwide for years afterwards and produced spectacular sunsets throughout the world for many months. British artist William Ashcroft made thousands of colour sketches of the red sunsets halfway around the world from Krakatoa in the years after the eruption. The ash caused “such vivid red sunsets that fire engines were called out in New York, Poughkeepsie, and New Haven to quench the apparent conflagration.”[18] This eruption also produced a Bishop’s Ring around the sun by day, and a volcanic purple light at twilight.
In 2004, an astronomer proposed the idea that the blood-red sky shown in Edvard Munch‘s famous 1893 painting The Scream is also an accurate depiction of the sky over Norway after the eruption.[19]
Weather watchers of the time tracked and mapped the effects on the sky. They labeled the phenomenon the “equatorial smoke stream”.[20] This was the first identification of what is known today as the jet stream.[21]
For several years following the eruption, it was reported that the moon appeared to be blue and sometimes green. This was because some of the ash clouds were filled with particles about 1 µm wide—the right size to strongly scatter red light, while allowing other colors to pass. White moonbeams shining through the clouds emerged blue, and sometimes green. People also saw lavender suns and, for the first time, recorded noctilucent clouds.[18]