The loudest sound ever recorded

On 27 August 1883, the eruption of the Krakatoa volcano in the Sunda Strait, between the islands of Java and Sumatra, generated an explosion that physicists and seismologists consider the loudest sound ever produced in the documented history of the planet. The sound travelled around the Earth not once but four times, recorded by barometers at meteorological stations worldwide in the following days. On Rodriguez Island, nearly 5,000 kilometres away, it was described by residents as the sound of cannons firing.

Estimates of the sound's intensity at the epicentre are around 310 decibels. To put that number in perspective: the threshold of pain for the human ear is around 130 decibels, and the sound of a jet engine at 30 metres is approximately 150. The decibel scale is logarithmic, not linear: each increase of 10 decibels implies a tenfold multiplication of sound pressure. The 310 decibels of Krakatoa represent an acoustic pressure that would have been lethal hundreds of kilometres away were it not for the rapid dissipation of energy with distance.

The eruption directly killed thousands of people on nearby islands, partly from the sound itself but mainly from the tsunami it generated, with waves of more than 30 metres that swept coasts throughout the region. The pressure waves of the explosion were detected by instruments in Europe and the Americas, and the climatic effects of the volcanic ash ejected into the stratosphere were felt globally for more than a year: the global temperature average dropped between 0.5 and 1.2 degrees Celsius in the following years, with abnormally red and orange skies that inspired works such as Edvard Munch's "The Scream."