The loudest sound ever heard around the world erupted from the depths of the Earth at roughly 10:02 AM on August 26, 1883. It bellowed from the island of Krakatoa, which sat between Java and Sumatra in Indonesia, when the island's volcano exploded in fire and choking black smoke, ripping the island apart from the inside.
Krakatoa volcano explosion begins to circle the planet
A British ship, the Norham Castle, was only 40 miles (64 km) from Krakatoa at the time of the explosion, and the captain wrote in his ship's log: "So violent are the explosions that the eardrums of over half my crew have been shattered. My last thoughts are with my dear wife. I am convinced that the Day of Judgement has come."
People living 1,300 miles (2,092 km) away from Krakatoa in the Andaman and Nicobar islands located between India and what is now Myanmar, reported hearing "extraordinary sounds ... as of guns firing." People in New Guinea and Western Australia — more than 2,000 miles (3,218 km) away — heard "a series of loud reports, resembling those of artillery in a north-westerly direction."
New Guinea volcano shockwave
Those living on the Indian Ocean island of Rodrigues, which was 3,000 miles away, reported hearing sounds "coming from the eastward, like the distant roar of heavy guns." Tourists captured the video below of a 2014 volcanic eruption in Papua New Guinea, seen from a cruise ship, which shows the sound of a shock wave crashing through the air 13 seconds after the eruption. It does sound like the blast of a cannon.
The science of sound, barometers, air pressure
Sound happens when fluctuations in atmospheric (air) pressure propagate across space — which we can measure with trusty tools, like a barometer. When Krakatoa exploded, mercury barometers were the norm — which used a vertical glass tube with a closed top, and sat in an open mercury-filled basin. The mercury adjusted so that its weight balanced the atmospheric pressure exerted on the reservoir. Higher atmospheric pressure placed greater force on the reservoir, forcing the mercury higher in the column.
At a gas works located 100 miles (161 km) away from Krakatoa on the day of the explosion, a barometer measured an increase in atmospheric pressure of more than 2.5 inches (6.35 cm) of mercury. This equates to a sound of more than 172 decibels. Comparatively, a jet engine emits 150 decibels, and jackhammers put out only 100 decibels.
Krakatoa shockwave circled Earth in 34 hours
On August 26, 1883, barometers around the world measured changes in atmospheric pressure — including those in Calcutta, India, six hours and 47 minutes after the explosion. Eight hours after the explosion, the increase was noted in Melbourne and Sydney, Australia — and the event repeated itself in St. Petersburg, Russia, 12 hours after the explosion.
The pressure rise then spread to Vienna, Berlin, Munich, Paris, and Rome. It finally reached New York City, Washington D.C., and Toronto, Canada 18 hours after the explosion.
Incredibly, the sound wave created by the volcano continued to reverberate around the globe, causing a spike in air pressure repeating roughly every 34 hours. Spikes were detected in more than 50 cities around the world, thus indicating how long it actually takes for sound to circle the entire Earth.
Krakatoa killed more than 36,000 people
The explosion of Krakatoa ripped through the air with the equivalent of 200 megatons of TNT, Live Science reports. This is nearly 13,000 times stronger than the Little Boy nuclear bomb that devastated Hiroshima, Japan on Aug 6, 1945 — and nearly four times stronger than the Tsar Bomba, the 57-megaton thermonuclear device, and the most powerful ever detonated on Earth.
Krakatoa's eruption ejected roughly 6 cubic miles (25 km3) of rock, and sent a plume of smoke 17 miles (27 km) into the atmosphere. It even created a tsunami with waves up to 490 feet (150 m) high, according to the South China Morning Post. These waves washed away 165 coastal villages and towns, officially killing 36,417 people, however, the death toll was likely much higher.
Anak Krakatau continues to erupt in Krakatoa's place
Coastal stations in India, England, and San Francisco in the U.S. saw a measured rise in ocean wave height, which — coupled with the increase in air pressure — comprised a phenomenon no one had ever seen before.
Since 1927, further eruptions in the area have pushed up a new island, where the doomed Krakatoa once stood. Named Anak Krakatau, which is Indonesian for "Child of Krakatoa," the island was roughly 2.4 miles (4 km) across with a height of 1,300 feet (400 m), as of 2017. In December 2018, the island suffered a collapse, and its height was reduced to 361 feet (110 m).
While "the shot heard round the world" typically refers to the battles of Lexington and Concord — which took place on April 19, 1775, and began the American Revolutionary War — the eruption of Krakatoa outscreamed it with three Earth-circling worlds to spare, as "the sound heard around the world."