On August 27, 1883, when a volcano erupted on the island of Krakatoa, the Earth emitted a sound louder than any sound in recorded history. The sound was so loud, it burst the eardrums of sailors in a boat forty miles away and circled around the Earth four times before succumbing to silence. No louder sound was thought to occur prior to this event and no louder sound has been created since.
It was 10:02 on a Monday morning in 1883 when the “boom” burst from the island of Krakatoa, which sits between Java and Sumatra in Indonesia. A volcano had erupted on Krakatoa and it literally tore the island apart. The plume of smoke and debris exploded from the volcano at 1,600 miles per hour (more than twice the speed of sound) and rose 50 miles above the island. As a result, weather patterns around the world changed and remained chaotic for several years afterward (global temperatures dropped over 2 degrees and did not return to normal until 1888). Coral blocks as heavy as 600 tons and bigger than a house were tossed through the air (see photo to the right). A tsunami was created with waves nearly 100 feet tall that moved through the area destroying nearly 200 coastal villages and killing between 36,000 and 120, 000 people. It was one of the deadliest and most destructive volcanic events in recorded history.
Forty miles offshore, the British ship Norham Castle witnessed the event. The ship’s captain wrote in his log:
“So violent are the explosions that the ear-drums of over half my crew have been shattered. My last thoughts are with my dear wife. I am convinced that the Day of Judgment has come.”
The sound wave (i.e. fluctuations in air pressure) from the explosion was stunning. To put it in context, an alarm clock sounds the alarm at 80 decibels. The sound of a jackhammer measures 100 decibels. A jet engine produces a deafening 150 decibel wave that instantly damages the ears of anyone not wearing protective muffles. If you add 10 decibels to that, the sound as perceived by a human is *twice* as loud. The Krakatoa eruptions produced a boom that measured an estimated 172 decibels – at 100 miles away! That’s only 20 decibels away from the limit of “loudness” (which is estimated to be 192 decibels, after which a sound wave just becomes moving air – a shock wave).
Closer to Krakatoa, the sound did indeed surpassed the limit and anyone within 10-20 miles heard nothing at all (but would have been flattened by the shock wave). The sound was heard 1,300 miles away in the Andaman and Nicobar islands (“extraordinary sounds were heard, as of guns firing”); 2,000 miles away in New Guinea and Western Australia (“a series of loud reports, resembling those of artillery in a north-westerly direction”); and even 3,000 miles away in the Indian Ocean island of Rodrigues (“coming from the eastward, like the distant roar of heavy guns.”)
Further away the sound was only slightly audible but weather stations across the world recorded changes in atmospheric pressure as the sound wave passed their station. Seven hours after the explosion, a spike in air pressure was detected in Calcutta. By eight hours the pressure wave had reached Sydney, Australia. After 12 hours, St. Petersburg detected the pulse followed by Vienna, Rome, Paris, and Berlin. By 18 hours, the wave had reached New York City, Washington, DC, and Toronto. Amazingly, for as many as five days after the explosion, weather stations in over 50 cities across the world observed the spike in pressure and noted that it reoccurred approximately every 34 hours – the length of time it took the sound wave to circle around the entire globe.
“In all, the pressure waves from Krakatoa circled the globe three to four times in each direction. (Each city felt up to seven pressure spikes because they experienced shock waves travelling in opposite directions from the volcano1.) Meanwhile, tidal stations as far away as India, England, and San Francisco measured a rise in ocean waves simultaneous with this air pulse, an effect that had never been seen before. It was a sound that could no longer be heard but that continued moving around the world, a phenomenon that people nicknamed “the great air-wave.”
And for those concerned readers that are wondering – yes, Krakatau is still active to this day.
Note: While justifiably rated as one of the most destructive volcanic eruptions of modern times, Krakatoa was not the largest eruption in the recent history of Indonesia. That “honor” belongs to the eruption of Mount Tambora on April 10, 1815. Tambora is the only eruption in modern history to rate a VEI of 7. Global temperatures were an average of five degrees cooler because of this eruption (in the United States, 1816 was known as the “year without a summer.”) Crops failed worldwide, and in Europe and the United States the bicycle was invented as horses had become too expensive to feed.