A Sound That Shook the World
On August 27, 1883, the island of Krakatoa produced the loudest sound recorded in modern history. The final, cataclysmic explosion at 10:02 AM was heard as "cannon fire" up to 4,800 kilometers away on Rodrigues Island, near Africa. It would have taken the sound nearly four hours to travel that distance. Closer to the volcano, the acoustic intensity was staggering. A gasworks 160 kilometers away in Batavia (now Jakarta) registered a pressure spike of over 8.5 kilopascals, equivalent to 172 decibels. This level of sound pressure is far beyond the human pain threshold and ruptured the eardrums of sailors on a ship 64 kilometers away.
The eruption's impact was not limited to audible sound. It generated an atmospheric pressure wave—an infrasonic pulse below the range of human hearing—that radiated outwards at over 1,000 km/h. This pressure wave was so powerful that barographs around the globe recorded its passage. Showing its energy, the wave circled the planet multiple times. Weather stations in cities from Calcutta to New York City recorded the initial pulse, followed by subsequent spikes approximately every 34 hours as the wave and its reflection from the opposite side of the Earth passed through. Barographs recorded at least seven distinct passages of the wave over five days, meaning it circled the globe three and a half times before dissipating.
A Planet Cooled and Repainted
The 1883 eruption injected a tremendous volume of material—an estimated 20 cubic kilometers of rock and ash—into the atmosphere. The main eruption column reached an altitude of at least 50 kilometers, punching deep into the stratosphere. This upper atmospheric layer lacks the weather and turbulence of the troposphere below, so the fine particles remained suspended for years. The most significant of these were droplets of sulfuric acid, formed when the volcano's massive sulfur dioxide emissions combined with water vapor.
This stratospheric aerosol layer acted as a planetary sunshade, reflecting incoming solar radiation back into space. The effect was a measurable drop in global temperatures. In the year following the eruption, average Northern Hemisphere summer temperatures fell by about 0.4°C. Some estimates place the total average global temperature drop as high as 1.2°C, with temperatures not returning to normal until 1888. This period of "volcanic winter" led to unseasonably cold years and record snowfalls worldwide. The cooling effect was so substantial that it delayed the rise in sea level and ocean warming into the 20th century.
The volcanic aerosols also produced dramatic optical effects. For more than two years, people worldwide witnessed intensely colored sunrises and sunsets. The fine sulfuric acid particles scattered sunlight in a specific way, producing red, orange, and purple hues that were so bright they were sometimes mistaken for large fires. Fire engines were reportedly called out in New York and other cities to quench the apparent conflagrations. British artist William Ascroft produced thousands of color sketches documenting these spectacular skies. The eruption also created a Bishop's Ring, a faint brownish or bluish halo around the sun, and made the moon appear blue at times. The famously blood-red sky in Edvard Munch's painting "The Scream" is thought to be an accurate depiction of the skies over Norway in the years following the eruption.