Some catastrophes are so vast that instruments can "hear" them on the other side of the planet. These cases became turning points for the science of infrasound — and proved that air can carry sound all the way around the globe.
Krakatoa, 1883 — the birth of a science
On 27 August 1883 the Indonesian volcano Krakatoa exploded with a force that is hard to imagine. 160 km away, at a gasworks in Batavia, a barometer recorded a pressure spike equivalent to more than 170 decibels — possibly the loudest sound in documented history.3
But something else is more astonishing: the air wave circled the globe several times. The barographs of more than 50 weather stations around the world recorded its passage roughly every 34 hours over several days.3 The Royal Society of London gathered this data into the famous report of the Krakatoa Committee (1888) — effectively the first global study of infrasound.12
The sound of the explosion itself was heard by people 4,800 km away — including on Rodrigues Island in the Indian Ocean, where it was mistaken for distant cannon fire. This is probably the record for the range of audible sound in history.
Hunga Tonga, 2022 — a repeat 140 years later
On 15 January 2022 the underwater volcano Hunga Tonga–Hunga Haʻapai exploded so powerfully that it produced a Lamb atmospheric wave that circled the planet several times. This time it was recorded not by a handful of barographs, but by a global network of precise instruments and thousands of amateur pressure sensors. The event became the most studied infrasound phenomenon in history and confirmed that even simple barometers catch a planetary-scale wave.4
Chelyabinsk, 2013 — a voice from space
On 15 February 2013 a meteor exploded over Chelyabinsk. The shock wave shattered windows in thousands of buildings — and its infrasound became the largest signal ever recorded by the infrasound network of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The wave was caught by stations around the world, some after it had gone around the planet.5 It was from such infrasound records that scientists learned to estimate the energy of incoming cosmic bodies in TNT equivalent — a working tool of planetary defence.6
- The Krakatoa air wave went around the globe several times — barographs caught its "ticking" for almost five days.
- The pressure spike from Tonga 2022 was noticed by home weather stations in Europe — almost 17,000 km from the volcano.
- The Chelyabinsk bolide produced infrasound more powerful than any the CTBTO network had recorded in its entire history of observation.
Tonga 2022 is our direct proof of concept: a planetary event's wave was recorded even by household barometers. That means a dense network of cheap sensors can catch large events — we just need to bring it up to the level of reliable early warning.
Sources for this article
- history Symons G.J. (ed.) (1888). The Eruption of Krakatoa, and Subsequent Phenomena. Royal Society Krakatoa Committee. archive.org
- reviewhistory Gabrielson T.B. (2004). Krakatoa and the Royal Society. Acoustics Today / ECHOES. acousticstoday.org
- pop-sci Cox A. (2014). The Sound So Loud That It Circled the Earth Four Times. Nautilus. nautil.us
- peer-reviewed Matoza R.S. et al. (2022). Global seismoacoustic observations of the January 2022 Hunga eruption, Tonga. Science 377. science.org
- peer-reviewed Le Pichon A. et al. (2013). The 2013 Russian fireball largest ever detected by CTBTO infrasound sensors. GRL 40. agupubs.wiley.com
- peer-reviewed Edwards W.N., Brown P.G., ReVelle D.O. (2006). Estimates of meteoroid kinetic energies from observations of infrasonic airwaves. J. Atmos. Sol.-Terr. Phys. 68. doi.org