The Loudest Sounds Ever Recorded: Krakatoa, Tonga, Sperm Whales, and the Physics of Decibels
Photo: Noor Mohammad Sowan / Pexels
In the pre-dawn hours of August 27, 1883, a ship's captain in the Sunda Strait, 64 kilometers from Krakatoa, described the noise as unlike anything a human could have heard before or since. The explosion that followed the partial collapse of the volcanic island detonated with a pressure wave that burst eardrums of sailors at that distance, was heard in Australia 3,500 kilometers away, reached the distant island of Rodrigues near Mauritius 4,800 kilometers distant as what witnesses described as artillery fire, and registered as pressure fluctuations on barometers across Europe and North America. Retroactive estimates place the sound at approximately 310 decibels at source — a number that, as we will see, breaks one of the fundamental rules of classical acoustics.
What a Decibel Actually Measures
Decibels confuse almost everyone because they are logarithmic, not linear. The decibel scale was designed around the enormous range of sound intensities that the human ear can detect — from the faint rustle of leaves to a jet engine — and linear numbers would be unwieldy. Instead, every 10 decibels represents a factor of 10 in sound intensity (power per unit area). Sound is also perceived differently than it is measured, as in why your voice sounds different on recordings.
The formula is: dB = 10 × log₁₀(I / I₀), where I is the sound intensity being measured and I₀ is a reference intensity of 10⁻¹² watts per square meter — the approximate threshold of human hearing.
Because the scale is logarithmic, the differences at high values are enormous in absolute terms:
| Sound | Approximate dB | Intensity vs Threshold |
|---|---|---|
| Threshold of hearing | 0 dB | 1× |
| Whisper at 1 m | 30 dB | 1,000× |
| Normal conversation | 60 dB | 1,000,000× |
| Busy city traffic | 85 dB | 316,000,000× |
| Rock concert, front row | 110 dB | 10,000,000,000× |
| Jet engine at 30 m | 150 dB | 10¹⁵× |
| Space Shuttle launch at 500 m | 165–170 dB | 10¹⁶·⁵–10¹⁷× |
| Sperm whale click (in water) | ~230 dB | 10²³× |
| Krakatoa eruption (estimated at source) | ~310 dB | 10³¹× |
Source: NIOSH (2022), "Noise and Hearing Loss Prevention," National Institute for Occupational Safety and Health — reference for occupational decibel levels and hearing damage thresholds.
Decibel (dB) — a logarithmic unit expressing the ratio of a measured quantity to a reference quantity. In acoustics, the reference is the threshold of human hearing (10⁻¹² W/m²). Because of the logarithm, a 10 dB increase represents a factor of 10 in intensity, and a 20 dB increase represents a factor of 100. A sound 30 dB louder is a thousand times more intense, not thirty times.
Note also the distinction between decibels in air and decibels in water. These use different reference pressures: 20 micropascals in air and 1 micropascal in water. A sperm whale click of 230 dB re 1 μPa (in water) does not directly translate to the same number in air — the medium matters.
Source: Carey, W.M. and Evans, R.B. (2011), Ocean Ambient Noise: Measurement and Theory, Springer — reference for underwater acoustic measurement conventions and the difference between airborne and waterborne decibel references.
The 194 dB Ceiling: Why Air Cannot Carry a Louder Sound
Here is the counterintuitive constraint that makes Krakatoa's 310 dB estimate physically paradoxical: there is a hard upper limit on how loud a sound can be in air at sea level, and it is approximately 194 decibels.
Sound is a pressure wave — alternating regions of compression (above atmospheric pressure) and rarefaction (below atmospheric pressure). The amplitude of the wave is how much the pressure deviates from the background. At 194 dB, the rarefaction half of the wave reaches a pressure of zero — a perfect vacuum. There is no lower pressure than zero. The wave cannot rarefact any further.
At sound levels above 194 dB, the physics of sound waves breaks down. Instead of a sinusoidal pressure oscillation, the wave steepens into a shockwave — a discontinuous front of compressed air that propagates faster than the speed of sound. Shockwaves follow different equations (Rankine-Hugoniot conditions for the shock jump) than linear acoustic waves. They are more properly described as supersonic blast waves than as sounds in the classical sense.
Shockwave — a propagating discontinuity in pressure, temperature, and density that forms when a disturbance exceeds the speed of sound in the medium. Unlike acoustic waves, which travel at the local speed of sound without changing speed as they propagate, shockwaves can travel faster than sound and deposit energy abruptly as they pass through material. Nuclear explosions, meteor impacts, and the loudest volcanic events all produce shockwaves rather than sounds.
The Krakatoa estimate of 310 dB is therefore not a sound in the classical acoustic sense — it is the energy of the initial explosion translated into sound-pressure units for comparison. The actual pressure wave that propagated from Krakatoa was a shockwave that, at distances of more than a few kilometers, had decayed to below 194 dB and was once again a very loud but conventional acoustic wave.
Source: Garces, M.A. (2019), "On infrasound standards: Part 1, time, frequency, and energy scaling," InfraMatics, Vol. 2 — technical discussion of shockwave-to-sound transition distances and the 194 dB atmospheric ceiling.
The 1883 Krakatoa Eruption: The Loudest Sound in Recorded History
Krakatoa (Krakatau) is a volcanic island in the Sunda Strait between Java and Sumatra. In the summer of 1883, the volcano had been showing increased activity for months. On August 26-27, the volcano entered a catastrophic eruption sequence. The loudest explosion occurred at approximately 10:02 a.m. local time on August 27, when the volcano partially collapsed into the sea, triggering a massive steam explosion as the superheated magma met seawater.
The evidence for the sound's reach is documented in historical records and contemporary meteorological reports:
- A British ship, the Norham Castle, approximately 64 km from the explosion, reported eardrums bursting among crew members
- Residents of Rodrigues Island near Mauritius, approximately 4,800 km away, reported hearing what they described as the sound of cannonfire — the farthest confirmed audible distance for any sound in recorded history
- Residents of Alice Springs in Australia, approximately 3,500 km away, reported hearing the explosion
- Barographs (pressure-recording barometers) at weather stations across the world, including in Calcutta, St. Petersburg, Vienna, Rome, and New York, all recorded distinct pressure spikes as the atmospheric wave passed — and then recorded it again, three more times, as the wave circled the globe in both directions
The barograph at the Batavia gasworks, approximately 160 km from Krakatoa, recorded a pressure spike equivalent to 172 dB at that distance. Working backward from that measurement using the known physical laws of sound propagation, and accounting for atmospheric absorption, scientists have estimated the source level at approximately 310 dB.
The eruption also generated a tsunami with waves up to 30 meters high, which killed approximately 36,000 people — the primary cause of the disaster's death toll.
Source: Winchester, S. (2003), Krakatoa: The Day the World Exploded, HarperCollins — narrative history drawing on primary records of the eruption's sound propagation and the Rodrigues Island testimony.
Source: Symons, G.J. (ed., 1888), The Eruption of Krakatoa and Subsequent Phenomena, Trübner & Co., London — the Royal Society's comprehensive scientific report on Krakatoa, including the barograph pressure records used to estimate the 172 dB measurement at 160 km.
The 2022 Hunga Tonga Eruption: The Loudest Modern Recording
On January 15, 2022, the submarine volcano Hunga Tonga-Hunga Ha'apai in the South Pacific erupted with an explosive energy estimated at 100–200 megatons of TNT equivalent — larger than any nuclear weapon ever tested. The eruption was detected by infrasound and hydroacoustic sensors of the International Monitoring System, the global network originally built to detect clandestine nuclear tests.
The eruption produced what researchers at Boise State University's infrasound laboratory described as the loudest sound recorded in the past century — since Krakatoa in 1883. Infrasound sensors in Idaho, approximately 9,200 km from Tonga, recorded peak pressures exceeding 10 pascals. The eruption's atmospheric pressure wave circled Earth multiple times, detected by weather stations globally.
Infrasound — sound at frequencies below 20 Hz, below the threshold of human hearing. Infrasound propagates with very low atmospheric absorption over thousands of kilometers, making it detectable at transcontinental distances. Major sources include large explosions, volcanoes, meteors entering the atmosphere, and severe storms.
The closest scientific pressure station to the eruption, in Nuku'alofa approximately 68 km away, recorded a pressure jump of approximately 1,800 pascals — corresponding to roughly 159 dB at that distance. The closest International Monitoring System hydroacoustic station (IS22), approximately 1,850 km away, recorded a peak-to-peak pressure of 340 pascals. These are the largest readings in the IMS network's operational history.
The Tonga eruption also injected an unprecedented amount of water vapor — estimated at 146 teragrams, roughly 10% of the total water vapor content of the stratosphere — into the upper atmosphere, a phenomenon not previously observed for any volcanic eruption. The water vapor injection is expected to produce a small but measurable temporary warming of the lower stratosphere, in contrast to the cooling effect of sulfur dioxide injections from past eruptions.
Source: Astafyeva, E. et al. (2022), "The 15 January 2022 Hunga Tonga Eruption History as Inferred from Ionospheric Observations," Geophysical Research Letters, Vol. 49 — analysis of the eruption's global atmospheric and ionospheric effects.
Source: Boise State University News (2022), "Boise State researchers record world's loudest sound since 1883, Hunga Tonga eruption" — confirmed IMS infrasound sensor readings and comparison to the Krakatoa record.
Sperm Whale Clicks: The Loudest Animal Sound
The loudest known biological sound is produced by the sperm whale (Physeter macrocephalus) — and it is not a song or a roar. It is a click. Sperm whale clicks are used for echolocation in the deep ocean: the whale emits a burst of sound that bounces off objects (including prey squid deep in the water column) and returns to the whale's lower jaw, which transmits the echo to the inner ear.
Measurements of sperm whale clicks have recorded peak levels of 230 to 236 dB re 1 μPa (in water). These are the highest sound pressure levels measured from any biological source. The clicks are generated by a specialized organ in the whale's enormous head — the spermaceti organ — which focuses sound through an oil-filled acoustic lens called the melon.
Spermaceti organ — a large cavity in the forehead of sperm whales filled with spermaceti, a waxy oil that changes from liquid to solid as it cools. The organ was historically harvested by whalers for its oil; its acoustic function is to focus and direct the whale's echolocation clicks through changes in the oil's sound-velocity properties as the whale adjusts blood flow to the organ.
To put 230 dB underwater in perspective: at 1 meter from the source, the pressure is approximately 63,000 pascals above ambient, roughly 630 times atmospheric pressure. The clicks are emitted in bursts lasting milliseconds; continuous exposure at this level would cause tissue damage, and there is documented speculation (though not definitive evidence) that sperm whale clicks can physically stun prey.
However, comparing underwater decibels directly to airborne decibels is misleading. Underwater acoustic dB measurements use a reference pressure of 1 micropascal, versus 20 micropascals for airborne measurements. Correcting for this reference difference and for the different acoustic impedance of water versus air, a 230 dB underwater click is roughly equivalent to about 170 dB in air — still extraordinarily loud by any standard, but not literally louder than a rocket launch.
| Animal | Recorded Level | Medium | Source |
|---|---|---|---|
| Sperm whale | 230–236 dB re 1μPa | Water | NOAA / Møhl et al. 2003 |
| Blue whale (low-frequency moans) | 188–189 dB re 1μPa | Water | NOAA |
| Snapping shrimp (cavitation click) | ~190 dB re 1μPa | Water | Versluis et al. 2000 |
| Pistol shrimp (cavitation bubble) | ~200 dB re 1μPa | Water | Lohse et al. 2001 |
| Greater bulldog bat (echolocation) | ~137 dB re 20μPa | Air | Surlykke & Kalko 2008 |
| White bellbird (mating call) | ~125 dB re 20μPa | Air | Podos & Cohn-Haft 2019 |
Source: Møhl, B. et al. (2003), "The monopulsed nature of sperm whale clicks," Journal of the Acoustical Society of America, Vol. 114 — direct hydrophone measurements establishing sperm whale click levels at 163–223 dB, with best estimates near 230 dB re 1 μPa.
Source: NOAA (2024), "Ocean Noise" — NOAA summary of marine mammal sound levels and the challenges of comparing water-referenced and air-referenced decibel measurements.
Rockets and Explosions: The Loudest Human-Made Sounds
The loudest controlled sounds produced by human technology come from rockets at launch. The Saturn V rocket, used in the Apollo lunar program, produced approximately 204 dB of sound pressure at the launch pad — enough to melt concrete and required massive water suppression systems (the "sound suppression system") that released over 300,000 gallons of water per minute to absorb the acoustic energy.
The Space Shuttle Main Engines and Solid Rocket Boosters together produced approximately 180 dB at the launch pad perimeter (500 meters from the pad). Modern launch vehicles including SpaceX's Falcon 9 and Starship produce comparable levels.
Acoustic fatigue — structural damage to aircraft, spacecraft, or other structures caused by intense sound pressure fluctuations. Rocket launches must be designed to avoid acoustic fatigue in payload structures, which is why water suppression systems exist not just to protect the launch pad but to protect the rocket and its payload from its own sound.
Nuclear weapons produce the highest instantaneous sound levels from any human-made event. The Tsar Bomba, the largest nuclear weapon ever detonated (October 30, 1961, Novaya Zemlya, Soviet Union), released approximately 50 megatons of explosive energy. The atmospheric pressure wave was detected multiple times around the globe, comparable to the Krakatoa record in global reach. Windows were shattered in Norway and Finland, approximately 900 km away.
Source: NASA (2009), "Saturn V — Sound Levels and Acoustic Environment," NASA Technical Reports Server — documentation of Saturn V launch acoustic levels and the water suppression system design.
How Far Sound Travels: Attenuation and the Limits of Hearing
Sound decreases in intensity with distance for two reasons: geometric spreading (the energy spreads over an ever-larger spherical surface area, so intensity falls as the inverse square of distance) and atmospheric absorption (energy is lost to molecular vibrations in the air, predominantly at higher frequencies).
The inverse square law: if you double the distance from a sound source, the intensity drops by a factor of four (6 dB). Triple the distance, and intensity drops by a factor of nine (about 9.5 dB). This is why the Krakatoa sound, which was estimated at 310 dB at source, had decayed to approximately 172 dB at 160 km — a reduction of 138 dB over that distance — and was still audible (as a barely perceptible pressure fluctuation) at 4,800 km.
Higher frequencies attenuate more rapidly in air than lower frequencies. This is why distant thunder sounds like a low rumble even though close lightning produces a full-frequency crack — the high frequencies are absorbed first, and only the low bass components survive to long distances. Similarly, the Krakatoa sound was detectable at planetary distances largely because of its infrasonic components (below 20 Hz), which experience almost no molecular absorption.
The ocean acts as a waveguide for very low frequency sound: the SOFAR (Sound Fixing and Ranging) channel, a depth layer of minimum sound velocity at approximately 600–1,200 meters depth, traps sound energy and allows it to propagate thousands of kilometers with little spreading loss. Submarine explosions and whale calls can be detected across entire ocean basins through the SOFAR channel.
Source: Urick, R.J. (1983), Principles of Underwater Sound, McGraw-Hill — the standard reference text for underwater acoustic propagation including the SOFAR channel and geometric spreading losses.
Frequently Asked Questions
Q: What was the loudest sound ever recorded?
A: The loudest sound for which we have quantitative historical evidence is the 1883 Krakatoa eruption, estimated at approximately 310 dB at source based on barograph pressure measurements at known distances. The 2022 Hunga Tonga eruption is the loudest event recorded by modern sensor networks (infrasound arrays and hydroacoustic stations), though its source level estimate is somewhat lower. Krakatoa remains the historical record holder by the available evidence.
Q: What does "194 dB is the limit for sound in air" mean?
A: At 194 dB, the rarefaction (low-pressure) phase of a sound wave would reach a pressure of zero — a complete vacuum. Since pressure cannot go below zero, sound waves at or above 194 dB cannot propagate as classical linear acoustic waves. Instead, the physics transitions to shockwave behavior: a supersonic blast front of compressed air. Events like Krakatoa and nuclear detonations produce shockwaves at close range that only become ordinary acoustic waves at distances of many kilometers.
Q: Are sperm whale clicks really louder than a rocket launch?
A: Not directly. The comparison is complicated by the different reference pressures used in water (1 micropascal) and in air (20 micropascals). A sperm whale click measured at 230 dB re 1 μPa in water converts to roughly 170 dB in air-equivalent terms. A Saturn V rocket launch produced approximately 204 dB at the launch pad. When corrected for the same reference, the rocket is considerably louder at its source. The whale clicks are measured far closer to the source, which also inflates the apparent comparison.
Q: How did scientists know that Krakatoa's sound circled the Earth?
A: Meteorological stations around the world in 1883 operated barographs — instruments that continuously record atmospheric pressure on a chart paper drum. When the Krakatoa pressure wave arrived, it produced a visible spike on the barograph record. Because all the stations had synchronized time, researchers could trace the wave's arrival times around the globe. The wave arrived from two directions simultaneously (having split and traveled in both directions around the Earth), and then arrived again as a reflection, for a total of four passes detected on barographs in Europe, Asia, and the Americas.
Q: What is the loudest sound a human can produce without a tool?
A: The loudest unassisted human vocal output ever measured was a shout recorded at approximately 129 dB (SPL) at 1 meter from the mouth, set by a teacher in Northern Ireland whose shout measured 129.4 dB. Trained singers at peak volume produce roughly 100–110 dB at 1 meter. The human voice is limited by the lung pressure that the respiratory muscles can generate, typically up to about 20 cm of water pressure above atmospheric, which sets a practical maximum of around 130 dB at the lips.
Q: What is infrasound and why does it travel so far?
A: Infrasound is sound at frequencies below 20 Hz — below the threshold of human hearing. At very low frequencies, the wavelength of sound (speed of sound divided by frequency) becomes extremely long: at 1 Hz, the wavelength in air is roughly 340 meters. Long wavelengths experience minimal diffraction around obstacles and almost no molecular absorption in the atmosphere. As a result, infrasound can propagate thousands of kilometers with very little attenuation. Major volcanic eruptions, nuclear explosions, large meteors, and some severe storms all generate infrasound that is detectable globally.
Read next:
Follow new articles
Add SciHub101 to your feed reader to see new science and technology stories.
About the Author
SciHub101 is an independent science and technology publication founded and edited by Buğra Sözeri, a software engineer and app developer based in Türkiye. AI tools assist with drafting and research. Source documentation in the existing archive is uneven, and articles are being reviewed and corrected. The Editorial Team byline identifies editorial responsibility; it does not certify specialist or independent human review. Where we compare products, anything built by our own team is labelled as such — see the editorial guidelines and About page for how corrections and disclosures work.
Related Articles
The Most Abundant Elements in the Universe: Why the Cosmos Is Mostly Hydrogen and Helium
Hydrogen makes up approximately 74% of all ordinary matter in the universe by mass — about 92% of all atoms. Helium accounts for roughly 24% of ordinary mass. Everything else — every carbon atom in every living cell, every silicon atom in every rock, every iron atom in every star's core — adds up to approximately 2% of the universe's total atomic mass. The dominance of hydrogen and helium is not a coincidence or a geological quirk. It is a direct record of the conditions that existed in the first three minutes after the Big Bang. Understanding why the cosmos is almost entirely these two lightest elements tells you how the universe was born and how it will eventually end.
The Largest Structures Ever Built: Towers, Bridges, Dams, and Walls
The Burj Khalifa in Dubai stands 828 meters tall — for context, you could stack almost two Empire State Buildings on top of each other and still not reach its antenna. But height is only one dimension of 'largest.' The world's longest bridge stretches 164.8 km across China. The Great Wall of China, including all branches, runs over 21,000 km. The largest building by floor area is a Boeing factory in Washington State that covers 398,000 square meters under a single roof. What engineering limits the next record depends on which dimension you're measuring and why physics makes every additional meter harder than the last.
The Largest Volcanoes in the World: The Mountain That's Mostly Underwater
Mauna Loa in Hawaii rises 4,170 metres above the sea — but that's only the tip. Measured from its true base on the ocean floor, it stands roughly 17 kilometres tall, more than twice Everest's height above sea level, and is so heavy it has pushed the seabed downward beneath it. It may not even be the largest volcano on Earth by volume. And lurking beneath Yellowstone is something that isn't a mountain at all: a supervolcano whose eruptions are measured not in metres but in continents.
The Most Extreme Pressure Conditions on Earth and Beyond
At the Challenger Deep, pressure reaches 1,086 bar — crushing enough to compress foam to thimble size. But Earth's extremes pale compared to the pressures inside neutron stars, where one teaspoon of matter weighs as much as Mount Everest. This guide explains the physics of pressure across the universe, from laboratory breakthroughs to the conditions that forge new elements.
The Largest Volcanic Eruptions in History
Toba, Yellowstone, Tambora, Krakatau, and Pinatubo compared by volume, climate effect, and death toll, with a plain explanation of the VEI scale and why the biggest eruption is rarely the deadliest.
The Deadliest Natural Disasters in History: Death Tolls, Causes, and the Science Behind the Catastrophes
The 1931 China floods killed an estimated 1 to 4 million people — the single most lethal natural disaster in recorded human history. The 1815 eruption of Mount Tambora cooled the entire planet and triggered crop failures across three continents, adding tens of thousands of deaths to the 71,000 who died directly from the volcano. The 2004 Indian Ocean tsunami killed 227,898 people in 14 countries within hours. These events share a common thread: the science of how Earth releases stored energy intersects with human vulnerability in ways that transform geological processes into humanitarian catastrophes.