The 1883 eruption of Krakatoa produced the loudest sound in recorded history, and people heard it as a distinct bang or series of booms at distances up to roughly 4,800 kilometers (about 3,000 miles) from the volcano. That is the equivalent of someone in New York hearing an explosion in Dublin. But the eruption’s reach extended far beyond what human ears could consciously register as sound: the pressure wave it generated was detected on barographs around the entire planet, circling the globe at least three times over the days that followed.
The Farthest Confirmed Earwitnesses
On the morning of August 27, 1883, the volcanic island of Krakatoa in the Sunda Strait between Java and Sumatra entered its final catastrophic phase, producing four enormous explosions. The third and largest, at roughly 10:02 a.m. local time, was the one that set records. People on Rodriguez Island, a small British territory in the Indian Ocean about 4,800 kilometers to the southwest, reported hearing what they described as distant cannon fire or the roar of heavy guns coming from the east. The chief of police on Rodriguez logged the sounds in an official report, noting they persisted for several hours. This remains the greatest distance at which any single event has been directly heard by human ears without technological aid.
Closer to the source, the sound was devastating. In parts of Java and Sumatra within a few hundred kilometers, the blast was loud enough to cause permanent hearing damage. Coastal towns that were not destroyed by the accompanying tsunamis reported windows shattering and walls cracking from the air pressure alone. In the Australian interior, nearly 3,500 kilometers to the southeast, settlers reported sounds resembling distant artillery and assumed a naval battle was underway offshore. Across the Indian Ocean, reports came in from Sri Lanka, Mauritius, and even parts of the East African coast. Taken together, the eruption was heard across roughly one-thirteenth of the Earth’s surface.
Why Sound Usually Dies Out Long Before 4,800 Kilometers
Under normal conditions, even extremely loud sounds fade into inaudibility within tens of kilometers. Sound waves lose energy as they spread outward, get absorbed by the atmosphere, and scatter off temperature gradients and wind layers. An explosion loud enough to hear 50 kilometers away is already remarkable. So how did Krakatoa reach nearly a hundred times that distance?
Part of the answer is sheer power. The main explosion released energy estimated at 100 to 150 megatons of TNT equivalent, far exceeding the largest nuclear weapon ever detonated.​1Earth and Planetary Science Letters. IMS observations of infrasound and acoustic-gravity waves produced by the January 2022 volcanic eruption of Hunga, Tonga: A global analysis That kind of energy creates a pressure disturbance so large that ordinary atmospheric attenuation cannot snuff it out over the distances that would silence a lesser source.
But energy alone does not explain everything. The eruption also generated sound across a wide range of frequencies, including very low frequencies (infrasound) that the atmosphere transmits far more efficiently than higher-pitched noise. Higher frequencies scatter and absorb quickly; low frequencies, with wavelengths stretching hundreds of meters, essentially ride over atmospheric obstacles. Krakatoa’s blast produced waves at frequencies well below the normal threshold of human hearing, and these components traveled with remarkably little loss. At extreme distances, the only parts of the signal that survived were those low-frequency components, which is why witnesses far away described what they heard as a dull, rumbling boom rather than a sharp crack.
Atmospheric waveguides also played a role. Under certain temperature and wind conditions, sound can become trapped in a layer of the atmosphere and channel along it for vast distances, much like light bouncing inside a fiber-optic cable. The stratosphere and the lower thermosphere both contain such ducts. The Krakatoa blast was powerful enough to excite waves in multiple atmospheric layers simultaneously, allowing its sound to propagate efficiently along several paths at once.
Beyond Hearing Range, the Pressure Wave Kept Going
What makes Krakatoa truly extraordinary is not just how far it was heard, but how far the pressure disturbance traveled after it dropped below audibility. Weather stations equipped with barographs, instruments that continuously record atmospheric pressure on a rotating drum, picked up a sudden pressure spike and then a series of oscillations in the hours following the eruption. These readings came from stations in every corner of the globe, from Berlin to Toronto to Sydney.
The Royal Society’s 1888 report, compiled by a committee that painstakingly collected barograph data from stations worldwide, documented the pressure wave circling the Earth at least three and possibly four times. Each passage showed up as a distinct pulse on the instruments, growing weaker with each lap but still measurable. The wave traveled at roughly the speed of sound in the upper atmosphere, around 1,100 kilometers per hour, and took about 36 hours for each complete circuit. A study comparing the 1883 Krakatoa wave with data from the 2022 Hunga Tonga eruption used a timing method similar to the one from that original Royal Society analysis and confirmed that both events produced waves detectable on multiple global passes.2Pure and Applied Geophysics. TIMING Analysis of the Multiple Passages of the Pressure Wave Generated by the 2022 Hunga Tonga-Hunga Ha’apai and Comparison with the 1883 Krakatoa Pressure Wave
So the honest answer to the title question depends on what you mean by “hear.” If you mean consciously perceive as a sound with your ears, about 4,800 kilometers. If you mean detect the pressure disturbance with any instrument, the answer is everywhere on Earth.
What Infrasound Does to the Body
At distances well beyond where people could consciously hear the eruption as a sound, the pressure wave still had effects that a human body could register. Infrasound, generally defined as sound below about 20 hertz, is too low-pitched for the ear to interpret as tone in the usual sense, but it is not invisible to the body. The ear remains the primary organ for detecting infrasound, but at sufficient intensity the vibrations can also be felt in the chest, abdomen, and through the skin.3PubMed. Hearing at low and infrasonic frequencies
Research on infrasound perception has established that the threshold of audibility at very low frequencies is much higher than for normal speech-range sound. At 4 hertz, a person needs roughly 110 decibels just to detect that anything is happening; at 20 hertz, the threshold drops to about 90 decibels. Physical sensation through body vibration kicks in at levels around 20 decibels above the hearing threshold.4Journal of Low Frequency Noise, Vibration and Active Control. Exposure to Infrasound — Perception and Changes in Wakefulness People in moderately distant locations from Krakatoa, places too far away to hear the eruption as a bang but close enough for the pressure wave to still carry serious energy, would have experienced a strange sensation: a feeling of pressure changes, chest tightness, or unease without any identifiable sound. Some historical accounts from intermediate distances describe exactly this, a sense that something was deeply wrong in the air even though no sound could be pinpointed.
This means there was a zone, probably extending well beyond the 4,800-kilometer audible radius, where people could feel the eruption’s effects in their bodies without hearing it in the conventional sense. The boundary between “heard it” and “did not hear it” was not clean. It was a gradient from deafening roar to faint boom to uncanny pressure sensation to nothing at all.
How Loud Was It at the Source?
Estimating the sound level at the eruption’s origin requires working backward from distant pressure readings, since no instruments survived near the volcano itself and most nearby witnesses did not either. The pressure pulse recorded at a gas works facility in Batavia (now Jakarta), roughly 160 kilometers away, was over 2.5 inches of mercury, an extraordinary atmospheric disturbance. Extrapolating from that and from the energy estimates, acoustic researchers have placed the sound level in the immediate vicinity of the eruption in the range of 170 to over 190 decibels. For context, 194 decibels is generally considered the theoretical maximum loudness for a sound wave in Earth’s atmosphere at sea level; beyond that, the pressure variations are so extreme that the wave is no longer really “sound” in the classical sense but a shock wave, a moving wall of compressed air.
At those levels, the blast was not something you would hear so much as something that would hit you. The pressure differential alone was lethal at close range, independently of the pyroclastic flows, tsunamis, and volcanic debris that killed most of the eruption’s estimated 36,000 victims. The towns closest to the volcano were obliterated so completely that separating the effects of the sound wave from the effects of everything else that destroyed them is essentially impossible.
The 2022 Eruption That Offered a Modern Comparison
For 139 years, Krakatoa stood alone as the only volcanic eruption known to have produced a pressure wave that circled the entire globe multiple times. Then, on January 15, 2022, the Hunga Tonga–Hunga Ha’apai volcano in the South Pacific erupted with a violence that scientists had not seen in the modern instrument era. Within hours, barometric stations on every continent were recording pressure signatures strikingly similar to those from 1883.
The Hunga Tonga event gave researchers their first chance to study a Krakatoa-class eruption with modern global sensor networks, including the International Monitoring System originally built to detect clandestine nuclear tests. Timing analysis of the pressure wave’s multiple passes around the Earth confirmed that the two eruptions behaved in remarkably similar ways, with pressure pulses arriving at predictable intervals consistent with a wave circling the planet at near the speed of sound.2Pure and Applied Geophysics. TIMING Analysis of the Multiple Passages of the Pressure Wave Generated by the 2022 Hunga Tonga-Hunga Ha’apai and Comparison with the 1883 Krakatoa Pressure Wave Yield estimates for Hunga Tonga, calculated from barometric recordings and infrasound data from stations within 7,000 kilometers of the source, came in around 100 to 200 megatons of TNT equivalent, putting it in the same class as Krakatoa.1Earth and Planetary Science Letters. IMS observations of infrasound and acoustic-gravity waves produced by the January 2022 volcanic eruption of Hunga, Tonga: A global analysis
One major difference: Hunga Tonga’s eruption occurred in a relatively remote part of the Pacific, far from large population centers. There were no cities within a few hundred kilometers to provide the kind of devastating close-range acoustic testimony that came from Java and Sumatra in 1883. People in New Zealand, about 2,000 kilometers away, reported hearing booms, and audible sound was noted in parts of Alaska, nearly 10,000 kilometers distant, though those Alaskan reports remain somewhat debated since atmospheric ducting can produce unusual long-range propagation. The comparison with Krakatoa is imperfect because 1883 population density, instrument placement, and record-keeping were all so different, but the two events remain the only confirmed volcanic eruptions whose atmospheric pressure waves were recorded on complete global circuits.
Why “Loudest Sound in History” Needs a Caveat
Krakatoa is routinely described as having produced the loudest sound in recorded history. That claim is almost certainly correct, but it carries a few asterisks worth knowing about. “Recorded history” matters because earlier eruptions may have been comparable or louder. The 1815 eruption of Mount Tambora, also in Indonesia, ejected far more material into the atmosphere and caused the famous “Year Without a Summer” in 1816. Tambora was heard at distances of roughly 2,600 kilometers, well short of Krakatoa’s range, but the barograph network in 1815 was almost nonexistent, so there is no way to compare the pressure waves directly. Tambora’s eruption may have been more energetic in total volcanic output while producing a less efficient atmospheric pressure pulse, or it may simply have lacked the measurement infrastructure to prove its reach.
Prehistoric eruptions were almost certainly louder still. The eruption of Toba in Sumatra roughly 74,000 years ago is estimated to have been orders of magnitude more powerful than Krakatoa. But without instruments or written records, comparing sound propagation is speculative. So “loudest sound in recorded history” is really “loudest sound we have good pressure data for,” which is a less catchy title but more honest.
There is also the question of what counts as a single sound event. Krakatoa’s eruption lasted hours and produced multiple distinct explosions. The “heard 4,800 kilometers away” figure refers to the cumulative acoustic output of the eruptive sequence, not necessarily a single instantaneous bang. Whether the people on Rodriguez Island were hearing one peak explosion or the sustained acoustic output of a multi-hour eruption is impossible to determine from their accounts. For practical purposes, it does not change the record, but it is a subtlety that gets lost in the retelling.
Volcanic Sound in the Ocean
The eruption’s acoustic effects were not limited to the atmosphere. Krakatoa sat in a strait between two landmasses, and its explosions generated massive underwater sound waves in addition to atmospheric ones. Water transmits sound far more efficiently than air because it is much denser and less compressible. Low-frequency underwater sound from large explosions can travel thousands of kilometers through the ocean with very little loss, propagating through a layer called the deep sound channel where temperature and pressure conditions create a natural waveguide.
In 1883, there were no hydrophones to record underwater sound, so the oceanic acoustic reach of Krakatoa is a matter of physics-based estimation rather than direct measurement. But the 2022 Hunga Tonga eruption, which occurred partially underwater, was detected by hydroacoustic stations that are part of the modern nuclear test monitoring network. Those recordings confirmed that a submarine volcanic explosion of that magnitude sends sound energy across entire ocean basins. It is likely that Krakatoa’s underwater sound component propagated across the full width of the Indian Ocean and possibly beyond, though no one in 1883 had the equipment to notice.
Marine mammals, many of which are sensitive to low-frequency underwater sound, may have experienced the eruption’s acoustic signature at distances where no human on land registered anything unusual. Whale species that communicate using low-frequency calls would have been in the frequency range of the eruption’s underwater sound energy. Whether this caused behavioral disruption is unknowable at this historical distance, but it is a reminder that the eruption’s acoustic footprint extended into environments we tend to overlook.
What About Echoes and Terrain Effects?
At shorter ranges, the sound of the eruption interacted with terrain in complex ways. The Sunda Strait is flanked by the mountainous coastlines of Java and Sumatra, and observers at different locations reported the sound arriving at different times and with different characteristics depending on their position relative to mountain ridges, valleys, and the open sea. Some locations that were geometrically closer to the volcano heard less than locations farther away that happened to be in acoustic “line of sight” across open water.
Temperature inversions over the sea surface also created zones of enhanced and diminished sound. In the tropics, the warm ocean surface heats the air above it, creating conditions where sound can be refracted downward and focused at particular distances while skipping over others entirely. This “skip zone” effect means some communities at intermediate distances heard nothing while others farther away heard clear booms. It is the same phenomenon that lets you sometimes hear a distant conversation across a still lake with uncanny clarity while someone closer hears nothing. At Krakatoa’s scale, these acoustic shadows and bright spots played out over hundreds of kilometers rather than the length of a lake, creating a patchwork of earwitness reports that confused investigators until the atmospheric physics was better understood.
The skip-zone effect also complicates the clean “4,800 kilometer” answer. Rodriguez Island may have been at a favorable position in an acoustic duct rather than at the absolute maximum range of audibility. It is possible that the sound could have been heard farther away in some other direction under the right atmospheric conditions, but no one was there to report it. The 4,800-kilometer figure is a lower bound on maximum audible range as much as it is a measurement of it. The eruption’s true acoustic horizon, the farthest distance at which it was theoretically audible under ideal conditions, is unknown and likely unknowable.