The 1883 eruption of Krakatoa, located in the Sunda Strait between the Indonesian islands of Java and Sumatra, was a monumental volcanic event. It is remembered for its immense destructive power and the extraordinary magnitude of the sound it produced, which sent shockwaves across the globe and captivated attention for its unprecedented reach.
Understanding Decibels: A Scale for Sound
To understand the scale of Krakatoa’s sound, it is helpful to understand the decibel (dB) scale, which measures sound intensity. The decibel is a logarithmic unit, meaning a small increase in decibel value represents a significant increase in sound power. For instance, a 10 dB increase signifies a sound that is ten times more intense. The quietest sound a human can hear is 0 dB.
Common sounds have varying decibel levels: a whisper is around 15 dB, normal conversation is 60 dB, and busy city traffic can reach 85 dB. Sounds above 85 dB, such as a hairdryer at 90 dB or a rock concert at 120 dB, can cause hearing damage with prolonged exposure. A jet engine taking off nearby might register around 120 dB, while fireworks or a gunshot can exceed 140 dB, nearing the threshold of pain.
The Krakatoa Eruption: A Cataclysmic Event
The volcanic island of Krakatoa experienced one of the most powerful eruptions in recorded history in 1883. The main explosive phase occurred on August 26-27, culminating in a cataclysmic blast on the morning of August 27. This eruption obliterated two-thirds of the island, causing it to collapse into a caldera.
The eruption reached a Volcanic Explosivity Index (VEI) of 6, equivalent to an estimated 200 megatons of TNT. This energy release propelled an estimated 25 cubic kilometers of rock, ash, and debris high into the atmosphere, darkening skies for days. The immediate aftermath included devastating tsunamis, with waves reaching up to 46 meters (151 feet) in height, claiming tens of thousands of lives in coastal areas of Java and Sumatra.
The Unprecedented Global Reach of the Sound
Krakatoa’s climactic explosion on August 27, 1883, produced a sound heard across an unprecedented portion of the Earth’s surface. Reports indicate the sound was audible as far away as Perth, Western Australia, approximately 3,110 kilometers (1,930 miles) distant. People on the island of Rodrigues, near Mauritius in the Indian Ocean, some 4,800 kilometers (3,000 miles) away, distinctly heard the roar, often mistaking it for distant cannon fire.
The eruption also created an atmospheric pressure wave that traveled around the entire globe. Barographs, instruments designed to record atmospheric pressure, detected this wave repeatedly. The pressure wave from Krakatoa circled the Earth multiple times, reverberating for up to five days and detected seven times in some locations. This global propagation provided scientific confirmation of the extraordinary energy released by the eruption.
Estimating Krakatoa’s Decibel Level and Its Impact
Precisely determining the decibel level of the Krakatoa eruption presents challenges due to the absence of modern sound-measuring equipment in 1883. Scientists estimated the sound’s intensity by analyzing the distances it was heard and recorded atmospheric pressure changes. For example, a gasworks in Batavia (now Jakarta), about 160 kilometers (100 miles) from the volcano, registered a pressure spike equivalent to 172 decibels. This provides a crucial data point for estimating the sound’s magnitude.
Near the source, the sound transformed into a powerful shock wave. At approximately 194 dB, acoustic vibration transitions into a shock wave or sonic boom, meaning the air itself is pushed along rather than just vibrating. The Krakatoa eruption produced a blast of high-pressure air so forceful it ruptured the eardrums of sailors on ships as far as 64 kilometers (40 miles) away. Anyone within 16 kilometers (10 miles) of the eruption would have experienced permanent deafness. Based on these observations and energy release, the sound at the source of the Krakatoa eruption has been estimated as high as 310 decibels, making it the loudest sound ever recorded.