The South Indian Ocean airburst, 1963
A huge explosion that no one saw, picked up by microphones listening for nuclear tests.
Key facts
- When
- 3 August 1963
- Where
- Southern Indian Ocean, west of the Prince Edward Islands
- What hit
- probably a few tens of metres
- Era
- Witnessed, 1908 to 1999
Estimated at roughly 260 kilotons of TNT, with a large uncertainty (perhaps 170 to 350 kilotons).
Around 17 Hiroshima bombs, and among the largest airbursts of the 20th century after Tunguska.
What happened
In the early 1960s, the United States ran a network of very sensitive microphones that listened for infrasound, sound too low for human ears, from nuclear weapons tests. On 3 August 1963 the network recorded a powerful blast over the remote southern Indian Ocean.
It was not a bomb. Analysis of the signals showed it was a large meteoroid exploding in the atmosphere, far from any ship or island. Re-analysis decades later gave an energy of about 260 kilotons, making it one of the most energetic airbursts recorded until Chelyabinsk in 2013.
The event showed that big airbursts happen more often than people had realised, but most go unnoticed because they occur over oceans or empty land.
Effects
None known: it happened high above the open ocean.
The evidence
Infrasound records from several stations, which give the time, direction and rough energy of the blast.
Did you know?
A worldwide infrasound network, built to check that countries keep to the nuclear test-ban treaty, now detects meteoroid airbursts several times a year.
Infrasound can travel thousands of kilometres through the atmosphere.
Related pages
How is impact energy measured? See energy explained, or try the impact calculator.