Krakatoa

In August of 1883 the volcano on the island of Krakatoa erupted violently with an enormous succession of blasts killing tens of thousands of people in the surrounding villages. Large pyroclastic flows swept down the flanks of the volcano, even crossing nearby ocean channels to devastate nearby islands. The biggest of these volcanic explosions was heard nearly 4800 km across the Indian Ocean basin on Rodriguez Island off of Africa’s eastern coast. The sound from this blast took roughly 4 hours to travel from the erupting Krakatoa volcano across the Indian Ocean and be heard by inhabitants of Rodriguez Island. Similarly, subsequent explosions and loud booms were heard in Perth, on the west coast of Australia and in Southeast Asia.

27th May 1883: Clouds pouring from the volcano on Krakatoa (aka Krakatau or Rakata) in southwestern Indonesia during the early stages of the eruption which eventually destroyed most of the island. Royal Society Report on Krakatoa Eruption - pub. 1888 Lithograph - Parker & Coward (Photo by Hulton Archive/Getty Images)

Locally, the sound waves created by the blasts were much more damaging. Broken windows and shaking homes resulting from the concussion sound waves of the explosion were reported up to 160km from the volcano around Krakatoa. People within this 160km vicinity of the eruption would have experienced intense ear pain and permanent hearing loss from exposure to these concussion waves. Estimates of exposure levels indicate it would have been like standing on a rocket launching pad with no ear protection.

The concussion or shock waves produced by the blasts at Krakatoa were remarkably high energy and could be heard by pressure sensors around the world. In fact, many stations recording barometric pressure revealed that the atmospheric shock waves created by the explosions travelled 7 times around the Earth before they were dissipated to immeasurable levels.