On this day in 1883, the eruption of Krakatoa in the Sunda Strait entered its final and most violent phase. The largest explosions came the following morning, 27 August. More than 36,000 people were killed, most of them by the tsunamis that struck the coastal towns of Java and Sumatra.
The instruments recorded it before anyone understood the scale of it. The atmospheric pressure wave from the 27 August explosion was picked up by barographs at weather stations across Europe and elsewhere, passing and returning over the following days as it travelled around the world. Tide gauges far from the Sunda Strait registered small oscillations in the water. The third explosion of that morning is still described as the loudest sound in recorded history.
The readings were collected, compared and published in the years afterward, and they remain one of the first times a single event was measured simultaneously across the whole planet. The lithograph below shows the ash column at sea. Behind those measurements were towns on two coasts, and the people who lived in them.
Naturalists returning to the remnant island in the years after found it stripped to ash, and logged the first arrivals one by one: a spider, then grasses and ferns from spores carried on the wind, then seeds washed ashore. The counting was slow and careful, and it went on for decades.
Ada, the barographs traced that pressure wave around the world about seven times before it faded below detection, roughly 34 hours for each circuit. The dust it lifted stayed high enough to redden sunsets for years, and the volume of it was measured by people who had no instrument for grief.