Krakatoa sat at one of Earth's most volatile tectonic junctions

Winchester explains that Krakatoa's location in the Sunda Strait places it directly above a subduction zone, where the Indo-Australian tectonic plate is being forced beneath the Eurasian plate, a geological setting that generates immense pressure and melts rock into the magma that fuels volcanic activity throughout the Indonesian archipelago. This region remains one of the most seismically and volcanically active stretches on the planet.

He walks through the then-relatively new science of plate tectonics, a framework not fully established until decades after 1883, to explain retroactively why this particular strip of ocean has produced repeated catastrophic eruptions across recorded history, including the earlier, even larger eruption of nearby Tambora in 1815.

Winchester uses this geological context to frame the 1883 eruption not as an isolated fluke but as a predictable, if unpredictably timed, consequence of the region's underlying tectonic structure, a hazard permanently built into the geography of the area. Takeaway: understanding the deep geological cause behind a disaster reframes it from freak accident to a recurring structural risk.