Frazer and Park trawled through records of the rumbles created by earthquakes as they passed through the Earth’s mantle below Bermuda. These vibrations can move through dense materials much faster, while less dense matter slows them down, so the waveforms they create can give us a sense of what’s going on down there.

In this case, the seismologists found evidence that a layer of relatively low-density rock, about 20 kilometers (12 miles) thick, is doing the job a rising mantle plume usually would: uplifting the crust with its buoyancy to create a swell that holds the archipelago just above its crystalline waters.