IN THE SUBTROPICAL Pacific Ocean, 160 kilometres southwest of Raoul Island, Lieutenant Tim Oscar stared out of the window of the ship’s bridge. Behind him were the heaving grey seas the ship had been battling all night. Before him, a vast white expanse glowed in the moonlight. Oscar braced himself, as if the ship was about to hit an ice shelf.

But there was no ice, not at this latitude. The ship’s lights soon revealed a raft of pumice stretching out either side of the ship, further than Oscar could see. The ship ploughed through the metre-thick jumble of floating rock for half an hour, then sailed on.