AHEAD WAS A peculiar vision. Black Island appeared to levitate above the Ross Ice Shelf. A shimmering dark lake had formed below it where there had not been rain for over two million years. I rest on my ski poles and in the thin Antarctic air catch my breath. I watch the lake grow legs, fold, collapse and gently lower Black Island back in place.

On a calm day mirages are common here. Roald Amundsen and his party, who were the first people to the South Pole in 1911, saw their fair share of them. Perhaps the most famous of these mirages was seen within days of their reaching the pole. ‘Our finest day up here,’ wrote Amundsen. ‘Calm most of the day with burning sunshine… As we were breaking camp Hassel called out, “Do you see that black thing over there?” Everyone saw it. “Can it be Scott?” someone called. Bjaaland skied forward to investigate. He did not have to ski far. “Mirage,” he reported laconically, “dog turds.”’