Jökulsárlón is a lagoon on the south coast of Iceland where the Vatnajökull ice cap calves icebergs a thousand years old into the water. The lake they float in is about a century old. The glacier reached almost to the sea until the 1930s, and the lagoon opened behind it as the ice pulled back. It has since grown to four times the size it was in the 1970s, and it is already the deepest lake in the country. The channel draining it to the ocean is the shortest river in Iceland, about 500 metres. In 1989 it ran three times that, and it keeps shortening as the lagoon eats its way inland. The bergs themselves drift for months, white and milky blue, turning over as they melt.
Across the road the outlet runs into the surf, and the waves push broken pieces of ice back onto the black volcanic sand beside it. They sit there polished and clear, and a low sun goes through them and lights each one from the inside. Harbour seals stay on the lagoon all year, hauling out to bask on a passing floe or rolling through the cold to hunt. Some of the bergs carry thin black lines through the ice. Each is a layer of ash from an eruption under the ice cap, and you can read a berg's age off them much as you would count rings in a tree. As the light goes the ice turns from white to deep blue with the sky, and once the buses have left the drift is the only thing still moving. On clear autumn nights the aurora comes up over the lagoon and doubles in the calm water between the floes. In summer the amphibian boats and Zodiacs run out among the bergs to the calving wall, close enough that the ice slides past you a few metres away. At some point the guide reaches over the side, lifts a lump of thousand-year-old ice out of the water and puts it in your hands.