At Thingvellir, three-quarters of an hour's drive east of Reykjavík, a gravel path runs along the floor of a canyon called Almannagjá. The wall on one side belongs, geologically speaking, to North America; the plain stretching away on the other lies on the Eurasian side of the divide. The two are moving apart, and the ground between them — cracked, faulted and slowly subsiding — is the visible seam of the planet. The Vikings, knowing nothing of plate tectonics, chose this rift valley in the year 930 as the meeting place of the Althing, the open-air general assembly of their new commonwealth. Icelanders like to point out the result: one of the world's oldest parliaments was founded, by accident, in the crack between two continents.
The crack is the Mid-Atlantic Ridge, the longest mountain range on Earth. It runs some 16,000 kilometres down the centre of the Atlantic, from the Arctic towards the Southern Ocean, and almost all of it lies drowned beneath two or three kilometres of water. Iceland is the great exception. Here the ridge happens to sit above a mantle plume — a hotspot pumping up unusual volumes of magma — and the combination has piled up enough basalt to lift the ridge crest into the open air. The island is, in effect, a piece of ocean floor you can walk on. And like the ocean floor, it is spreading: the North American and Eurasian plates pull apart at roughly two centimetres a year, about the speed at which fingernails grow.
An island being born
The spreading is not gentle. On the morning of 14 November 1963, the crew of a fishing boat south of the Westman Islands noticed a column of dark smoke rising from the open sea and went to investigate, suspecting a burning ship. What they found was the sea itself erupting. Within days a new island of black tephra had broken the surface; the eruption continued until 1967, by which time the island — named Surtsey, after Surtur, the fire giant of Norse myth — covered about two and a half square kilometres. Surtsey was declared a nature reserve while still cooling, and access has been restricted to a small number of scientists ever since, making it a pristine laboratory for watching life colonise bare rock: first seeds washed ashore, then insects, then gulls, then soil and an ecosystem.
Living on the seam has always been a mixed blessing. In 1973 a fissure opened with little warning on Heimaey, the only inhabited Westman island, and lava advanced on the fishing harbour; the islanders famously fought back by pumping seawater onto the flow front, slowing and thickening it until the harbour was saved — arguably improved, since the new lava narrowed its entrance into better shelter. Two centuries earlier the country had not been so lucky. The Laki fissure eruption of 1783 poured out one of the largest lava floods in recorded history and blanketed the island in poisonous haze; in the famine that followed, roughly a fifth of Iceland's population died, along with more than half its livestock. The haze drifted across Europe, dimming the sun for months — and some historians argue the failed harvests that followed helped stoke the unrest that led to the French Revolution, though that remains a debated footnote rather than a settled fact. In 2010 the world got a milder reminder when ash from Eyjafjallajökull closed most of European airspace for nearly a week, stranding millions of passengers in the largest air-traffic shutdown since the Second World War.
The dividends of the rift
Icelanders have learned to bank the volcano as well as fear it. Geothermal heat, tapped from the young volcanic rock, warms around nine in ten of the country's homes, and geothermal and hydro power between them give Iceland electricity that is almost entirely renewable. Even the country's most famous tourist attraction is industrial runoff: the milky-blue water of the Blue Lagoon is discharge from the neighbouring Svartsengi geothermal plant. Back at Thingvellir, divers pay to swim the Silfra fissure, a flooded crack filled with glacial meltwater so clear that visibility stretches for a hundred metres. Tour operators sell it as the chance to touch two continents at once — a simplification that makes geologists sigh, since the plate boundary is really a diffuse zone of fissures kilometres wide, but as marketing it is irresistible.
The deeper point is that Iceland is not so much a place as a process. Every year the island grows about two centimetres wider, new land quietly stitched into the middle while the coasts ride outward on their separate plates. Somewhere beneath Thingvellir, the Atlantic is still being made.
Quiz nuggets
- The Althing, Iceland's parliament, was founded at Thingvellir in 930 — in the rift valley between the North American and Eurasian plates.
- The island of Surtsey was born in a submarine eruption that began in November 1963 and continued until 1967.
- The Mid-Atlantic Ridge spreads at roughly two centimetres a year — about the speed at which fingernails grow.
- The Laki eruption of 1783 caused a famine that killed roughly a fifth of Iceland's population.
- Ash from Eyjafjallajökull in 2010 triggered the largest European air-traffic shutdown since the Second World War.