9 March 2011

Pulsating planet: Superhot rocks make the Earth roll

Gushing larva in Iceland hints at the vast hotspot that created the island

Animated graphic: “Ups and downs

An invisible force is creating giant ripples in the Earth’s crust – in a geological blink of an eye

BRYAN LOVELL likes to show his fellow geologists an image of a network of river valleys. “I ask them where they think this might be on Earth,” he says. It is, as you probably guessed, a trick question. The river valleys are in the North Sea, north of Scotland, beneath a kilometre of water and a further 2 kilometres of sediment.

The sea floor here has been slowly sinking ever since it formed. Yet 55 million years ago, something very strange happened. In a geological blink of an eye the sea floor was thrust upwards nearly a kilometre, until it was high and dry above the waves. It remained above the sea for about a million years, long enough for rainwater to carve deep valleys. Then it sank down again. It all happened astonishingly fast.

The big question is why. None of the usual explanations apply. The collision of tectonic plates can lift vast regions many kilometres up into the air, but there are no colliding plates under the North Sea. Sea level can fall when huge ice sheets form, but not by a kilometre and not in only one area. Volcanic hotspots, where hot molten rock rises up from deep within the Earth, can also produce uplift, but the nearest hotspot is hundreds of kilometres to the west, where it has lifted up Iceland. What’s more, hotspots produce slow uplift over tens of millions of years, not a relatively sudden rise and fall.

The North Sea

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