Why does Iceland have so many volcanoes?

Iceland has so many volcanoes because it gets a double dose of molten rock. First, it sits on the Mid-Atlantic Ridge, a crack in the ocean floor where the North American and Eurasian plates are slowly pulling apart. As they separate, hot rock rises to fill the gap and erupts. Second, Iceland is thought to sit over a hotspot, the top of a plume of unusually hot rock rising from deep in the mantle. Together they make the island one of the most volcanic places on Earth, with around 30 active volcanic systems. Over the past 500 years, Icelandic volcanoes produced a third of all the lava erupted on the planet.

Iceland is one of the few places where you can see a mid-ocean ridge on dry land. At Þingvellir, cracks open in the ground as the plates drift apart, and the biggest, Almannagjá, is a real canyon. In the Silfra fissure nearby, divers and snorkellers swim in clear water in the gap between the plates. It is also where Iceland's parliament, the Alþingi, met every summer from 930 to 1798.

Living on top of all this has a cost. The Laki eruption of 1783–1784 killed about a fifth of Iceland's population, mostly through the climate changes and livestock illness that followed. And in 2010, ash from Eyjafjallajökull closed the airspace of about 20 countries and stranded some 10 million travellers.