Which country sits astride a mid-ocean ridge?

Iceland, which is the Mid-Atlantic Ridge poking above sea level. The North American and Eurasian plates are pulling apart underneath it at about two centimetres a year, and the island is a volcanic pile built up where the ridge coincides with a hot spot in the mantle - which is why it is above water when the rest of the ridge is two kilometres down.

That gives it a rift running across it, visible on the ground. At Thingvellir you can walk in the valley between the two plates, which is also where the Althing, one of the oldest parliaments in the world, met from AD 930 - the assembly was held there partly for the acoustics of the rift wall.

It runs on the consequences. Nearly all Icelandic electricity is hydro and geothermal, and something like nine in ten homes are heated by piped hot water pulled straight out of the ground. The cost is the eruptions: Laki in 1783 caused a famine that killed a fifth of the population, and Eyjafjallajokull in 2010 closed European airspace for a week, which is a modest reminder of what the island is standing on.