James Stewart

But over millions of years, this process has built the longest mountain range on Earth, running down the centre of the Atlantic Ocean.

Almost all 16,000 kilometres lies two to three kilometres beneath the waves.

That is, until you reach Iceland.

Here, land pokes its head above the surface.

Why?

Well, Iceland isn't just on a tectonic plate boundary.

Here, the Mid-Atlantic Ridge intersects another geological phenomenon, a mantle hotspot.

These are best known for creating island chains such as Hawaii, the Galapagos and the Canary Islands, all of which I might add lie in the middle of tectonic plates, not at the edge.

The hotspot under Iceland instead creates the geological equivalent of a pressure cooker left on high for millions of years, turning an already active boundary into something far more volatile.

producing a third of all the lava that's erupted onto Earth's surface in the last 500 years, which is not bad for a country smaller than England.

Now, mantle hotspots are somewhat of an enigma, which is sort of a nice way of saying that scientists don't exactly know what causes them.

Actually, let me know in the comments below if you'd like to see a video on that another time.

But for now, what we need to know is that they are driven by columns of unusually hot, buoyant rock rising from deep within the Earth and pushing up through the mantle, and that they can last for tens of millions of years.

Now, the important thing to note here is that these hot spots can raise mantle temperatures by as much as 200 degrees Celsius.

And in doing so, the drop in pressure causes hot, solid rock to melt into magma.

The result is an unusually thick crust, up to 40 kilometres compared to typically 7 kilometres, and enough buoyancy to lift the ridge out of the ocean.

Et voila, an island, or in this case, an Iceland.

This is the only inhabited mid-ocean ridge on Earth.

In fact, visit Thinkvitlia National Park and you can literally stand in the separation zone between two continents.

But it's what's inside that ridge that's problematic.