The Cappadocia area in the middle of Turkey is filled with bizarre rock formations, which look a bit like this – a lump of rock perched precariously on top of a tapered spire.

And here’s what they really look like. They’re called ‘Fairy Chimneys.’

30 million years ago, a volcanic eruption covered the whole area in a thick layer of ash. Over time, that became a layer of soft, easy to carve rock – but it was topped with a layer of much harder basalt.

You can see lumps of basalt on top of the ash layers here. But how did these pillars form?

Back to Fred’s model. Here’s the lump of basalt, on top of the tapered pillar.

That particular region of Turkey has a fairly extreme climate – baking hot during the day, bitterly cold at night, and lots of rainfall. The basalt tended to break up and erode, leaving just odd lumps behind.

The rainwater also washed away the softer ash layer. However, in some places the basalt lumps work a bit like umbrellas, shielding the ash beneath them from the worst of the elements.

Here’s a model of that process – the polystyrene block represents the ash…

…and this pebble represents a thumping great lump of basalt.

As the rains come down – or, in Fred’s model, a shower of a chemical that dissolves polystyrene – they start to erode the soft rock.

But the pebble protects the material below, leading to the characteristic cone shape.

There you go, a precariously-balanced pebble, on a pillar carved not over millions of years, but before your very eyes.

There are similar formations elsewhere in the world – here’s a balanced rock in the High Desert just outside Moab in Utah, USA. The lower layer that’s been eroded away here is sandstone, not ash, but the process is very similar.