# How do fold mountains form?

I know mountains form due to the collision of tectonic plates. But how does such a slow collision have such great impact as to create huge mountains. Is there any intuitive explanation for this?

• Welcome to stackexchange! I edited the title to be a little more specific - as otherwise the question might have been closed as "too broad". – Semidiurnal Simon Oct 15 '19 at 19:59

Some mountains form from the collision of tectonic plates; volcanoes are different, and there are some other mechanisms too.

IANAgeologist, and perhaps one will be along to give a more technical explanation, but intuitively, it's about viscosity:

If you push an object very slowly into a bowl of water, nothing much happens - the water flows around the object.

If you push the object equally slowly into a tray of treacle, it's harder work, and you can form a "hill" in front of the object. The treacle flows too slowly to get out of the way.

At very high pressures, rock behaves a bit like the treacle[1] - only much more so. It takes a huge force to push one lump of rock into another, but because the rock flows very slowly, by pushing very slowly you can still create a mountain.

[1] I realise it's not exactly like treacle. If you're an expert here, feel free to post another answer getting it right :-)

The mountains may seem huge, but they are as nothing compared with the multi-trillion-ton mass of a tectonic plate moving at a few centimetres per year. The buckling of an adjacent continental plate is only one way in which mountains are created. Often a moving oceanic plate is deflected downward by the continental plate with which it collides. Driven down into the mantle, the leading edge of the oceanic plate melts, causing plumes of magma to make their way to the surface and form volcanoes along the edge of the continental plate above. The larger mountains of N.Wales and some of Scotland are the remains of ancient volcanoes.

Not all volcanoes are a result of plate tectonics (though most are), but they can all create mountains. A much rarer cause of mountain building is the impact of a very large meteorite or small asteroid, whichever you care to call it. Fortunately, this only happens every hundred million years or so. Such mountains can be found in Canada, South Africa, and no doubt other parts of the world, usually heavily eroded by the passage of time,