What you Need
What to do
Melt about 100g of lard, by placing it in a cup and putting the cup in a bowl of hot water.
Fill a large, ideally flat and transparent, container with water.
Pour the lard over the surface to form a 2-3mm thick plate on the surface.
Wait until it congeals and then cut it into two plates with a pair of scissors.
Push the two plates together and make them crumple up to make lard mountains (they may need a little assistance).
Look at the mountains you have made, above and below the water.
What may happen
When the two plates collide they fold (possibly with a little help) to form mountains.
Why does it happen?
Lard is slightly less dense than water so it floats on the surface, but only just. This means that when you crush the two plates together they shorten. Because lard is only slightly less dense than water it sinks so that most of the mountains that are formed are under water.
Real mountains are made in a similar way. The hard surface we walk on is called the crust and is sitting on the upper mantle. There are two main types of crust. The oceanic crust which is thinner and about as dense as the mantle, sits under the oceans. Tthe continental crust is slightly less dense than the mantle. So this floats on the upper mantle.
The density difference is small so where mountains are formed they have much deeper roots than their height.
A related effect explains why Scotland is slowly rising at a few mm a year and England is sinking