Earth & climate
Mountain building
Mountains grow when huge plates of the Earth's crust collide. How rock folds up and why the Alps and Himalaya are still rising today.
Mountains seem ancient and unmovable, but they were not always there. Long ago, where the Alps now rise, there were shallow seas. Mountains form when the is pushed together and folds up. This slow process is called mountain building.
Plates in motion
The outer shell of the Earth is not one piece but broken into large plates. Below them lies no liquid but hot, solid rock that flows over very long stretches of time like extremely thick honey. That is why the plates can travel on it, but only very slowly, a few centimetres per year. That is about as fast as your fingernails grow. Over millions of years this adds up to enormous distances.
Apart: new crust at the mid-ocean ridge
Divergent boundary: magma rises in the gap and solidifies into new seafloor.
When continents collide
When two plates carrying continents crash together, the rock runs out of space and is pushed together. Like a tablecloth that you push together from two sides, the rock folds up. Ranges that form this way are called fold mountains. This is how the Alps formed, when Africa pressed against Europe. The Himalaya is still growing today because India has been pushing against Asia for some 50 million years.
Mountains shrink again too
While plates push mountains up, wind, water and ice constantly wear them down again. So a mountain only keeps growing taller as long as it rises faster than it is worn away. The Alps are still lifting by about one millimetre per year, yet gnaws at them just as steadily. Very old mountain ranges are therefore often rounded and low.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
What causes fold mountains like the Alps to form?
Which mountain range forms because India pushes against Asia?
A plate moves about 2 cm per year. How many centimetres does it travel in 5 years?
Put the steps of mountain building into the correct order.
- 1Two plates slowly push towards each other
- 2The rock between them runs out of space
- 3Wind, water and ice slowly wear the mountains down again
- 4The rock folds up and rises
- 5A fold mountain range like the Alps forms
A mountain lifts by 5 mm per year. By how many millimetres does it rise in 8 years if nothing is worn away?
Match each mountain range or feature to the cause that fits it.