How mountains form

I love being in the mountains! Just think. They’ve been standing since the beginning of time, never changing... Well actually, mountains haven’t been here forever. They formed over time, and some are still growing today!

They did? They are?! But… how? Before we talk more about mountains themselves, we need to take a closer look at how planet earth is made up. It has four main layers.

At the centre is the inner core. Outside that is the outer core. Around this lies the mantle, made of molten rock called magma. The outer layer of the earth is the crust. The crust is made of different sections, called tectonic plates.

These gigantic plates float on top of the magma, moving slowly. When two plates move closer together, converge, they fold, like two rugs being pushed together. The crust crumples upwards, until eventually, over millions of years, a mountain forms! We call a mountain that forms this way a fold mountain. Because fold mountains form along plate boundaries, they sometimes stretch for thousands of kilometers, creating mountain ranges.

The Indian plate, for example, was pushed into the Eurasian plate causing the Himalayan Mountains to rise up. The Himalayas started to form around 50 million years ago — after dinosaurs were extinct, but before the first human-like life forms. Look at the Himalayas’ steep slopes and pointed peaks. They have this jagged shape because they are being continuously pushed up. These peaks grow up to one centimetre per year!

Another type of mountain can form at the boundary between two plates… or, wherever there is a line of weakness across the crust, called a fault line. Along fault lines, the crust cracks, breaking into a block which is pushed upwards. A fault block mountain forms. Often, these mountains have a steep front side and a sloping back side, like here: the Harz Mountains in Germany. They formed hundreds of millions of years ago when land animals and large primitive trees first appeared.

Other mountains form from the magma beneath the earth’s crust. The magma erupts and piles up on the earth’s surface. When magma has broken through the crust, it is called lava. As the lava cools, it builds a cone of rock. Rock and lava keep piling up, layer on top of layer, and a volcano mountain forms.

Volcano mountains can form in the middle of a plate, like Mount Kilimanjaro, in Tanzania. or at a plate boundary… Sometimes, the magma doesn’t break through the earth’s surface, but builds up just below. It forces the rock above to bulge upward, forming a dome mountain. Like here: Mount Starr King in the United States. You might guess how this mountain formed from its arched shape.

Mountain formation, like many geological processes, is extremely slow. But if we could speed up time, we would see tectonic plates breaking apart and moving together, the earth’s layers crumpling and bubbling up, mountains forming. One day, long, long into the future, humans… or some other life form… will have new slopes to play in!