Fold mountains

How are mountains formed?

Mountains are landforms that rise above the surrounding terrain, usually thousands of feet high. Some mountains stand on their own; others are part of long chains called mountain ranges. Mountains are formed in one of three ways:

  • Volcanic explosions
  • Tectonic faults that occur when tectonic plates slide over each other
  • Tectonic collisions

The height of a mountain depends, in part, on its origin. Mountains that start under the sea are higher, from top to bottom, than those that start on land. Another important factor is the age of the mountain. Older mountains have had more time to erode, making them smaller (in general) than newer mountains.

Why do tectonic plates move?

There are between 15 and 20 tectonic plates on Earth, under the sea or on land, which fit together like puzzle pieces. Beneath the tectonic plates, which make up the Earth’s lithosphere (the two outer layers), lies a sea of ​​molten rock. Tectonic plates float on molten rock and, due to the heat of radioactive processes, move closer and further away from each other. While the plates move incredibly slowly, this movement has caused vast changes to the Earth’s surface. The continent, oceans, seas and mountains that we know today all exist because of the movement of tectonic plates.

The science behind mountain formations

All mountains are formed by the movement of tectonic plates, which lie beneath the earth’s crust and the upper mantle (the layer just below the crust). When tectonic plates separate or come together, the impact can be explosive. Below are three tectonic plate movements that create geological changes.

Divergent tectonic plates

When the boundaries between two tectonic plates move apart, the result is described as a divergent boundary. Molten rock (magma) rises from between the plates. As it cools, the magma creates a new oceanic crust. In the process, however, the magma can explode upward in the form of a volcano. In fact, the most volcanic parts of the planet – the Mid-Atlantic Ridge and the Pacific Ring of Fire – are the result of divergent tectonic plates.

Colliding tectonic plates

When two plates collide, the result is called the converging border. The incredible force of the collision can cause parts of the tectonic plates to move upward to form mountain ranges. Earthquakes are often the result of the collision of two tectonic plates. Alternatively, a plate can move downward to form an oceanic trench. When this happens, magma rises across the ocean floor and solidifies, forming granite.

Tectonic plates sliding above and below each other

When two tectonic plates slide over each other, earthquakes occur. The San Andreas fault is a major example of a point where this is happening. Earthquakes do occur in these places, but because the magma beneath the Earth’s surface is undisturbed, no new crust is created or destroyed. This is called a transformed plate boundary.

Types of mountain formations

Volcanic mountains, faults and folds all occur as a result of the movement of tectonic plates. The process can be rapid, as in the case of an exploding volcano, or it can take millions of years. Erosion Mountains are actually folded mountains that are so old that they have been eroded from huge peaks to become much smaller, gentler mountains like those found in the New Catskills. York.

Volcanic mountains


People walking on cooled lava; Mauna Loa volcano in the background.

Sami Sarkis / Getty Images


Volcanoes form when molten rock collects in an underground chamber. As the pressure increases, the magma is pushed upwards. It can escape as a slow lava flow or as an explosive event. In either case, the magma hardens into volcanic rock, creating new earth.

Volcanic events occur at the bottom of the sea and on land. When they occur in the sea, the volcano can become a mountain which, over time, appears on the surface like an island. In some cases, islands form almost instantly as a result of an underwater volcanic eruption.

Mauna Loa is an active volcano on the island of Hawaii that rises 13,100 feet above sea level. For context, Mount Everest rises to 29,032 feet. Yet Mauna Loa is actually a higher mountain than Everest because its base is far below the sea where volcanic activity still takes place. Mauna Loa is also still an active volcano – the largest in the world – and it continues to grow. From base to summit, Mauna Loa rises to 55,700 feet, while its neighboring sister, Mauna Kea, rises even higher.

Rift Mountains

Photograph by Gene Wahrlich / Getty Images


Faults are places where two tectonic plates slide one above and below the other. Earthquakes occur and new landforms, called fault block mountains, emerge.

The Sierra Nevada Mountains, as well as the Grand Tetons, are examples of Block Fault Mountains. Mountains of fault blocks form when tectonic plates slide above and below each other. Blocks of rock are lifted and tilted during fault events, while other areas are tilted down. The raised blocks become mountains; mountain erosion fills the depressions below.

Bend the mountains

Kriangkrai Thitimakorn / Getty Images


Two vast tectonic plates collide, very slowly. As they squeeze in, their boundaries move upward and begin to fold up. This process continues for millennia until the folds become vast mountain ranges like the Himalayas, Andes and Alps. While some folded mountain ranges are huge, others, like the Appalachians, are so ancient that they have eroded into softer hills. At one point in the planet’s history, however, the Appalachians were even higher than the Himalayas.

There are more folded mountains than any other type of mountain, and there are many different types of folds. Synclines and anticlines are the ascending and descending folds resulting from compression. Domes are folds in the shape of hemispheres, while basins are hollows on the surface of the Earth. Most mountains have several types of folds.


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