Fold mountains

The main types of mountains – the ups and downs of the Earth

Mountains have always played a central role in human culture, but it is only recently that we have understood how they form and develop. To this day, these magnificent reliefs still hold many secrets. There are several ways to analyze and classify mountains depending on your science discipline. Here we will describe in detail some of the most common classifications of mountains.

Aerial view of Mount Everest from the south. The Himalayas are folded mountains. Image credits: Drukair airline in Bhutan.

Types of mountains

Generally, mountains are classified as: folded mountains, boulder mountains, dome-shaped mountains, and volcanic mountains. Plateau Mountains, Raised Passive Margins, and Hot Spot Mountains are also sometimes considered.

  • Bend the mountains – the most common type, they are formed when two or more tectonic plates collide.
  • Block the mountains (or fault block) – formed by geological processes pushing some rocks up and others down.
  • Dome mountains – formed as a result of hot magma growing under the crust.
  • Volcanic mountains – also known by a simpler name: volcanoes.
  • Other types of mountains sometimes included in the classifications are plateau mountains, increased passive margins, and hot spot mountains.

Bend the mountains

The Rocky Mountains are a prime example of folded mountains. Image credits: National Park Service Digital Image Archive.

Folded mountains are the most common and massive types of mountains (on Earth, at least). Folded mountain ranges can stretch for thousands of miles – we’re talking the Himalayas, the Alps, the Rockies, the Andes – all great. They’re also relatively young (another reason they’re so big, because they haven’t been completely eroded), but it’s “young” in geological terms – still tens of millions of years old.

To understand how folded mountains form and develop, we have to think about plate tectonics. The Earth’s lithosphere is divided into rigid plates that move independently of each other. There are seven major tectonic plates and several smaller in the world.

When two plates collide, several things can happen. For example, if one plate is denser than the other (oceanic plates are usually denser due to the type of rocks it is made of), a process called subduction will begin: the heavier will slowly slide under the lighter. If they have relatively similar densities, then they will start to wrinkle, causing upward movement. Essentially, the tectonic plates are pushed, and since neither can slide under the other, they form geological folds. To get a better idea of ​​what this looks like, try pushing two pieces of paper towards each other: some parts will lift up, representing the process of forming the mountain.

Sometimes folding occurs within the continent and is associated with faults. This is a representation of this process in northern Montana, United States, and southern Alberta, Canada. Image credits: Greg Beaumont, National Park Service.

This process is called orogeny (giving birth to mountains) and it usually takes millions of years for it to complete. Many folded mountains today are still developing as the tectonic process unfolds. The process does not occur at tectonic edges – sometimes the mountain-generating folding process can take place well inside a tectonic plate.

Block mountains (or fault block)

While the previous category was entirely devoted to folds, this one is entirely devoted to faults: geological faults, that is to say.

Representation of the block fault process. Image credits: US Geological Survey.

Let’s go back to the previous idea for a moment. Let’s say that under pressure, parts of a tectonic plate begin to bend. As the pressure increases, the rock will simply shatter at some point. The faults are these breaks: they are the plane fractures or the discontinuities in the volumes of rock. Their size can vary enormously, from a few centimeters to the size of a mountain.

Basically, when large boulders of rock are shattered by faults, some of them can be pushed up or down, resulting in mountains of boulders. The upper blocks are called horsts and the hollows are called catch. Their size can also be impressive, although they are usually not as large as folded mountains, as the process that generates them takes place on a smaller scale and involves less pressure. Yet the Sierra Nevada Mountains (an example of a boulder mountain) feature a boulder 650 km long and 80 km wide. Another good example is the Rhine Valley and the Vosges Mountains in Europe. Rift valleys can also generate boulder mountains, as is the case in the East African Rift.

Mount Alice and Temple Crag in the Sierra Nevada. Image credits: Miguel.v

It can be quite difficult to identify a boulder mountain without knowing its underlying geology, but generally they tend to have a steep side and a slow sloping side.

Volcanic mountains

The annotated view includes the Ushkovsky, Tolbachik, Bezymianny, Zimina, and Udina stratovolcanoes of Kamchatka, Russia. Image taken on board the ISS in 2013.

Everyone knows something about volcanoes, although we rarely think of them as mountains (and frankly, they’re not always mountains).

Volcanic mountains are created when magma deep below the surface begins to rise. At one point, it erupts as lava and then cools, solidifies, and piles up to create a mountain. Mount Fuji in Japan and Mount Rainier are classic examples of volcanic mountains, with Mount Rainier one of the most dangerous volcanoes in the world. However, the volcano does not have to be active to be a volcanic mountain.

The summit of Mauna Kea. Image credits: Pixabay.

Several types of volcanoes can generate mountains, with stratovolcanoes generally creating the largest. Despite the fact that Mount Everest is the highest mountain above sea level, Mauna Kea is actually much higher than Everest at a total height of over 10,000 meters. However, much of it is submerged, with only 4,205 meters of elevation above sea level.

Dome mountains

The Dome Mountains are also the result of magmatic activity, although they are not volcanic in nature.

Southeast face of Fairview Dome in Yosemite National Park. Image credits: Jennie.

Sometimes a lot of magma can collect under the ground and start to swell the surface. Sometimes this magma will not reach the surface but will still form a dome. As this magma cools and solidifies, it is often harder than other surrounding rocks and will eventually be exposed after millions of years of erosion. The mountain is that dome – an ancient buildup of magma that has cooled and been exposed by erosion.

Round Mountain is a relatively new dome-shaped mountain. It represents a volcanic feature of the volcanic province of the Canadian Northern Cordillera that has formed over the past 1.6 million years. Black Dome Mountain is another popular example, which is also located in Canada.

Other types of mountains

As we mentioned above, there is no strict definition of mountain classifications, so other types are sometimes mentioned.

Plateau mountains

The mountains of the plateau are not formed by something going up – they are formed by something going down. For example, imagine a board with a river on it. Year after year, this river gradually carves part of the plateau. After a while, there may only be a small part of the original uneroded plateau, which essentially becomes a mountain. It usually takes a long time, even by geological standards, up to billions of years. Some geologists group these mountains with dome-shaped mountains into a larger category called erosion mountains.

Passive margins increased

There is no geological model to fully explain how high passive margins formed, but we see them in the world. The Scandinavian mountains, eastern Greenland, the Brazilian highlands or the Australian Great Dividing Range are such examples, due to their existence at an elevation mechanism.

Hotspot mountains

The underwater mountain trail created when the tectonic plate moved through the Hawaii hotspot for millions of years. Image credits: USGS.

Although they were once thought to be identical to volcanic mountains, new research has shed light on this belief. Hot spots are volcanic regions believed to be fed by a portion of the underlying mantle that is significantly warmer than its surroundings. However, even though this hot area is fixed, the plates move around it causing it to leave a trail of mountains.

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