How Are Mountains Formed?

Mountains are formed by movement within the Earth’s crust.
  • There are three main catagories of mountains: Volcanic, Fold and Bock
  • Mountains are formed along fissures, cracks, or tectonic plate edges, where movement in the earth's crust causes pressure or friction
  • Some of the most famous mountains on earth are, Mount Everest, the Andes mountains, the volcanic islands of Hawaii and Fiji, and the cliffs of the Great Rift Valley

Mountains are formed by movement within the Earth’s crust. The crust itself is made up of several large plates, called tectonic plates, which are free floating. These huge chunks of the Earth’s crust move within molten rock called magma, which allows them to shift and collide over time. Even though humans live on the crust, they do not often feel these movements as they are very slow, and the sheer size of each plate is so large. Nevertheless, these shifts still have great impacts on human life as the movement of plates is what creates changes in the geographical structure of the surface of the earth. In this way, mountains are created over time. When these plates collide, there is a great deal of mass and pressure which suddenly comes to a stop, and it is this movement that forces the Earth into buckles or protrusions which are known as mountains. Depending on how these plates move or collide, one of three types of mountains can be formed. The three types of mountains or mountain ranges are: volcanic, fold, and block mountains, each of which is formed in a different way.

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Formation Of Volcanic Mountains

Volcanic mountains are formed in areas where there is volcanic activity. This means that there is a place in the Earth’s crust where there is a crack or volcanic vent. Magma, or molten rock, is lighter in weight than the solid rock around it. Because of this, it tends to rise to the surface. Similarly, pressure and heat can build up underground, and force an eruption of lava out of the volcanic areas. This magma bursts out of the ground and creates lava flows, which cool and harden in the open air. Similarly, ash and magma can be ejected high into the air, where they cool and fall to the earth as debris. Both lava flows and debris build up around the volcano’s opening, creating volcanic mountains. In many cases of larger mountains, this process has happened over centuries, with multiple eruptions, slowly building the mountain higher and higher. These two different ways in which volcanoes form mountains are described as cones, or shield mountains.

Cinder Cones

A cinder cone volcano. Image credit: VectorMine/Shutterstock.com

Cinder cone mountains are volcanic mountains that build up when debris is ejected out of a volcanic vent and then rains down to the surface. The nature of the buildup of molten rock and ash also means these mountains are usually more jagged or rough in texture.

Cinder cones exist across the globe, in areas of volcanic activity and plate fissures. They include: Kula and Karapina cones in Turkey, the Taal mountain the Philippines, Hverfjall of Iceland, Paricutin and Pinacate in Mexico, the Luera, Fox and Elephant mountains in Australia, Manda-Inakir, which is found on the Ethiopia/Djibouti border and a number of smaller cones across the North American west coast, in British Columbia, Oregon and California. Nicaragua is home to the most active cinder cone volcano, called Cerro Negro.

Shield Mountains

Shield volcano formation. Image credit: VectorMine/Shutterstock.com

The other type of volcanic mountain is known as a shield mountain. Shield volcanoes are made from stratovolcanoes or composite volcanoes. In these cases, mountains are slowly built up over time. Like all volcanic mountains, these are also produced when magma escapes to the Earth’s surface from vents or cracks, but this is usually a slower process, in that rather than violently expelling magma, these volcanoes produce oozing lava flows. The flows of liquid rock ooze out of the cracks in viscous rivers of lava, and then solidify and cool on the surface. Sometimes these are fast moving flows, and sometimes they move slowly, but in either case they build layers of rock over time. A number of famous mountains on earth were created in this way. Volcanic mountains can be found all over the world, and many island chains are actually volcanic rock, such as much of Hawaii. Mauna Kea is a well-known shield rock in the area, which incidentally is surrounded by almost 100 cinder cones.

Examples of shield mountains can also be found in many different countries, including: Santorini, in Greece, Pantelleria in Italy, Fukue-jima of Japan, in a wide variety of cities across Kamchatka, Upolu in Samoa, and Socorro, and San martin in Mexico.

Formation Of Fold Mountains

Like all mountains, fold type mountains are created in areas where tectonic plates meet. These areas are known as convergent plate boundaries. Because these are areas where two plates come together, there is often a great deal of friction or pressure that builds up along the plate edges as they shift and move against one another. Fold mountains are created when the plates push up against one another in such a way that the Earth’s crust bends, folds or warps. This process can create large, rippling mountain ranges, or sharp mountains, but usually occurs over thousands or even millions of years. Plates will continue to push up against one another, and the earth will begin to slowly bend and become misshapen as the pressure is maintained.

Fold mountains are the most commonly found mountains on earth, and include some of the most famous mountain ranges. The longest mountain range in the world, the Andes Mountains of South America, are fold mountains, created where the Nazca plate and South American plate meet. Similarly, the impressive Himalayan Mountains are forming where the Indian plate hits the Eurasian plate, and the Alps exist for much the same reason in Europe. Even the Appalachian Mountains are fold mountains, once taller than any other range on earth, which have been worn down and eroded with time. Fold mountains can be categorized further, based on their shape and fold types, even though most fold mountains have a variety of folds within their range. Mountain folds can be concave or convex meaning they either dip inward, or bulge outward, respectively. Similarly, fold mountains can have anticlines or synclines, both types of up-and-down ripples in compressed rock. Anticlines dome upwards, with the middle of the ripple being the highest point, and also the area where the oldest rock is located. Conversely, syncline folds create more of a u shape, and have the youngest rock at their center. These formations are very similar to domes and basins, which look and act in much the same way in a fold mountain range. If the layers of rock all incline in the same direction, it is known as a monocline, meaning it does not dip or dome, but progresses in incline from one point upwards.

Other types of patterns in fold rocks include chevron shapes, which describe a zig-zagging edge of sharp, straight folds; slump folds, where folds collapse in on themselves due to soft –usually sedimentary – rock types; ptygmatic where dikes are formed due to viscous material; or disharmonic where a variety of rock formation types are present.

Formation Of Block Mountains

Illustration showing block mountain formation.

Block mountains, also exist in places of faults or along edges of tectonic plates. Unlike fold mountains, that buckle and ripple under pressure, block mountains break into large chunks, or blocks, as cracks in the crust are created from fault lines up to the surface. The extreme pressure caused by tectonic plates pushing against each other, or the gap as they move apart, forces one block of earth upward, and the other down. This type of movement often results in geological formations known as rift valleys, where one area, near a fault, drops down, creating large valleys with steep cliff walls on either side. The greatest example of this phenomenon is the Great Rift Valley which runs from Lebanon all the way to Mozambique.

Due to the way in which block mountains are formed, they tend to have a characteristically block-like shape and appearance. These large chunks of earth rise up out of the ground, in solid, relatively straight-edged pieces. These can be further categorized into one of two main types of fold rocks: tilted and lifted.

Lifted

Lifted block mountains are the type that have mainly been described above. These mountains are created when blocks of the Earth’s crust are forced upward, in a relatively straight motion. This means that the resulting shape is generally flat on top, or tabular, with straight, sharp sides. These sides show clearly the faults or cracks along which the earth broke. These mountains can also be known as horst mountains.

Tilted

The other main type of block mountain is called a tilted mountain, and is made in a similar way with one major difference. While the earth still cracks and splits along a fault due to compression, a tilted rock, as the name suggests, appears to have a tilted angle to it. This is caused by an imbalance in the cracks on either side of the block. Usually, one side, the steeper one, indicates the fault, while the other side is a much more gentle slope. When a crack occurs only on one side of a large chunk of land, that side will jut up, while the other remains, forcing a tilted sloping top. There are a number of well-known block mountains on Earth. The Sierra Nevada mountain in California, USA is known as Earth’s most extensive block mountain. Some other examples include: the Vosges and Black Forest mountains along the Rhine Rift in Europe, the Salt Range of Pakistan, and areas of the Steen Mountain District of Oregon.

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