Form along both destructive and collision plate boundaries, in other words where two plates are pushing towards each other.
The best examples are the Himalayas, the Rockies, the Andes and the Alps, all of which are huge fold mountain ranges caused by the collision of two plates.
The general theory is that as two plates, with land masses on them, move towards each other they push layers of accumulated sediment in the sea between them up into folds. Thus most fold mountains will continue to grow, as the plates constantly move towards each other.
The Formation of Fold Mountains at Destructive Plate Boundaries:
- As already seen, at a destructive plate boundary the oceanic plate is subducted beneath the continental one. The molten material then rises to the surface to form volcanoes, either in an island arc (e.g. the West Indies) or on the continental land mass (e.g. the volcanoes of the Andes). In both cases Fold Mountains can be formed.
- When the Nazca plate dives under the South American one, their motion forward also has been pushing sediment together. This, over millions of years, has been pushed up into huge fold mountains: The Andes. Within them there are also volcanoes as the mountains are above the subduction zone.
- If an island arc has been formed, the same idea occurs. Over millions of years the movement of the two plates together will push the island arc nearer to the continent. As this occurs the sediments on the seabed are folded up to become huge mountains.
The Formation of Fold Mountains at Collision Margins:
- These occur less frequently, but two excellent examples are the Himalayas, where the Indian plate is moving North and East towards the stationary European plate, and the Alps, formed by the collision between the African and Eurasian plates.
- In these examples both plates are Continental ones, and so can neither sink nor be destroyed. The material between them is therefore forced upwards to form the mountains.
- For the Himalayas the material that now forms the mountains was originally on the bottom of the non-existent Tethy's Sea. As the Indian plate pushed towards the Eurasian one, the sediments were folded up to form the Himalayas, leaving the only trace of the sea to be the fossilised shells that you can find high up in the mountains.
Humans use Fold Mountains for a wide variety of purposes:
Farming is a primary activity in all of the fold mountain ranges around the world. Mainly, due to the height and steepness of many of the slopes, this is restricted to cattle and sheep farming. However in the foothills of the Himalayas the Nepalese people use terraces in the mountainside to help them grow crops, and some southern facing Alpine slopes are used for vines and fruits.
In the Alps a system called transhumance was used. This basically is the seasonal movement of grazing animals between the high ground in the warmer summer months and the valley floors in the colder autumn months. Nowadays transhumance is a little outdated as modern technology has meant that farmers can stay in one place all year.
Tourism is another major use of the Fold Mountains of the world. Because they are in more economically developed countries,the Alps and the Rockies are perhaps the best examples of the impact of tourism.However, it is an increasing industry in both the Andes and the Himalayas,as people look for less crowded places to go to.
- The main tourist attraction in the Rockies and the Alps is skiing. Hundreds of thousands of people ski each year and this has brought great changes and problems to the main areas.
- The increase in tourism has meant much-improved infrastructure, a huge increase in hotels and restaurants and the development of entire resorts. It has brought a large amount of much needed money into these areas and allowed local people to diversify from farming into many other jobs.
- Fold Mountains have a lot of other things to attract visitors. These include hill walking, the attractive scenery, river rafting, and climbing. All these have contributed to areas in the Alps and the Rockies becoming all year round holiday resorts.
Forestry is another big business in these mountainous regions. Examples of cultivated coniferous forests can be seen in the Alps, where the trees have been deliberately planted as crops. However in the foothills of the Himalayas large-scale deforestation is also taking place, with logging companies cutting down vast tracts of the deciduous rainforest there.
Many of the Fold Mountain regions of the world are prime spots for the generation of hydroelectric power (HEP). They have a plentiful supply of water; deep, narrow valleys with quick flowing rivers, and they are sparsely populated, meaning that few people are displaced when a reservoir is created.
The HEP is then used either for electricity in cities some distance away, or as a power source for local industries, such as saw and paper mills.
- Mountainous regions are particularly difficult to build in due to the steep sided valleys and cold climate. Roads and other communications links have to snake their way up wherever they can, and often these roads are not big enough to adequately service a large community.
- The climate is very cold and wet, meaning that most industrial and agricultural activity is difficult. For farmers they have a very short growing season, and it is difficult to use machinery on the steep slopes.
- Avalanches are a constant threat, as was seen to devastating effect in Ranrahirca, Peru, in 1962. Huge amounts of money are spent each year to try and combat the avalanche threat, especially with the large amount of tourists using the mountains.