Mountains-
The Penguin Dictionary of Geography defines a mountain as any natural elevation on earth’s surface with a summit small in proportion to its base, rising more or less abruptly from the surrounding level.
Based on their mode of formation, mountains can be classified into four main types-
- Fold Mountain
- Block Mountain
- Volcanic Mountain
- Residual Mountain
Fold Mountains-
Fold mountains are the result of folding of the Earth’s crustal rocks by compressive forces. They are considered as the “true mountains” and the term Orogenesis or mountain building is commonly used for Fold mountains.
Types of Fold Mountains-
On the basis of Nature of Fold-
- Simple folded mountains – folds are arranged in waves like pattern with a well-developed system of anticline and synclines.
- Complex folded mountains – folds are complex in nature due to extreme compressional forces like overfold, recumbent fold and nappe.
On the basis of the Period of Origin-
- Old fold mountains – Those mountains which originated before the Tertiary period. These mountains have been so greatly denuded (or eroded) that they have become residual fold mountains. For example, Aravalis, Appalachians etc.
- Young or New fold mountains – These are the fold mountains of the Tertiary period. They are further subdivided based on their location –
- Andean type of fold mountains – At the ocean – continental convergent boundaries (C-O). They are prone to both earthquakes and volcanic activities. Example – the Rockies, Andes.
- Himalayan type of fold mountains – At the continental – continental convergent boundaries (C-C). There is an absence of active volcanism here. Example – Great Himalayas.
Characteristics of Fold Mountains –
Rock Type – Formed due to the folding of sedimentary rocks by strong compressive forces. Furthermore, these rocks are of marine origin i.e. formed due to deposition and consolidation of sediments in water bodies.
Shallow water deposits – The marine fossils found in the sedimentary rocks belong to such organisms which can survive only in shallow waters.
Size – They are the loftiest, most extensive and elongated mountain chains on the Earth s surface. Their length is far greater than their width. For example, the Himalayas have an east-west length of 2400 km but their maximum width is only 400 km.
Volcanicity – They may or may not have active volcanism but volcanic rocks of ancient times may be found there. For example, Himalayas don t have active volcanism but volcanic rocks are found in Pir Panjal, Dalhauji (Himachal Pradesh) and Bhimtal (Kumaun).
Earthquake – Generally the region is prone to earthquakes due to the presence of active plate boundaries.
They are one of the youngest mountains of the world. Generally found in an arc shape with one side having a concave slope and the other having convex slope.
Where are the Fold Mountains Located?
- Preliminary analysis of the above world map shows that
- They aren’t located randomly on the Earth s surface.
- Young fold mountains are generally located on the margins of the continents.
- They are present mostly in the northern and western direction of the continents, like the Atlas in Africa, the Rockies and the Andes in North and south America.
- If we consider the former Tethys sea, then the Himalayas were also once located along the margins of the continent.
- They mark some of the major plate boundaries.
- Old fold mountains are present inside the current continents. They represent the ancient plate boundaries and orogenic movements of those times.
Fold Mountains of India –
Himalayan mountains – Young fold mountains, formed during the Tertiary period.
Aravali Range – Oldest fold mountain of India, formed during the Archean period (2500 million years ago). Erosion over time has reduced their size.
Vindhyan Range – formed during a Proterozoic period (500 million years ago), erosion over time has left them.
Satpura Mountains – meaning “seven folds”, they are the fold mountains of the Precambrian era and are highly deluded.
Eastern Ghat – they were once fold mountains but have been eroded by the east-flowing peninsular rivers.
Some fold mountains of world are –
- The Himalayas
- The Atlas mountain
- The Andes
- The Alps
- The Rockies
- The Appalachian Mountains
- The Jura Mountains
- The Zagros
- The Hindukush
- The Cascade Range
-Shikhar Swami