Mountains

Notes

A mountain is a natural elevation of the Earth's surface with a narrow summit and steep slopes.

Types of mountains

Fold mountains: formed by compression of sediments in geosynclines (e.g., the Tethys). Young fold mountains: Himalayas, Alps, Rockies, Andes (Alpine orogeny, tens of millions of years old). Old fold mountains: Appalachians, Urals, Aravallis (the Aravallis are among the oldest fold mountains in the world; Guru Shikhar at Mount Abu is the highest peak).
Block (fault-block) mountains: formed when land is uplifted or dropped between faults (horst and graben): Vosges, Black Forest, Sierra Nevada, Rhine rift valley.
Volcanic mountains: built by eruptions: Mt Fuji, Kilimanjaro, Mt St Helens, Cotopaxi.
Residual (relict) mountains: left after erosion of a plateau or old range: Vindhyas, Satpuras, Nilgiris.
Dome mountains: uplifted by magma without erupting (Black Hills, USA).

Orogenic phases: Caledonian (about 400 million years ago), Hercynian (Variscan) (about 300 million years ago) and Alpine (from about 65 million years ago).

Facts

The Himalayas are the highest range; Mount Everest is about 8,849 m. K2 (Godwin Austen) is the second highest at 8,611 m, in the Karakoram. Kangchenjunga is the third highest.
The Andes are the longest continental range (about 7,000 km); the Mid-Oceanic Ridge is the longest overall.
Highest peaks by continent: Everest (Asia), Aconcagua (South America), Denali (North America), Kilimanjaro (Africa), Elbrus (Europe), Vinson Massif (Antarctica), Puncak Jaya (Oceania).
In peninsular India, Anai Mudi (Western Ghats, about 2,695 m) is the highest peak south of the Himalaya; Doddabetta (Nilgiris) is the highest in the Nilgiris.

Significance: climate barriers and rain-bearing, source of rivers, biodiversity, minerals, forests, hydropower, tourism; hazards include landslides, avalanches and earthquakes.

Key Points

Types: fold, block, volcanic, residual, dome.
Young fold mountains: Himalayas, Alps, Rockies, Andes; old: Aravallis, Appalachians, Urals.
Mt Fuji and Kilimanjaro: volcanic; Vindhyas and Satpuras: residual.
Andes: longest continental range; Everest: highest peak.
Anai Mudi: highest peak in peninsular India.

MCQs

Q1. The Aravalli Range is an example of:

(a) Young fold mountains
(b) Old fold mountains
(c) Volcanic mountains
(d) Block mountains
Ans: (b).

Q2. Mount Fuji is a:

(a) Fold mountain
(b) Volcanic mountain
(c) Block mountain
(d) Residual mountain
Ans: (b).

Q3. Which of the following is a young fold mountain system?

(a) Urals
(b) Appalachians
(c) Alps
(d) Aravallis
Ans: (c).