Folding and faulting: fold mountains, block mountains and rift valleys

Detail

1. Where folding and faulting fit

• Endogenic forces are forces from inside the Earth. They build up the land. Exogenic forces (weathering, erosion) work on the surface and wear it down.
• Diastrophism means all the processes that move, lift or build up parts of the Earth's crust. Folding and faulting are its two main forms.
• Slow movements (folding, faulting) work over millions of years. Sudden movements (earthquakes, volcanoes) happen in moments.
• The heat inside the Earth moves the plates (large, rigid pieces of the crust and upper mantle). This movement squeezes some rocks and pulls others apart.

2. Folding — how fold mountains form

• Folding happens when rocks are squeezed from the sides. This sideways push is called horizontal compression.

• Two plates push towards each other → soft, layered rocks (often seabed sediments) are squeezed → the layers bend instead of breaking.

• Anticline: an upfold, where the layers arch upward like an "A".

• Syncline: a downfold, where the layers sag down like a "U".
• Carpet analogy: push a carpet against a wall and it rises into ridges and troughs. Rock layers fold the same way when plates collide.
• Fold mountains: strong folding along narrow belts piles the layers up into long, high ranges.
• India: the Himalayas formed when the Indian Plate pushed into the Eurasian Plate.

• World: the Alps (Europe), the Andes (South America) and the Rockies (North America) are other young fold mountains.

• Anticlines and petroleum: oil and natural gas are lighter than water, so they move upward through porous rock. They collect at the crest (top) of an anticline, under a layer of rock they cannot pass through (an impermeable cap rock). This makes anticlines key targets when searching for oil.

3. Faulting — how rocks break

• A fault is a crack in the crust along which blocks of rock have moved.
• Faulting happens when rocks are too brittle to bend. It has two causes:
• Tension (pulling apart) → the crust stretches → it cracks → some blocks drop down.

• Compression (squeezing) → the crust breaks → one block is pushed up over another.

• A normal fault (dip-slip fault) forms under tension. The rock above the crack slides downward compared with the rock below it [4].

4. Block mountain (horst)

• Block mountain / horst: a block of crust that stands high between two faults. It forms in one of two ways:
• the block is pushed up between two faults, or

• the block stays in place while the land on both sides sinks.

• Shape: flat top and steep sides, because the sides are fault planes.

• A horst is a raised block bounded by faults. It usually sits beside a sunken rift valley (graben) [5].
• World: the Vosges (France) are a typical horst [5]. The Black Forest (Germany) is its partner block east of the Rhine. It runs about 160 km north-east from Säckingen to Durlach [6].
• India: NCERT cites the Satpura range as a block mountain.

5. Rift valley (graben)

• Rift valley / graben: a long, narrow strip of crust that sinks between two parallel faults.

• Tension pulls the crust apart → two parallel normal faults form → the middle strip drops → a long trough with steep walls.

• Graben is German for "ditch". The word usually means a smaller rift valley [7].

• A rift valley is a long trough formed when a piece of crust sinks between normal faults [4].

Feature	Force	How it moves	Shape	World example	Indian example
Fold mountain	Compression	Layers bend (anticlines and synclines)	Long ridges and valleys	Alps, Andes, Rockies	Himalayas
Block mountain (horst)	Tension or compression	Block rises, or land around it sinks	Flat top, steep sides	Vosges, Black Forest	Satpura
Rift valley (graben)	Tension	Strip sinks between parallel faults	Long, narrow trough, steep walls	Rhine, East African Rift, Dead Sea	Narmada, Tapi, Damodar

6. World rift valleys

• Rhine Rift Valley (Europe)
• The Vosges and the Black Forest were once one block of land.
• A central strip sank and split them. This formed the Rhine Rift Valley, about 300 km long [6].

• Order from west to east: Vosges (France) → Rhine graben → Black Forest (Germany).

• East African Rift System

• These are the largest continental rift valleys. They run north to the Red Sea and east into the Indian Ocean [4].

• Dead Sea and Jordan Valley (West Asia)

• The Dead Sea rift is the land part of the Syrian–African Rift System. This rift runs along a plate boundary from the Indian Ocean through the Red Sea and the Gulf of Eilat (Aqaba) [8].
• The Jordan Valley is part of this system. It follows the Jordan River from the Sea of Galilee to the Dead Sea and is about 10 km wide [9].
• The Dead Sea is a rift lake. Its surface is about 429 m below sea level, the lowest land on Earth [7].

7. Indian rift valleys and block mountains

• Narmada–Son trough: a long trough in central India between the Vindhya and Satpura ranges [10]. Geologists call this line of weakness the Narmada–Son Lineament (a lineament is a long, straight line of weakness in the crust) [2].
• Narmada River
• Origin: Narmada Kund at Amarkantak, Madhya Pradesh, in the Maikala Range, about 1,080 m high [11].
• Length: about 1,312 km. It has 41 tributaries [11].
• Course: it flows west through Madhya Pradesh, Maharashtra and Gujarat. After Mandla it enters the valley between the Vindhyas and the Satpuras [11][12]. It passes the Marble Rocks gorge near Jabalpur and the Dhuandhar Falls. It flows over Deccan Trap rocks (layers of old lava) [13].
• Mouth: the Gulf of Khambhat (Cambay), Arabian Sea, through an estuary about 21 km wide, just below Bharuch [12].
• Rank: the largest west-flowing river in India and the fifth largest river in India [13].
• Basin: 98,796 sq km. Madhya Pradesh has 86.9%, Gujarat 11.6% and Maharashtra 1.5% [13].

• Location: latitude 21°20′–23°45′ N, longitude 72°32′–81°45′ E [13].

• Tapi (Tapti) River

• It rises near Multai, Betul district (Madhya Pradesh). It flows west, south of the Satpuras and parallel to the Narmada, also through a rift, and reaches the Gulf of Khambhat near Surat.
• Basin location: latitude 20°05′–22°03′ N, longitude 72°38′–78°17′ E [14].
• Main tributaries: Purna, Girna, Panjhra, Bori, Vaghur, Aner, among others [14].

• Main projects: Ukai Dam and Kakrapar Weir (Gujarat), Hatnur Dam and Girna Dam (Maharashtra) [14].

• Why the Narmada and Tapi form estuaries, not deltas

• They flow in straight, fault-bounded troughs, with hard rock on both sides → so they meander very little.
• They flow fast down a narrow trough and carry little silt → so little sediment is dropped at the mouth.
• Strong tides in the Gulf of Khambhat wash the silt away → an estuary forms (a funnel-shaped river mouth where fresh water mixes with sea water), not a large delta.

• Compare: the east-flowing rivers (Mahanadi, Godavari, Krishna, Kaveri) cross wide plains and build large deltas on the Bay of Bengal.

• Damodar valley and Gondwana coal

• The Damodar River flows east through Jharkhand and West Bengal and joins the Hooghly. It follows a rift.
• The Damodar and Koel valley basins run east–west along a tectonic trend. They contain Gondwana rocks [3].
• Gondwana coal formed about 250 million years ago. Forests that grew in these sinking troughs were buried and pressed into coal. Main coalfields: Jharia, Raniganj, Bokaro, Giridih, Karanpura.
• The Mahanadi, Godavari and Son valleys also hold Gondwana coal in similar troughs.

8. The Narmada–Son Lineament today

• The Narmada–Son Lineament (NSL) is a failed rift: the crust began to pull apart here long ago but never split fully into an ocean [2][3].
• It was a zone of tension in the past. Today India keeps pushing into Asia, so the zone is being squeezed again (compression) [2].
• It is a weak zone in the crust. Earthquakes happen along it, for example the Jabalpur earthquake (1997).

9. Map practice

• Mark the Narmada rift from Amarkantak (east) to the Gulf of Khambhat (west), with the Vindhyas to the north and the Satpuras to the south.
• Mark the Tapi rift south of the Satpuras, from Multai to Surat.
• Mark the Satpura range: it runs west to east across Maharashtra and Madhya Pradesh, joins the Maikala Range and ends near Amarkantak. Its highest peak is Dhupgarh (about 1,350 m, Pachmarhi).
• Mark the Damodar valley (Jharkhand–West Bengal) with Jharia and Raniganj coalfields.
• Link to: Peninsular drainage (west-flowing compared with east-flowing rivers) and physiography (Central Highlands compared with the Deccan Plateau).

Prelims Hooks

• Anticline = upfold; syncline = downfold. Oil and gas collect at the crest of anticlines.
• Horst = raised block (block mountain); graben = sunken block (rift valley). Both are bounded by faults.
• A rift valley forms by tension along normal faults, not by compression [4].
• Order from west to east: Vosges → Rhine rift valley → Black Forest. The Rhine rift is about 300 km long [6].
• Order from north to south: Vindhyas → Narmada rift → Satpuras → Tapi rift.
• The Narmada rises at Amarkantak (Maikala Range, MP) and reaches the sea through a 21 km-wide estuary below Bharuch in the Gulf of Khambhat [11][12].
• The Narmada is the largest west-flowing river of India. About 87% of its basin lies in Madhya Pradesh [13].
• Trap: the Narmada and Tapi form estuaries, not deltas. The Mahanadi, Godavari, Krishna and Kaveri form deltas.
• The Dead Sea, about 429 m below sea level, is a rift lake and the lowest land point on Earth [7].
• Damodar valley = rift (graben) containing Gondwana coal (Jharia, Raniganj).

Mains Points

• Tectonics shapes India's drainage: the Narmada and Tapi follow fault troughs, so they flow west against the general eastward slope of the Peninsula. They have straight channels with few meanders and end in estuaries. This affects ports (Bharuch, Surat), tidal flooding risk and the sites of dams such as Sardar Sarovar and Ukai.
• Tectonics decides where resources lie (GS-III): anticlines trap petroleum (for example, the Assam and Mumbai High oilfields lie in folded or arched rocks). Gondwana grabens (Damodar, Son, Mahanadi, Godavari) hold almost all of India's coal. This explains why the coal and steel industry clusters in the Chota Nagpur region.
• Hazard angle (GS-III): fold mountains such as the Himalayas are young and still rising. They face earthquakes and landslides. The Narmada–Son Lineament is a failed rift that is now being squeezed again [2]. It shows that "stable" Peninsular India also has earthquake risk (Jabalpur 1997). Seismic zoning and building codes must allow for this.
• World comparison: active rifts such as the East African Rift and the Dead Sea–Jordan rift are plate boundaries still pulling apart [4][8]. India's Narmada–Damodar rifts are old, failed rifts [3]. This shows the full life cycle of rifting: rift valley → (if it continues) a new ocean, as in the Red Sea.