Deccan Plateau

Geography glossary

Topic: Structure and Physiography of India: Himalayas, Plains, Peninsula, Coasts and Islands · NCERT: Class 6, Ch 3 "Landforms and Life"; Class 7, Ch 1 "Geographical Diversity of India"; Class 7, Ch 3 "Climates of India"; Class 11, Ch 2 "Structure and Physiography"

Meaning

The Deccan Plateau is a large, roughly triangular tableland (high, mostly flat land) that forms the southern part of the Peninsular Plateau. It is bounded by the Western Ghats on the west, the Eastern Ghats on the east, and the Satpura, Maikal and Mahadeo hills on the north.

It matters because its shape and rocks control a lot of Peninsular India:

Its slope decides which way the big rivers flow.
The Western Ghats on its edge decide how much rain it gets.
Its lava rock gives the black cotton soil of Maharashtra and nearby states.

Explanation

Structure and boundaries

Old, hard rock base: the Deccan is made of the rocks of the Peninsular Block. This is an old, hard and stable part of the Earth's crust.
Shape: it is a rough triangle. It is wide in the north and narrows to a point in the south.
West edge (Western Ghats): a steep escarpment (a cliff-like slope). It rises about 1,000 m or more above the coast [2].
The Western Ghats are a continuous wall. Their average height is about 1,500 m, and they get higher from north to south.
East edge (Eastern Ghats): low, broken hills. Large rivers have worn them down and cut them into separate blocks.
North edge (Satpura–Maikal–Mahadeo line):
Satpura range: runs east–west, mostly in Madhya Pradesh and Maharashtra.
Mahadeo hills: part of the Satpura system. Pachmarhi (Madhya Pradesh) lies here.
Maikal range: the eastern end of the line. The Narmada and the Son rise at its Amarkantak plateau.
Southern meeting point: the Western and Eastern Ghats meet at the Nilgiri hills, which close the southern tip of the plateau.

Deccan Trap and black soil (cause → process → result)

Cause: volcanic eruptions about 66 million years ago, near the end of the Cretaceous period.
Lava poured out of long cracks in the crust. These were fissure eruptions, not cone-shaped volcanoes.
The lava cooled into thick layers of basalt (a dark volcanic rock).
Process: the Deccan Trap was built up.
The lava flows are more than 1,200 m thick and cover about 5,00,000 sq km [2].
Together they form a large igneous province (a very large area built up by volcanic eruptions) in west-central India [2].
The name "trap" comes from a Swedish word for "stairs". Each lava flow cooled into a flat sheet, so the hillsides look like steps.
The trap covers much of the north-western Deccan, not the whole plateau.
Result: the basalt slowly turns into black soil.
Basalt is rich in iron, lime and magnesium.
Weathering (sun, rain and temperature changes breaking rock into small pieces) slowly turns it into black soil. This soil is also called regur or black cotton soil.
Black soil is rich in clay and holds moisture well. It cracks deeply in the dry season and is good for growing cotton.

Slope, drainage and rain shadow

Eastward tilt: the plateau is highest along the Western Ghats and slopes gently down towards the Bay of Bengal.
The watershed (the line of high ground that divides rivers flowing to different seas) lies close to the west coast.
Because of this, the big rivers rise in the Western Ghats and flow east across the whole plateau to the Bay of Bengal. These are the Godavari, Krishna and Kaveri.
Short, fast streams run west down the steep Ghat face to the Arabian Sea. They form waterfalls in the monsoon.
Exception: the Narmada and the Tapi flow west to the Arabian Sea. They run through rift valleys (long, narrow valleys formed where land sank between two faults) north of the Deccan proper.
Rain shadow over the inner Deccan:
The moist south-west monsoon wind from the Arabian Sea hits the Western Ghats and is pushed up.
Rising air cools and its water vapour condenses. Heavy rain of 250–400 cm falls on the windward (wind-facing) slope.
The air then sinks down the eastern side. Sinking air warms up and keeps its remaining moisture.
Result: the inner Deccan is a rain shadow (a dry area on the side of the mountain away from the wind, called the leeward side). Pune, Marathwada and interior Karnataka get much less rain and are drought-prone.

Where it occurs

Position in India: the southern part of the Peninsular Plateau, south of the Satpura–Maikal–Mahadeo line and between the two Ghats.
States it covers: mainly Maharashtra, Karnataka, Telangana and Andhra Pradesh, with parts of Tamil Nadu.
Deccan Trap and black soil belt: Maharashtra, western Madhya Pradesh, Gujarat (Saurashtra), northern Karnataka and western Telangana.
River sources on its western edge:
Godavari: Trimbakeshwar (Nashik, Maharashtra).
Krishna: near Mahabaleshwar (Maharashtra).
Kaveri: Talakaveri in the Brahmagiri hills (Kodagu, Karnataka).
Northern rim: the Satpura range (Madhya Pradesh–Maharashtra), the Mahadeo hills (Pachmarhi, Madhya Pradesh) and the Maikal range (Amarkantak).
Rain-shadow areas: Pune, Marathwada and interior Karnataka.
World context: the Deccan Traps are one of the world's large igneous provinces, found in west-central India [2].

Don't confuse with

Peninsular Plateau vs Deccan Plateau: the Peninsular Plateau is the whole old tableland of southern India. The Deccan is only its southern, triangular part, south of the Satpura–Maikal–Mahadeo line.
Deccan Trap vs Deccan Plateau: the Deccan Trap is the basalt lava cover, about 66 million years old, mainly in the north-western Deccan. The plateau itself is much older Peninsular Block rock, and the trap does not cover all of it.
Rift valley rivers vs Deccan rivers: the Godavari, Krishna and Kaveri follow the eastward tilt and flow into the Bay of Bengal. The Narmada and Tapi run in rift valleys and flow west into the Arabian Sea.
Western Ghats vs Eastern Ghats (as borders): the western border is a high, continuous escarpment where rivers rise. The eastern border is low and broken, and rivers cut through it.

Prelims Hooks

Boundaries: West → Western Ghats. East → Eastern Ghats. North → Satpura, Maikal and Mahadeo hills. The two Ghats meet at the Nilgiri hills.
Amarkantak (Maikal range) is the source of the Narmada and the Son. Pachmarhi lies in the Mahadeo hills (Madhya Pradesh).
Deccan Trap: basalt about 66 million years old, over 1,200 m thick, covering about 5,00,000 sq km. It is a large igneous province [2]. "Trap" means "stairs" (Swedish).
Process → result: weathering of basalt → black (regur) soil → cotton belt of Maharashtra and Gujarat.
Trap question: the Deccan tilts east, but the Narmada and Tapi flow west because they run in rift valleys.
River–source pairs: Godavari → Trimbakeshwar (Nashik). Krishna → near Mahabaleshwar. Kaveri → Talakaveri (Brahmagiri hills, Kodagu).

Mains Points

Relief controls rainfall and water (GS-I, GS-III): the Western Ghats get 250–400 cm of rain on their windward slope and leave the inner Deccan in rain shadow.
This explains drought in Marathwada and north interior Karnataka.
It makes the plateau depend on east-flowing rivers.
It feeds interstate water disputes over the Krishna and the Kaveri.
Geology shapes the economy (GS-I): Deccan Trap basalt → black soil that holds moisture → the cotton and sugarcane belt of Maharashtra and Gujarat. This is a clear example of how rock type decides land use and agriculture.
Eastward tilt shapes the river system and settlement (GS-I): the watershed lies near the west coast, so the long Peninsular rivers cross the whole plateau. They build fertile deltas on the east coast. On the west side, only short, fast streams reach the Arabian Sea.

Related concepts

The Deccan Plateau and the Western and Eastern Ghats

Sources

1Class 6, Ch 3 "Landforms and Life"; Class 7, Ch 1 "Geographical Diversity of India"; Class 7, Ch 3 "Climates of India"; Class 11, Ch 2 "Structure and Physiography" (primary)
2Deccan Traps — Britannicabritannica.com · tier 3