The Deccan Plateau and the Western and Eastern Ghats

Detail

1. The Deccan Plateau: where it is and what bounds it

• Deccan Plateau: the large, roughly triangular tableland (a high, mostly flat land) that forms the southern part of the Peninsular Plateau. Its rocks belong to the old, hard and stable Peninsular Block.
• Its borders:
• West: the Western Ghats.
• East: the Eastern Ghats.

• North: the Satpura range, the Maikal range and the Mahadeo hills.

• Satpura–Maikal–Mahadeo line (north edge):

• The Satpura range runs east–west, mostly in Madhya Pradesh and Maharashtra.
• The Mahadeo hills are part of the Satpura system. Pachmarhi in Madhya Pradesh lies in them.

• The Maikal range is the eastern end of this line. Its Amarkantak plateau is where the Narmada and the Son rise.

• Western Ghats escarpment: the Western Ghats rise as a steep slope of about 1,000 m or more along the western edge of the Deccan [5]. An escarpment is a steep, cliff-like slope.

2. Deccan Trap basalt and black soil

• Deccan Trap: thick layers of basalt (a dark volcanic rock) that cover much of the north-western Deccan. The lava poured out of long cracks in the crust about 66 million years ago, near the end of the Cretaceous period.
• The Deccan Traps are a large igneous province (a very large area built up by volcanic eruptions) in west-central India [5].
• They are made of more than 1,200 m of lava flows over about 5,00,000 sq km [5].

• "Trap" comes from a Swedish word for "stairs". Each lava flow cooled into a flat sheet, so the hillsides look like steps.

• How basalt becomes black soil:

• Basalt is rich in iron, lime and magnesium.
• It breaks down slowly through weathering (rock breaking into small pieces under sun, rain and changes in temperature).
• The result is black soil, also called regur or black cotton soil. It is clay-rich, holds moisture well, cracks deeply in the dry season and suits cotton.
• Main belt: Maharashtra, western Madhya Pradesh, Gujarat (Saurashtra), northern Karnataka and western Telangana (see soils-of-india).

3. Slope and drainage: why rivers flow east

• Eastward tilt: the Deccan 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.
• So the big rivers rise in the Western Ghats and flow east across the whole plateau.
• Godavari: rises at Trimbakeshwar (Nashik, Maharashtra) and flows into the Bay of Bengal.
• Krishna: rises near Mahabaleshwar (Maharashtra) and flows into the Bay of Bengal.

• Kaveri: rises at Talakaveri in the Brahmagiri hills (Kodagu, Karnataka) and flows into the Bay of Bengal.

• Exceptions to remember: the Narmada and the Tapi flow west into the Arabian Sea. They run through rift valleys (long, narrow valleys formed where land sank between two faults) north of the Deccan proper.

• Short, fast streams run west down the steep Ghat face to the Arabian Sea. They form monsoon waterfalls.

4. The Western Ghats: extent, names and height

• Western Ghats: a long, continuous chain of hills along the western edge of the Peninsula, running parallel to the Arabian Sea coast.
• Length and area: about 1,600 km, covering about 1,40,000 sq km [2].

• States: six states, from Gujarat, Maharashtra and Goa in the north to Karnataka, Kerala and Tamil Nadu in the south [2].

• Height: an average of about 1,500 m. The height rises from north to south.

• Local names, north to south:

Local name	State(s)
Sahyadri	Maharashtra (also Goa and northern Karnataka)
Nilgiri hills	Karnataka, Tamil Nadu (and Kerala border)
Anaimalai hills	Kerala–Tamil Nadu
Cardamom hills	Kerala–Tamil Nadu
Agasthyamalai hills	southern tip, Kerala–Tamil Nadu

• River source: most Peninsular rivers rise here, including the Godavari, Krishna and Kaveri.

5. Highest peaks

• Anamudi (also spelled Anaimudi), 2,695 m: the highest peak of the Peninsula (that is, of India south of the Himalayas).
• It is in the Anaimalai hills in Idukki district, Kerala.

• It lies inside Eravikulam National Park, the main home of the Nilgiri tahr (a wild mountain goat found only in the southern Western Ghats).

• Dodabetta, 2,637 m: the second highest peak of the Peninsula. It is in the Nilgiri hills near Ooty (Udhagamandalam), Tamil Nadu.

• Order (highest first): Anamudi (2,695 m) > Dodabetta (2,637 m).

6. Nilgiri hills: the knot where the two Ghats meet

• Nilgiri hills: the high block where the Western Ghats and the Eastern Ghats meet. It lies where Tamil Nadu, Karnataka and Kerala join.
• Shola-grassland forests:
• Shola forests are small patches of stunted, evergreen forest in sheltered valleys of the high hills.
• Open, rolling montane grasslands (high-altitude grasslands) lie between these patches.

• The two together work like a sponge that stores rainwater and feeds streams.

• Nilgiri Biosphere Reserve (1986): India's first biosphere reserve. A biosphere reserve is a large protected area. Its core is kept strictly protected, and local people live and work in the outer zones.

7. Western Ghats ecology and conservation

• UNESCO World Heritage Site (2012): listed for its rich and unique natural heritage.
• The site has 39 component parts in 7 sub-clusters. The total property is 7,95,315 hectares [2].

• These parts are tiger reserves, national parks, wildlife sanctuaries and reserved forests. The Wildlife (Protection) Act, 1972, the Indian Forest Act, 1927 and the Forest (Conservation) Act, 1980 protect them [2].

• Biodiversity hotspot: a region that has a very large number of endemic species (species found nowhere else) and has lost much of its original vegetation. The Western Ghats and Sri Lanka together form one of the world's hotspots.

• Key species: the lion-tailed macaque (a monkey with a silver-white mane, found only in the Western Ghats), the king cobra, the Nilgiri tahr and insectivorous plants (plants that trap insects to get nutrients).
• Monsoon waterfalls: short, steep west-flowing streams drop over the escarpment in the rainy season.
• The Gadgil vs Kasturirangan debate on eco-sensitive areas:
• Ecologically Sensitive Area (ESA): an area notified by the government where activities such as mining, quarrying and large polluting industry are limited to protect nature.
• Gadgil report (WGEEP, 2011): the Western Ghats Ecology Expert Panel treated the whole Western Ghats as ecologically sensitive. It split the region into three zones of different protection levels [3].
• Kasturirangan report (HLWG, 2013): the High Level Working Group marked about 60,000 sq km of the "natural landscape", about 37% of the Western Ghats region, as ESA [3].
• What happened next: a draft ESA notification came out in October 2018. The draft was re-issued for the fifth time on 6 July 2022 [4]. States still disagree over villages, mining and plantations, so the final notification is delayed.
• Link: biodiversity-conservation.

8. Gaps and passes in the Western Ghats

• Pass / gap: a low break in a mountain chain that lets roads, railways, rivers or winds cross it.
• Thal Ghat (Kasara Ghat): carries the Mumbai–Nashik road and rail line up the northern Sahyadri.
• Bhor Ghat (Khandala Ghat): carries the Mumbai–Pune road and rail line up the Sahyadri.
• Palghat Gap (Palakkad Gap): 30–40 km wide, between the Nilgiris (north) and the Anaimalai (south).
• It links Kerala and Tamil Nadu (Palakkad to Coimbatore) by road and rail.

• Moist south-west monsoon winds pass through the gap, so Coimbatore gets some rain even though it lies east of the Ghats.

• Shencottah Gap: further south, between the Cardamom hills and the Agasthyamalai hills. It links Kollam (Kerala) with Tirunelveli side (Tamil Nadu).

• Order of gaps and passes (north to south): Thal Ghat → Bhor Ghat → Palghat Gap → Shencottah Gap.

9. The Eastern Ghats

• Eastern Ghats: a chain of low, broken hills along the eastern edge of the Peninsula, roughly parallel to the Bay of Bengal coast. They run from Odisha to Tamil Nadu.
• Why they are broken:
• Big east-flowing rivers have worn them down over a very long time.
• The Mahanadi, Godavari, Krishna and Kaveri cut right through them.

• As a result, the hills stand as separate blocks with wide river gaps and deltas between them.

• Main ranges:

Range	Location	Note
Mahendragiri hills	southern Odisha	northern part; Mahendragiri is a well-known high peak
Nallamala hills	Andhra Pradesh and Telangana	between the Krishna and the Pennar; Nagarjunasagar-Srisailam Tiger Reserve, India's largest tiger reserve by area
Palkonda range	southern Andhra Pradesh	near Tirupati
Javadi hills	northern Tamil Nadu	Vellore–Tiruvannamalai area
Shevaroy hills	Salem, Tamil Nadu	hill station of Yercaud
Biligirirangan hills	Karnataka–Tamil Nadu border	link the Eastern and Western Ghats; BRT Tiger Reserve

• Nallamala hills: a forested range that is part of the Eastern Ghats in Andhra Pradesh and Telangana. The Krishna cuts through them at Srisailam.

10. Western vs Eastern Ghats

Feature	Western Ghats	Eastern Ghats
Continuity	continuous wall	broken, separate hill blocks
Height	higher; average ~1,500 m, rising north to south	lower; worn down by erosion
Highest peak	Anamudi (2,695 m)	Mahendragiri area (Odisha)
Rivers	most Peninsular rivers rise here	cut through by Mahanadi, Godavari, Krishna, Kaveri
Rainfall	windward slope 250–400 cm	less rain
Forests	tropical evergreen and semi-evergreen; shola-grassland on top	mostly tropical dry and moist deciduous
Passes/breaks	Thal Ghat, Bhor Ghat, Palghat Gap, Shencottah Gap	wide river gaps and deltas
Status	UNESCO site (2012); biodiversity hotspot	no UNESCO natural listing

11. Rain shadow over the Deccan

• Rain shadow: an area on the side of a mountain away from the wind (the leeward side) that gets little rain.
• How it forms:
• The moist south-west monsoon wind blows in from the Arabian Sea and hits the Western Ghats.
• The wind is pushed up. Rising air cools, its water vapour condenses, and heavy rain falls on the windward (wind-facing) slope: 250–400 cm.
• The air crosses the crest and comes down the eastern side. Sinking air warms up and holds on to its remaining moisture.

• Result: the inner Deccan (for example, Pune, Marathwada and interior Karnataka) gets much less rain. These areas are drought-prone.

• Link: indian-climate-monsoon.

Prelims Hooks

• Highest peaks of the Peninsula: Anamudi (2,695 m, Anaimalai hills, Idukki, Kerala) > Dodabetta (2,637 m, Nilgiris, Tamil Nadu). Anamudi lies in Eravikulam NP, home of the Nilgiri tahr.
• Palghat Gap lies between the Nilgiris and the Anaimalai (Kerala–Tamil Nadu). Shencottah Gap lies between the Cardamom and Agasthyamalai hills.
• Pass and route pairs: Thal Ghat → Mumbai–Nashik. Bhor Ghat → Mumbai–Pune.
• Local names, north to south: Sahyadri → Nilgiri → Anaimalai → Cardamom → Agasthyamalai.
• The Western and Eastern Ghats meet at the Nilgiri hills. The Nilgiri Biosphere Reserve (1986) is India's first.
• The Western Ghats World Heritage Site (2012) has 39 components in 7 sub-clusters [2].
• Kasturirangan (HLWG 2013): about 37% (about 60,000 sq km) of the Western Ghats proposed as ESA. Gadgil (WGEEP 2011): the whole Ghats, in three zones [3].
• Nallamala hills (AP–Telangana) hold the Nagarjunasagar-Srisailam Tiger Reserve.
• Trap: the Deccan tilts east, yet the Narmada and Tapi flow west, because they run in rift valleys.
• Deccan Trap basalt (about 66 million years old) → black (regur) soil → cotton belt of Maharashtra and Gujarat.

Mains Points

• Relief controls rainfall and water: the Western Ghats force heavy windward rain (250–400 cm) and leave the inner Deccan in rain shadow. This explains drought in Marathwada and north interior Karnataka, the dependence on east-flowing rivers, and interstate water disputes over the Krishna and Kaveri (GS-I and GS-III).
• Conservation vs development: the Western Ghats are a UNESCO site and a biodiversity hotspot. Mining, quarrying, hill roads and plantations add to landslide risk (Kerala 2018 and 2024). The draft ESA notification has been re-issued at least five times since 2018 [4]. Gadgil's whole-region approach vs Kasturirangan's 37% shows the trade-off [3].
• Passes shape connectivity: Thal, Bhor and Palghat set the routes of rail and highway corridors (Mumbai–Pune, Mumbai–Nashik, Kochi–Coimbatore). The Palghat Gap also lets monsoon winds through to Coimbatore, which helps its textile and farming base.
• Geology shapes the economy: Deccan basalt → black soil → the cotton and sugarcane belt. In contrast, the eroded Eastern Ghats hold minerals and forests (Odisha, Andhra Pradesh) and tribal homelands, where development has to be balanced with forest rights.