1. Formation of Peninsular Indian Mountain Systems
The mountains of Peninsular India (the Deccan Plateau region) are very different from the Himalayas. They are not young, tectonically active mountains. Instead, they are ancient, stable, and highly eroded remnants of the old Gondwanaland supercontinent.
They are primarily fault-block mountains or relict mountains (erosional remnants).
The Aravallis
Location: Northwest India (Rajasthan, Delhi).
Formation: One of the oldest fold mountain ranges in the world. They were formed during the Proterozoic Eon (over 1.5 billion years ago) from a tectonic collision.
Current State: Today, they are "relict mountains," meaning they have been eroded down by billions of years of weathering to just the "stumps" of their former selves.
The Vindhyas
Location: Central India, forms the northern border of the Deccan Plateau.
Formation: They are fault-block mountains. They formed when a block of crust (a "horst") was uplifted between two parallel faults (grabens).
Western and Eastern Ghats
Western Ghats: These are not true mountains in the traditional "fold" sense. They are the faulted, uplifted escarpment (edge) of the Deccan Plateau.
Formation: When India broke away from Africa/Madagascar (~150 Ma), the western edge of the Indian continent was uplifted, creating a steep cliff facing the new Arabian Sea.
Features: Very steep on the west, with a gentle slope on the east (the tilt of the Deccan Plateau). They are a major barrier to the monsoon winds.
Eastern Ghats:
Formation: A much older, discontinuous, and heavily eroded series of hills. They are much lower and "broken" compared to the continuous wall of the Western Ghats.
2. Origin of the Himalayas
The Himalayas are the classic and most spectacular example of a continental-continental collision. They are the world's youngest and highest mountain range.
The Collision Process:
Breakup of Gondwana: About 150 Ma, the Indian plate (part of Gondwanaland) broke off and started moving rapidly northward, "drifting" across the Tethys Ocean.
Subduction of Tethys: As India moved north, the oceanic crust of the Tethys Ocean was subducted (forced under) the Eurasian plate, creating a volcanic arc (like the Andes today).
The "Hard" Collision: About 50-60 million years ago, the Tethys Ocean closed, and the continental crust of India collided with the continental crust of Eurasia.
Mountain Building (Orogeny): Since both continental crusts are thick and buoyant (not dense enough to subduct), they had nowhere to go but up. The crust buckled, folded, and faulted, stacking up on top of itself to form the massive Himalayan range.
Diagram: A three-stage diagram.
1. Indian plate (continental) moving north, subducting the Tethys Ocean (oceanic) under the Eurasian plate (continental).
2. The "soft" collision, where the plates first meet.
3. The "hard" collision, showing the Tethys Ocean gone, and the two continental plates buckling and folding to create the Himalayan mountains.
Key Points:
The Himalayas are still rising (a few mm per year) because the Indian plate is still pushing into the Eurasian plate.
This ongoing collision is why the entire region is highly seismically active (frequent, strong earthquakes).
3. Development of Glaciers and Perennial River Systems
The formation of the Himalayas had a profound effect on the region's climate and water resources.
Development of Glaciers
The immense height of the Himalayas (with many peaks over 8,000 meters) places them far above the snow line (the altitude where it is cold enough for snow to remain year-round). Over millennia, this snow has compacted into vast icefields and glaciers (e.g., Gangotri, Yamunotri, Siachen). The Himalayas are sometimes called the "Third Pole" because they contain the largest mass of ice outside the polar regions.
Perennial River Systems
These Himalayan glaciers act as massive, natural "water towers."
Perennial means "year-round."
In the dry season, when there is no monsoon rain, these glaciers continue to melt slowly, feeding a constant, reliable supply of water to the great rivers of North India.
This is the origin of the Indus, the Ganges (Ganga), and the Brahmaputra.
This is a key difference from Peninsular rivers (like Godavari, Krishna), which are seasonal (rain-fed) and often run dry in the winter.
4. Formation of Indo-Gangetic Plains
The formation of the vast, flat, and fertile Indo-Gangetic Plains is a direct consequence of the Himalayan uplift.
Formation Process:
Formation of a Foreland Basin: As the Himalayas were pushed up, their immense weight caused the Earth's crust just to the south (the Indian plate) to bend and warp downwards, like a bowling ball on a mattress. This created a massive, long, and deep trough or depression called a foreland basin, parallel to the mountains.
Alluvial Deposition: The newly formed, fast-flowing Himalayan rivers (Indus, Ganges, Brahmaputra) were powered by the steep slopes. They carved into the rising mountains, eroding vast quantities of rock and carrying it as sediment (silt, sand, and clay, collectively known as alluvium).
Filling the Basin: When these rivers exited the mountains and entered the flat basin, they slowed down and dumped their massive sediment load. Over millions of years, this continuous deposition of alluvium completely filled the foreland basin.
The result is the Indo-Gangetic Plain—one of the largest stretches of flat, alluvium-filled land on Earth, with sediment deposits thousands of meters deep. This deep, rich alluvial soil is what makes the region one of the most fertile and agriculturally productive in the world.