Northward movement of the Indian plate

Also called: Northward drift of India · Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Class 11, Ch 2 "Structure and Physiography"; Class 11, Ch 6 "Natural Hazards and Disasters: Causes, Consequences and Management"; Class 11, Ch 4 "Distribution of Oceans and Continents"

Meaning

The northward movement of the Indian plate (also called the northward drift of India) is the long journey of the Indian land mass. It broke away from Gondwana when Pangaea split about 200 million years ago. It then moved north across the old Tethys Sea until it hit Asia about 40–50 million years ago.

This journey explains much of India's landscape. It explains the Himalayas and the Tibetan Plateau, the Deccan Traps, and the hotspot ridges of the Indian Ocean. It also explains why the Himalayas and the Andaman region still have big earthquakes today.

Explanation

Cause: plates moving over the mantle

• Lithospheric plate: a large, stiff slab of the Earth's outer shell (the crust plus the top part of the mantle). It moves slowly over the softer layer below it.
• The Indian plate carries:
• Peninsular India, the old and stable land block
• the continental parts of Australia (so NCERT calls it the Indo-Australian plate)

• most of the Indian Ocean floor between them

• Sea-floor spreading (Hess, 1960s) pushes the plate along. At an oceanic ridge (an underwater mountain chain), plates move apart and magma rises to make new sea floor.

• The Indian plate's southern boundary is such a ridge, shared with the Antarctic plate. It is divergent: new ocean floor is made there.

The journey step by step (NCERT Figure 4.6)

• Start: India was a large island off the coast of Australia. It was part of Gondwana (South America, Africa, India, Australia and Antarctica), the southern half of Pangaea.
• Tethys Sea: an ancient ocean between Gondwana and Asia. It separated India from Asia until about 225 million years ago. Fossils show that this sea sometimes flooded the Tibetan region while India moved north [2].

Time	Event
~225 million years ago	Tethys Sea separates India from Asia
~200 million years ago	Pangaea breaks up. India starts moving north.
~140 million years ago	India lies as far south as 50°S
~80 million years ago	India is about 6,400 km south of Asia and moves at about 9 m a century (~9 cm a year) [2]
~60–66 million years ago	Deccan Traps lava pours out. India is near the equator.
~40–50 million years ago	India hits Asia (Class 7 NCERT: about 50 million years ago)
Today	The Himalayas still rise by more than 1 cm a year, which adds up to about 10 km in a million years [2]

• Speed:
• After leaving Gondwana, India moved unusually fast, at up to about 15–20 cm a year.
• USGS gives about 9 cm a year for the time around 80 million years ago [2].
• After the collision, its northward movement slowed by about half [2]. But the push did not stop.

Result: the collision and the Himalayas

• Step 1: The Tethys ocean floor sank under Asia. This is subduction (one plate diving under another into the mantle).
• Step 2: The Tethys closed, and India's continental crust met Asian crust.
• Step 3: Continental crust is light, so it does not sink. It crumples, folds and gets thicker.
• Step 4: Sediments from the old Tethys floor were pushed up. This made the Himalayas and the Tibetan Plateau.
• So the northern boundary is a continent-continent convergence: two land masses push into each other and neither sinks easily.

Evidence left on the way: hotspot tracks

• Hotspot: a fixed, very hot spot deep in the mantle. Plumes of magma rise from it. The plate moves over it, but the hotspot stays where it is. So it leaves a line of volcanoes, called a hotspot track, like a candle held under moving paper.
• Reunion hotspot:
• About 66 million years ago, it lay under western India and made the Deccan Traps. These are thick, step-like sheets of basalt (dark volcanic rock). Trap comes from the Swedish word for "stairs".
• India kept moving north, so the hotspot "drew" a line southward. That line is the Chagos-Laccadive Ridge: Lakshadweep → Maldives → Chagos.

• The volcanoes get younger from north to south. Today the hotspot sits under Réunion Island, east of Madagascar.

• Kerguelen hotspot:

• It made the Ninety East Ridge, a straight underwater ridge about 5,000 km long along about 90°E.
• The ridge is straight because India moved almost due north over the hotspot.

Where it occurs

• Himalayas: the northern boundary of the Indian plate, where it collides with Asia.
• Tibetan Plateau: pushed up by the same collision. Tethys fossils are found here [2].
• Deccan Traps: in Maharashtra, Gujarat and Madhya Pradesh. They weathered into black (regur) soil.
• Chagos-Laccadive Ridge: Lakshadweep (India) → Maldives → Chagos in the Arabian Sea and western Indian Ocean. Mauritius and Réunion lie at the young end of the same track.
• Ninety East Ridge: in the eastern Indian Ocean, running north towards the Bay of Bengal. The Kerguelen hotspot now lies under the Kerguelen Islands in the southern Indian Ocean.
• Other plate boundaries:
• East: Rakinyoma (Arakan Yoma) in Myanmar, then the island arc along the Java (Sunda) Trench. An island arc is a curved chain of volcanic islands above a subduction zone, such as Sumatra and Java.
• West: Kirthar mountains (Pakistan) → Makran coast → the spreading site from the Red Sea rift → along the Chagos Archipelago.

• Far east: a divergent oceanic ridge in the south-west Pacific, east of Australia.

• Andaman-Sumatra subduction zone:

• Here the oceanic part of the Indian plate goes down beneath the Burma microplate, which is part of the larger Sunda plate, at about 6 cm a year [3].
• The 26 December 2004 earthquake (Mw 9.1) started here [3]. It broke about 1,300 km of the boundary, from northern Sumatra to the Andaman Islands.

Don't confuse with

• Continental drift (Wegener, 1912): the older idea that continents moved, but it could not explain how. The Indian plate's movement is explained by plate tectonics (1967), which is driven by sea-floor spreading.
• Ocean-continent convergence: here the oceanic plate sinks, as at the Java Trench and the Andaman-Sumatra zone. The Himalayan boundary is continent-continent: neither side sinks, so the crust folds and thickens.
• Island arc: formed by subduction, as along the Java Trench. Lakshadweep, Maldives and Chagos are hotspot tracks, not island arcs.
• Burma microplate: the Andaman and Nicobar Islands sit on this small plate between the Indian and Sunda plates. They are not on the Indian plate.

Prelims Hooks

• About 140 million years ago, India lay at about 50°S. During the Deccan Traps eruptions (~60–66 million years ago), it lay near the equator.
• Collision with Asia: 40–50 million years ago (Class 7 NCERT: ~50 million years). After it, India's northward movement slowed by about half [2].
• Speed about 80 million years ago: about 9 cm a year, when India was about 6,400 km south of Asia [2].
• Hotspot pairs: Deccan Traps + Chagos-Laccadive Ridge → Reunion. Ninety East Ridge → Kerguelen.
• Ageing order on the Reunion track: India (oldest) → Lakshadweep and Maldives → Chagos → Mauritius and Réunion (youngest).
• Northern boundary = Himalayas = continent-continent convergence. Southern boundary = divergent ridge with the Antarctic plate.

Mains Points

• The journey shaped India's landforms (GS-I):
• The collision in the north made young fold mountains (the Himalayas) and the Indo-Gangetic foredeep, which filled with river sediment.
• The stable shield in the south is the old Peninsular plateau.

• The Reunion hotspot made the Deccan Traps and their fertile black soils.

• The drift has not stopped, so the hazard continues (GS-III, disasters):

• India still pushes into Asia. The Himalayas rise by more than 1 cm a year [2], strain builds up, and the Himalayas and North-East fall in Seismic Zones IV–V.
• At the eastern edge, subduction under the Burma microplate caused the 2004 Mw 9.1 earthquake and the Indian Ocean tsunami [3].

• So India needs earthquake-resistant buildings and the INCOIS tsunami early-warning system.

• The Indian Ocean floor shows proof of plate tectonics:

• The Chagos-Laccadive and Ninety East ridges record which way India moved and how fast.
• The sea floor gets older as you move away from the ridges. This supports Hess's sea-floor spreading and the 1967 plate tectonics theory over Wegener's drift alone.

Related concepts

• Indian plate
• Tethys Sea
• Burma microplate
• Reunion hotspot
• Ninety East Ridge

Read more

• The Indian plate: boundaries and the journey north