Origin of the Himalayas

Getectonic Evolution and Origin of the Himalayas

The Himalayas, the highest and youngest fold mountain range in the world, act as a formidable physical, climatic, and geopolitical barrier for the Indian subcontinent. Understanding their origin requires an analysis of endogenic forces, plate tectonics, and continental drift.

Continental Drift and the Tethys Geosyncline

During the Mesozoic Era, the Earth’s landmass was divided into the northern supercontinent Laurasia (Angaraland) and the southern supercontinent Gondwanaland.

The Role of the Tethys Sea

• A long, narrow, and shallow sea known as the Tethys Geosyncline existed between these two giant landmasses.
• For millions of years, rivers flowing from both Angaraland and Gondwanaland deposited vast amounts of sediments into the Tethys Sea.
• This continuous deposition led to the gradual subsidence of the geosynclinal bed, accumulating thick layers of sedimentary strata.

Plate Tectonics Theory of Himalayan Upliftment

The most widely accepted explanation for the origin of the Himalayas is based on the Theory of Plate Tectonics, formulated by W.J. Morgan, McKenzie, and Parker.

The Breakup of Gondwanaland

• During the Late Cretaceous period (approximately 84 million years ago), the Indian Plate broke away from Gondwanaland and began its northward journey at a speed of about 12 cm per year to 16 cm per year.
• The northward drift was driven by convective currents in the Earth’s mantle.

The Convergent Boundary Collision

• Around 40 to 50 million years ago, during the Eocene Epoch of the Cenozoic Era, the northern margin of the Indian Plate collided with the Eurasian Plate.
• This collision represents a Continent-Continent Convergence. Because both plates were continental, neither could completely subduct into the mantle due to their low density.
• The sedimentary rocks deposited in the Tethys Geosyncline were squeezed, compressed, and folded due to the intense lateral compressive forces generated by the colliding plates.

Chronological Phases of Upliftment

The Himalayas did not rise all at once but were formed in three major successive phases corresponding to different geological epochs.

Phase 1: The Great Himalayas (Greater Himalayas / Inner Himalayas)

• Geological Epoch: Oligocene Epoch (around 25–30 million years ago).
• Process: This was the first and most intense phase of folding. It resulted in the formation of the highest, continuous range composed of central crystalline rocks (granite and gneiss).

Phase 2: The Lesser Himalayas (Middle Himalayas)

• Geological Epoch: Miocene Epoch (around 14–18 million years ago).
• Process: Further northward movement of the Indian Plate caused another major upheaval. The sediments of the Tethys as well as the northern fringes of the Indian shield were folded to form ranges like the Pir Panjal and Dhauladhar.

Phase 3: The Outer Himalayas (Shiwalik Range)

• Geological Epoch: Pliocene to Early Pleistocene Epoch (around 2–5 million years ago).
• Process: The rivers originating from the newly formed Greater and Lesser Himalayas brought down massive amounts of molasses and detritus, depositing them in a foredeep (a long trench) formed south of the Middle Himalayas. Continued compression folded these fresh fluvial sediments into the Shiwalik hills.

Major Faults and Suture Zones

The compression of the Indian crust created massive thrust faults that separate the different morphotectonic zones of the Himalayas from north to south.

Indus-Tsangpo Suture Zone (ITSZ)

This zone marks the actual collision boundary or the line of welding between the Indian Plate and the Eurasian Plate. It lies to the north of the Great Himalayas.

Main Central Thrust (MCT)

A major fault zone that separates the Higher Himalayas from the Lesser Himalayas. It is characterized by high-grade metamorphic rocks.

Main Boundary Thrust (MBT)

This fault separates the Lesser Himalayas from the Outer Himalayas (Shiwaliks). It is highly active seismically.

Himalayan Frontal Fault (HFF)

Also known as the Main Frontal Thrust (MFT), this fault marks the boundary where the Shiwaliks end and the Indo-Gangetic Alluvial Plains begin.

Evidence Supporting the Ongoing Rise of the Himalayas

The Himalayas are still rising at a rate of approximately 5 mm to 1 cm per year. Multiple geological and geographical observations prove this ongoing orogeny.

Frequent Seismic Activity

The entire Himalayan arc is highly prone to severe earthquakes (falling under Seismic Zones IV and V of India) due to the continuous locked stress being released along the MCT, MBT, and HFF.

Youthful Topography

The presence of deep V-shaped valleys, gorges (e.g., Indus Gorge, Shipki La Gorge), waterfalls, and rapidly flowing rivers indicates that the landscape is still in its youthful stage of the geomorphic cycle.

Karewa Formations of Kashmir

Karewas are lacustrine deposits (lake sediments) found in the Kashmir Valley containing fossils of mammals. Their presence at high altitudes proves that the valley floor has been uplifted in recent geological times.

Displaced River Courses

Many Himalayan rivers are antecedent rivers (e.g., Indus, Satluj, Brahmaputra). They existed before the mountains were raised and have cut deep gorges to maintain their paths, proving that the land rose beneath them.

Changing Heights of Peaks

Periodic satellite measurements indicate minor increases in the altitude of major peaks, including Mount Everest.

Prelims-Specific Trivia and Key Facts

Syntaxial Bends

The Himalayan ranges run in a west-east direction from the Indus River to the Brahmaputra River. At its western extremity (Nanga Parbat) and eastern extremity (Namcha Barwa), the ranges take sharp, hairpin southward turns known as Syntaxial Bends. These bends are caused by the terminal corners of the rigid Indian peninsular shield pushing deep into the Eurasian plate.

Structural Asymmetry

The southern slopes of the Himalayas facing India are very steep, whereas the northern slopes facing Tibet are gentle. This is because the compressive force acted from the south to the north, pushing the strata forward against the Tibetan plateau.

Marine Fossils at High Altitudes

The presence of marine fossils such as Ammonites (Shaligram stones) in the upper reaches of the Himalayas (e.g., Spiti Valley) serves as indisputable evidence that the sedimentary rocks of these mountains were once submerged under the ancient Tethys Sea.