Himalayas Formation, Relief, and Structure - Geomorphology: Tectonic Plates, Mountain Building, and Landform Characteristics

Formation Overview

• The Himalayan mountain range and the Tibetan plateau were formed as a result of the collision between the Indian Plate and the Eurasian Plate, which began 40-50 million years ago and continues today.
  • Collision Impact:
    • Both plates have about the same rock density, preventing subduction.
    • 
    • Pressure from the collision caused thrusting upwards.
    • Resulted in the formation of the jagged Himalayan peaks.
• 

Himalayas Formation

• The Himalayas are the youngest mountain chain in the world.
  • Origin:
    • Formed from a geosyncline called the Tethys Sea.
    • Uplift occurred in phases.
• Permian Period (250 million years ago):
  • The supercontinent Pangaea existed, consisting of:
    • Laurasia: Northern part, made up of present-day North America and Eurasia.
    • Gondwanaland: Southern part, made up of present-day South America, Africa, India, Australia, and Antarctica.
• The Tethys Sea existed between Laurasia and Gondwanaland.
  • Rivers deposited sediments in the Tethys Sea.
• These sediments were compressed due to the northward movement of the Indian Plate.
  • Resulted in folding and the eventual formation of the Himalayas.
• 
• Mount Everest: The summit is made of marine limestone from the ancient Tethys Sea.
• The Indian plate continues to move northward at 5 cm/year, raising the Himalayas.
• The Tibetan plateau was formed due to the upthrusting of the southern block of the Eurasian Plate.
• The Indo-Gangetic plain was formed from the alluvium deposited by Himalayan rivers.
• The Himalayas have a curved shape due to the maximum push at the ends of the Indian Peninsula.

Phases of Himalayas Formation

• The Himalayas consist of three parallel ranges that emerged from the Himalayan Geosyncline (Tethys Sea) in six distinct phases.
  • Each phase marked a significant stage in the formation of the ranges.

6 Phases of Himalayas Formation

• Phase 1 – 100 million years ago:
  • During the Cretaceous Period:
    • The Indian plate was located between 10⁰S and 40⁰S, over the Reunion hotspot.
    • The plate's movement towards the equator at a rate of 14 cm/year initiated the squeezing of the Tethys Sea.
• Phase 2 – 71 million years ago:
  • Himalayan orogenesis began:
    • The Indian plate drifted northeast and collided with the Aravalli series.
    • Collision formed the Indus–Tsangpo Suture Zone (ITSZ), a compressional tectonic fault line.
    • Crustal doubling below Tibet created the high Tibetan plateau.
    • The Murree Foredeep and Shiwalik Foredeep were formed south of the ITSZ.
• Phase 3 – The Drass Volcanic Arc (Oligocene Period):
  • Volcanic eruptions occurred:
    • In the Tethys crust, forming the Drass volcanic area.
    • Anti-clockwise rotation of the Indian plate released pressure in the west but squeezed Tethyan sediments in the east.
    • 
    • Marked the rise of the Tethyan Himalayas.
• Phase 4 – Greater Himalayas Raised (30-35 million years ago):
  • Continued compression caused a major thrust:
    • Raised the Greater Himalayas.
    • The Main Central Thrust (MCT) was the compressional line that raised the Greater Himalayas.
    • 
• Phase 5 – Rise of Lesser Himalayas (15-20 million years ago):
  • Sediments deposited in the Shiwalik foredeep were compressed:
    • Leading to the rise of the Lesser Himalayas during the Miocene.
    • The Boundary Thrust/Fault (MBT) separates the Greater and Lesser Himalayas.
• Phase 6 – Rise of the Shiwalik Ranges:
  • Sedimentation by Himalayan rivers filled the Shiwalik foredeep:
    • Partial folding along the Himalayan Frontal Fault (HFF) led to the rise of the Shiwalik ranges.

Tibetan Plateau

• The Tibetan Plateau:
  • Not part of the Himalayas but formed due to Himalayan orogeny.
  • Often referred to as the "Roof of the World" due to its high elevation.
  • Significance:
    • Serves as a major factor influencing the regional climate.
    • Acts as a barrier to the cold winds from the north, affecting weather patterns in the Indian subcontinent.

Indus–Tsangpo Suture Zone (ITSZ)

• ITSZ:
  • A compressional fault line extending 3200 km from the Indus Gorge to the Tsangpo Gorge.
  • Represents the collision zone between the Indian Plate and the Eurasian Plate:
    • Rocks in this zone are crushed and pulverized.
    • Mostly consists of Paleozoic and ancient rocks.
  • Rivers:
    • Indus and Tsangpo flow through this reverse faulted line.
    • These rivers have cut through the suture zone, influencing the landscape.

Tethyan Himalayas

• Tethyan Himalayas:
  • Average height: around 4000 m.
  • Characteristics:
    • 
    • Compressed against the Greater Himalayas.
    • High compressional forces due to the absence of a longitudinal valley between them.
  • Composition:
    • Submarine sedimentary and metamorphic rocks.
    • Represents the initial upliftment in the Tethyan Geosyncline or Murree Foredeep.

Greater Himalayas

• Greater Himalayas:
  • Average height: around 6000 m, extending from Mt. Namcha Barwa to Nanga Parbat for 2500 km.
  • Features:
    • Considered the mightiest and most majestic mountain range.
    • Numerous peaks rising above 7000 m.
    • Characterized by high relief, deep gorges, vertical slopes, and symmetrical convexity.
    • 
  • Relief:
    • Sharp peaks and escarped valleys due to isostatic adjustment.
    • Composed of metamorphic and sedimentary rocks.
    • Core includes granitic magma (batholith).
    • Features asymmetrical folds and fractured rocks due to high compression.

Main Central Thrust (MCT)

• Main Central Thrust (MCT):
  • Major tectonic thrust line along which the Greater Himalayas were uplifted.
  • 
  • Characteristics:
    • A compressional valley.
    • Rocks are fractured and pulverized between the Greater and Lesser Himalayas.
  • Examples:
    • Kathmandu Valley
    • Kashmiri Valley
    • Kulu Valley
    • Kangra Valley
  • Valley Types:
    • Kulu: Transverse valley.
    • Kangra and Manali: Straight valleys, more prone to earthquakes due to underlying faults.

Lesser Himalayas

• Lesser Himalayas:
  • 
  • Average height: around 3800 m, extending about 2400 km.
  • Characteristics:
    • Runs parallel to the Greater Himalayas.
    • Segmented into several parallel and transverse ranges in the western section.
  • Ranges:
    • Parallel Ranges: Pir Panjal, Dhaula Dhar.
    • Transverse Ranges: Ratan Pir, Nagtiba, Mussourie Range.
    • 
  • Regional Names:
    • Central Nepal: Mahabharatha Range.
    • Eastern Nepal: Dafla Hills, Mishmi Hills, Miri Hills, Abor.
  • Structural Complexity:
    • The central part has a complex structure with fractures and faults.
    • The width of the Himalayas here is much less compared to the western section.

Main Boundary Fault (MBF)

• Main Boundary Fault (MBF):
  • A major thrust fault in the Himalayas but not as deep as MCT.
  • Characteristics:
    • Wide-angle reverse fault.
    • Valleys are wide with rivers forming lakes in these valleys, known as Lakestrene sediments.
  • Examples of Doons:
    • Dehra Dun
    • Patli Dun
  • Regional Names:
    • Western and Central Himalayas: Doons.
    • Eastern Himalayas: Duars.

Shiwaliks

• Shiwaliks:
  • 
  • Average height: 800-1200 m.
  • Characteristics:
    • Partially folded and formed from river sediments deposited in the foredeep.
    • Hogback topography with a clear boundary with the Gangetic Plain at the 300 m contour line.
  • Regional Names:
    • Western Section: Shiwalik.
    • Nepal: Churiaghat Hills.
    • Assam: Mishmi, Abor, Dafla Hills.
  • Geographical Significance:
    • Closer to Greater Himalayas in Nepal, disappearing after the River Ganges.

Himalayan Frontal Fault (HFF)

• Himalayan Frontal Fault (HFF):
  • 
  • Marks the boundary between the Himalayan ranges and the Gangetic Basin.
  • Characteristics:
    • Wide-angle thrust line.
    • Represents the final compressional forces during the Himalayan orogeny.

Indo Gangetic Basin

• Indo Gangetic Basin:
  • Extensive lowland area between the Himalayas and the Indian Peninsula.
  • Characteristics:
    • Rich alluvial soils deposited by rivers originating from the Himalayas.