Q3 (c) With suitable sketches elaborate the bottom topography of the Indian Ocean. 15 Marks (PYQ/2024)

Oceanography – Bottom topography of Ocean – Bottom topography of Indian Ocean

Answer:

Introduction

The Indian Ocean, third largest among the world’s oceans, is bounded by Asia to the north, Africa to the west, Australia to the east, and merges with the Southern Ocean to the south. Unlike the Atlantic and Pacific, it is landlocked in the north and asymmetrical. Its bottom topography reflects a combination of tectonic processes, sedimentation, oceanic spreading, and volcanic activity.

Major Features of Indian Ocean Floor

1. Mid-Ocean Ridge System

• The Mid-Indian Oceanic Ridge (MIOR) is a prominent feature running north-south and is divided into three segments:
  • Carlsberg Ridge (north)
  • Central Indian Ridge
  • Southwest Indian Ridge
• These ridges are divergent boundaries, formed due to seafloor spreading as per Plate Tectonics Theory (McKenzie & Parker).

Sketch 1: Longitudinal section showing ridge system from Carlsberg to Southwest Indian Ridge.

2. Basins and Deeps

• Arabian Basin, Bay of Bengal Basin, Somali Basin, Perth Basin, and Crozet Basin are major abyssal plains and sediment-filled depressions.
• Important deeps include:
  • Sunda Trench (Java Trench): Deepest part, ~7,725 m.
  • Diamantina Trench (off Western Australia)

These are results of subduction and isostatic adjustments.

3. Plateaus and Rises

• Chagos-Laccadive Ridge, Ninety East Ridge, Seychelles Plateau, and Kerguelen Plateau are major elevated volcanic features.
• Formed due to hotspots and mantle plumes (W.J. Morgan’s Hotspot Theory).

Example: Ninety East Ridge aligns nearly along 90°E longitude and is a classic hotspot trail.

4. Submarine Canyons and Seamounts

• Found off the eastern and western continental shelves of India.
• Indus Canyon and Ganges Canyon are prominent.
• Seamounts and guyots (e.g., Meteor Seamount, Seychelles Bank) formed due to volcanic eruptions.

These structures reflect erosional activity, turbidity currents, and tectonic uplift.

Case Study 1: Chagos-Laccadive Ridge System

• A north-south trending aseismic ridge formed due to hotspot volcanism.
• Connects Laccadive Islands, Maldives, and Chagos Archipelago.
• It divides the Arabian Basin and Central Indian Basin.

Provides evidence for Plate movement over a stationary hotspot—analogous to Hawaiian Ridge in the Pacific.

Case Study 2: Sunda Trench

• Located along Java-Sumatra plate boundary.
• Result of subduction of the Indo-Australian Plate beneath the Eurasian Plate.
• Zone of frequent earthquakes and tsunami generation.

The 2004 Indian Ocean Tsunami originated here due to a massive undersea megathrust earthquake.

Perspectives and Theories

• Plate Tectonic Theory explains ridge, trench, and basin formation.
• Isostasy (Airy & Pratt) accounts for uplift and subsidence of oceanic features.
• Law of Uniformitarianism supports that present tectonic activity has long-term impacts on topography.

Geophysical tools like sonar sounding and satellite altimetry have enabled quantitative mapping of seafloor topography (Quantitative Revolution in Geography).