Mid-Ocean Ridges | Geology Optional Notes for UPSC PDF Download

Introduction

Underwater mountain ranges, known as Mid-Oceanic Ridges, are significant features formed by plate tectonics. These ridges are characterized by two mountain chains separated by a large depression. Some peaks of these ridges rise above the ocean’s surface, reaching heights of up to 2,500 meters.

Underwater Exploration and Tsunamis

• Numerous underwater expeditions have been conducted to study the ocean floor, revealing diverse and spectacular features. When tsunamis occur, they are often attributed to earthquakes beneath the sea floor, indicating the role of tectonic processes along plate boundaries.

Modern Mapping and Understanding

• Modern ocean floor maps have significantly expanded our understanding of underwater features and the ongoing tectonic processes of the Earth. These maps have aided in comprehending the morphological variations of the ocean based on factors such as location, origin, morphology, lithology, and water mass dynamics.

Mid Ocean Ridges Formation

• Distinctive Structures
  • Mid-Ocean Ridges are prominent structures primarily located in the middle of ocean basins, where divergent plate boundaries exist. They are associated with major tectonic processes, including the release of convection currents and the spreading of the sea floor, as explained by Plate Tectonics Theory.
• Mid-Indian Ridge
  • The Mid-Indian Ridge is a submarine ridge in the Indian Ocean, a part of the global midoceanic ridge system. It extends from the South Atlantic into the Indian Ocean, dividing near Rodrigues Island into two sections.
• Branches and Seismic Activity
  • One segment extends northward toward the Gulf of Aden, connecting with the East African Rift System, while the other branch extends southeast toward the Macquarie Islands. The Carlsberg Ridge, located within the Mid-Indian Ridge, is seismically active, associated with earthquake epicentres.

Mid-Oceanic Ridges Types

1. Fast-Spreading Mid-Ocean Ridge
   • Fast-spreading ridges, such as the northern and southern East Pacific Rise, exhibit more magma beneath the ridge axis and frequent volcanic eruptions. The rapid spreading is attributed to the hotter plate beneath the ridge crest, responding fluidly to divergent processes.
2. Slow-Spreading Mid-Ocean Ridge
   • Slow-spreading ridges, like the northern Mid-Atlantic Ridge, display characteristics of nougat or cold chocolate bars when pulled apart. The seafloor breaks into ridges and valleys due to the slower spreading process.

Mid Ocean Ridges Principal Characteristics

1. New Oceanic Crust Formation
   • At the crests of oceanic ridges, new oceanic crust and part of the Earth's upper mantle are formed, constituting the lithosphere. Fresh basaltic lavas are exposed on the seafloor at these locations, gradually buried by sediments as the seafloor spreads.
2. Heat Flow and Earthquakes
   • Heat flow at ridge crests is significantly higher than elsewhere on the planet. Earthquakes are common along offset ridge segments' crests and transform faults, indicating tension in the oceanic crust.
3. Depth Correlation and Cooling
   • The depth over oceanic ridges correlates precisely with the age of the ocean crust, with depth proportional to the square root of crustal age. Cooling of the oceanic crust and upper mantle as they move away from the spreading center causes an increase in depth. Slow-spreading ridges are narrower than fast-spreading ridges due to the cooling process.
4. Global Spreading Rates and Oceanic Relief
   • A link exists between global spreading rates and ocean water transgression and regression onto continents, influencing the relief of oceanic ridges.

Mid-Oceanic Ridges Major Distribution

Mid-oceanic ridges, the sites of oceanic spreading centers, are present in all ocean basins. These spreading centers exhibit varying rates of spreading and distinct geological features across different oceanic regions.

Arctic Ocean

• A slow-rate spreading center is located in the Eurasian basin of the Arctic Ocean, extending from the eastern side. This ridge can be traced south to Iceland, characterized by transform faults. Iceland itself was formed by a hot spot beneath an oceanic spreading center. The Reykjanes Ridge, extending south from Iceland, lacks a rift valley due to the influence of the hot spot.

Atlantic Ocean

• The Mid-Atlantic Ridge spans from Iceland southward to approximately 60° S latitude in the extreme South Atlantic Ocean. Initially referred to as a mid-ocean ridge, it was vaguely known until the nineteenth century. American oceanographers in the 1950s identified it as a continuous mountain range. The crest of fast-spreading segments exhibits an axial high, while slower-spreading rifted ridges have rough, faulted topography.

Indian Ocean

• The Southwest Indian Ridge, a very slow oceanic ridge, traverses between Africa and Antarctica, connecting with the Mid-Indian and Southeast Indian ridges east of Madagascar. The Carlsberg Ridge is situated at the northern end of the Mid-Indian Ridge, extending northward to join spreading centers in the Gulf of Aden and the Red Sea. The Southeast Indian Ridge spreads at a medium rate, with rifted crests and rugged flanks. Magnetic anomalies suggest asymmetric spreading south of Australia.

Pacific Ocean

• The Pacific-Antarctic Ridge extends northeast from a point between New Zealand and Antarctica to meet the East Pacific Rise near South America. The former spreads at intermediate to fast rates, while the latter extends northward to the Gulf of California. The East Pacific Rise, discovered during the 1870s, exhibits interrupted and offset spreading centers. Smaller spreading centers exist in the western Pacific, the Fiji Plateau, the Woodlark Basin, and the Scotia Sea, among others.

Spreading Centre Zones and Associated Phenomena

• Detailed studies of spreading centers since the 1970s have revealed hydrothermal vents and unique biological communities. These discoveries have provided new insights into seafloor spreading processes and associated phenomena.

Mid Oceanic Ridges UPSC

Plate tectonics, the theory describing the movement of Earth's lithospheric plates, gives rise to diverse geological features, including mid-oceanic ridges. These underwater mountain ranges consist of two parallel chains separated by a large depression. Some peaks of these ridges rise above the ocean's surface, reaching heights of up to 2,500 meters.

Geological Significance

• Mid-ocean ridges hold immense geological significance as they occur along a specific type of plate boundary known as a "spreading center" or "divergent plate boundary." At these boundaries, tectonic plates move apart from each other. Consequently, mid-ocean ridges serve as sites where new oceanic crust is formed as magma wells up from beneath the Earth's surface. This process of seafloor spreading contributes significantly to the renewal and expansion of the oceanic crust.

Rate of Plate Separation

• The plates at mid-ocean ridges separate at varying rates, typically ranging from 1 cm to 20 cm per year. This rate of spreading determines the geological characteristics of the ridge, including its morphology and the type of volcanic activity occurring along its axis. Fast-spreading ridges exhibit higher rates of plate separation, leading to more pronounced volcanic activity and smoother topography, whereas slow-spreading ridges display lower rates of plate separation, resulting in rugged terrain and less frequent volcanic eruptions.

Conclusion

• Mid-oceanic ridges represent dynamic geological features shaped by the processes of plate tectonics. Their formation and characteristics play a crucial role in the Earth's geological evolution and the ongoing renewal of the oceanic crust. Understanding mid-ocean ridges is essential for comprehending the broader mechanisms driving plate tectonics and the geological dynamics of our planet.