The Major and Minor Ocean Relief Features are formed over millions of years through natural processes such as tectonic activity, volcanic eruptions, sediment deposition, and erosion. From the expansive continental shelves to the deep, mysterious oceanic trenches, each feature on the seafloor provides valuable insights into Earth’s geological history. Understanding these underwater landscapes is important for studying the dynamic processes that continually shape our planet. The ocean floor is not just a flat, uniform surface; it is a varied terrain with mountains, valleys, plateaus, ridges, and depressions that reveal the story of Earth's evolution and the interplay of internal and external geological forces. In this article, we are going to cover Major and Minor Ocean Relief Features.
Major and Minor Ocean Floor Relief Features
The ocean floor consists of both major and minor relief features, including mountain ranges, deep trenches, mid-ocean ridges, hills, seamounts, guyots, submarine canyons, atolls, and more.
- Each of these features has a unique origin and provides crucial information about the planet’s tectonic and sedimentary processes.
- Formation: The seafloor is primarily shaped by tectonic activities, such as plate movements, subduction, and rifting, as well as volcanic activity that forms mountains and seamounts.
- In addition, deposition by rivers, ocean currents, and underwater events plays a significant role in sculpting features like continental rises and abyssal plains.
- Erosion and sedimentation processes continually modify the seafloor, creating a dynamic and ever-changing underwater landscape.
Major Ocean Relief Features
The Major Ocean Relief Features include:
Continental Shelf
According to the United Nations Convention on the Law of the Sea, the continental shelf of a coastal state is defined as the submerged prolongation of its land territory, including the seabed and subsoil beyond the territorial sea, extending to the outer edge of the continental margin, or up to 200 nautical miles if the margin does not reach that distance.
Characteristics of the Continental Shelf:
- Seaward Extension: The continental shelf extends from the coastline to the continental edge, generally reaching depths of 100–200 meters.
- Area: It covers approximately 7.5% of the total oceanic area.
- Depth: It is the shallowest part of the ocean, with an average gradient of less than 1°.
- Shelf Break: The shelf terminates at a steep slope called the shelf break.
- Width: The width varies from one region to another, averaging about 80 kilometers.
- Absence: Shelves are narrow or absent along margins of ocean–continent or ocean to ocean convergence zones.
- Examples: Notable shelves include the coasts of Chile and the west coast of Sumatra.
- Largest Shelf: The Siberian Shelf in the Arctic Ocean is the largest continental shelf in the world.
- The shelf contains thick sedimentary deposits that serve as sources of fossil fuels, such as oil and natural gas.
- Shelves are formed through a combination of land tilting, marine erosion, submergence of continental margins, relative sea-level rise, and sediment deposition by rivers.
Continental Slope
The continental slope connects the continental shelf to the deep ocean basins and marks the edge of the continent. Its gradient typically ranges between 2° and 5°, and it is characterized by the presence of submarine canyons and trenches formed by erosion and tectonic activity. The slope region represents a transition between shallow coastal areas and the deep ocean floor.
Continental Rise
The continental rise is a major depositional feature formed at the base of the continental slope, consisting of thick sequences of sediments transported from the continents. Sediments accumulate here through underwater landslides, river deposition, and turbidity currents. The rise has a gentle slope, typically ranging from 1:50 to 1:500, and serves as a sedimentary bridge between the slope and the deep abyssal plains.
Deep Sea Plain / Abyssal Plain
Abyssal plains are flat, gently sloping regions of the ocean floor covered with fine sediments such as clay and silt. These plains typically lie at depths between 3,000 and 6,000 meters and occupy nearly 40% of the oceanic area. They are formed as sediments from continental sources and shallow marine environments bury the irregular topography of the seafloor, creating an extensive flat relief that dominates much of the ocean basins.
Oceanic Deeps / Trenches
Oceanic trenches are the deepest parts of the oceans, located at the base of continental slopes and along island arcs. These long, narrow, steep-sided depressions are often associated with active volcanoes and strong earthquakes. Trenches form at convergent plate boundaries due to subduction processes, where one tectonic plate sinks beneath another. The Pacific Ocean contains the largest number of trenches, including the Mariana Trench, which is the deepest point on Earth.
Minor Ocean Relief Features
The Minor Ocean Relief Features include:
Mid-Oceanic Ridges
Mid-ocean ridges consist of two mountain chains separated by a central rift valley. Peaks may even rise above the ocean surface, as seen in Iceland, which is part of the Mid-Atlantic Ridge. Ridges are generally formed at divergent plate boundaries, where tectonic plates move apart, allowing magma to rise and form new crust. Rift valleys at the center of these ridges provide crucial evidence for seafloor spreading and plate tectonics.
Seamounts and Guyots
Seamounts are submarine mountains with pointed summits rising over 1,000 meters from the seafloor, primarily of volcanic origin. Flat-topped seamounts are called guyots, which indicate gradual subsidence over time. An example is the Emperor Seamount in the Pacific Ocean.
Submarine Canyons
These are long, narrow, and deep valleys cutting across continental shelves and slopes, often extending from the mouths of large rivers. They are formed through erosion and mass wasting on steep slopes. A notable example is the Hudson Canyon off the coast of the United States.
Atolls
Atolls are low islands in tropical oceans, consisting of coral reefs encircling a central lagoon. They may enclose a body of water that is fresh, brackish, or saline, and are formed through coral growth and subsidence of volcanic islands.
Other Ocean Relief Features
- Volcanic Island Arcs: Chains of volcanic islands formed along subduction zones; examples include Japan and Indonesia.
- Fracture Zones: Linear features with faults cutting across mid-ocean ridges, created by variable tectonic plate movements; e.g., Mid-Atlantic Fracture Zone.
- Abyssal Hills: Small, well-defined hills rising from the abyssal seafloor.
- Banks: Flat-topped elevations near continental margins, often in shallow water; examples include Dogger Bank and Grand Bank.
Hydrothermal Vents: Openings in the ocean floor that release mineral-rich, heated water, usually near volcanically active areas, supporting unique ecosystems.
Major and Minor Ocean Relief Features FAQs
Q1: Which of these is a minor feature of the ocean floor?
Ans: Seamounts, guyots, atolls, submarine canyons, and abyssal hills are minor features of the ocean floor.
Q2: What are the major features of the ocean basin?
Ans: The major features of the ocean basin are the continental shelf, continental slope, continental rise, abyssal plain, and oceanic trenches.
Q3: Which of these is a minor feature of ocean floor, continental shelf, continental slope, guyot, abyssal plain?
Ans: Among these, a guyot is a minor feature of the ocean floor.
Q4: What is a continental shelf?
Ans: A continental shelf is the shallow, submerged extension of a continent that stretches from the coastline to the continental slope.
Q5: What are seamounts and guyots?
Ans: Seamounts are underwater volcanic mountains with pointed peaks, while guyots are flat-topped seamounts formed due to subsidence.
