Introduction

Ocean relief is caused due to volcanic, depositional, tectonic, and erosional processes and their interactions. Ocean relief features are divided into minor and major relief features. The ocean floor mapping can be further divided into four major divisions.

Ocean Relief Features 

Unlike the continents, the oceans merge naturally, making it hard to separate them. The geographers have divided the oceans into five oceanic parts of the world, namely India, The arctic, the Atlantic, Southern, and the Pacific. The various bays, gulfs, seas, and many other inlets are parts of such four large oceans.

A major portion of the ocean floor mapping is found between 3 to 6 km below the average sea level. The land below the water of the oceans, the ocean floor reveals various and complex features compared to those observed above the land.

The ocean floor mapping shows that the topography is rugged with the world’s deepest trenches, largest plains, and most extensive mountain ranges. Such features are formed by depositional, tectonic, and volcanic processes.

 Minor Relief of the Oceans

Some of the minor relief features in the ocean floor mapping are:

• Seamounts
• Mid-Oceanic Ridges
• Fracture Zone
• Guyots
• Trenches
• Ridges
• Hills
• Coral reefs
• Island Arcs
• Atolls
• Sleeps
• Canyons
• Submerged Volcanoes
• Sea Scarps

Mid Oceanic Ridges

• Mid-ocean ridges are underwater mountain ranges that are formed through divergence of plates, involving plate tectonics
• Mid oceanic Ridge is crafted from two mountain chains divided by a large depression
• Mid-oceanic ridges are classified on the basis of
•   Axial Ridge
•   Magnetics & Polarity
•   Fast/Slow Spreading
• The mountain ranges could have peaks of 2500 m high, and some mountain ranges can even reach the ocean’s surface
• Examples of Mid-oceanic ridges are the Mid-Atlantic Ridge in Atlantic Ocean, Pacific Antarctic Ridge, and East pacific rise

Atoll

• The atoll is a ring-shaped coral reef containing a coral rim to completely or incompletely encompass a lagoon
• The atoll is low islands that are found in tropical oceans
• It may be a part of the lagoon sea or occasionally encircling a body of highline, fresh, or brackish saline water

Example: Palmyra atoll, south of the Hawaiian Islands

Seamount

• The seamount is formed by volcanic activities and is an underwater mountain. The morphology of these undersea mountains contributes to the ecological diversity of seamount habitats
• Nutrients are pushed upwards through the depths of the sea toward the sunlit surface by the hillsides of seamounts, providing food for organisms varying from coral to fishes to crabs
• Seamounts are the type of mountains that have pointed peaks and are mounted from the seafloor

• They can not reach the ocean’s surface
• Seamounts are volcanic in origin
• They can be 3000 to 4500 m tall
• An example of seamount is an extension of the Hawaiian Islands in the Pacific Ocean known as The Emperor

Submarine Canyons

• On Earth, there are an estimated 9,477 undersea canyons, which cover roughly 11% of the continental slope

• Submarine canyons transport sand-sized particles from geographical boundaries to the ocean depths
• Submarine Canyons are those that have narrow steep-sided valleys
• Submarine Canyon originates either on a continental shelf or within continental slopes
• The Hudson Canyon is one of the best-known submarine canyons in the world
• Congo Canyon is considered the largest river canyon ever
• Zhemchug Canyon is the largest submarine canyon in the world as a whole

Guyots

• Guyot is a type of flat-topped seamount
• Guyots are also known as table mounts
• More than 10000 seamounts and guyots are expected to occur in the Pacific Ocean. However, Guyots are most prevalent in the Pacific Ocean, but they have been discovered in all oceans excluding the Arctic Ocean
• They show evidence of slow subsidence through stages to become flat-topped submerged mountains. When the seafloor eventually falls as the ocean floor moves away from oceanic ridges, the flattened guyots are buried to create undersea flat-topped peaks
• A Guyot is important because the sediment-covered guyot tops, with their terraces and, in some cases, emergent cones, offer a variety of habitats not seen on conical seamounts, perhaps increasing the diversity of deep-sea organisms that live there

Reefs

• A Reef is an ocean relief feature, predominantly an organic deposit made by dead or living organisms that form a rock or mound elevation like a ridge
• Coral reefs are a characteristic feature of the Pacific ocean from where they are associated with guyots and seamounts

• Coral heads are made up of polyps, which are individual animals grouped in various shapes
•  Polyps are normally little, but they can grow to be as large as 12 inches (30 cm) across
• Coral polyp colonies are bound together by calcium carbonate to build reefs. The majority of coral reefs are made up of stony corals, which have polyps that cluster together
• Coral polyps do not carry out photosynthesis, although they do have a symbiotic interaction with tiny algae

• The Queensland coast of Australia is the largest reef in the world
• Reefs are dangerous for navigation as they can extend above the surface

Significance of Study of Oceanic Relief

• Ocean relief features control the sea-water motions
• The bottom relief of the ocean floor has a great influence on fishing and navigation
• The oceanic movements in currents form causes several variations in the atmosphere and the oceans

Conclusion

 The ocean floor mapping is rugged with the world’s deepest trenches, the largest plains, and largest mountain ranges. Such features are formed like continent features by depositional, tectonic, and volcanic processes. It is caused due to many factors such as tectonic, erosional, volcanic, and depositional and their interactions. The ocean floor mapping is further divided into minor and major features. The minor features are mid-oceanic ridges, Atoll, submarine guyots reefs, and many others mentioned above.