Oceanography
Chapter 31: Ocean Relief
1. Major Ocean Relief Features
o Continental Shelf
o Continental Slope
o Continental Rise
o Deep Sea Plain or Abyssal Plain
2. Minor Ocean Relief Features
o Oceanic Deeps or Trenches
o Mid-Oceanic Ridges or Submarine Ridges
o Abyssal Hills (Seamounts And Guyots)
o Submarine Canyons
o Atoll
o Bank, Shoal and Reef
1. Major Ocean Relief Features
Continental Shelf
Definition: The extended perimeter of each continent, submerged
under shallow seas.
Characteristics:
o Shallow, gently sloping seabed extending from the shoreline to
the continental slope.
o Depth usually up to 200 meters.
o Rich in marine life and resources like oil, natural gas, and
minerals.
o Important for fishing and marine biodiversity.
Examples: North Sea Shelf, Grand Banks (off Newfoundland).
Continental Slope
Definition: The steep slope where the continental shelf drops down
to the ocean floor.
Characteristics:
o Marks the boundary between continental crust and oceanic
crust.
o Depth ranges from about 200 meters to 3,000 meters.
o Steeper than the continental shelf, with slopes typically ranging
from 4 to 6 degrees.
o Features submarine canyons formed by sediment-laden
currents.
Examples: The slope off the eastern coast of the USA, which leads
into the deep waters of the Atlantic Ocean.
Continental Rise
Definition: The area of the ocean floor between the continental slope
and the abyssal plain.
Characteristics:
o Formed by the accumulation of sediments from the continental
shelf, transported by turbidity currents.
o Gentle slope, typically less steep than the continental slope.
o Acts as a sedimentary buffer zone.
o Depth can extend from around 3,000 to 4,000 meters.
Examples: Found at the base of the continental slope around the
world, such as the Bay of Bengal's continental rise.
Deep Sea Plain or Abyssal Plain
Definition: The flat, nearly level areas of the ocean floor between the
continental rise and mid-oceanic ridges.
Characteristics:
o Among the flattest, smoothest, and least explored regions on
Earth.
o Depth typically ranges from 3,000 to 6,000 meters.
o Covered by fine-grained sediments, such as clay and silt, often
mixed with organic matter.
o Supports unique deep-sea ecosystems with specialized
organisms.
Examples: The Sohm Plain in the North Atlantic, the Hatteras Plain
off the east coast of the USA.
2. Minor Ocean Relief Features
Oceanic Deeps or Trenches
Definition: Long, narrow depressions on the ocean floor.
Characteristics: The deepest parts of the ocean; formed by
subduction zones where one tectonic plate slides beneath another.
Examples: Mariana Trench (Pacific Ocean), Puerto Rico Trench
(Atlantic Ocean).
Mid-Oceanic Ridges or Submarine Ridges
Definition: Underwater mountain ranges formed by plate tectonics.
Characteristics: Created by divergent plate boundaries where new
oceanic crust is formed; characterized by a central rift valley.
Examples: Mid-Atlantic Ridge, East Pacific Rise.
Abyssal Hills (Seamounts and Guyots)
Abyssal Hills: Small, rolling hills on the ocean floor, typically found
in abyssal plains.
Seamounts: Underwater volcanic mountains rising from the ocean
floor but not reaching the surface.
Guyots: Seamounts with flat tops, eroded by wave action when they
were above sea level.
Examples: Emperor Seamounts (Pacific Ocean).
Submarine Canyons
Definition: Deep, steep-sided valleys cut into the seabed of the
continental slope.
Characteristics: Often extend from river mouths and formed by
underwater currents and sediment flows.
Examples: Monterey Canyon (off the coast of California), Hudson
Canyon (off the coast of New York).
Atoll
Definition: Ring-shaped coral reef, island, or series of islets
surrounding a lagoon.
Formation: Develops from fringing reefs around volcanic islands that
subside over time.
Examples: Bikini Atoll (Marshall Islands), Maldives Atolls.
Bank, Shoal, and Reef
Bank: Elevated area on the continental shelf, often rich in marine life
due to shallow depths.
o Example: Grand Banks (off Newfoundland).
Shoal: Shallow area in a body of water, often composed of sand or
gravel; can be hazardous to navigation.
o Example: Dogger Bank (North Sea).
Reef: A ridge of rock, coral, or sand at or near the surface of the
water.
o Coral Reefs: Formed from the calcium carbonate skeletons of
coral organisms.
o Example: Great Barrier Reef (Australia).
