Chapter 14.2Ocean Floor Features
• The ocean floor has 3 major regions – the continental margins, the ocean basin floor, and the mid-ocean ridge.
Continental Margins
• A continental margin is a zone of transition between a continent and the ocean basin floor.
• In the Atlantic Ocean, a thick layer of undisturbed sediment cover the continental margin. This area have very little volcanic or earthquake activity.
• In the Pacific Ocean the oceanic crust is moving below the continental crust. This make a very narrow continental margin that has volcanic activity and earthquakes.
Continental Shelf
• The continental shelf is a gently sloping submerged surface that extends from the shoreline.
• Some areas have very small continental shelves and some have very large shelves.
• Many continental shelves have mineral deposits, large reservoirs of oil and natural gas, and huge sand and gravel deposits.
• They can also be important fishing grounds.
Continental Slope
• The continental slope is at the edge of the continental shelf (seaward). This is an area that is steeper than the shelf.
• Some slopes have submarine canyons – these may go into the ocean basin floor.
• Turbidity currents are movements of dense, sediment-rich water down the continental slope.
Continental Rise
• Where trenches do not exist and the continental slope moves into a more gradual incline this is called the continental rise.
Ocean Basin Floor
• Ocean basin floor is between the continental margin and a mid-ocean ridge. This area makes up 30% of the Earth’s surface. This area has deep-ocean trenches, abyssal plains, and volcanic peaks called seamounts and guyots.
Deep-Ocean Trenches
• These are long, narrow creases in the ocean floor that form the deepest parts of the ocean.
• The deepest place on Earth is part of the Mariana Trench called the Challenger Deep.
• Trenches form where plates converge and one plate moves under another.
• There are many earthquakes and volcanoes in these areas – like the Ring of Fire.
Abyssal Plains
• These are deep, extremely flat parts of the ocean. They have a lot of fine sediment.
• These sediments are carried by turbidity currents or deposited as a result of sediments that were suspended settling.
• The Atlantic Ocean has the most extensive abyssal plains with few trenches.
Seamount and Guyots
• Seamounts are submerged volcanic peaks on the ocean floor. They are volcanoes that have not reached the ocean surface.
• There are seamounts everywhere but the Pacific Ocean has the most.
• Guyots are once-active, now-submerged, flat-topped structures. They were volcanic islands that have been eroded away.
Mid-Ocean Ridges
• This is found near the center of most ocean basins. It is underwater mountains that have developed on newly formed ocean crust.
Seafloor Spreading
• Seafloor spreading is where divergent plates are moving apart. New ocean floor is formed at this point.
Hydrothermal Vents
• Hydrothermal vents also form along mid-ocean ridges. They have mineral-rich water that is very hot. This area will have a lot of minerals and metals like sulfur, iron, copper, and zinc to precipitate (become solid) out of the water.
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