Chapter 14.2 Ocean 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.