Part 2 Chap 14.2 Ocean floor features

Chapter 14.2 : 

Chapter 14.2 Ocean Floor Features

Ocean floor features : 

Ocean floor features Oceanographers have divided the ocean floor into three main regions The continental margins The ocean basin floor The mid-ocean ridge

Ocean floor features : 

Ocean floor features The three main regions

Ocean floor features : 

Ocean floor features Continental Margins This is the zone of transition between a continent and the adjacent ocean basin floor

Ocean floor features : 

Ocean floor features Continental margins Atlantic Ocean Thick layers of undisturbed sediment cover the continental margin There is very little volcanic or earthquake activity because the continental margins of the Atlantic are not associated with plate boundaries

Ocean floor features : 

Ocean floor features An illustration of the Atlantic Continental Margin

Ocean floor features : 

Ocean floor features Continental margins Pacific Ocean Oceanic crust is plunging beneath continental crust The result is a narrow continental margin that experiences both volcanic activity and earthquakes

Ocean floor features : 

Ocean floor features Continental Margins Consist of three main areas Continental Shelf Continental Slope Continental Rise

Ocean floor features : 

Ocean floor features Continental Margins Continental Shelf Is a gently sloping submerged surface extending from the shoreline May be non-existent in some areas May extend seaward for 1500 km in other areas Average is 80 km wide and 130 km deep at the seaward edge and equal to a drop of only 2 meters per kilometer This change is so slight that it looks flat to the human eye

Ocean floor features : 

Ocean floor features Continental Margins Continental Shelf Contains important mineral deposits, large reservoirs of oil and natural gas, and huge sand and gravel deposits The waters above the shelf contain important fishing grounds

Ocean floor features : 

Ocean floor features Continental Margins Continental Slope Marks the seaward edge of the continental shelf and the boundary between the continental crust and oceanic crust It is steeper than the shelf Steepness varies from an average of 5o to steeper than 25o It is relatively narrow – only about 20 km wide

Ocean floor features : 

Ocean floor features Continental Margins Continental Slope Deep-sided valleys that cut into the slope are known as submarine canyons Most are believed to have originally been formed as river valleys during periods of low sea level during recent ice ages They continue to be formed today by turbidity currents

Ocean floor features : 

Ocean floor features Turbidity currents Occasional movements of dense, sediment-rich water down the continental slope Created when sand and mud on the shelf and slope are disturbed (such as by earthquakes) and become suspended in the water As muddy water is more dense than normal seawater, it flows down the slope and erodes and collects more sediment Erosion from these muddy torrents is believed to be the major force in forming the canyons Turbidity currents also known to be important way sediment is transported to the ocean and deposited on the ocean floor

Ocean floor features : 

Ocean floor features The relationship between turbidity currents and submarine canyons

Ocean floor features : 

Ocean floor features Continental Margins Continental Rise A gently sloping surface at the base of the continental slope May be 100s of km wide

Ocean floor features : 

Ocean floor features Ocean basin floor The area of the deep ocean floor between the continental margin and the oceanic ridge Comprises almost 30% of Earth’s surface Comparable to percentage of land above sea level

Ocean floor features : 

Ocean floor features Ocean Basin Floor Includes deep-ocean trenches, very flat areas, and tall volcanic peaks

Ocean floor features : 

Ocean floor features Ocean Basin Floor Deep-Ocean Trenches Long, narrow creases in the ocean floor that form the deepest parts of the ocean Most are located along the margins of the Pacific Ocean Many exceed 10,000 meters in depth The deepest place on Earth is the Challenger Deep, part of the Mariana Trench. It has been measured to 11,022 m below sea level

Ocean floor features : 

Ocean floor features Ocean Basin Floor Deep-Ocean Trenches Form at sites of plate convergence where one moving plate descends beneath another and plunges back into the mantle Earthquakes and volcanic activity are associated with these regions

Ocean floor features : 

Ocean floor features Ocean Basin Floor Abyssal Plains Are deep, extremely flat features Are possibly the most level places on Earth! Made up of thick accumulations of fine sediment that have buried an otherwise rugged ocean floor The sediments that make up the abyssal plains are carried there by turbidity currents or deposited as a result of suspended sediments settling

Ocean floor features : 

Ocean floor features Ocean Basin Floor Abyssal Plains They are found in all oceans of the world Atlantic has most extensive because it has the fewest trenches to catch sediment carried down continental slopes

Ocean floor features : 

Ocean floor features Ocean Basin Floor Tall volcanic peaks The submerged volcanic peaks that dot the ocean floor are called seamounts These steep-sided cone-shaped peaks are found on the floors of all oceans The greatest number are found in the Pacific If the seamount reaches above the surface it becomes an island

Ocean floor features : 

Ocean floor features Ocean Basin Floor The life of a seamount Stage 1: A seamount is a volcanic peak in the ocean that is submerged Stage 2: The seamount continues to grow until it reaches above the surface and becomes an island Stage 3: Over time, the source of growth for the seamount disappears, the island erodes away and sink. Once it is below sea level again the once-active, now submerged, flat topped structure is called a guyot

Ocean floor features : 

Ocean floor features Ocean Basin Floor Coral Atolls Can form where former volcanic Islands are becoming guyots. In the right conditions (average temp 24oC) the coral grows on top of the submerged remains of the island forming atolls and lagoons

Ocean floor features : 

Ocean floor features Mid-Ocean Ridges An interconnected system of underwater mountains that have developed on newly formed ocean crust They are found near the center of most ocean basins The mid-ocean ridge is the longest topographic feature on the Earth’s surface Winding through all the major oceans similar to the way a seam winds over the surface of a baseball, it exceeds 70,000 km in length

Ocean floor features : 

Ocean floor features Mid-Ocean Ridge It is not narrow It has widths from 1000 to 4000 km and may occupy as much as one half of the total area of the ocean floor It is offset in areas by large transform faults giving it a segmented appearance These faults create shallow earthquakes

Ocean floor features : 

Ocean floor features Mid-Ocean Ridge Seafloor spreading A high amount of volcanic activity takes place along the crest of the ridge At this point divergent plates allow magma to rise between them and cool forming new ocean floor This results in seafloor spreading The spreading of the sea floor that takes place at divergent plate boundaries where two lithospheric plates are moving apart

Ocean floor features : 

Ocean floor features Mid-Ocean Ridge Hydrothermal vents Zones where mineral-rich water, heated by the hot, newly formed oceanic crust, escapes through cracks in the oceanic crust into the surrounding water They form along mid-ocean trenches As the super-heated, mineral-rich water comes in contact with the surrounding colder water, the minerals and metals such as sulfur, copper, iron, and zinc precipitate out and are deposited