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The Ocean Basins Physical Oceanography Features of the Ocean Basins • Continental margin: portion of ocean made up of continental crust Features of the Ocean Basins • continental shelf: flat part of continental margin covered by shallow ocean water Formed by changes in sea level Avg depth = 60 m Shelf • Relatively shallow • 0 – 200 m • Relatively flat with a gradient of 2 m drop per kilometre Features of the Ocean Basins • continental slope: boundary between continental crust and oceanic crust - The average angle displayed by the slope is about 5 degrees. Features of the Ocean Basins • submarine canyons: deep, v-shaped valley that cuts through shelf & slope Features of the Ocean Basins • continental rise: wedge of sediments that separates slope from ocean floor Features of the Ocean Basins • abyssal plain (floor): very flat areas at depths of 3-5 km Features of the Ocean Basins • mid-ocean ridge: mountain range on ocean floor due to seafloor spreading Features of the Ocean Basins • trench: deep narrow valleys along the edges of subduction zones in the ocean floor; 90% of trenches are found around the Pacific rim. Marianas Trench in Pacific ocean is the deepest point on earth - 10,668 meters Bathymetric Charts – show the contours and depths of the seafloor topography General Slope Features • Sharp break from the shelf • Angle is gentle, averaging less than 5 degrees • Continues to a depth of 3600 m • Often carved by deep canyons - Hudson Canyon is famous in N.A. Submarine Canyons • V-shaped • Hudson Canyon steeper than the Grand Canyon • Form deep sea fans from sediments • Originated from rivers during ice ages The Gully! Submarine canyon off Nova Scotia • • Marine protected area because of the rare corals found there • The natural gas pipeline goes right by it…problems? The Gully Turbidity currents • Turbidity currents are caused by the slumping of sediments from the continental slope. • can travel at over 55 km/h • can spread 700 km+ • Can damage underwater pipelines, transatlantic cables Rise • Slope about ½ degree toward the abyssal plain • Sediment deposition from continent • Range from 100 to 1000 km in width • Only occur along passive margins, often off the mouth of large rivers Another look Features of the Ocean Basins • seamount: underwater volcanic mountain (some more than 1000 m high) • Features of the Ocean Basins Atolls A ring shaped island of coral reefs and coral debris. These often form over sinking inactive volcanoes. Features of the Ocean Basins • coral reef: limestone structures containing shells of animals that surround volcanic islands Features of the Ocean Basins • guyot: a flat-topped submerged seamount due to erosion Features of the Ocean Basins • rift valley: deep crevice in between mountain ranges Which coast has the wider shelf?
