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The Ocean Basin Ocean Basin Features Continental Margins Composed of the Continental shelf Continental slope Continental rise Continental Shelf A shallow submerged extension of the continent. Exposed during times of low sea-level. Composed of continental crust. Gentle slope – 1.7 m/km (9 ft/mile) Ends at shelf break – the abrupt increase in slope at the junction between the continental shelf and continental slope. Usually 140m deep. Continental Slope The transition between the gently descending continental shelf and the deep-ocean floor. Average angle 4 degrees. (The same as a movie theater.) Extends from shelf break to the continental rise or a trench. Submarine Canyons Cut into continental shelf and slope and terminate on the sea-floor in a fan shaped wedge of sediment. Mainly formed by turbidity currents – underwater landslides. Sediment mixes with water and the more dense mixture moves downslope eroding the continental slope with it. Submarine Canyon Turbidity Current Sediments produced are called turbidites. Submarine Canyons – Con’t. Some are drowned valleys or are extensions of continental rivers. Hudson River Canyon. 3 km deep 300 km out to sea. Continental Rise Wedge of sediment at the base of the continental slope. Width varies from 100 km to 1000 km. Active Continental Margins Associated with active tectonic processes. – Subduction, earthquakes, volcanoes, faulting. Narrow continental shelf No continental rise. Continental slope usually terminates in a deep-sea trench. Active Continental Margins Passive Continental Margins No active tectonic process. Typically broad continental shelf. Continental slope terminates at the continental rise. No trench. Passive Continental Margin Deep-Ocean Basins Abyssal Plains Flattened places on the ocean floor. Basaltic crust covered by sediments up to 3 miles thick. Abyssal Hills 1-10 km across. Approximately 100 m in height. Sea Mounts Undersea Mountains Guyots Flat topped seamount. Top eroded off by wave action, then the mountain sank below sea level. Trenches Form at subduction zones. Deepest places in the ocean. Mid Ocean Ridges Divergent boundaries which usually occur in the middle of oceans. Constantly forming new oceanic crust. Mid Ocean ridge system is 40,000 miles long. Mid Ocean Ridges More M.O.R