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Warm Up 2/6/09 What technology do scientists use to measure ocean depth? a. sonar c. rope b. submersible d. laser 2. Differences in ocean-surface height can be measured by ____. a. satellites c. submersibles b. sonar d. none of the above 3. Approximately how much of Earth’s surface is covered by land? a. 60 percent c. 30 percent b. 70 percent d. 50 percent Answers: 1) a. 2) a. 3) c. 1. Ocean Floor Features Chapter 14, Section 2 Profile of North Atlantic Ocean Continental Margins Continental Margin – the zone of transition between a continent and the adjacent ocean basin floor In the Atlantic Ocean, thick layers of undisturbed sediment cover the continental margin. This region has very little volcanic or earthquake activity In the Pacific Ocean, oceanic crust is plunging beneath continental crust. This force results in a narrow continental margin that experiences both volcanic activity and earthquakes Passive Continental Margin Continental Shelves, Slopes, and Rises Continental Shelf – the gently sloping submerged surface extending from the shoreline Continental shelves contain important mineral deposits, large reservoirs of oil and natural gas, and huge sand and gravel deposits Continental Slope – the seaward edge of the continental shelf The continental slope is a relatively narrow feature along the continental shelf Continental Shelves, Slopes, and Rises Continued Submarine Canyon – deep, steep-sided valleys cut into the continental slope Turbidity Currents – occasional movements of dense, sediment-rich water down the continental slope Turbidity currents are known to be an important factor in sediment transfer in the ocean Continental Rise – a gradual incline which merges with the steep continental margin, occurs in regions where trenches do not exist Submarine Canyons Concept Check Compare and contrast the continental slope and continental rise. Continental slope marks the steep boundary between continental crust and oceanic crust. The continental rise occurs at the end of the continental slope and has a more gradual incline. Ocean Basin Floor Ocean Basin Floor – area between the continental margin and the mid-ocean ridge Deep-ocean trenches are long, narrow creases in the ocean floor that form the deepest parts of the ocean Trenches form at sites of plate convergence where one moving plate descends beneath another and plunges back into the mantle Abyssal Plains – deep, extremely flat features and are the most level places on Earth The sediments that make up abyssal plains are carried there by turbidity currents or deposited as a result of suspended sediments settling Ocean Basin Floor Continued Seamounts – the submerged volcanic peaks which dot the ocean floor Once underwater volcanoes reach the surface, they form islands After millions of years, the tops are eroded away and the once active islands sink back into the ocean, forming guyots Abyssal Plain Concept Check What are abyssal plains? Deep, extremely flat regions of the ocean floor. Mid-Ocean Ridges Mid-Ocean Ridge – found near the center of most ocean basins; an interconnected system of underwater mountains that have developed on newly formed ocean crust Seafloor Spreading – occurs at divergent plate boundaries where two lithospheric plates are moving apart New ocean floor is formed at mid-ocean ridges as magma rises between the diverging plates and cools Hydrothermal vents form along mid-ocean ridges and are zones where mineral-rich water escapes through cracks in oceanic crust into the surrounding cooler water Profile of North Atlantic Ocean Assignment (Due 2/13) Read Chapter 14 (pg. 394-413) Do Chapter 14 Assessment #1-33 (pg. 417-418) Cool Down What is formed at mid-ocean ridges? New ocean floor Compare and contrast seamounts and guyots. A seamount is an underwater volcano that has not reached the surface yet. A guyot is a volcanic island that has been eroded and sunk back under the water’s surface. What is one thing new that you learned today? Explain what it is.