Chapter 14

1. Chapter 14 The Ocean Floor

2. Section 14.2 Ocean Floor Features

3. Ocean Floor Features • Mapping the ocean Floor • The ocean floor regions are the continental margins, the ocean basin floor and the mid-ocean ridge.

4. Ocean Floor Features Continental Margins • A continental margin is 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.

5. Atlantic Continental Margin

6. Ocean Floor Features Continental Margins • In the Pacific Ocean, oceanic crust plunges beneath continental crust. This force results in a narrow continental margin that experiences both volcanic activity and earthquakes.

7. Which of the following areas is NOT one of the three main regions of the ocean floor? • Ocean floor basin • Continental margins • Continental rock • Mid-ocean ridge

8. The continental margins of the Pacific Ocean are • Wider than those of the Atlantic and have more earthquake activity. • Narrower than those of the Atlantic and are not covered with thick layers of sediment. • Wider than those of the Atlantic and have no volcanic or earthquake activity. • Narrower than those of the Atlantic and are covered with thick layers of sediment.

9. Ocean Floor Features Continental Margins • Continental Shelf • A continental shelf is 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.

10. Ocean Floor Features Continental Margins • Continental Slope • A continental slope is the steep gradient that leads to the deep-ocean floor and marks the seaward edge of the continental shelf. • Asubmarine canyon is the seaward extension of a valley that was cut on the continental shelf during a time when sea level was lower—a canyon carved into the outer continental shelf, slope, and rise by turbidity currents.

11. Ocean Floor Features Continental Margins • Continental Slope • Aturbidity current is the downslope movement of dense, sediment-laden water created when sand and mud on the continental shelf and slope are dislodged and thrown into suspension.

12. Submarine Canyons

13. Ocean Floor Features Continental Margins • Continental Rise • A continental rise is the gently sloping surface at the base of the continental slope. • Located in regions where trenches do not exist.

14. Which area of the continental margin contains mineral deposits, large reservoirs of oil and natural gas, and huge deposits of sand and gravel? • Continental shelf • Continental slope • Continental rise • Continental plain

15. Which area of the continental margin are submarine canyons cut into? • Continental shelf • Continental slope • Continental rise • Ocean floor basin

16. What are turbidity currents? • Fast moving currents near the shoreline • Sediment-rich water that moves down the continental slope • Currents that carry trash out to the open ocean • Currents that wear aware the shoreline

17. Ocean Floor Features Ocean Basin Floor • The ocean basin floor is the area of the deep-ocean floor between the continental margin and the oceanic ridge. • Deep-Ocean Trenches • Trenches form at the sites of plate convergence where one moving plate descends beneath another and plunges back into the mantle.

18. Ocean Floor Features Ocean Basin Floor • Abyssal Plains • Anabyssal plain is a very level area of the deep-ocean floor, usually lying at the foot of the continental rise. • The sediments that make up abyssal plains are carried there by turbidity currents or are deposited as suspended sediment settles out.

19. Ocean Floor Features Ocean Basin Floor • Seamounts and Guyots • Aseamount is an isolated volcanic peak that rises at least 1000 meters above the deep-ocean floor, and a guyot is an eroded, submerged seamount.

20. Abyssal Plain Cross Section

21. Trenches form at sites where • One plate descends beneath another. • Erosion cuts into the continental shelf. • Two plates diverge under the sea. • The tops of undersea volcanoes collapse.

22. Abyssal plains are very flat features that form when • Volcanoes spread lava on the ocean bottom. • Turbidity currents deposit sediments on the ocean floor. • Ocean waters flood plains on land. • Plates diverge on the ocean floor, causing seafloor spreading.

23. Guyots are • Active underwater volcanoes • Volcanoes that have turned into islands • Eroded, flat topped, underwater volcanoes • Underwater volcanic craters

24. Ocean Floor Features Mid-Ocean Ridges • A mid-ocean ridge is found near the center of most ocean basins. It is an interconnected system of under water mountains that have developed on newly formed ocean crust. • Seafloor Spreading • Seafloor spreading is the process by which plate tectonics produces new oceanic lithosphere at ocean ridges. • New ocean floor is formed at mid-ocean ridges as magma rises between the diverging plates and cools.

25. Ocean Floor Features Mid-Ocean Ridges • Hydrothermal Vents • Hydrothermal vents form along mid-ocean ridges. These are zones where mineral-rich water, heated by the hot, newly-formed oceanic crust, escapes through cracks in the oceanic crust into surrounding water.

26. Hydrothermal Vents

27. Which of the following forms at mid-ocean ridges? • Island arcs • Deep-sea trenches • Guyots • New ocean floor

28. Where do hydrothermal vents form? • Near subduction zones • Near deep-ocean trenches • Along mid-ocean ridges • In the deep-ocean basin floor