Chapter 20 Ocean Basins

1. Chapter 20Ocean Basins Section 2 Features on the Ocean Floor Notes 20-2

2. Ocean Floor • Continental Margins • Shallower parts of the ocean floor • Made of continental crust and thick sediment layer • Deep Ocean Basin • Made of oceanic crust and thin sediment layer

4. Monterey Bay, San Francisco, CA

5. Continental Margins • Often the boundary between continent and ocean floor is found offshore beneath ocean and thick sediments • Continental Shelf: • Slopes gently • Covered by shallow water – only about 60 m • Part of continental margin • Average = 70 km wide • Widest is from Siberia to Alaska in the Arctic Ocean

6. Continental Margins • United States: • East coast = 170 km on average • West coast = about 40 km on average • Affected by ocean levels • Lower sea level = more erosion and weathering • Higher sea level = places for deposits of sediments

7. Continental Margins • Continental Slope: • Steep side to the continental shelf • Boundary between continental crust and oceanic crust is at the base of the slope • Submarine canyons: • Deep valleys cut into the continental shelf and slope • Can be associated with river mouths or turbidity currents • Turbidity Currents: dense currents that carry large amounts of sediments down the slope

8. Turbidity Currents • Form when landslides of material run down a slope • Can be caused by earthquakes or by excessive sediment loads • When the sediments come to a stop, at the bottom of the slope, will cause a continental rise

9. Deep Ocean Basin • In the deep ocean, there are mountains, plains, trenches and volcanoes. • Mountains are higher and plains flatter in the ocean • Trenches: • Deepest land features on the earth • Long, narrow • Mariana Trench is deepest place in the world • Over 11,000 m deep (11 km) • Found near the island Guam • Most are found along the Pacific Ring of Fire

10. Mariana Trench

11. Deep Ocean Basin • Abyssal Plain: • Extremely flat area – flattest on the earth • Usually over 4 km below the ocean surface • Cover over half the ocean basin • Sediments fall to the abyssal plain from the continental margins • Atlantic Ocean has thick sediments • Pacific Ocean doesn’t • Trenches catch most of the sediments and hold them

12. Deep Ocean Basin • Mid-Ocean Ridges: • Continuous series of mountain ranges that run along the floors of all the oceans • Most are under the water • Iceland is one exception • Form when plates move away from each other • Causes a rift in the middle of the mountain range • Different parts break at different rates • Creates fracture zones – series of faults

15. Deep Ocean Basin • Seamounts: • Submerged volcanic mountains • At least 1,000 m high • Anything less is called an abyssal hill • Generally associated with hotspots • Hawaii and Canary Islands • Erosion occurs and seamounts sink • Flat-topped, submerged seamounts – guyots (GEE-oze) or tablemounts

16. Emperor Chain Seamounts Hawaiian Chain Seamounts

17. Hawaiian Seamounts/Hot Spots

18. Links • Seamounts • http://www.coast-nopp.org/visualization_modules/physical_chemical/basin_coastal_morphology/principal_features/deep_ocean/seamounts/seamounts.html • General Info • http://oceanexplorer.noaa.gov/ • http://www.noaa.gov/

19. Homework Sec. Rev. p. 398 1-3