1. Quiz #3 Due Wednesday before Midnight
Exam #1: 7PM, 2/15 (Tuesday) Here

2. Class #9 OCEAN BASINS AND SEA FLOOR_ What’s down there?
Understanding the ocean basins in light of Plate Tectonics

3. The shape of the ocean bottom
Plate Tectonics Theory provides a way to understand:
Why we have ocean basins
The origins of many undersea features

5. The "hypsographic" curve
Gives percent of Earth surface at each elevation
Observations:
Sharp, narrow transition between continents and ocean
Reflects fundamental differences in the crust (oceanic versus continental crust)

6. What percentage of Earth surface is higher than xxx meters elevation?
Mean elevation of continents = +840 m
Mean depth of oceans = -3,700 m

8. Provinces of the sea floor:
Major Provinces
Continental margins
Ocean basin floor
Mid-ocean ridges
Trenches

9. Provinces of the sea floor:
Major Provinces
Continental margins
Continental Shelf
Shelf Break
Continental Slope
Continental Rise
Submarine canyons

11. Continental Shelf is an underwater extension of the continent.
Continental Margin ends near where continental crust (incl. sediments) ends

12. General Diagram of a Continental Margin Note: Vertical dimension is expanded!!!!

13. (Here’s the same figure, no vertical exaggeration)

15. Provinces of the sea floor:
Major Provinces
1. Continental Margins- Last time
2. Ocean basin floor
Ave. depth = 4,000m - 6,000 m
Many areas flat (mantled by sediments)
Volcanic features
-Islands, often in chains (e.g., Hawaii)
-Underwater hills, seamounts, "guyots"

16. Sea Floor Features

17. Seismic (= sound wave) Profiling: Reveals layers of sediment and rock

20. Provinces of the sea floor:
Major Provinces
1. Continental Margins- Last time
2. Ocean basin floor
3. Mid-ocean ridges and rises
Curvilinear feature circling the earth
Higher than surrounding areas
Divergent plate boundary
Young, hot oceanic lithosphere

23. Mid-Ocean Ridges: Details
Composed of basalt from undersea volcanoes
Rift valley at the plate boundary- earthquakes
Heat flow high
Magmas carry additional heat into upper crust
Some magmas erupt to form lavas
Water circulation driven by this heat
Hydrothermal vents

29. Fracture Zones

31. Provinces of the sea floor:
Smaller Provinces (small area, still important)
Trenches
6,000m - 11,000 m deep -- deepest regions
Occur at margins of oceans, especially Pacific
East Pacific -- edge of continental margin
West Pacific -- associated with volcanic island chains

32. Trenches Where are they? Almost all found around the Pacific
Why are they deep?
Bending of plate
Downward pull of dense, sinking lithosphere
Continental margins greatly altered by trenches

33. Trenches

40. Shallow
<100km
Deep