1. Ocean Floor

3. The ocean basins are characterized by recognizable geologic/topographic features . While the size of each feature may change within the various ocean basins they are always present:

4. Continental shelf
- the gently (<1°) sloping platform at the edge of the continent.
not part of the ocean basin.
average water depth 75 meters (0-150 m)
avg. 60 kilometers wide

5. Width of the slope is determined by proximity to a plate boundary
Passive margins have longer shelves than active margins
18,000 years ago we had 18% more land than we do now…slopes are greatly affected by sea level changes. Why?

6. Shelf Break
Marks the abrupt transition from shelf to slope

7. Continental slope
- the continental slope marks the transition between the shelf and deep ocean floor.
It has an average slope of 3-6°. 100 kilometers water depth increases from 75 meters to 4000 meters.

8. Submarine canyons
continental slopes are crisscrossed by a series of deep submarine canyons the origin of which is controversial.
Some represent drowned stream valleys, but others were clearly never above sea level and can not have been cut downward by stream erosion.

10. Continental rise
- represents the accumulation of sediment at the base of the continental slope. Result is a gentler slope and the buildup of "turbidite" deposits.

12. Abyssal plain - the ocean floor (covers about 30% of the earth's surface).
The average water depth is around 5000 meters. Consists of a layer of unconsolidated sediment underlain by sedimentary rock and pillow basalt .

15. Ocean ridges

16. Does not run in a straight line because it is offset by transform faults
Hydrothermal vents are found here

18. Abyssal plain vs. Abyssal hills
Plains are flat flat flat
Hills are small sediment covered extinct volcanoes---less than 200 meters high
No abyssal plains in pacific…very little in Indian. Mostly Atlantic…why?

20. Seamounts
Volcanic projections that do not rise above the surface of the ocean
Usually circular or elliptical
Higher than Ikm
May be alone or in groups
May form over hot spots
More common in the pacific

22. Guyots
Flat topped seamounts that were once tall enough o break the surface of the ocean

24. Trenches Arc shaped depression in deep ocean floor
Where converging plates are subducting
Most active areas

26. Island Arcs Curving chains of volcanic islands Seamounts also
Found parallel to concave edges of a trench
Aleutian islands
Marianna islands