1. The Ocean Floor

2. Studying the Ocean Floor
Scientists use sonar to determine the oceans depth
The sound moves through the water, bounces off the ocean floor, and returns to the ship

4. Ocean basins are low areas of Earth that are filled with water
The continental shelf is the gradually sloping end of a continent that extends under the ocean to 350 m deep

5. The Ocean Floor
Beyond the shelf, the ocean floor drops more steeply, forming the continental slope.
The continental slope extends from the outer edge of the continental shelf down to the ocean floor.

7. Ocean Basins
Beyond the continental slope lie the trenches, valleys, plains, mountains, and ridges of the ocean basin

8. Ocean Basins
In the deep ocean, sediment, derived mostly from land, settles constantly on the ocean floor.
These deposits fill in valleys and create flat seafloor areas called abyssal plains.

10. Some areas of abyssal plains have small hills and seamounts.
The Ocean Basins
Some areas of abyssal plains have small hills and seamounts.
Seamounts are underwater, inactive volcanic peaks

12. Mid-ocean ridges can be found at the bottom of all ocean basins.
Ridges and Trenches
Mid-ocean ridges can be found at the bottom of all ocean basins.
A mid-ocean ridge is the area in an ocean basin where new ocean floor is formed.

14. Ridges and Trenches
On the ocean floor, subduction zones are marked by deep ocean trenches.

15. Trenches and Ridges
A trench is a long, narrow, steep-sided depression where one plate sinks beneath another.

17. What is the continental shelf?
Question 1
What is the continental shelf?

18. Answer
The continental shelf is the gradually sloping end of a continent that extends under the ocean.

19. Question 2
Which structure extends from the outer edge of the continental shelf to the ocean floor?
A. abyssal plain
B. continental slope
C. oceanic trench
D. seamount

20. The answer is B. The other features lie beyond the continental slope.

21. What is the area in an ocean basin where new ocean floor is forming?
Question 3
What is the area in an ocean basin where new ocean floor is forming?

22. Answer
New seafloor forms at mid-ocean ridges as lava erupts through cracks in Earth’s crust.