Elements of The Oceans:
General Information About Ocean Topography:
Few people have seen the ocean floor, however scientists have learned a great deal about the structure of the floor. The solid outer layer of the earth is divided into a number of large pieces called plates, which move very slowly over the earth.
When two plates move apart, melted material rises from inside the earth forming new crust. Huge underwater mountains can grow where the new crust is forming called rift valleys. The Mid-Atlantic Ridge is an example of a chain of towering mountains on the floor of the Atlantic Ocean. Scientists think the Atlantic Ocean is getting larger because new crust is forming there.
When two plates bump into each other, the edge of one plate slowly sinks into the earth, melts, and is destroyed, thus developing trenches. The trenches are deep, narrow ditches in the ocean floor. These ditches are the deepest parts of the ocean. Scientists think that the Pacific Ocean is getting smaller because crust is being destroyed there. The change in the movement of the plates is slow, only a few centimeters a year.
Other parts of the ocean floor include the continental shelf, which is part of a continent that extends from the edge of the landmass into the ocean. Beyond the shelf is the continent slope. The ocean floor slopes steeply downward to the ocean basin or abyssal plain. The ocean basin or abyssal plain is the flat plain on the ocean floor. Seamounts are underwater peaks with rounded tops, while guyots are underwater peaks with flat tops. Islands are peaks, which stick up above water level.
Much of the ocean's topography has been mapped by the use of sonar. A sound is sent from a ship's transmitter to the ocean's bottom at an angle. It bounces back to the ship at the same angle and is picked up by a receiver on the same ship. We know the speed of sound is about 1534 meters per second. By using this information and applying a formula, ocean depth can be measured and mapped. The formula is D=1/2T x V.
D = depth, T = time, V = speed or velocity of sound in water (1534 meters per second)
Additional Resoucres For Ocean Topography:
- A Couple Hundred Years Of History Of Ocean Exploration
- NOAA Estimated Satellite Image of the Topography of the World's Ocean Floor
- Interactive 3D Map of the Planet Earth Showing The Ocean Floor
Downloadable Student Activities:
- Graphic Organizer
- Ocean Topography Data Worksheet Page One
- Ocean Topography Data Worksheet Page Two
- Ocean Depth Activity Page One
- Ocean Depth Activity Page Two
- Ocean Depth Activity Page Three
- Topography of the Ocean Floor Activity
- Diagram of the Features of the Ocean Floor