1. The Ocean floor

2. Formation of the Ocean Floor
Ocean floor formation a result of seafloor spreading
Process has been occurring for millions of years
Evidence shown in the symmetrical, parallel bands of basalt that spread out along either side of the ridge
Youngest rocks are closer to the ridge

3. Features of the Ocean Floor
Ocean basins have the same geological features as continents (i.e. plains, volcanic mountains, valleys)
Far more exaggerated on ocean floor
Average depth of 12,000 feet
Formation of ocean floor features result of movement in plate tectonics

4. Features of the Ocean Floor
Subduction Zone – a region of the Earth’s crust where tectonic plates meet
Mountain formation and volcanic activity occur at these zones
Formation of deep ocean trenches
Result of oceanic plate sinking below continental plate

5. Features of the Ocean Floor
Continental Shelf – a stretch of the seabed adjacent to the shores of a particular country
Extends out under the ocean; geologically part of the continental crust
Area of shallow water known as a shelf sea
Shelves were exposed during glacial periods (15,000 y.a.)

6. Features of the Ocean Floor
Continental slope – extent of ocean floor that connects continental shelf to abyssal plain
Abyssal plain – flat and gently sloping areas found at the deepest parts of the ocean
Found at depths between 10,000 – 20,000 ft
Covers more than 50% of Earth’s surface
Formed as a result of sediment buildup on the oceanic crust

7. Features of the Ocean Floor
Abyssal plains contain small hills and underwater volcanic peaks (seamounts)
Peaks of seamounts have been worn down over time to create plateau-like tops (guyots)
A chain of seamounts and volcanic islands can form island arcs
Often occur at subduction zones
Run parallel and close to a plate boundary

9. Sea Floor Topography
Topography: study of Earth’s surface features, on land and on the ocean floor
Topographical maps show seafloor elevation and depressions
Ocean depth can be calculated automatically by sonar
Two pieces of information are needed: the speed of sound in water (1454 m/s) and time it takes for the sound signal to travel
D = 1454 x t/2; D = depth, t = time

10. Sea Floor Topography
Oceanographers can obtain a profile of the ocean floor by using sonar
Uses sound propagation to detect objects under the surface of water
Most modern ships are equipped with sonar
Series of events with sonar:
A ship’s sonar device beams a continuous sound signal downward
Sound reaches bottom and returns with an echo
Produces a line tracing of the ocean floor