1. 9-4 Sea Floor Spreading What is the process of sea-floor spreading?
What happens to the ocean floor at deep ocean trenches.

2. Mapping the Mid-Ocean Ridge
During the mid 1900’s sonar made it possible to map the ocean floor.
Prior to mapping it was believed that the abyssal plain was smooth and featureless.
Mapping with sonar revealed the Mid Ocean Ridge MOR

3. Features of the MOR Longest mountain chain on the earth
Rift valley at its center that is deeper than the Grand Canyon.
Volcanoes along the ridge at various locations Surtsey Iceland.

4. Sea floor Spreading Harry Hess US Naval Officer
Observed Magnetic anomalies in the Ocean Crust
Proposed that the ocean floors move like conveyor belts carrying along the continents.
At the mid ocean ridge, molten material rises from the mantle and spreads out pushing older rock to the side.

5. Sea Floor Spreading Video

6. Sea floor spreading is supported by
New molten material discovered by deep ocean submarines like “Alvin” at the MOR
Magnetic Banding running parallel to the sea floor caused by shifts in the earth’s magnetic field about every 780,000 years
Rock samples from deep ocean drilling show that rocks get older as you move outward in both directions from the ridge.

7. Subduction Video

8. Subduction at deep ocean trenched
Subduction is the process by which crustal material is drawn deep into the earth and recycled to become new crust at divergent boundaries.
Subduction occurs at deep ocean trenches found where the crust is being pushed together. (Convergent boundaries)
The ocean floor is renewed in this process about every 200 million years
Most subduction zones (deep ocean trenches) are found n the pacific

9. Deep ocean trenches

10. Summary What is the role of the mid ocean ridge?
At the mid ocean ridge, molten material rises from the mantle and erupts. This material then spreads out pushing older rocks to both sides of the ridge
Describe the process of subduction at deep ocean trenches.
In the process of subduction, oceanic crust sinks down beneath the trench into the mantle.
What is the evidence for sea floor spreading?
Evidence of sea floor spreading includes molten material, magnetic stripes, and evidence from drilling samples
Where would the oldest rocks in the ocean floor be found?
The oldest rocks would be found the farthest away from the MOR.