Sea-Floor Spreading

What is a deep-ocean trench?

a deep valley along the ocean floor where oceanic crust slowly sinks toward the mantle; a convergent boundary

sonar

a device that bounces sound waves off underwater objects and then records the echoes of these sound waves. The time it takes for the echo to arrive, indicates the distance to the object.

deep-ocean trench

A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.

What happens as subduction occurs?

As subduction occurs, crust closer to a mid-ocean ridge moves away from the ridge and toward a deep-ocean trench. Sea-floor spreading and subduction work together. They move the ocean floor as if it were on a giant conveyor belt.

What happens to oceanic crust at a deep-ocean trench?

At a deep-ocean trench, the oceanic crust bends downward. In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.

What happens at ocean trenches?

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.

Wht occurs at trenches?

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.

What is the process of sea-floor spreading?

In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

Along what feature of the ocean floor does sea-floor spreading begin?

Mid-Ocean ridge

Where would you expect to find the oldest rock on the ocean floor?

Nearer to deep ocean trenches

What is the evidence for sea-floor spreading?

Several types of evidence supported Hess's theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

What device is used to map the ocean floor?

Sonar

What happens to the rock along the ridge when new molten material erupts?

The older rock moves outward on both sides of the ridge as new rock forms in the center of the ridge from cooling of molten material. This process is sea floor spreading.

Subduction

The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.

Subduction and Earth's oceans

The process of subduction and sea-floor spreading can change the size and shape of the oceans. Because of these processes, the ocean floor is renewed about every 200 million years. That is the time it takes for new rock to form at the mid- ocean ridge, move atoss the ocean, and sink into a trench.

How does new oceanic crust form?

When molten material erupts through the mid ocean ridge called sea-floor spreading

Magnetic Stripes

____________________ in the rock of the ocean floor show the direction of Earth's magnetic field at the time the rock hardened.

Mid-ocean ridges

an undersea mountain chain where new ocean floor is produced.

What three types of evidence provided support for the theory of sea floor spreading?

eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

How can the ocean floor keep getting wider and wider?

the ocean floor generally does not just keep spreading. Instead, the ocean floor plunges into deep underwater canyons called deep-ocean trenches. At a deep-ocean trench, the oceanic crust bends downward.

sea-floor spreading

the process by which molten material adds new oceanic crust to the ocean floor