07. Seafloor Spreading

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OUTCOMES:

> Create an explanation of how new rock is formed at plate boundaries

> Explain why some rocks are magnetic

> Generate questions to check the knowledge and Understanding of other students

At a divergent plate boundary, new crust is created. This process is responsible for sea floor spreading that occurs in the Atlantic Ocean, Pacific Ocean and Indian Ocean.

Sea Floor Spreading

• • Sea Floor Spreading is the creation of new crust or lithosphere at a divergent plate boundary. It is called so because most divergent boundaries occur between oceanic plates and causes our oceans to spread apart or widen.

  • As the plates move apart, magma rises through the boundary. The magma creates new crust at the boundary. Specifically, the magma creates an ocean ridge. The magma creates mountains on both sides of the boundary. Between the boundary is a rift (a deep valley).

  • New crust is continually made at the boundary as long as the plates move apart.

  • Older crust is found further away from the boundary.

  • Sea floor spreading helps explain how and why the continents on Earth are located where they are.

Examples (as shown on the map below)

• • Sea floor spreading occurs in the Atlantic Ocean along the Mid-Atlantic Ridge. This ridge forms the longest mountain range in the world. The ridge spreads approximately 2.5 cm per year.

  • Sea floor spreading occurs in the Pacific Ocean along the East Pacific Rise. On the east side of the ridge, the Cocos and Nazca plate moves towards South America. The ridge spreads quickly at a rate of 8-12 cm per year.