5.11: Divergent Plate Boundaries in the Ocean

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Why a photo of a bridge with some bleak looking rock?

In Iceland, the Mid-Atlantic Ridge is above sea level. It's the only place we can see a mid-ocean ridge out of the water. The Midlina Bridge connects two plates. On the west side is the North American plate. On the east side is the Eurasian plate. A mid-ocean ridge is where new crust is created. Eventually this spot will be beneath the Atlantic Ocean.

Divergent Plate Boundaries

Plates move apart at divergent plate boundaries. In oceans, this happens at mid-ocean ridges -- on land, at continental rift zones.

Mid-ocean Ridges

In the oceans, plates move apart at mid-ocean ridges. Lava rises upward, erupts, and cools. Later, more lava erupts and pushes the original seafloor outward. This is seafloor spreading. Seafloor spreading forms new oceanic crust. The rising magma causes the ridge to be buoyant. This is why there are mountain ranges running through the oceans. The plates pulling apart cause earthquakes.

Most mid-ocean ridges are located deep below the sea. The island of Iceland sits right on the Mid-Atlantic ridge (Figure below).

The rift valley in Iceland that is part of the Mid-Atlantic Ridge

The rift valley in Iceland that is part of the Mid-Atlantic Ridge.

Continental Rifting

A divergent plate boundary can also occur on a continent. This is called continental rifting. Magma rises beneath the continent. The crust thins, breaks, and then splits apart. This first produces a rift valley. The East African Rift is a rift valley. Eastern Africa is splitting away from the African continent. Eventually, as the continental crust breaks apart, oceanic crust will form. This is how the Atlantic Ocean formed when Pangaea broke up.

Summary

Divergent plate boundaries in the ocean create mid-ocean ridges. This is where new seafloor is created by upwelling magma.
Divergent plate boundaries rift a continent apart. Eventually a new ocean will form between the two continents.
Iceland is a location where we can see a mid-ocean ridge above sea level.

Review

In what direction are the plates moving at a divergent plate boundary?
How does a convection cell in the mantle lead to volcanism at the mid-ocean ridge?
How does a continent break apart to form an ocean basin?

Explore More

Use the resource below to answer the questions that follow.

What causes divergence?
How is new crust created?
What erupts on the ocean floor?
How fast does divergence occur?
What is formed at a divergent boundary?