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Divergent boundaries occur when two of Earth’s tectonic plates are moving away (diverging) from each other. There are

divergent boundaries both on land in the continental crust and under the ocean in the oceanic crust.

1. In what direction do divergent boundaries move?

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2. Draw two arrows that represent this movement in the box below:

When two tectonic plates on the continental crust are diverging

(moving apart), a rift valley can form. A rift valley is like a dip in the

Earth. It’s similar to the space in between two mountains. Over

millions of years, as the two plates continue to diverge, a rift valley

can sink so low that it is below sea level. As sea water moves in,

new oceans are formed. Sometimes, rising magma can make its

way through cracks in the rift valley. This can cause volcanic

activity and volcanic rocks to be formed.

1. What is formed at two diverging continental plates?

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The most interesting divergent boundary is

found underneath the ocean. Deep down

under the ocean, you will find a divergent

boundary. This is known as the Mid-Atlantic

Ridge. All along the Mid-Atlantic Ridge, you

will find two oceanic plates moving away

from each other. As the ocean plates move

away from each other, magma pushes up to

the ocean floor. The lava cools and forms a

new layer of oceanic crust. This continues to happen at the mid-ocean ridge: the plates move away from each other,

magma comes up, it cools and forms a new layer on the ocean floor. This can also produce huge volcanic eruptions of

basalt (a type of igneous rock) which builds the longest chain of volcanoes in the world! Since most of the Mid-Atlantic

Ridge is over 2000 meters deep, most of the volcanic eruptions go unnoticed.

1. Describe what happens to the magma when ocean plates move away from each other.

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2. What happens at mid-ocean ridges? In your response include the words, plates, magma, cools, and ocean floor.

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3. You can find a large amount of volcanic activity at divergent boundaries. Based on this information, what type of

rock do you think you would find at divergent boundaries? Explain your answer.

Remember that a convergent boundary is one in which two plates are moving toward each other. Converge

means collide or come together. What happens when plates converge depends on the type of crust that the

plate edges are made of. A plate interaction in which two plates converge can involve two oceanic plates, or

one continental and one oceanic plate.

1. In what direction do the plates move at a convergent boundary?

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2. In the box below, draw two arrows that represent the movement at a convergent boundary.

Remember that a convergent boundary is one in which two plates are moving toward each other. When two continental

plates converge, they smash into each other. One plate doesn’t go underneath the other because the plates are the

same density.

As the two plates slowly collide, the huge force causes rocks at the edges of the plates to fold over. The edges of these

plates thicken and push upward. This means that large mountains are forming. Some of the largest and highest

mountain ranges in the world were created in this way! Some mountain ranges, such as the Himalayas, are still being

pushed up today as the plates involved continue to collide.

Mountains

1. Why doesn’t one of the plates go underneath the other at a convergent boundary between two continental plates?

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2. What geologic feature forms at a convergent boundary between two continental plates?

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3. There is a lot of pressure applied to the crust when mountains are formed at convergent boundaries. Using this

information, what type of rock do you think forms at a convergent boundary on land? Explain your answer.

A convergent boundary is one in which two plates are moving toward each other. What happens when plates converge depends on the type of crust that the plate edges are made of. Oceanic crust is more dense than continental crust. When oceanic crust and continental crust converge, the more-dense oceanic crust moves under the continental crust. This causes a subduction zone.

1. What two types of crust are involved at a subduction zone?

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2. Why does the oceanic crust move under the continental crust when they converge?

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At a subduction zone, the edge of the oceanic plate sinks down toward the mantle. It becomes hotter and

hotter until it melts into magma. This creates a pocket of magma underneath the continental plate. If there is

a lot of magma that has built up, it might make its way back up to the crust of the earth. If it makes its way all

the way to the surface, it will break through as a volcanic eruption. This is why volcanoes are formed at

subduction zones!

1. What geologic feature results from a subduction zone?

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2. There is a great deal of magma that builds up and can eventually erupt at a subduction zone. Using this

information, what type of rock do you think forms at a subduction zone? Explain your answer.