Plate Boundaries Where things happen!!!!

Crust is created and destroyed at plate boundaries

Session #1 Divergent Boundaries Earth’s crust is created

Where are divergent boundaries?

What is a divergent boundary?

What happens at a divergent boundary? The plates push away from each other. This is called “ridge push”. Magma rises and solidifies onto the edges of the two plates New crust is created The new crust is the igneous rock basalt.

As new crust is added at the divergent boundary, the older “new” crust is pushed farther away from the boundary. Most divergent boundaries are under the ocean. Sea-floor spreading occurs because new crust is constantly forming.

Let’s look at sea-floor spreading…. Divergent Boundary Animation

What drives divergent boundaries? Convection causes the magma to fill the gap between the two plates and causes the plates to push away from each other.

Summary of the effects of divergent boundaries Underwater mountain ranges are formed with a gap (called a rift) in the middle. Volcanoes are created but are not explosive. Earthquakes occur but are shallow (near the surface). The ocean basin widens

Session #2 Convergent Boundaries Earth’s Crust is destroyed

Three types of Convergent Boundaries? Converging occurs between ocean crust and continental crust. Converging occurs between ocean crust and ocean crust Converging occurs between continental crust and continental crust

Convergent Boundaries Oceanic Crust meets Continental Crust

What is a convergent boundary where ocean crust meets continental crust?

Where does oceanic crust meet continental crust?

What happens when oceanic crust meets continental crust What happens when oceanic crust meets continental crust? Subduction occurs!!! Subduction is the sinking of a denser plate under a less dense plate The part of the plate sliding under the other plate is called the subduction zone.

As the plate subducts, the crust melts back into the magma. A trench is formed along the edge as the plate subducts. On the continental crust, volcanoes will form Earthquakes will occur where the subduction is taking place.

Why does subduction occur? Convection! The magma that has risen as part of convection begins to cool as it is moving under the lithosphere. As it cools, it becomes denser. The magma begins to sink as gravity is pulling it toward the interior of the Earth.

As the magma gets pulled toward the interior of the Earth, the edge of the oceanic crust gets pulled under also. This is known as “slab-pull”.

What else occurs at this convergent boundary What else occurs at this convergent boundary? Volcanoes from on the Continent As subduction occurs, the oceanic crust melts into the mantle Some of the magma collects under the continental crust. Pressure causes the magma to rise creating volcanoes on the surface of the continental crust This is called a volcanic arc = mountains form

Summary of the effects of the ocean crust to continental crust convergent boundary Shallow (near the surface) earthquakes will occur along the edge of the continent Deeper earthquakes will occur beneath the continent Volanoes will occur a few hundred miles from the shore A trench is created near the shoreline

Convergent Boundaries Oceanic Crust meets Oceanic Crust

What is a convergent boundary where oceanic crust collides with oceanic crust?

Where does oceanic boundaries meet oceanic boundaries?

What happens when oceanic crust meets oceanic crust? Subduction occurs!!! Subduction is the sinking of a denser plate under a less dense plate When one oceanic plate is denser than the other, it will subduct under the other.

What are the results of oceanic crust subduction under oceanic crust? The denser oceanic crust will melt into the mantle, while the less dense oceanic crust will slide above it. A trench will form where the subduction is taking place. Some of the melted rock will become trapped and rise to the surface creating islands.

These volcanic islands are referred to as an island arc. Volcanoes occur Earthquakes caused from the sliding of the plates occur Island arc can be found along the boundaries of the Pacific Plate

Earthquakes occur deep in the Earth’s crust. Summary of the effects of a convergent boundary where ocean crust meets ocean crust? Earthquakes occur deep in the Earth’s crust. Volcanic Island arcs are created from the melting of the plates The oceanic plate is destroyed A trench is created

Convergent Boundaries Continental Crust meets Continental Crust

What is a convergent plate where continental crust collides with continental crust?

Where is a convergent boundary of two continental crusts?

What happens when continental crust collides into continental crust? This convergent boundary occurred when the Indian plate met the Eurasian. First subduction took place when the oceanic crust moved under the less dense continental crust and then…..

The two continental crusts collided Both continental crusts are equal in density so subduction stopped and the crust began to crumble. This created the Himalaya Mountain ranges in India

Summary of the effects of continental crust colliding into continental crust Mountains are created from the faulting and folding of the crust Earthquakes occur in the shallow areas of the crust (near the surface) Volcanoes would not occur.

Session #3 Transform Boundary Crust moves past crust

What is a transform boundary?

Where is there an important transform boundary?

What happens at a transform boundary? Two plates sliding horizontally past one another Most transform faults are found on the ocean floor San Andreas fault zone - California

Activity Assessment 1)Open the Moodle site called: “Plate Boundary Activity Assessment - Web Page” You will find a map with indicators for plate boundaries throughout the world 2) Open the Moodle site called: Worksheet” 3)Answer the questions on the worksheet using the map and this presentation. ***A copy of the Power Point for this presentation will be found on Moodle under the site called “Plate Boundary Power Point”.***