Download An introduction to processes at plate boundaries

An introduction to processes at plate boundaries
Student tasks
1. Draw diagrams of the three main types of plate boundary.
a. Destructive plate boundary
b. Constructive plate boundary
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An introduction to processes at plate boundaries
c. Conservative plate boundary
2. Use the statements below to label your diagrams correctly to show the physical
processes at each plate boundary.
The continental and oceanic plates move towards each other.
Molten rock rises from the mantle through cracks to the surface, to create a
composite volcano.
Lava creates a new oceanic crust.
Lava is able to escape through small cracks in the Earth’s surface.
Mid-ocean ridges are formed.
Mild earthquakes may happen here.
Two tectonic plates slide past each other.
Severe earthquakes can occur at these types of plate boundaries.
Shield volcanoes are formed. These produce gentle, less violent eruptions.
Earthquakes at this plate boundary are very violent and dangerous.
The oceanic crust melts in the subduction zone.
The tectonic plates are moving in the same direction.
The tectonic plates move at different speeds.
The heavier oceanic crust is forced underneath the lighter continental crust.
The two plates move away / apart from each other. This creates a gap between the
two plates.
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An introduction to processes at plate boundaries
3. Use your diagrams and the statements provided to write your own paragraphs to
explain the physical processes that occur at each type of plate boundary.
Use key terms and phrases and include any additional information you know about
plate boundaries.
a. Destructive plate boundary
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b. Constructive plate boundary
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c. Conservative plate boundary
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An introduction to processes at plate boundaries
Teaching notes and answers
The US Geological Survey provides a useful introduction with excellent diagrams at
pubs.usgs.gov/gip/dynamic/understanding.html and
geomaps.wr.usgs.gov/parks/pltec/pltec3.html
Destructive Plate Boundary
1. The continental and oceanic plates move towards each other.
2. The heavier oceanic crust is forced underneath the lighter continental crust.
3. The oceanic crust melts in the subduction zone. Molten rock rises from the mantle
through cracks to the surface, to create a composite volcano.
4. Earthquakes at this plate boundary are very violent and dangerous.
Constructive Plate Boundary
1. The two plates move away / apart from each other. This creates a gap between
the two plates.
2. Lava is able to escape through small cracks in the Earth’s surface.
3. Lava creates a new oceanic crust.
4. Mid-ocean ridges are formed.
5. Shield volcanoes are formed. These produce gentle, less violent eruptions.
6. Mild earthquakes may happen here.
Conservative Plate Boundaries
1. Two tectonic plates slide past each other.
2. The tectonic plates are moving in the same direction.
3. The tectonic plates move at different speeds.
4. Severe earthquakes can occur at these types of plate boundaries.
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An introduction to processes at plate boundaries
Sample answers for each type of plate boundary

Destructive plate boundary
At a destructive plate boundary, there is one continental and one oceanic crust. The
two plates move towards each other and the denser oceanic crust subducts (sinks)
beneath the continental crust. This forms an ocean trench.
The sinking oceanic crust eventually melts due to heat and pressure created by
friction, which is caused by the tectonic plates moving. There is also heat and
pressure coming from inside the Earth itself. The oceanic plate melting in the
subduction zone creates magma. This is less dense (lighter) than the material of the
mantle and rises through cracks in the Earth’s surface to form composite volcanoes.
The South American and Nazca plates are a good example of a destructive plate
boundary.

Constructive plate boundary sample answer
At a constructive plate boundary, the two tectonic plates move away from each
other. As the two plates separate or diverge, rising magma is able to fill the gap
created. This creates a new crust over time and causes mountain ranges to form
under the sea. These mountain ranges create mid-ocean ridges.
Volcanic islands can also be formed where magma continues to rise and build up
above the ocean surface.
The North American and Eurasian plates, which formed the Mid-Atlantic ridge, are a
good example of a constructive plate boundary.

Conservative plate boundary sample answer
At a conservative plate boundary, the two tectonic plates move alongside/slide past
each other. The existing crust is not destroyed and new crust is not created. The
tectonic plates move in the same direction but at different speeds. This results in an
increase of both pressure and friction at the plate margins. Massive earthquakes are
created when this pressure is released.
The San Andreas Fault, which forms along the North American and Pacific plates, is a
good example of a conservative plate boundary.
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