Transcript tectonic plates

Unit 7 Lesson 2 Plate Tectonics and
Landforms
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Unit 7 Lesson 2 Tectonic Plates and Landforms
Stressed Out
What does the theory of plate tectonics
explain?
• Earth’s outermost layer is called the lithosphere,
and the layer directly below is called the
asthenosphere. Both are solid layers of rock.
• The lithosphere is divided into large, moving
pieces called tectonic plates.
• The theory of plate tectonics explains how
lithospheric plates move around on the slowflowing rock of the asthenosphere.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What are some properties of tectonic
plates?
• The lithosphere is broken into 15 major tectonic
plates that differ in size, shape, density, thickness,
and composition.
• Continental lithosphere is thicker and older than
oceanic lithosphere.
• Tectonic plates move slowly around Earth’s
surface and interact with one another.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What types of stress are related to the
movement of tectonic plates?
• As tectonic plates move and interact, stress is put
on rock.
• This stress causes deformation, which is the
bending, tilting, and breaking of rock.
• Deformation changes the size and shape of
features on or below Earth’s surface.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What types of stress are related to the
movement of tectonic plates?
• Compression is a stress that squeezes or shortens
material.
• This type of stress can cause folds as rock is
squeezed and shortened.
• Compression can also cause breaks in rock, or
faults, where Earth’s lithosphere is more rigid.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What types of stress are related to the
movement of tectonic plates?
• Tension is a stress that lengthens a material or
pulls a material apart.
• Two plates moving away from one another cause
tension.
• When tension is greater than the strength of the
rock, the rock break and faults form.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What types of stress are related to the
movement of tectonic plates?
• Shear stress causes material to twist or become
distorted.
• This type of stress can occur when two tectonic
plates move past one another and grind against
each other.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What are the different types of plate
boundaries?
• Most deformation occurs at boundaries where
tectonic plates meet.
• These plate boundaries may be on the ocean floor,
around the edges of continents, or even within
continents.
• Certain landforms are formed at different types of
boundaries.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What are the different types of plate
boundaries?
• A convergent boundary forms when tectonic
plates collide.
• In oceanic-continental convergence, the denser
oceanic plate sinks beneath the continental plate.
• In continental-continental convergence, the plates
push against each other and buckle.
• In oceanic-oceanic convergence, the denser plate
sinks beneath the less dense plate.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What are the different types of plate
boundaries?
• A divergent boundary forms when two tectonic
plates move away from one another.
• Magma rises up through cracks that form when
two plates move away from each other along a
divergent boundary.
• Most divergent boundaries are under the ocean.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What are the different types of plate
boundaries?
• A transform boundary forms when two tectonic
plates move past one another in opposite
directions.
• The plates slowly scrape against one another
before shifting suddenly, which shear stress
breaks or distorts rock.
• The San Andreas Fault is a transform boundary,
but most transform boundaries are on the ocean
floor.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
Push Up
What features are associated with
convergent boundaries?
• Compression along convergent boundaries can
cause rock to be folded and move upwards,
forming mountain ranges
• The Appalachian Mountains formed from faulting
and folding when the North American plates
collided with the Eurasian and African plates.
• The Himalayas formed when the Indian plate
collided with the Eurasian plate.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What features are associated with
convergent boundaries?
• When oceanic and continental plates collide,
magma can rise to Earth’s surface and eventually
form a continental volcanic arc.
• Volcanoes can also form when two oceanic plates
converge and one sinks beneath the other. This
type of collision results in a volcanic island arc.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What features are associated with
convergent boundaries?
• Ocean trenches are the deepest landforms found
on the ocean floor.
• They can form when a oceanic plate collides with
and slides beneath an oceanic or continental
plate.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What features are associated with
divergent boundaries?
• Mountains may also form at divergent boundaries.
• Fault-block mountains form when block of
lithosphere drop down or are lifted up along
faults.
• Tension at diverging plates also causes rifting,
where Earth’s lithosphere pulls apart to form long,
narrow, faulted rift valleys.
• Rifting also forms rift zones, which can form
volcanic mountains and tall, flat-topped plateaus.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What features are associated with
transform boundaries?
• Some chains of volcanic islands, known as hot
spots, form far from plate boundaries.
• At a hot spot, magma rises from deep within the
Earth. Repeated lava flows form an undersea
volcano that eventually reaches above the ocean’s
surface to form a volcanic island.
• As the oceanic plate shifts, a new island may form
over the hot spot.
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Unit 7 Lesson 2 Tectonic Plates and Landforms
What volcanic landforms occur way
from plate boundaries?
• Major and minor earthquakes are associated with
transform boundaries
• Transform boundaries can also cause mid-ocean
ridges to be offset.
• Offset streams and fences can be a sign of a
transform boundary on land.
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