unit 7 lesson 2 plate tectonics and landforms copyright © houghton mifflin harcourt publishing...

Unit 7 Lesson 2 Plate Tectonics and Landforms

Copyright © Houghton Mifflin Harcourt Publishing Company

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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 slow-flowing rock of the asthenosphere.

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.



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.



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.



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.



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.



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.



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.



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.



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.



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.


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.



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.



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.



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.



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.

