Earthquakes, Mountains, Volcanoes,

and 
Sea-Floor Spreading

Lesson 17

What You Will Learn

● The Earth’s surface is made up of huge, slowly moving pieces of Earth’s crust called tectonic plates.

● The tectonic plates are otherwise known as the lithosphere.

● These plates move and push on each other in various ways.

● In this lesson, you will learn how plate movements cause changes in earth’s surface features.

Plate Boundaries

● The places where tectonic plates interact are called plate boundaries. ●At plate boundaries, plates may slide past each other, push each other, or pull apart from each other.

The Earth’s Plates 
(The numbers here are cm of movement per year.)

The Three Types of Boundaries

!Divergent- plates pull apart Convergent- Plates push together !Transform- Plates slide by each other

What Do You Know?

●Show me divergent. ●Show me convergent. ● Show me transform.

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Events at Transform Boundaries

● A boundary where plates slide past each other is called a transform boundary.

● A transform boundary is a kind of a fault. ● A fault is a break in earth’s crust that has movement along

the break. ● As the plates move past each other, pressure builds in the

rock. ● If the pressure becomes great enough, huge areas of rock

suddenly move or break. ● The pressure is released quickly, and the ground shakes

causing an earthquake. ● Earthquakes are most common near transform boundaries. ● When an earthquake or a volcano forming occurs under

water, they can cause a tsunami. ● https://www.youtube.com/watch?v=4Y-62Ti5_6s ● http://video.nationalgeographic.com/video/inside-

earthquake

https://www.youtube.com/watch?v=4Y-62Ti5_6shttps://www.youtube.com/watch?v=4Y-62Ti5_6shttp://video.nationalgeographic.com/video/inside-earthquake

Locating an Epicenter● Geologists use seismic waves to

locate the epicenter, which is the point at the surface directly above where the earthquake occurred. !

● They measure the difference between the P (primary) waves and S (surface) waves. !

● The farther away the earthquake the greater the time between the arrival of the P and S waves. !

● Geologists then draw at least 3 circles of data from different seismograph stations. The point where all 3 circles intersect is the epicenter.

● The epicenter is where the most violent shaking occurs.

● Why do you think we need to know where the epicenter is?

Events at Convergent Boundaries

● A boundary where plates push together is called a convergent boundary.

● What happens when plates meet depends on the type of crust involved: ◦ A boundary between two continental plates ◦ A boundary between a continental plate and an oceanic plate ◦ A boundary between two oceanic plates

Two Continental Plates at Convergent Boundaries

●Who made a mountain last nine weeks?

●When two continental plates push together at convergent boundaries, non-volcanic mountains (regular) form.

●Slowly, over millions of years, pressure from the colliding plates pushes rock upward.

Two Oceanic Plates at Convergent Boundaries

● At a boundary where two oceanic plates meet, one plate is subducted, or pushed under the other.

● A deep canyon called a trench forms under the ocean where the plates meet.

● As the subducted plate sinks into the mantle, some rock melts into magma.

● Magma reaches the earth’s surface as a volcano.

Volcanoes

● Who made a volcano last nine weeks? ● A volcano is an opening in earth’s crust from which

melted rock, gases, and ash can escape. ● Over time, rock builds up to form volcanic

mountains on the ocean floor. ● Mountains that become tall enough to rise out of

water form islands. ● Volcanoes are temporary features on the earth's

surface. ● There are currently about 1500 active volcanoes in

the world. About ten percent of these are located in the United States.

● https://www.youtube.com/watch?v=xP2dreOI8gI ● https://www.youtube.com/watch?v=4aYQixhdWY4

https://www.youtube.com/watch?v=xP2dreOI8gIhttps://www.youtube.com/watch?v=xP2dreOI8gIhttps://www.youtube.com/watch?v=4aYQixhdWY4

A Continental Plate and an Oceanic Plate

●When a continental plate and an oceanic plate collide, the oceanic plate tends to slide under the continental plate. ● Chains of volcanic mountains can

form on the edge of the continental plate.

Event at Divergent Boundaries

● At a divergent boundary, two plates move away from each other.

● A crack called a rift forms between the plates.

● As magma rises up through the rift, new crust forms.

● When this happens on the ocean floor, the process is called sea-floor spreading.

● https://www.youtube.com/watch?v=6CsTTmvX6mc

Sea-floor Spreading

● During sea-floor spreading, new ocean floor forms in the area of the rift.

● An underwater chain of volcanic mountains, called the mid-ocean ridge, forms on either side of the rift.

● The valley between the mountains is called the rift valley.

● The new floor is called a trench.

Hot Spots

Hot Spots

● A hot spot is an area of volcanic activity that is not near a plate boundary.

● When a hot spot forms under a tectonic plate, the hot spot stays in one place, while the plate moves slowly over it.

● This movement produces a chain of volcanoes.

● The Hawaiian Islands are a chain of volcanoes that have formed this way.

The Ring of Fire

● The Ring of Fire is a zone of frequent earthquakes and volcanoes.

● The Ring of Fire follows a path of plate boundaries around the edge of the Pacific Ocean.

● More than 75% of earth’s volcanoes are located in the Ring of Fire.

● We know plates are like giant rafts of the earth's surface which often slide next to, collide with, and are forced underneath other plates.

● Around the Ring of Fire, the Pacific Plate is colliding with and sliding underneath other plates. This process is known as subduction and the volcanically and seismically active area nearby is known as a subduction zone.

● There is a tremendous amount of energy created by these plates and they easily melt rock into magma, which rises to the surface as lava and forms volcanoes.

What Do You Think?

● Now that you know about the relationship between plate movements and earthquakes, mountain building, volcanoes, and sea floor spreading, explain which one of these you would most like to build a house near and why.

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Vocabulary!● In this lesson, we have learned several

new vocabulary words. Use your notes, glossary, or your book to define these words:

● epicenter ● trench ● hot spot ● transform boundary ● divergent boundary ● convergent boundary ● subduction

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Let’s Review Earthquakes!

Where are earthquakes most likely to take place? !a) along the core-mantle interface b) where the composition of the Earth tends to be uniform c) near the Earth's Equator d) near a fault zone

http://www.troy.k12.ny.us/faculty/dibarij/earth%20science/unit12.html

Where are earthquakes most likely to take place? !a) along the core-mantle interface b) where the composition of the Earth tends to be uniform c) near the Earth's Equator d) near a fault zone

http://www.troy.k12.ny.us/faculty/dibarij/earth%20science/unit12.html

1. A ___________ is term describing a series of waves created by an underwater earthquake or a volcano erupting.

a) wildfire b) flood c) tsunami d) tornado

2. How many seismograph stations are needed to locate the epicenter of an earthquake?

a) 1 b) 2 c) 3 d) 4 or more

3. Which layer do earthquakes occur in? a) Troposphere
b) Lithosphere
c) Asthenosphere
d) Mesosphere

1. A ___________ is term describing a series of waves created by an underwater earthquake or a volcano erupting.

a) wildfire b) flood c) tsunami d) tornado

2. How many seismograph stations are needed to locate the epicenter of an earthquake?

a) 1 b) 2 c) 3 d) 4 or more

3. Which layer do earthquakes occur in? a) Troposphere
b) Lithosphere 
c) Asthenosphere
d) Mesosphere

4. During an earthquake, the most violent shaking occurs at the a) vent b) focus c) Ring of Fire d) epicenter

5. The seismic waves that cause the most damage during an earthquake are a) P waves b) S waves c) Surface waves d) X-rays

6. Which of the following describes primary waves created by an earthquake? a) they cause damage on the surface b) they cause up-and-down movement in the rock c) they are the fastest-moving waves d) they are the slowest-moving waves

During an earthquake, the most violent shaking occurs at the a) vent b) focus c) Ring of Fire d) epicenter

The seismic waves that cause the most damage during an earthquake are a) P waves b) S waves c) Surface waves d) X-rays

Which of the following describes primary waves created by an earthquake? a) they cause damage on the surface b) they cause up-and-down movement in the rock c) they are the fastest-moving waves d) they are the slowest-moving waves