CVHS Unleashing Devastation at a Convergent Plate Boundary Paper

NAME:_________________________
Rev. 5/5/21
CREDIT 3A: EARTH’S INTERNAL PROCESSES
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Lesson
Title
INTRODUCTION
3.1
Deformation of Earth’s Crust
3.2
How Mountains Form
3.3
Earthquakes and Volcanoes
Assignments

 Connect to Essential Question
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Deformation of Crust Concept Map
 Review Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Calculating Pressure on Earth’s Crust
 Review Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Plate Tectonics and the Ring of Fire
 Review Questions


PERFORMANCE TASK
QUIZ
Student Support Icons
Title
Icon
Description
Review
Activity
This provides the students with a reminder that they need to answer questions.
Technology
Guides students through the tasks and assignments that require the use of
technology and manipulatives.
Reading
This icon lets the students know they will be completing a reading activity.
Credit Materials



Materials
Pen/Pencil
HMH Earth Science
Textbook (optional)
Packet



Technology Needs
Internet
Computer
HMH Online Resources
(optional)
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General Science 1A
Credit 3
NAME:_________________________
CREDIT 3A: INTRODUCTION
Read “How do Earth’s Internal Processes Produce Earth’s Surface Features?” and watch the video “How Tall
Can Mountains Be?” below. Then answer the essential question.
How Do Earth’s Internal Processes Produce Earth’s Surface Features?
The Earth’s surface has large landmasses that are called tectonic plates. The convection currents occurring
inside the Earth cause the tectonic plates to move at varying speeds and in different directions atop a hotter,
softer, and more malleable rock layer called the asthenosphere. This difference in movement causes plate
boundaries where Earth’s plates collide with each other. These collisions can result in the formation of
mountains and volcanoes, and can cause earthquakes.
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General Science 1A
Credit 3
NAME:_________________________
An essential question allows you to explore the content of the credit. Before you answer the question, watch
the video. Then answer the essential question to the best of your ability. You will revisit the essential
question at the end of the credit to see if your answer has evolved.
Video: How Tall Can Mountains Be? (1:54)

“How Tall Can Mountains Be?” YouTube. MinuteEarth, 30 Mar. 2013. Web. 20 Oct. 2015.
Located in Nepal, Mount Everest is the tallest mountain on Earth with an elevation of 29,029 feet (5.497 miles).
Essential Question
How do you think Earth’s internal processes cause surface features on Earth as tall as Mount Everest?
Based on the materials in the textbook excerpt, Earth’s internal processes can cause surface features as tall as Mount
__________________________________________________________________________________________
Everest through the collision and movement of tectonic plates. Specifically:
__________________________________________________________________________________________
– Convection currents in the mantle cause tectonic plates to move and collide with each other. When two continental
plates collide, the thick continental crust resists subduction and is pushed upwards, forming very tall mountains like the
__________________________________________________________________________________________
Himalayas, which contain Mount Everest.
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– The collision of tectonic plates causes compression and folding of the crust, which can form tall mountain ranges. As
plates push together, the crust wrinkles and folds over itself, thrusting rock layers upwards. This folded mountain building
process has created many of the world’s tallest peaks.
– When oceanic and continental plates collide, the dense oceanic plate is pushed underneath the continental plate. This
subduction melts rock and produces magma that can erupt to form volcanic mountains, adding height to the landscape.
The volcanism resulting from subduction has contributed to the growth of tall mountains.
– Isostatic adjustments, caused by changes in the weight and density of the crust from mountain building and erosion,
produce uplift that can further increase elevation. As mountains are eroded, the lighter crust rises upwards in isostatic
rebound.
So in summary, the internal churning of the mantle, the collisions and subduction of tectonic plates, folding and thrusting
of the crust, volcanism, and isostatic adjustments all contribute to building surface features as tall as the Himalayas and
Mount Everest. The processes that build mountains are powered by Earth’s internal heat engine.
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General Science 1A
Credit 3
LESSON 3.1: DEFORMATION OF CRUST
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Learning Goals for this Lesson
 Summarize the principle of isostasy.
 Identify the three main types of stress.
 Compare folds and faults.
Lesson Assignments
 Connect to Essential Question
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Deformation of Crust Concept Map
 Review Questions
Engage
Connect to Essential Question
You are watching a lab experiment in which a rock sample is being gently heated and slowly bent. Would you
expect the rock to fold or to fracture? Explain your reasoning.
I would expect the rock sample to fold rather than fracture if it is gently heated and slowly bent in the lab experiment. My
_________________________________________________________________________________________
reasoning is that heating the rock makes it more ductile and deformable. Higher temperatures allow rocks to bend and
fold more easily without breaking. Applying the force slowly and gradually allows time for the rock to respond through
_________________________________________________________________________________________
ductile deformation. Quick, sudden stresses are more likely to cause brittle fracture. Bending specifically puts the
_________________________________________________________________________________________
sample under compression and shear stress. These types of stresses favor folding rather than faulting and fracturing.
Under experimental conditions, with controlled, gentle heating and bending, the rock is unlikely to reach the threshold
_________________________________________________________________________________________
for brittle failure. It will deform plastically and bend. In a natural setting near the surface, cool temperatures would make
fracture more likely. But in a lab with controlled heating, the rock can deform ductilely. So because the rock is heated
and the force is applied gradually, I would expect the sample to respond by folding without fracturing. The heating and
slow bending promote ductile rather than brittle deformation.
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General Science 1A
Credit 3
Explore
Exploration Activity
California’s coastal mountains run from the northern part
of the state south to the Mexican border, separating the
coast from the Great Central Valley and the deserts of the
interior. The geologic history of California’s coastal
mountains begins with the collision of the North American
plate and the Pacific plate about 250 million years ago.
The Pacific plate slipped beneath the North American
plate, heating and melting rock in the process. Between
about 150 million and 140 million years ago, magma began
to push upward, forming the Klamath and Peninsular
ranges. Then about 30 million years ago, the Pacific plate
and the North American plate changed from head-on
contact and began to slip against each other laterally,
forming the San Andreas Fault.
1. In what way has plate tectonic activity affected the geologic history of California’s coastal
mountains?
Plate
tectonic activity has affected the geologic history of California’s coastal mountains in several key ways:
____________________________________________________________________________________
The initial collision and subduction of the Pacific plate under the North American plate provided the compressive
____________________________________________________________________________________
forces that pushed up and formed the early coastal mountain ranges like the Klamath and Peninsular ranges
2.
do youyears
thinkago.
the plates began to slip against each other laterally 30 million years ago?
overWhy
100 million
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are
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the Sancollision
Andreas
____________________________________________________________________________________
slipping
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each ago.
otherMovement
about 30 million
years
ago: boundary fault continues to shape the coastal
Fault around
30 million
along this
transform
____________________________________________________________________________________
ranges.
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infaulting,
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Ongoing
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plate
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3.
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than
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North
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over
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What
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example
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deformation
of
Earth’s
crust
in
California?
Magma production and volcanism resulting from the plate interactions have contributed material to build the
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mountains
over
time
____________________________________________________________________________________
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that to
allowed
the plates
____________________________________________________________________________________
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moveChapter
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it. Worksheet. Austin, TX: Houghton Mifflin Harcourt
Publishing Company, 2010. PDF.
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and
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Some combination
of these
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of over
the crust.
conditions areas
evolved
tens of millions of years at the complex plate boundary.
Bending and deforming of rock layers has produced geological structures like folds, faults, joints, and shear
zones throughout California’s complex geological history.
Ongoing deformation continues today as tectonic stresses act on the crust, producing earthquakes, uplift, and
further structural deformation over time.
6
General Science 1A
Credit 3
Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Is Isostasy?
Mountain ranges are proof that the shape of Earth’s surface is constantly changing. These changes are caused
by deformation. Deformation is the bending and breaking of Earth’s crust. Deformation can happen when the
weight of some part of Earth’s crust changes. If the lithosphere becomes thicker and heavier, it sinks down into
the asthenosphere. If the lithosphere becomes thinner and lighter, it rises in the asthenosphere. The vertical
movement of the lithosphere depends on two opposing forces. One is the force of gravity, which pulls the
lithosphere down. The other is the buoyant force of the asthenosphere, which pushes up on the lithosphere.
When these two forces are balanced, the lithosphere and asthenosphere are in a state of isostasy. When the
weight of the lithosphere changes, the lithosphere sinks or rises until the forces balance again. The movement
of the lithosphere puts forces on the rock in it. These forces can cause deformation.
An isostatic adjustment happens when Earth’s lithosphere rises or sinks to maintain isostasy. Isostatic
adjustments are happening all the time in Earth’s crust. For example, a mountain goes through isostatic
adjustments as it erodes. Over millions of years, wind, water, and ice wear away the rock. The mountain
becomes shorter and lighter. As the mountain shrinks, it rises in a process called uplift. The opposite of uplift
is subsidence. During subsidence, the lithosphere becomes heavier. It sinks into the asthenosphere.
Subsidence is common in places where large rivers flow into oceans. Large rivers generally carry large amounts
of sediment, including mud, sand, and gravel. When the river flows into the ocean, the sediment drops onto the
ocean floor. The extra weight of the sediment makes the ocean floor sink.
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General Science 1A
Credit 3
Isostatic adjustments can also happen when glaciers grow or shrink. A glacier is a huge river of ice. Glaciers
can hold huge amounts of water. Therefore, they are very heavy. The weight of the ice makes the lithosphere
beneath the glacier sink. At the same time, the ocean floor rises because the weight of the ocean water is less.
The water has moved onto land and has been frozen in the glacier. When the glacier melts, the water returns to
the ocean. The extra weight of the water causes the ocean floor to sink. At the same time, the land that was
covered with ice rises because the weight of the crust has decreased.
Isostatic Adjustments
Cause
Wind, water, and ice carry away rock from
mountains.
Rivers deposit sediment on the ocean floor.
Glaciers form as ice and snow build up.
Glaciers melt as the climate gets warmer.
Effect
The mountains become lighter and uplift occurs.
The ocean floor becomes heavier and subsidence
occurs.
The weight of the glacier causes subsidence under the
glacier. The decreased weight of ocean water causes
uplift in the oceans.
The decreased weight of the glacier causes uplift on
land. The increased weight of ocean water causes
subsidence in the oceans.
1. What are the two forces that must balance out to maintain a state of isostasy?
The two forces that must balance out to maintain a state of isostasy are the force of gravity and the buoyant
____________________________________________________________________________________
force of the asthenosphere. Gravity acts to pull the lithosphere down, while the asthenosphere pushes up against
the lithosphere with its buoyant force.
____________________________________________________________________________________
____________________________________________________________________________________
Isostasy involves the vertical motion of Earth’s lithosphere as it floats in gravitational equilibrium on the
asthenosphere. If the lithosphere becomes denser for some reason, the extra weight causes it to sink lower into
the asthenosphere until the buoyant force balances out the greater gravitational force again. On the other hand,
What Kinds
of Stress Can
Act on
if the lithosphere
becomes
lessRocks?
dense, the decreased weight means the buoyant force will push it higher until
reaching a new point of balanced forces.
As Earth’s lithosphere moves, the rock in the crust is squeezed,
These
forces actions
are in a state
of isostasy
are equal.
The lithosphere will adjust up or down in
stretched,
and opposing
twisted. These
put force
on thewhen
rock.they
Stress
is
order to maintain this balance. For example, when a glacier forms, its weight causes subsidence of the
the amount
of forceunderneath
applied toit.a But
given
area
rock. melts,
Stressuplift
occurs
lithosphere
when
theofglacier
occurs as the decreased gravitational force allows
when thethelithosphere
sinks and is squeezed
the weight
of rock Isostatic adjustments like this work to keep the two
buoyant asthenosphere
to raise theby
lighter
crust upwards.
above it.forces
It also
occurs So
when
rock
in the and
crusttherises
and is
balanced.
thethe
force
of gravity
buoyant
force of the asthenosphere must be in equilibrium for
isostasy
to
be
maintained.
The
motion
of
the
lithosphere
acts
to restore this balance when disturbances occur.
stretched out. The movement of tectonic plates past one another can
also produce stress. There are three main types of stress:
compression, tension, and shear stress. Compression is a type of
stress that squeezes rock. Compression can change the shape of a
rock or reduce the amount of space the rock takes up. Compression
is a common kind of stress in places where tectonic plates are
moving together. Tension is the opposite of compression. Tension
is stress that stretches rock. Tension can make rock longer and
thinner. Tension is a common kind of stress in places where tectonic
plates are moving apart. Shear stress deforms rock by pushing its
different parts in opposite directions. Sheared rock can bend, twist,
or break apart as it moves past other rocks. Shear stress is a common
kind of stress in places where tectonic plates slide past each other.
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General Science 1A
Credit 3
Stress can cause deformation. Deformation that is caused by stress is called strain. Changes in shape and size
are examples of strain. Strain is not always permanent. If the stress is applied slowly, the rock might go back to
its original shape when the stress is removed. However, if too much stress is put on the rock, the strain may
become permanent. There are two main types of permanent strain: brittle and ductile. Rocks that break or
fracture under stress are brittle. Cracks and breaks in rock are types of brittle strain. In contrast, ductile rocks
respond to stress by bending without breaking. Folds and bends in rock are types of ductile strain. The type of
strain a rock shows depends on several factors. These factors include temperature, pressure, the composition of
the rock, and how fast the stress is applied. Near Earth’s surface, where temperature and pressure are low, brittle
strain is most common. Brittle strain is also more common when a lot of stress is applied quickly. At higher
temperature and pressure, ductile strain is more common. Small amounts of stress applied over long periods of
time can also cause ductile strain.
2. What would you expect a rock that has experienced tension to look like?
I would expect a rock that has experienced tension to appear stretched and elongated. Tension causes strain
____________________________________________________________________________________
that pulls the rock material apart, making the rock lengthen along the axis of the applied tensional force. This
would make the overall shape of the rock longer and thinner compared to its original dimensions. There may be
____________________________________________________________________________________
visible necking where the rock width narrows in the middle. Joints or fractures perpendicular to the tension
____________________________________________________________________________________
direction might also be present if the rock failed under the tensile stress
3. Which kind of stress can cause rock to bend, twist, or break apart?
Shear stress can cause rock to bend, twist, or break apart. Shear stress pushes the rock in opposite lateral
____________________________________________________________________________________
directions, deforming the rock by bending, twisting, or fracturing it along the shear plane. This makes it different
from compression or tension which act inward or outward on the rock. The shearing forces of the sliding plates
____________________________________________________________________________________
causes the rock to deform in more complex ways than simple axial compression or tension
____________________________________________________________________________________
4. Which type of strain can cause a rock to bend without breaking?
Ductile strain can cause a rock to bend without breaking. Ductile strain allows rocks to deform plastically under
____________________________________________________________________________________
stress, folding and bending rather than fracturing. Ductile strain happens where temperatures and pressures are
higher, which makes rocks more malleable. Slow amounts of shear stress can cause ductile rock layers to warp
____________________________________________________________________________________
and bend into folds over time without snapping. In contrast, brittle strain would cause the rocks to break when
____________________________________________________________________________________
bent or folded.
What Features Can Strain Produce?
Different kinds of strain produce different features in rock. Two main kinds of strain are folds and faults. A fold
occurs when a rock responds to stress in a ductile way. A fault occurs when a rock responds to stress in a brittle
way. A fold is a bend in a rock layer. Most folds form when rocks are compressed. As compression acts on the
rock, the rock layers wrinkle and fold over themselves. Some folds also form because of shear stress. Folds
have different parts. They have sloping sides called limbs. The limbs meet at the bend, or hinge, of the rock
layers. Folds can be symmetrical or asymmetrical. If a fold can be sliced in two identical halves, it is
symmetrical. The dividing line is called the axial plane. However, most folds are not symmetrical.
Folds can have many different shapes. Many folds are bent vertically. However, some are overturned and seem
to be lying on their sides. Folds can be open or very tight. The limbs can be even, or one can be steeper than the
other. The hinge can be a smooth bend or a sharp point. Each fold is unique because it formed under a unique
combination of conditions. Folds can vary in size as well as shape. Some are smaller than your hand. Others
cover thousands of square kilometers. Some folds are so large that they form ridges and valleys. Geologists
classify folds based on their characteristics. There are three main kinds of folds: anticlines, synclines, and
monoclines. In an anticline, the oldest rocks are in the middle of the fold. In a syncline, the oldest rocks are on
the outside of the fold. In a monocline, the two limbs are horizontal or almost horizontal. The pictures below
show examples of these kinds of folds.
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General Science 1A
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Faults form when rock deforms in a brittle way. A fault is a break in the body of a rock along which the
surrounding rock moves. The fault plane is the plane along which the rock moves. If the fault plane is not
vertical, the rock above the fault plane is known as the hanging wall. The rock below the fault plane is called
the footwall. Like folds, faults can vary greatly in size. Small faults may affect only a few layers of rock found
in a small region. Other faults are thousands of kilometers long. These large faults are often composed of
smaller, connected faults, rather than a single fault. There are two main types of faults: normal faults and
reverse faults. In a normal fault, the hanging wall moves down relative to the footwall. In a reverse fault, the
hanging wall moves up relative to the footwall. A thrust fault is a type of reverse fault in which the fault plane
is almost horizontal.
In some faults, the rock does not move up and down. Instead, it moves horizontally. The two pieces of rock
slide past one another. This type of fault is called a strike-slip fault. The rock in a strike-slip fault moves
parallel to the direction of the fault’s length. The fault plane in a strike-slip fault may be vertical or tilted.
Strike-slip faults are most commonly found at transform boundaries, where tectonic plates grind past each other.
They may also occur at fracture zones between segments of mid-ocean ridges.
Answer the following questions using evidence from the reading.
5. How can a geologist tell if a fold is a syncline or an anticline?
A geologist can tell if a fold is a syncline or an anticline based on the orientation of the oldest rock layers. In a
____________________________________________________________________________________
syncline, the oldest rocks are on the outer sides of the fold, while the youngest rocks are in the center. In an
anticline, this is reversed – the oldest rocks are in the middle of the fold core and the youngest rocks are on the
____________________________________________________________________________________
outer limbs. So a geologist just needs to observe where the relatively older vs younger rock units are located to
____________________________________________________________________________________
identify synclines and anticlines
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General Science 1A
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6. How is a strike-slip fault different from a normal fault?
A strike-slip fault is different from a normal fault in the direction of rock motion. In a strike-slip fault, the blocks of
____________________________________________________________________________________
rock on either side slide horizontally past each other, parallel to the orientation of the fault plane. In a normal
fault, the rock moves vertically, with the hanging wall dropping down relative to the footwall. Strike-slip faults
____________________________________________________________________________________
involve lateral motion while normal faults have vertical displacement of rock blocks. Additionally, normal faults
____________________________________________________________________________________
typically have a dip-slip fault plane, while strike-slip faults have near vertical orientations. The types of stress
producing each fault are also different – tension for normal faults and shear for strike-slip
Allison, Mead A., et al. “Chapter 11: Deformation of Crust/Section 1: How Rocks Deform.” Holt McDougal Earth Science Interactive Reader, Holt McDougal, a
Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 161-168.
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
The Principle of Isostasy (2:39)
http://www.hhmi.org/biointeractive/principle-isostasy
“The Principle of Isostasy | HHMI’s BioInteractive.” The Principle of Isostasy.
Howard Hughes Medical Institute, n.d. Web. 22 Oct. 2015.
Can the weight of massive objects like glaciers cause Earth’s crust to
deform? This video will explain how continents rose after ice sheets from
the last ice age retreated.
Earthquake Faults – 3 Basic Types (0:51)

What types of faults occur from stress on rocks? This video will explain
why different faults form and what kinds of stress cause them to occur.
“Earthquake Faults – 3 basic types…in brief (educational)”. IRIS Earthquake Science. Web. 22 Oct. 2015.
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General Science 1A
Credit 3
Elaborate
Deformation of Crust Concept Map
Complete the concept map below to show the relationship between the types of stress rocks undergo during
deformation using the following terms. Each term can be found in the reading section for this lesson.
Reverse faults
Stress
Strain
Brittle
Thrust faults
Strike-slip faults
Folds
Normal faults
Ductile
Faults
Allison, Mead A., et al. “Chapter 11: Deformation of Crust/Section 1: How Rocks Deform/Concept Map: Deformation of Crust.” Holt McDougal Earth Science, Holt
McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010.
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Evaluate
Review Questions
Answer the following questions.
1. Compare folding and faulting. What type of factors affect whether rocks fold or fault?
Folding and faulting are both types of strain that rocks can undergo when stressed, but they occur under different
_______________________________________________________________________________________
conditions. Folding is ductile strain that causes rocks to bend without breaking, while faulting is brittle strain that
fractures and breaks the rocks. Folding tends to occur with slower compression over long periods, at high
_______________________________________________________________________________________
temperatures/pressures and in ductile rocks. Faulting happens with rapid stress that exceeds rock strength, usually
_______________________________________________________________________________________
near surface where rocks are cooler and more brittle. Factors like temperature, pressure, rock type, and stress rate
affect whether rocks will fold or fault when deformed.
2. Why would faulting be more likely to occur near Earth’s surface and not deep within Earth?
Faulting would be more likely near Earth’s surface because rocks are cooler and more brittle in the upper crust. Near
_______________________________________________________________________________________
the surface, temperatures and pressures are lower, so when stress is applied, rocks fracture instead of folding
ductilely. Deep below the surface, higher temperatures make rocks more plastic and pressures help keep fractures
_______________________________________________________________________________________
closed, so ductile folding is more common there. Sudden stress applied at the surface can exceed rock strength and
_______________________________________________________________________________________
cause brittle faults before the rocks have time to deform plastically.
3. Summarize how isostatic adjustments affect isostasy.
Isostatic adjustments occur as Earth’s crust moves vertically to maintain gravitational equilibrium and balance its
_______________________________________________________________________________________
buoyant force with its weight. If the crust thickens or density increases, it will sink lower into the mantle until buoyant
forces lift it back to an isostatic balance. If the crust thins or loses mass, uplift will occur as the buoyant
_______________________________________________________________________________________
asthenosphere pushes up the lighter crust. Isostatic adjustments restore isostasy any time the crustal weight
_______________________________________________________________________________________
changes and upsets the balance of forces supporting it.
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General Science 1A
Credit 3
LESSON 3.2: HOW MOUNTAINS FORM
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Learning Goals for this Lesson
 Identify the types of plate collisions that form mountains.
 Identify four types of mountains.
 Compare how folded and fault-block mountains form.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Calculating Pressure on Earth’s Crust
 Review Questions
Engage
Connect to Prior Knowledge
Have you ever visited any mountain ranges? If so, where were they located? If not, where do you feel that
you generally find mountain ranges?
I have visited several mountain ranges, mostly in the western United States. I have seen the Rocky Mountains in
_________________________________________________________________________________________
Colorado, the Sierra Nevada in California, and the Cascade Range in Washington. I have also viewed the Appalachian
Mountains on the East Coast.
_________________________________________________________________________________________
In general, major mountain ranges seem to be located along plate boundaries or in areas where tectonic activity occurs.
_________________________________________________________________________________________
The compression and uplift associated with plate collisions tends to produce significant mountain building. Ranges like
the Himalayas, Andes, and Alps all formed along convergent plate boundaries. The extensions of mid-ocean ridges also
_________________________________________________________________________________________
create undersea mountain chains. Mountains can form in the interior of plates as well, usually due to localized uplift or
volcanic activity. But the tallest, longest ranges do seem to align with tectonic processes and plate motions. The
connection between plate tectonics and mountain formation is a key part of geology.
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Explore
Exploration Activity
Scientists use bar graphs as a way to display data. Bar graphs can make it easier to visualize a comparison of
data values. A bar graph may be created from data in a table or from data described in text. Typically, a bar
graph has item names or numerical values on the x-axis and numerical values on the y-axis. This allows
scientists to compare the relative heights of the bars. Scientists might use a bar graph like the one below to
indicate the elevations of mountain peaks on various continents.
Use the bar graph to answer the following questions.
1. Which mountain has the second lowest elevation?
Mount elbrus
_______________________________________________________________________________________
_______________________________________________________________________________________
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2. On which continent is the mountain with the lowest elevation?
asia
_______________________________________________________________________________________
_______________________________________________________________________________________
3. What is the approximate elevation of Mount Aconcagua?
7000
_______________________________________________________________________________________
_______________________________________________________________________________________
4. What is the approximate elevation of Mount Kilimanjaro?
6000
_______________________________________________________________________________________
_______________________________________________________________________________________
5. Using the data in the table below, create a bar graph comparing the elevations, in feet, of some North
American mountain peaks.
Mountain
Elevation (feet)
Mount McKinley
20,320
Mount Rainier
14,410
Bear Mountain
7,166
Mount Washington
6,288
Black Dome Mountain
3,980
Holt McDougal. Graphing Skills Worksheet: Bar Graphs and Mountain Elevations. Austin, TX: Houghton Mifflin Harcourt Publishing Company, 2010. PDF.
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What is a Mountain Range?
A mountain range is a group of mountains that have similar ages, shapes, and sizes, and that are close together.
The mountains in a mountain range all formed in a similar way. Mount Everest, Earth’s highest mountain, is
part of the Great Himalaya Range. Mount St. Helens, a volcanic mountain in the northwest United States, is part
of the Cascade Range. Groups of nearby mountain ranges form mountain systems. For example, the
Appalachian mountain system is found in eastern North America. It is made up of the Great Smoky, Blue
Ridge, Cumberland, Green, and White mountain ranges. Mountain systems, in turn, are part of even larger
systems called mountain belts. Two of Earth’s major mountain belts are the circum-Pacific belt and the
Eurasian-Melanesian belt. Many well-known mountain systems are part of these two belts. Both of these belts
are located along convergent plate boundaries. The location of the belts is evidence that many mountains form
as a result of tectonic plate collisions. The types of plates that collide affect the mountains that form.
1. What characteristics do the mountains in a mountain range have in common?
Mountains have similar ages due to tectonics. Mountains rose. Similar shapes, sizes, suggest common formation
_______________________________________________________________________________________
processes, forces. Mountains form from plate collision. They’re close. The mountains are nearby. Created by
tectonics. Similar rocks and structures have a shared origin. Mountains often share common rocks. Geo patterns by
_______________________________________________________________________________________
geo structures.
_______________________________________________________________________________________
How Do Mountains Form?
Mountains generally form when the lithospheres of two tectonic plates collide. Remember that there are two
main kinds of lithosphere: oceanic and continental. The type of lithosphere at the edge of each of the colliding
plates affects the type of mountains that form. Some mountains form when oceanic lithosphere and continental
lithosphere collide. Oceanic lithosphere is denser than continental lithosphere. Therefore, when they collide, the
oceanic lithosphere subducts, or sinks, beneath the continental lithosphere. The continental lithosphere is
uplifted, so tall mountains form. The subduction of the oceanic lithosphere can cause some of the mantle to
melt. This produces magma that can erupt and form volcanic mountains. Mountains can also form at these plate
boundaries when pieces of crust are scraped off the ocean lithosphere. These pieces of crust, which are called
terranes, become part of the continent. Volcanic mountains can also form when two plates containing oceanic
lithosphere collide. When two oceanic plates collide, the denser plate subducts beneath the other plate. Fluids
from the subducting lithosphere can cause the mantle to melt. Magma rises and breaks through the lithosphere.
These eruptions form a chain of volcanic mountains on the ocean floor. The chain of mountains is called an
island arc. In some areas, two continental plates collide. Continental lithosphere is less dense than the
asthenosphere. Therefore, continental lithosphere cannot subduct. When two continental plates collide, the
lithosphere on both plates is pushed up. The continental lithosphere is very thick. Therefore, continentalcontinental plate collisions produce extremely tall mountains.
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2. What are three types of plate collisions that
can form mountains?
Oceanic-continental
convergence (subduction)
________________________________________
Oceanic-oceanic convergence (subduction)
Continental-continental convergence
________________________________________
________________________________________
________________________________________
3. Why does oceanic lithosphere subduct below
continental lithosphere?
Oceanic lithosphere is denser than continental lithosphere,
________________________________________
so when the two collide the denser oceanic plate sinks
beneath the more buoyant continental plate. Subduction
________________________________________
occurs due to the difference in density.
________________________________________
________________________________________
4. What are the main differences between
mountains that form where two continents
collide and mountains that form where an
oceanic plate collides with a continental plate?
In oceanic-continental collisions, subduction leads to
________________________________________
volcanic arcs and mountains. In continental-continental
collisions, thick buoyant crust resists subduction, leading to
________________________________________
massive compressed mountains but little volcanism.
Mountains from oceanic-continental convergence have
________________________________________
volcanoes, while mountains from continental-continental
convergence are very tall and folded but have minimal
________________________________________
volcanism
What Are the Different Types of Mountains?
Mountains are more than just elevated parts of Earth’s crust. They also contain important evidence of the
stresses that created them. Geologists classify mountains based on their shapes and the ways they form. Many
of Earth’s highest mountain ranges consist of folded mountains. Folded mountains form when tectonic plate
movements squeeze rock layers together. The compression on the rocks makes them fold. Parts of the Alps, the
Himalayas, and the Appalachians are folded mountains. The stresses that form folded mountains can also form
plateaus. A plateau is a large, flat area of rock high above sea level. They can form when thick, horizontal
layers of rock are slowly uplifted. This allows the layers to remain flat instead of folding. Plateaus can also form
when layers of melted rock harden or when large areas of rock erode. Many plateaus are found near folded
mountains.
In places where parts of Earth’s crust have been stretched and broken into large blocks, fault-block mountains
can form. These mountains form when faulting causes blocks of rock to tilt and drop relative to other blocks.
The higher blocks become mountain peaks. The Sierra Nevada range in California consists of many fault-block
mountains. The faulting that results in fault-block mountains can also form long, narrow valleys called
grabens. Grabens and fault-block mountain ranges generally occur together. The mountains form when one
block of rock rises relative to other blocks. Grabens form when one block slips downward. A famous graben
found in the United States is Death Valley in California.
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Dome mountains are not as common as folded mountains or fault-block mountains. Dome mountains form
when magma rising through Earth’s crust pushes rock layers up, but does not erupt. Dome mountains may also
form when tectonic forces gently uplift rock layers. Dome mountains are generally round and have gently
sloping sides. Mountains that form when magma erupts onto Earth’s surface are called volcanic mountains.
Most volcanic mountains are part of mid-ocean ridges along divergent plate boundaries. The peaks of these
mountains sometimes rise above sea level to form islands. Volcanic mountains are also common in places
where oceanic-oceanic and oceanic-continental plate collisions happen. Other volcanic mountains form at
hot spots. Most hot spots are far from plate boundaries. At a hot spot, hot, solid rock rises through the
lithosphere. When the rock melts, the magma can erupt and form islands. Scientists are still not sure exactly
what causes hot spots to form.
Types on Mountains
Type of Mountain
Description
Example
Folded Mountains
Mountains formed by compression Alps, Appalachian Mountains,
and folding of the crust.
Himalaya Mountains
Fault-Block Mountains
Mountains formed when blocks of Sierra Nevada
rock move along a large fault.
Dome Mountains
Small, round mountains formed
Black Hills, Adirondack
when magma pushes rock layers
Mountains
up.
Volcanic Mountains
Mountains formed when lava
Hawaiian Islands, Mid-Atlantic
erupts on Earth’s surface.
Ridge, Cascade Range
5. What is one difference between the way folded mountains form and fault-block mountains form?
One key difference is that folded mountains form due to compression and folding of rock layers, while fault-block
_______________________________________________________________________________________
mountains form from uplifted blocks bounded by faults.
_______________________________________________________________________________________
Folded mountains arise when tectonic forces squeeze and crumple rigid rock strata, creating wrinkles and folds in the
_______________________________________________________________________________________
crust. Fault-block mountains occur when large blocks of crust are uplifted along faults, tilting the blocks to form high
ridges.
Allison,
Mead A., et al. “Chapter 11: Deformation of Crust/Section 2: How Mountains Form.” Holt McDougal Earth Science Interactive Reader, Holt McDougal, a
Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 169-174.
Folded mountains undergo ductile deformation and bending of layers. Fault-block mountains experience brittle
fracturing and displacement of fault-bounded blocks. Their shapes and structures reflect these different formation
mechanisms.
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Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Convergent Boundaries (2:45)

What type of collisions occur at convergent plate boundaries? This
interactive video will explain how colliding plates result in different surface
features on Earth.
“Convergent Boundries”. YouTube. MooMoo Math and Science. 26 Jan 2020. Web. 26 Apr. 2021.
How Fold Mountains are Formed (2:16)

How are volcanic mountains formed? How does this differ from
volcanic ones? This video will explain the different tectonic processes that cause
different types of mountain formations.
“How fold mountains are formed”. YouTube. Classroom Nation. 3 Jul 2020. Web. 26 Apr. 2021.
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Elaborate
Calculating Pressure on Earth’s Crust
The megapascal (MPa) and pounds per square inch (psi) are two units used to describe the stress, or pressure,
on Earth’s crust. Knowing simple algebra comes in handy when using these units to describe stress on Earth’s
crust. Algebraic equations contain constants and variables. Constants are numbers that are known, and
variables are numbers that are unknown. Variables are usually represented by letters.
For example, 2x = 24 is an algebraic equation in which x is the variable and 2 and 24 are constants. When a
variable and constant are shown together, it means that the variable is multiplied by the constant. For example,
with the value 2x, the x is multiplied by 2. The purpose of algebraic equations is to determine the variable, or
unknown, using addition, subtraction, multiplication, and division. To determine the value of the variable, the
quantity on one side of the equals sign must always equal the quantity on the other side. That is, the equation
must always be balanced. Performing the same operation on both sides of an equation keeps it balanced, allows
you to simplify it, and allows you to determine the value of the variable.
Sample Problem:
In region A, the pressure on Earth’s crust is 24 MPa. This pressure is twice the amount of pressure in region B.
Write an algebraic equation that allows you to determine the pressure in region B, and then solve the equation.
Step 1: Write an equation in which x is the variable or the amount of pressure in region B.
𝟐𝒙 = 𝟐𝟒 𝑴𝑷𝒂
Step 2: To solve for x, perform the same operation on both sides of the equation. For this equation we divide
both sides by 2.
𝟐𝒙 ÷ 𝟐 = 𝟐𝟒 ÷ 𝟐 𝑴𝑷𝒂
Step 3: Perform the division.
Step 4: Write the answer.
𝒙 = 𝟏𝟐 𝑴𝑷𝒂
The pressure in region B is 12 MPa.
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Using the sample problem as a guide, answer the following questions. Remember to show your work.
1. In region A, the pressure on Earth’s crust is 4,000 psi, which is double the pressure in region B. Using
the algebraic equation below, calculate the pressure in region B.
𝟐𝒙 = 𝟒, 𝟎𝟎𝟎 𝒑𝒔𝒊
2. The pressure on Earth’s crust in region A is 10 MPa, which is half the pressure in region B. Using the
algebraic equation below, calculate the pressure in region B.
𝒙
= 𝟏𝟎 𝑴𝑷𝒂
𝟐
3. Convert 725 psi to megapascals using the equation below. 1 MPa = 145 psi.
𝟏𝟒𝟓𝒙 = 𝟕𝟐𝟓
4. The pressure on Earth’s crust in region A is three times greater than the pressure on Earth’s crust in
region B. The pressure in region B is 10 MPa. Write and solve an algebraic equation to calculate the
pressure in region A.
5. Convert 580 psi to megapascals. 1 MPa = 145 psi. Write an algebraic equation to show your solution.
crust.
Allison, Mead A., et al. “Chapter 11: Deformation of Crust/Section 2: How Mountains Form/Math Skills Worksheet: Algebraic Rearrangements and Pressure on
Earth’s Crust.” Holt McDougal Earth Science, Holt McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 23-24.
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Evaluate
Review Questions
Answer the following questions.
1. What type of plate collision results in the formation of an arc of volcanic islands such as the Mariana
Islands in the North Pacific Ocean?
The collision of an oceanic plate and a continental plate, where the denser oceanic plate is subducted beneath the
_______________________________________________________________________________________
continental plate, results in the formation of volcanic island arcs like the Mariana Islands.
_______________________________________________________________________________________
As the oceanic plate sinks into the mantle at these oceanic-continental convergent boundaries, fluids released from
_______________________________________________________________________________________
the subducting slab lower the melting point of the overlying mantle. Magma forms, rises, and erupts to create
volcanoes on the overriding continental plate, forming an arc of volcanic islands parallel to the trench.
2. How do folded mountains form?
Folded mountains form when compressional forces caused by converging tectonic plates push layers of rock
_______________________________________________________________________________________
So the Mariana Islands formed due to the subduction of the Pacific Plate beneath the Philippine Plate, creating a
together. This compression causes the rock layers to buckle, bend, and fold:
volcanic island arc on the overriding continental crust. In general, island arcs require the subduction of oceanic
_______________________________________________________________________________________
lithosphere under more buoyant continental lithosphere at convergent plate boundaries
As plates collide, they squeeze and shorten the crust along the convergent boundary. This horizontal compression
_______________________________________________________________________________________
forces rock strata to push together.
Because rock can deform ductilely under high pressure, the compressed rock layers bend rather than breaking.
3.
How docompression
fault-blockcauses
mountains
form?
Continued
the rock
layers to fold over on top of each other, creating wrinkles and waves in the
Fault-block
mountains
form
through
the
following processes:
_______________________________________________________________________________________
crust.
Over time, continued folding increases in complexity, with limbs being pushed past vertical to become overturned
Tensional
forces stretch and thin the crust, causing normal faults to develop. These faults cut the crust into large
_______________________________________________________________________________________
folds.
tilted blocks.
Eventually, whole sections of folded rock layers are thrust upwards as large blocks or nappes, stacked on top of
_______________________________________________________________________________________
As the faults slip, some blocks of crust drop downward relative to other blocks, creating relief between them.
each other.
The
downdropped
down-dropped
valleys
or basins.
The
relatively
uplifted
blocks become
mountain
Erosion
acts on
theblocks
foldedbecome
mountains
over
of years,
carving
out valleys
and
exposing
structure
of the
4.
Compare
how
dome
mountains
formmillions
with how
volcanic
mountains
form.
What arethe
some
similarities?
ranges.
folded
rocks
Differences?
Continued
slippage along the normal faults causes the blocks to tilt even more steeply. The higher side of the tilted
There
are some
and differences between how dome mountains and volcanic mountains form:
fault
blocks
formskey
thesimilarities
mountains.
_______________________________________________________________________________________
Erosion then sculpts the steeply tilted blocks into angular, linear mountain ridges separated by the down-dropped
Similarities:
_______________________________________________________________________________________
valleys.
Examples of this are the Basin and Range Province and Sierra Nevada mountains.
_______________________________________________________________________________________
Both
uprising
magma/molten
So in involve
summary,
fault-block
mountainsrock.
are made of crustal blocks that have been uplifted along faults relative to other
They
can
create
mountainous
topography.
blocks. The tensional forces that
produce the faults also tilt the blocks to form high ridges. The pattern of alternating
Igneous
processes
are reflects
involvedthe
in fault
their boundaries
formation.
mountains
and valleys
Differences:
Dome mountains form when magma pushes up rock layers but does not break the surface. Volcanic mountains form
when magma fully erupts through the crust.
Dome mountains have a rounded dome shape with gentle slopes. Volcanic mountains can have steeper conical
shapes.
Dome mountains are made of uplifted sedimentary layers. Volcanic mountains consist of igneous rock from lava
flows.
Dome mountains form from localized deformation of the crust. Volcanic mountains often form at plate boundaries.
Dome mountains may result from tectonic forces. Volcanic mountains are products of volcanism/magma movements.
So while both involve igneous intrusions, dome mountains form subtly through uplift whereas volcanic mountains are
built rapidly by eruptions of magma onto the surface. Their shapes and compositions reflect these differences.
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LESSON 3.3: EARTHQUAKES AND VOLCANOES
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Learning Goals for this Lesson
 Explain why earthquakes generally occur at plate boundaries.
 Explain how the structure of Earth’s interior affects seismic waves.
 Identify the three tectonic settings where volcanoes form.
 Describe the three main types of volcanoes.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Plate Tectonics and the Ring of Fire
 Review Questions
Engage
Connect to Prior Knowledge
Have you ever experienced a volcano or an earthquake? If so, what was it like?
I have experienced several small earthquakes, but never a major one or a volcano. The small earthquakes I’ve felt were
_________________________________________________________________________________________
a bit unnerving, but did not cause any real damage.
_________________________________________________________________________________________
Typically, you first feel a gentle rumbling and shaking sensation. Everything starts wobbling or swaying – the floor
beneath you, furniture, hanging lights. It feels like the ground has turned to jelly. Sometimes there is a loud rattling noise
_________________________________________________________________________________________
as windows and objects start vibrating. The shaking usually only lasts for several seconds, but it makes your heart race
with anxiety.
_________________________________________________________________________________________
In the largest earthquake I felt, about magnitude 5, the shaking was strong enough to knock some glasses off shelves
and tip over potted plants. I can only imagine how terrifying a major 7+ magnitude quake would be, with buildings
potentially crumbling and the ground rolling in waves. Getting under sturdy cover would be critical.
Fortunately, I have not yet experienced an erupting volcano up close. However, I have seen spectacular displays of
volcanoes like Hawaii’s Kilauea from a safe distance. The bright red lava spewing from the crater, the giant plumes of
ash and smoke, and the slowly creeping lava flows are both beautiful and frightening to behold. I cannot imagine
witnessing one of the huge violent eruptions that have occurred throughout history – it would be absolutely devastating. I
feel very fortunate to not have experienced major geologic disasters like massive quakes and eruptions up close and
personal. The raw power of the Earth unleashed must be inconceivably terrifying.
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Explore
Exploration Activity
In 1980, after 123 years of inactivity, Mount St. Helens literally blew its top.
This was the first volcanic event in the continental United States in 63 years. By
the time it was over, more than 150 miles of trout and salmon streams and 26
lakes had been destroyed. An avalanche of mud and felled trees—some more
than 300 years old—roared through the Toutle River valley, destroying
everything in its path. More than 2 million animals died. Volcanic ash circled
Earth in just 17 days. People died, too. For example, a U.S. Geological Survey
scientist, who was working just over five miles from the vent, was killed before
he could escape. Why were people unready for the explosion? Mount St. Helens
gave plenty of warning before it blew. As magma intruded into the rock under
the volcano’s crust, a bulge that eventually measured 320 feet developed. Steam
and ash spit from the vent for weeks before the eruption. The hot ash created a
new crater in the glacial snow. Earthquakes shook the mountain. Perhaps one of
the greatest lessons to be learned is that when nature sends a sign, it is in our
best interest to take heed. Against such power, humans are still outmatched.
Use the information in the passage above to answer the following questions.
1. Why was the eruption of Mount St. Helens significant?
The 1980 eruption of Mount St. Helens was significant because it was the deadliest and most destructive volcanic
_______________________________________________________________________________________
event in U.S. history. It was also the first major volcanic eruption in the continental U.S. in over 60 years.
_______________________________________________________________________________________
2. What signs did the mountain give to warn that it was about to erupt?
Mount St. Helens showed many warning signs before its eruption, including a growing bulge on the north face,
_______________________________________________________________________________________
increased seismic activity with thousands of small quakes, and weeks of steam eruptions and ash venting from the
crater.
_______________________________________________________________________________________
3. What can be learned from the experience of the Mount St. Helens eruption?
The Mount St. Helens eruption shows we should heed nature’s warning signs of impending volcanic eruptions and
_______________________________________________________________________________________
take precautions such as evacuations when an eruption appears imminent. It also shows the incredible power and
danger volcanoes can pose.
_______________________________________________________________________________________
4. What role do you think volcanoes have played in the formation of Earth’s surface features as they exist
today? Explain your answer.
Volcanoes have played a major role in building up landmass, creating islands, and forming many surface features we
_______________________________________________________________________________________
see today. Their eruptions produce lava flows, ash deposits, and igneous landforms. Volcanic material builds up over
time to create mountains, plateaus, and other landscapes. Volcanism is a key part of tectonic processes.
_______________________________________________________________________________________
Holt McDougal. Holt McDougal Earth Science Chapter 13: Volcanoes: Critical Thinking Skills Worksheet. Austin, TX: Houghton Mifflin Harcourt Publishing
Company, 2010. PDF.
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Makes Earthquakes Happen?
Remember that a fault is a crack in rock. If there is pressure on the rock around a fault, the rock is under stress.
Friction along the fault keeps the rock from moving. The stress can build up. Eventually, the stress becomes too
high. The rock moves suddenly along the fault. It releases a great deal of energy. The energy makes the ground
shake. The shaking is an earthquake. Elastic rebound is important in causing earthquakes. Elastic rebound
happens when a rock that is deformed goes back to its original shape.
When rock moves along a fault, the first motion on the fault is generally underground. The focus (plural, foci)
of an earthquake is the point where the first motion occurs. The energy an earthquake releases moves outward
in all directions from the focus. The epicenter of an earthquake is the point on Earth’s surface directly above
the focus. Scientists group earthquakes based on how deep their foci are. A shallow-focus earthquake has a
focus less than 70 km below Earth’s surface. An intermediate-focus earthquake has a focus between 70 km and
300 km below Earth’s surface. A deep-focus earthquake has a focus more than 300 km below Earth’s surface.
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1. How is elastic rebound related to earthquakes?
Elastic rebound is an important part of the earthquake process. As tectonic forces stress and deform rocks along a
_______________________________________________________________________________________
fault, they bend and accumulate stored elastic energy. Eventually this stress is released as the rocks rebound to their
original undeformed shape. The sudden rebound generates seismic waves that cause the ground shaking felt as an
_______________________________________________________________________________________
earthquake. So the buildup and release of elastic strain energy, known as elastic rebound, is what powers the
_______________________________________________________________________________________
seismic waves and ground motions during an earthquake event. The rocks act like a compressed spring that
eventually springs back when the force is released, generating the earthquake.
What Are Seismic Waves?
Look again at the figure on the previous page. You can see that there are seismic waves moving outward from
the focus. Seismic waves are vibrations caused by the energy released in an earthquake. When a pebble falls
into a pond, small waves ripple outward from the point the pebble hits. Similarly, seismic waves ripple outward
from the focus of an earthquake. The seismic waves travel in all directions from the focus through the rock
around it. There are two main types of seismic waves: body waves and surface waves. Body waves travel
through rock. Surface waves travel along the surface of Earth.
There are two types of body waves: P waves and S waves. P waves cause rocks to move back and forth, parallel
to the direction that the wave is moving. S waves cause rocks to move side to side, perpendicular to the
direction that the wave is moving. Surface waves move along Earth’s surface. Surface waves move more
slowly than body waves, but surface waves can cause more damage. Most surface waves form in one of two
ways: movement along a fault that is close to the surface, and change in the way rock moves when a body wave
reaches Earth’s surface. There are two main types of surface waves: Love waves and Rayleigh waves.
2. Describe the differences between P waves and S waves.
P waves and S waves are the two main types of seismic body waves. The key differences between them are:
_______________________________________________________________________________________
P waves are longitudinal or compression waves. They cause particles to oscillate back and forth parallel to the
_______________________________________________________________________________________
direction the wave travels.
_______________________________________________________________________________________
S waves are transverse or shear waves. They cause particles to oscillate perpendicular to the direction of travel, in
an up-down or side-to-side motion.
P waves travel faster than S waves and are the first to arrive from an earthquake.
What
Can Seismic
Waves
Tell liquids,
Us About
S waves
cannot travel
through
whileEarth’s
P wavesStructure?
can.
P waves cause expanding and contracting of material. S waves cause shearing and deformation from the particle
motion.study seismic waves to learn more about Earth’s structure. Seismic waves move at different speeds in
Scientists
P waves
can travelInthrough
boththe
solid
and liquid
waves wave
can only
propagate
through
material.
different
substances.
addition,
direction
in material.
which a S
seismic
travels
changes
whensolid
it moves
from one
substance to another. By studying how seismic waves change as they move through Earth, scientists can learn
about the makeup of Earth’s interior. In 1909, a Croatian scientist named Andrija Mohorovicic discovered that
seismic waves change speed about 30 km below the continents. The change in speed happens suddenly. The
place where this change happens is where the crust and mantle meet. Today, scientists call this boundary the
Mohorovicic discontinuity, or just the Moho. Below the continents, the Moho is about 30 km deep. Below the
oceans, it is about 10 km deep. Scientists have been able to use seismic waves to learn about other layers inside
Earth. They now know that Earth has three main compositional zones: the crust, mantle, and core. Earth has
five main structural zones: the lithosphere, asthenosphere, mesosphere, outer core, and inner core.
Remember that seismic waves change speed and direction as they move through Earth. Those changes can bend
the waves in specific ways. The bending of the waves produces shadow zones. Shadow zones are areas on
Earth’s surface where waves from an earthquake cannot be detected.
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3. What is the Moho?
The Moho is the Mohorovicic discontinuity, the boundary between the crust and the mantle underneath the Earth’s
_______________________________________________________________________________________
surface
_______________________________________________________________________________________
_______________________________________________________________________________________
Where Do Earthquakes Happen?
Most earthquakes happen near the boundaries between plates. The movements of the plates put stress on the
rock in the plates. The stress can cause the rock to slip and cause earthquakes. Some earthquakes happen in the
oceans. Others happen on land. Most faults exist in groups. An area that contains a lot of faults that are close
together is called a fault zone. Fault zones can exist at any kind of plate boundary. One example of a fault zone
is the North Anatolian fault zone in Turkey. Movement of the crust along the faults in this fault zone produces
many earthquakes in Turkey. Most earthquakes happen at plate boundaries. However, earthquakes can also
happen far from plate boundaries. For example, in 1811 and 1812, several large earthquakes happened near
New Madrid, Missouri. New Madrid is far from any plate boundaries. Scientists are not sure why these
earthquakes happened. However, they have discovered a very old fault zone underneath New Madrid. The fault
zone is more than 600 million years old. It is buried under many layers of rock and sediment. Scientists think
the New Madrid earthquakes may have happened when rock around the fault zone moved. However, they are
not sure what made the rock move, or whether it might move again in the future.
4. Why do most earthquakes happen at plate boundaries?
The Moho is the Mohorovicic discontinuity, the boundary between the crust and the mantle underneath the Earth’s
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surface.
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How Does Magma Form?
Remember that Earth has three compositional layers: the crust, the mantle, and the core. Even though the rock
in the mantle is very hot, most of it is solid. It is solid because it is under a great deal of pressure from the
weight of the rock above it. Sometimes, however, the rock in the mantle can melt. When it does, it forms
magma. Magma is melted rock under Earth’s surface. There are three main conditions that can cause rock to
melt:
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The temperature rises until it is higher than the rock’s melting point.
The pressure on the rock decreases, and its melting point also decreases.
Water or other fluids seep into the rock and lower its melting point.
Because magma is less dense than solid rock, magma rises toward Earth’s surface. As magma moves upward,
it can affect the rock around it. For example, the heat from the magma may melt the rock around it. The melted
rock becomes more magma. The magma can also enter cracks in the rock and break off pieces of solid rock.
The solid rock may melt and become magma. Sometimes, the pieces of rock the magma breaks off do not melt
completely. When the magma cools, these pieces of rock become trapped in the newly formed rock.
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How Does a Volcano Form?
Magma rises toward Earth’s surface because magma is less dense than the solid rock that surrounds it. As the
magma rises, it may collect in a magma chamber under Earth’s surface. It may also flow out of an opening in
Earth’s surface called a vent. Magma that has flowed onto Earth’s surface is called lava. When lava flows
through a vent onto Earth’s surface, the vent is called a volcano. Volcanism is the movement of magma onto
Earth’s surface. A volcano can be a small hole in the ground or a huge mountain.
Where Do Most Volcanoes Form?
Like earthquakes, most volcanoes form along plate boundaries. Volcanoes form at subduction zones, mid-ocean
ridges, and hot spots. Many volcanoes form along subduction zones, which are areas where one tectonic plate
sinks under another. Some subduction zones form when two oceanic plates collide, and one sinks beneath the
other. The Aleutian Islands are a row of islands in the North Pacific Ocean. They formed along a subduction
zone. Japan also formed along a subduction zone. The main island of Japan used to be a row of smaller volcanic
islands. As more magma reached the surface, the islands joined together into one large piece of land. Some
subduction zones form when an oceanic plate and a continental plate collide. The denser oceanic plate sinks
beneath the continental plate. Water and fluids are squeezed out of the sinking plate. They make the mantle rock
melt, just as they do when two oceanic plates collide. The magma rises to the surface and erupts on the
continental plate. Because the continental crust is very thick, the mountains that form are generally very tall.
The Andes Mountains and the Cascade Mountains are examples of volcanic mountains that formed in this way.
Most of Earth’s volcanoes are not found on land. They are under the oceans, at mid-ocean ridges. Remember
that a mid-ocean ridge is a place where two plates are moving apart. Where the plates move apart, magma can
erupt to form new crust. Because most of the volcanism at mid-ocean ridges happens below the ocean, most
people do not know about it. However, there are some places where mid-ocean ridges rise above the ocean
surface. Iceland is an example. Large fissures, or cracks, exist in Iceland. Half of Iceland is on the North
American plate, and half is on the European plate. The fissures have formed where the two plates are moving
apart.
Some volcanoes do not form at plate boundaries. Instead, these volcanoes form over mantle plumes. A mantle
plume is a column of solid, hot rock in the mantle. As the plume rises toward the surface, the pressure on it
decreases. Some of the rock melts. The magma rises to the surface and breaks through Earth’s crust, forming a
volcano. A place where a mantle plume erupts on Earth’s surface is called a hot spot. Mantle plumes do not
move very much. However, the plate over the plume does move. As the plate drifts away from the plume, the
magma stops flowing through the volcano. Another volcano forms over the plume. As the plate continues to
move, a chain of volcanoes forms as seen below with the Hawaiian Islands. Some mantle plumes are long and
shaped like a horizontal line. Magma from these plumes erupts through Earth’s crust in many places along the
line. This forms a line of volcanoes.
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5. Where do most volcanoes form?
Most volcanoes form at subduction zones, mid-ocean ridges, and hot spots. Many volcanoes form along subduction
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zones where one tectonic plate sinks under another. Volcanoes also form at mid-ocean ridges where two plates
move apart and magma erupts to form new crust. Some volcanoes form over mantle plumes called hot spots.
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6. Why does magma form at mid-ocean ridges?
Magma forms at mid-ocean ridges because that is where two tectonic plates are moving apart. As the plates move
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apart, magma from the mantle can rise up and erupt at the surface to form new oceanic crust. The diverging plates
allow magma to reach the surface.
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7. What happens as a tectonic plate moves over a mantle plume?
Magma forms at mid-ocean ridges because that is where two tectonic plates are moving apart. As the plates move
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apart, magma from the mantle can rise up and erupt at the surface to form new oceanic crust. The diverging plates
allow magma to reach the surface.
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What Is a Pluton?
When magma does not reach Earth’s surface, it may cool and solidify inside the crust. This process forms a
pluton. Plutons can vary in size and shape. For example, dikes are small, narrow plutons. They may be only a
few centimeters wide. Dikes form when magma cuts through rock layers as it rises. Very large plutons are
called batholiths. A batholith has an area of at least 100 km2.
8. How do dikes form?
Dikes form when magma cuts through rock layers as it rises towards the surface. They are small, narrow plutons that
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can be just a few centimeters wide. As magma rises, it intrudes into cracks and fractures in the surrounding rock.
This forms the narrow, vertical bodies of igneous rock called dikes.
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Allison, Mead A., et al. “Chapter 12: Earthquakes/Section 1: How and Where Earthquakes Happen.” Holt McDougal Earth Science Interactive Reader, Holt McDougal,
a Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 175-180.
Allison, Mead A., et al. “Chapter 13: Volcanoes/Section 1: Volcanoes and Plate Tectonics.” Holt McDougal Earth Science Interactive Reader, Holt McDougal, a
Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 189-194.
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Earthquake Science, and the Disaster That Create It (8:12)

“Earthquake Science, and the Disaster That Created It.” YouTube. SciShow, 13 June 2014. Web. 28 Jan. 2015.
What is the science behind earthquakes and when did it all start? Hank Green
discusses the March 27, 1964 earthquake in Alaska that changed scientists’ views on
earthquakes and plate tectonics.
Geography Lesson: What is a Volcano? (3:13)

Geography Lesson: What Is a Volcano?” YouTube. YouTube, 12 Nov. 2012. Web.
Have you ever wondered what exactly a volcano is? This video will explain the
basics of volcanoes, how they form, and how they function.
Yellowstone Super Volcano (4:02)

“Yellowstone Super Volcano.” YouTube. SciShow, 24 Apr. 2012. Web. 22 May 2014.
What’s the largest volcano in the US and one of the largest in the world? Learn
about the Yellowstone super volcano located in the northern United States.
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Elaborate
Plate Tectonics and the Ring of Fire
Background:
The Ring of Fire is an area that occurs in and around the Pacific Ocean in a 25,000-mile horseshoe shape. It
contains over 450 volcanoes and some of the world’s deepest ocean trenches. Over 90% of the world’s
earthquakes take place along the Ring of Fire. It stretches up the western coast of South America and North
America, along Alaska’s west coast to the Aleutian Islands, down the eastern coast of Japan through the
Philippines, and on into New Zealand. Map 1 below shows the frequency of activity of Earthquakes along the
plate boundaries and the Ring of Fire. Map 2 shows the frequency of volcanoes along the plate boundaries and
the Ring of Fire.
Map 1: Earthquake Activity
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Map 2: Volcano Activity
Answer the questions below using the maps.
1. What relationship do you notice about the location of the Ring of Fire and the plate boundaries?
The Ring of Fire closely follows the plate boundaries around the Pacific Ocean. The majority of the Ring of Fire
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overlies the boundaries between the Pacific Plate and surrounding plate
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2. What relationship do you notice about the location of earthquakes, volcanoes, and the Ring of Fire?
The earthquakes and volcanoes are concentrated along the Ring of Fire. There is a strong correlation between areas
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with frequent earthquakes, volcanoes, and the location of the Ring of Fire.
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3. What do you notice about the location of the majority of the volcanoes and earthquakes compared to the
plate boundaries?
The majority of the earthquakes and volcanoes occur right on or very close to the plate boundaries. There is a close
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association between plate boundaries and seismic/volcanic activity.
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4. Why would the majority of volcanoes and earthquakes be found on or around plate boundaries?
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Plate boundaries are zones of tectonic activity, with movement and collisions between plates. This motion causes stresses and
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5. Are there examples of earthquakes that do not occur along plate boundaries? If so, where do they occur?
Explain why you think this may be true.
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Yes, some earthquakes occur within plates away from plate boundaries. These intraplate earthquakes occur at faults far from p
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6. The Hawaiian Islands are located in the middle of the Pacific plate, but they contain volcanoes. What
accounts for the volcanoes on these islands even though they aren’t found along a plate boundary?
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The Hawaiian volcanoes are caused by a stationary hotspot – a plume of hot mantle material rising up beneath the plate. As th
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Allison, Mead A., et al. “Chapter 12: Earthquakes/Section 1: How and Where Earthquakes Happen/Transparency 64: Earthquakes and Tectonic Plate Boundaries.”
Holt McDougal Earth Science, Holt McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010.
Allison, Mead A., et al. “Chapter 13: Volcanoes/Section 1: Volcanoes and Plate Tectonics/Transparency 67: Volcanoes and Tectonic Plate Boundaries.” Holt
McDougal Earth Science, Holt McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010.
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Evaluate
Review Questions
Answer the following questions.
1. Explain the difference between the epicenter and the focus of an earthquake.
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2. Explain how the structure of Earth’s interior affects seismic wave speed and direction.
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3. Where do fault zones occur?
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4. Compare magma and lava.
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5. Identify three tectonic settings where volcanoes commonly occur.
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Revisit the essential question. Did your answer change? Why or why not?
Essential Question
How do you think Earth’s internal processes cause surface features on Earth as large as Mount Everest?
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