Download Chapter 9 Volcanoes

Name
Chapter 9
Volcanoes
Date
Period
Section 9.1: How and Where Volcanoes Form
Objectives:


Analyze how magma forms as a result of plate motion and interaction
Explain why plate boundaries are the sites of most volcanic activity
Vocabulary:
•
Volcano
•
Hot spot
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Magma
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Lava
How and Where Volcanoes Form
__________________________ - the _______________________________________________ through which
molten rock, gases, and ash erupt and the __________________________ that develops around this opening.
A __________________________ __________________________ occurs when __________________________
(__________________________ that has formed deep within Earth) ___________________________________.
Magma Formation
Most of the asthenosphere is solid because of the __________________________________________________
above it. The pressure raises the melting temperatures of materials in the asthenosphere. For magma to form,
some of these materials must melt.
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Checking for Understanding
Why is the asthenosphere solid?
What needs to happen for magma to form?
1.
A __________________________________________ can lower the melting temperatures of materials in
the asthenosphere (occurs along the _______________________________________________).
Conditions for Magma Formation
2.
An ____________________________________________ can cause materials in the asthenosphere to melt
(occurs at _________________________).
3.
An _____________________________________________________ in the asthenosphere can lower the
melting temperatures of materials there (occurs at _______________________________________________).
Checking for Understanding
What are the three ways that magma forms? Where do they occur?
Conditions at both __________________________ and __________________________ boundaries are
____________________________________________________.
Magma Formation
________________________________ are found along mid-ocean ridges and at _________________________
______________________________(convergent).
Magma ______________________________________ because it has a __________________________ than the
solid materials that surround it.
__________________________ __________________________ on the __________________________
At Subduction (Convergent) Boundaries
__________________________ at a subduction boundary.
__________________________________________________________________________ (example: the
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Cascade Range which extends along the Pacific coast from northern California to British Columbia, Canada).
__________________________________________________________________________ (example: the
Mariana Islands in the Pacific Ocean).
_____________________________________________________________________________.
At Divergent Boundaries
While ___________________________________________ are under the ocean,________________________
where a mid-ocean ridge rises ________________________________________________________________.
Checking for Understanding
Describe the volcanic activity that occurs at a divergent boundary
Not all volcanic activity occurs at plate boundaries. __________________________ are areas of volcanic activity
that result from ___________________________________________________ that have risen from deep within
Earth’s mantle.
A hot spot _____________________________________, while the lithospheric plate continues to move across it.
Over Hot Spots
The ______________________________________have __________________________ as the Pacific Plate has
moved northwest ____________________________________________________.
Today, the youngest island, Hawaii, lies above the hot spot.
Island formation continues. An underwater volcano, the _____________________________________________, is
slowly growing into the next Hawaiian Island. Loihi is still below sea level.
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Section 9.1 Review
1. Describe how magma forms at a subduction boundary
2. Explain the difference between the volcanic activity that occurs at a hot spot and the volcanic activity that occurs at a subduction boundary between an
oceanic plate and a continental plate
3. Describe the volcanic activity that occurs at a divergent boundary
Section 9.2: Magma and Erupted Materials
Objectives:



Identify three types of magma and locate where each on forms
Compare characteristics of magma and lava
Describe pyroclastic materials
Key Vocabulary:
•
viscosity
•
lava
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pahoehoe
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aa
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pillow lava
•
pyroclastic material
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pyroclastic flow
Kilauea, a Hawaiian volcano, has spewed molten rock for decades. In contrast, Mount St. Helens exploded
Magma and Erupted Materials
violently in 1980 after more than a century of being quiet.
_________________________________________________________ at these two sites ________________
partly from __________________________________________________ that rise to the surface there.
A magma’s __________________________ is its __________________________________________________.
__________________________ determines the magma’s viscosity.
Magmas ____________________________________________________. Andesitic and rhyolitic magmas contain
more silica and are more resistant to flow. (More explosive)
Magmas ____________________________________________________. Basaltic magmas contain the least silica
and flow most easily.
Magmas also __________________________ – ____________________________________________________.
Types of Magma
The gases, dissolved in the magmas at the depths where they form, may bubble out of solution as the magma
rises.
__________________________ gases ____________________________________________________. When
these magmas reach the surface, any remaining gases usually produce relatively harmless fountains and floods.
____________________________________________________ andesitic and rhyolitic magmas
____________________________________________________. When these magmas reach the surface, the
gases expand and cause ____________________________________________________.
Each type of magma tends to form at specific locations. _____________________________________________
________________________________________________________ _.
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______________________________________________________________________________.
__________________________ magmas generally _________________________________________________
__________________________________________________.
Checking for Understanding
How do basaltic, rhyolitic, and andesitic magmas differ?
Factors that determine the violence of an eruption
Factors Affecting Eruption

__________________________ of the magma

__________________________ of the magma

__________________________ in the magma
Viscosity is the measure of a material’s resistance to flow
Factors Affecting Viscosity
o
__________________________ (hotter magmas are less viscous)
o
__________________________ (silica content)

High silica – high viscosity (rhyolitic lava)

Low silica – more fluid (basaltic lava)
Magma that reaches Earth’s surface is called __________________________.
Lava Flows
Like magma, lava is primarily molten rock. However, the __________________________
__________________________ from magma because materials may be added to or removed from the magma as
it rises to the surface.
__________________________ flows are usually associated with _____________________________________.
Lava Flows on Land
As these cool, they form basaltic rock.
Volcanologists use two Hawaiian terms to describe solidified lava flows on land: __________________________
and __________________________.
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__________________________ forms from high temperature lava that cools into smooth, ropelike surfaces.
__________________________ forms from cooler lava that quickly cools with rough, jagged surfaces.
Lava that cools underwater have a distinctive shape – a rounded, “pillow-like” form with a hard crust.
Lava Flows Underwater
Pressure builds up inside the lava until its crust cracks, and more lava pours out, forming yet another pillow shape.
The resulting mass of rounded lumps is called __________________________.
Checking for Understanding
Describe pahoehoe, Aa and pillow lava
More explosive eruptions usually involve magmas which contain trapped gases.
Volcanic Material
When these gases are released, solid fragments called __________________________ _____________________
may be ejected.
Pyroclastic materials are __________________________ __________________________ .
Types of pyroclastic material
o __________________________ – fine glassy fragments
o __________________________ – frothy, air filled lava
Types of Pyroclastic Material
o __________________________ – walnut-sized particles
o __________________________ – pea-sized particles
Particles larger than Lapilli
o __________________________ – hardened lava
o __________________________ – ejected as hot lava
In some violent eruptions, pyroclastic material combines with hot gases to form a __________________________
Pyroclastic Flow
– a dense, superheated cloud that travels downhill with amazing speed.
The cloud may follow the course of a valley, moving faster than 100 kilometers per hour.
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The eruption of __________________________ in A.D. 79 produced a pyroclastic flow that buried the Roman city
of Pompeii under pumice and ash.
Section 9.2 Review
1. How do basaltic, rhyolitic, and andesitic magmas differ?
2. Describe pahoehoe, aa, and pillow lava
3. Explain why rhyolitic and andesitic magmas are associated with more-explosive eruptions, whereas basaltic magma is associated with less-explosive
eruptions
4. Use the information in this section to infer whether a volcano that erupts explosively would be more likely to form at a subduction boundary or at a
divergent boundary
Section 9.3: Volcanic Landforms
Objectives

Compare and contrast landforms that result from volcanic activity

Hypothesize how predicting eruptions and emergency preparedness can reduce loss of life and loss of property
Key Vocabulary:
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shield volcano
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cinder volcano
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composite volcano
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lahar
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caldera
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lava plateau
The term __________________________ refers not only to a volcanic vent, but also to the landform that
develops as the materials from a volcanic eruption harden.
Volcanic Landforms
The __________________________ __________________________ of a volcano are _____________________
______________________________________________________________________________.
Draw a volcano picture
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Because of its __________________________ , basaltic lava tends to flow long distances before hardening.
In some cases, the lava builds up in layers, forming __________________________ _______________________
Shield Volcanoes
____________________________________________________.
Shield volcanoes __________________________ __________________________ that is _________________
__________________________ than other types of volcanoes.
Lava flows from shield volcanoes can damage homes, highways, and other property.
__________________________ ___________ built primarily of pyroclastic material ejected from a ____________
__________________________ .
Cinder Cones
__________________________ angle
Rather __________________________ in size
Frequently occur in __________________________
Checking for Understanding
Compare and contrast the ways in which shield volcanoes and cinder volcanoes are formed
____________________________________________________ develop when layers of materials from
__________________________ __________________________ accumulate around a vent. The materials
include __________________________ _____________________ and other ______________________________
___________________________________.
Composite Volcanoes
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o
Most are adjacent to the Pacific Ocean
o
Large in size
o
Interbedded lavas and pyroclastics
o
Most violent type of activity
Magma, water, and gases from composite volcanoes explode into a massive cloud of superheated ash and stones.
Lahar
Some of the hot ash mixes with snow and ice on the mountain to form fast-moving mudflows called a
__________________________.
Calderas
Sometimes magma beneath a volcano is released after the top of the volcano collapses, forming a large cratershaped basin called a __________________________.
__________________________ __________________________ form as basaltic lava pours out of a fissure (or
crack) on the Earth’s surface.
Lava Plateaus
The basaltic lava that formed the Columbia Plateau in the northwestern U.S. is over one kilometer thick in some
places and covers and area of about 164,000 square kilometers.
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Section 9.3 Review
1. Compare and contrast the ways in which shield volcanoes and cinder cones are formed
2. Describe the formation of a composite volcano
3. The eruption of Mt. Ranier, a composite volcano, could pose a serious threat to local residents. Write a description of the potential hazards that people
living near Mt. Ranier might face.
Section 9.4: Extraterrestrial Volcanoes
Objectives

Classify volcanic activity on other planets and moons

Analyze the tectonics behind extraterrestrial volcanic activity
Extraterrestrial Volcanoes
We are aware of volcanic activity that exists elsewhere in our solar system. Data has been gathered from
telescopes and orbiting probes, helping us to understand volcanic activity.
About 15% of the moon’s surface is covered by dark areas known as __________________________.
Maria consist mostly of ____________________________________________________, the result of volcanic
The Moon
activity that began 3 – 4 billion years ago.
__________________________ __________________________ beneath the moon’s surface probably provided
the energy necessary for the volcanic activity to begin.
Mars
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Mars is home to many ____________________________________________________.
__________________________ __________________________ is the largest known volcano in our solar system,
towering almost 26 kilometers (about 16.5 miles high).
Mars __________________________ have moving plates.
We are not sure if any of the volcanoes on Mars are still active (some flows appear to be only 20 – 60 million years
old).
It rises about 16.5 miles above the surface of the planet -- that's 3 times higher than commercial airliners fly. It is
372 miles from edge to edge at the base -- that's larger than the state of Washington! The crater in the center is
40 miles wide from rim to rim. ___________________________________________________________________
______________________________________________________________________________.
Orbiting satellites using radar have found more than 1600 large volcanoes, as well as volcanic features such as
lava flows and calderas. Many smaller volcanoes also cover the surface.
Venus
__________________________ of the volcanoes here are _____________________________________________.
Although most of the volcanoes are probably inactive, some may still be active.
This is a perspective view of the __________________________________. This volcano is about 2 km high and
nearly 300 km across. It lies near the equator and is in a region called Western Eistla Regio.
Jupiter’s third largest moon.
One of the __________________________ __________________________ in the solar system.
Jupiter (Io)
This moon is caught in a gravitational tug of war between Jupiter and two other moons. This causes the surface of
the moon to regularly move up and down by as much as 100 meters.
The most prominent red oval surrounds the volcano Pele (far right) on Io.
Section 9.4 Review
1. What type of lava flows are found on the moon?
2. Why is Olympus Mons much larger than Earth’s shield volcanoes?
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3. How do scientists know that there are volcanoes on Venus?
4. What is the source of heat responsible for the volcanic activity on Io?
5. Would you expect to find composite volcanoes on Mars? Explain.
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