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Table of Contents. Volcanoes and Plate Tectonics Properties of Magma Volcanic Eruptions Volcanic Landforms. - Volcanoes and Plate Tectonics. Volcanoes and Plate Boundaries. Volcanic belts form along the boundaries of Earth’s plates. Discussion Questions. What is a volcano?

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table of contents
Table of Contents
  • Volcanoes and Plate Tectonics
  • Properties of Magma
  • Volcanic Eruptions
  • Volcanic Landforms
volcanoes and plate boundaries

- Volcanoes and Plate Tectonics

Volcanoes and Plate Boundaries
  • Volcanic belts form along the boundaries of Earth’s plates.
discussion questions
Discussion Questions
  • What is a volcano?
  • A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from below the surface.
  • What is the difference between magma and lava?
  • Magma (from Greek μάγμα "paste") is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets.
  • Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling.
volcanoes and plate boundaries1

- Volcanoes and Plate Tectonics

Volcanoes and Plate Boundaries
  • Volcanoes often form where two oceanic plates collide or where an oceanic plate collides with a continental plate.
  • In both situations, an oceanic plate sinks through a trench. Rock above the plate melts to form magma, which then erupts to the surface as lava.
hot spot volcanoes

- Volcanoes and Plate Tectonics

Hot Spot Volcanoes
  • A volcano forms above a hot spot when magma erupts through the crust and reaches the surface.
ring of fire
Ring of Fire
asking questions



- Volcanoes and Plate Tectonics

Asking Questions
  • Before you read, preview the red headings. In a graphic organizer like the one below, ask a where, what, or how question for each heading. As you read, write the answers to your questions.

Where are volcanoes found?

Most volcanoes are found along plate boundaries.

A hot spot is an area where material from deep within the mantle rises and then melts, forming magma.

What are hot spots?

  • Viscosity refers to the resistance of a liquid to flowing
  • Different liquids have different viscosities allowing some to flow more easily compared to others
  • This is due to the particles that make up the liquid and the friction that exists when they are in motion
  • Different types of magma have different viscosities which are a result of temperature and silica content
  • Silica (SiO2) is a compound consisting of Silicon and Oxygen particles bonded together
  • Silica content of magma varies between 50-70% on average
  • Temperature of magma and lava varies between 750 – 1200 C
magma composition

- Properties of Magma

Magma Composition
  • Magma varies in composition and is classified according to the amount of silica it contains. The graphs show the average composition of the two types of magma. Use the graphs to answer the questions.
magma composition1
Silica, other oxides, and other solids.

Reading Graphs:

Study both graphs. What materials make up both types of magma?

- Properties of Magma

Magma Composition
magma composition2
Rhyolite-forming magma; about 70 percent.

Reading Graphs:

Which type of magma has more silica? About how much silica does this type of magma contain?

- Properties of Magma

Magma Composition
magma composition3
About 60 percent


A third type of magma has a silica content that is halfway between that of the other two types. About how much silica does this type of magma contain?

- Properties of Magma

Magma Composition
magma composition4
Rhyolite-forming magma would have higher viscosity because it is higher in silica.


What type of magma would have a higher viscosity? Explain.

- Properties of Magma

Magma Composition


        There are three categories of lava, classified on the basis of        its silica (SiO2) content, which affects how readily it flows. 

        1.  BASALTIC LAVA

             a.  Relatively low SiO2 content (less than 52%)             b.  Relatively low viscosity (flows readily when hot)  

        2.  ANDESITIC LAVA

              a.  Intermediate SiO2 content (between 52 and 63%)                           b.  Intermediate viscosity (does not flow readily) 

        3.  RHYOLITIC LAVA

             a.  Relatively high SiO2 content (above 68%)             b.  Relatively high viscosity (flows like wet concrete)


Pahoehoelava is characterized by a smooth, billowy, or ropy surface. Pahoehoe is hot, moves fast, and has lower viscosity.


Aa is characterized by a rough or jagged surface. Aa lava flows tend to be relatively thick compared to pahoehoe flows meaning they have lower temperature and higher viscosity.

identifying main ideas

- Properties of Magma

Identifying Main Ideas
  • As you read the section “Types of Viscosity of Magma,” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea.

Main Idea

Magma’s viscosity depends on its physical and chemical properties.




Magma is made of elements and of compounds, among them silica.

Viscosity is a property of magma.

Viscosity depends on silica content and temperature.

anatomy of a volcano

- Volcanic Eruptions

Anatomy of a Volcano
  • When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent.
key terms
Key Terms
  • Magma chamber is the area beneath the volcano where magma collects
  • The pipe is the vertical tube connecting the magma chamber to the vent (or outside world)
  • The vent is the opening near the top of the volcano where gas and magma flow out towards the surface
  • Side vents refer to pipe like projections that run on the sides of the volcanoes mountainous structure
  • A crater is the bowl-shaped area that can form around the top of the volcano or vent
volcanic eruptions
Volcanic Eruptions
  • Basically there are two types of volcanic eruptions: Quiet & Explosive
  • Quiet eruptions are what you have on the island of Hawaii
  • *Quiet eruptions occur when the magma has:
  • Lower silica content
  • Higher temperature
  • Lower viscosity
  • Explosive eruptions are what you typically have along subduction zones
  • *Explosive eruptions occur when the magma has:
  • Higher silica content
  • Lower temperature
  • Higher viscosity
volcanic hazards
Volcanic Hazards
  • Ash
  • Gas
  • Lahars
  • Tephra
  • Landslides
  • Lava Flows
  • Pyroclastic Flows
volcanic activity classification
Volcanic Activity Classification
  • Volcanologists use the terms active, dormant, or extinct to describe a volcano’s stage of activity
  • An active volcano refers to a current eruption taking place or a possibility of it erupting in the near future
  • A dormant volcano refers to a volcano that has not erupted for an extended period of time, but still can erupt at any given time
  • An extinct volcano also has not erupted for a very long time and poses little to no threat of erupting again
  • *The prediction of a volcano eruption is more accurate than earthquake prediction, but still not perfected!
kinds of volcanic eruptions

- Volcanic Eruptions

Kinds of Volcanic Eruptions
  • Within the last 150 years, major volcanic eruptions have greatly affected the land and people around them.
using prior knowledge

- Volcanic Eruptions

Using Prior Knowledge
  • Before you read, look at the section headings and visuals to see what this section is about. Then write what you know about volcanic eruptions in a graphic organizer like the one below. As you read, write what you learn.

What You Know

Lava flows out of a volcano.

Eruptions are not all the same.

Some volcanoes are dormant.

What You Learned

Magma rises toward Earth’s surface through a pipe that leads to a vent.

Differences in gas and silica content cause some eruptions to be explosive and others to be quiet.

Dormant volcanoes can become active at any time.

landforms from lava and ash

- Volcanic Landforms

Landforms From Lava and Ash
  • Volcanic eruptions create landforms made of lava, ash, and other materials. These landforms include composite volcanoes, shield volcanoes, cinder cone volcanoes, and lava plateaus.
landforms from lava and ash1

- Volcanic Landforms

Landforms From Lava and Ash
  • A caldera forms when an volcano’s magma chamber empties and the roof of the chamber collapses. The result is a large, bowl-shaped caldera.
landforms from magma

- Volcanic Landforms

Landforms From Magma
  • Features formed by magma include volcanic necks, dikes, and sills, as well as batholiths and dome mountains.

- Volcanic Landforms

  • A batholith is a mass of rock formed when a large body of magma cools inside the crust. Several large batholiths form the core of mountain ranges in western North America. Half Dome in Yosemite National Park, California, is part of the Sierra Nevada batholith.

- Volcanic Landforms


Volcanic Landforms

  • As you read, make an outline about volcanic landforms that you can use for review. Use the red headings for the main topics and the blue headings for the subtopics.
  • Landforms From Lava and Ash
    • Shield Volcanoes
    • Cinder Cone Volcanoes
    • Composite Volcanoes
    • Lava Plateaus
    • Calderas
    • Soils From Lava and Ash
  • Landforms From Magma
    • Volcanic Necks, Dikes and Sills
    • Dikes and Sills
    • Batholiths
    • Dome Mountains
  • Geothermal Activity
    • Hot Springs
    • Geysers
    • Geothermic Energy
graphic organizer
Graphic Organizer

Shield volcanoes

Cinder cones

Ash, cinders, and bombs

Lava and ash