Article issued September 24, 2001

Understanding Volcanoes

What is a Volcano?
Let's first take a look at the earth. The earth is made up of 4 main layers-the inner core, the outer core, the mantle and the crust. The crust is where we live, on the surface of the earth. Below the crust lies the mantle, which is made up of solids, liquids and gases.

The lithosphere is made up of the crust and the upper most layer of the mantle, and is divided up into 16 major plates. As the plates of the lithosphere shift, they disrupt portions and pockets of the mantle below it. This disruption causes steam and gasses within the mantle to into liquid magna-these pockets of liquid magma are called "hot spots". The liquid magma then makes its way up through the lithosphere and erupts from onto the earth as lava. The places where they erupt are called volcanoes.

How, Where, Why?
Take a look at this map provided by USGS. The lines depict the boundaries of the major lithospheric plates on earth. Where these plates meet are where most of the earth's volcanoes are located.

What is Plate Tectonics?
"Plate" depicts the plates of the lithosphere of earth. "Tectonics" is the study of geological features. Therefore, "plate tectonics" is the study of the shifting of the lithospheric plates which cause the eruption of volcanoes and the advent of earthquakes.

Let's take an even closer look at these plates. Plates can shift towards each other, away from each other, or they can shift side by side. The way in which these plates move in relation to each other cause the different types of physical conditions that create volcanoes and earthquakes.

Types of Eruptions
Depending on the pressure that forces the magna up, and depending on the viscosity (how liquid the magma is) and amount of gas in the magna, eruptions vary in size, explosiveness and danger.

Plinian eruptions are the most dangerous and explosive. The magna is high in viscosity and gas content, and can cause a lava plume over 10 miles high in the air. The Pompeii explosion of Mount Vesuvius is an example of a Plinian eruption.

Effusive eruptions are defined as those which have lava outpouring onto the ground. These eruptions are less dangerous, and the magna has lower viscosity and levels of gas. Lava flows generated by effusive eruptions vary in shape, thickness, length, and width depending on the type of lava erupted, discharge, slope of the ground over which the lava travels, and duration of eruption.

Strombolian eruptions are characterized by the intermittent explosion or fountaining of lava from a single vent or crater. Each episode is caused by the release of volcanic gases, and they typically occur every few minutes or so, sometimes rhythmically and sometimes irregularly.

Hydrovolcanic eruptions - When volcanic eruptions occur near oceans, saturated clouds or other wet areas, the interaction of water and magma can create a unique sort of eruptive column. The hot magma heats the water so that it becomes steam. This rapid change of state causes an explosive type of expansion in the water, which breaks apart the magma, creating a fine ash.

Fissure eruptions occur when magma flows up through cracks in the ground and leaks out onto the surface. These often occur where plate movement has caused large fractures in the earth's crust, and may also spring up around the base of a volcano with a central vent.

Learn more about eruptions from Marshall Brain's How Stuff Works.

Types of Volcanoes
Volcanoes come in all different shapes and sizes, which is often a result of the types of eruptions that occur.

Composite Volcanoes (also called Stratovolcanoes) are the most familiar type of volcano. They are tall, symmetrical, and slope steeply towards a small summit crater. They are usually formed by multiple Plinian eruptions, which omit large amounts of lava in violent, tall eruptions which add quickly to the height of the volcano.

Scoria Cone Volcanoes (also called cinder cone volcanoes) are small cones which are often the result of a single eruption event-usually a strombolian eruption. These types of volcanoes are the most common.

Shield Volcanoes are low, wide volcanoes, formed by low viscosity, slow moving lava which spreads over a many kilometers.

Volcanoes in Our World
There are over 1,000 volcanoes in our world. These volcanoes are can be active, dormant or extinct. Active volcanoes are those that have erupted within recent history, dormant volcanoes are those which have not erupted in recent history, and extinct volcanoes are those which have been deemed to have not erupted in the last 10,000 years, or are thought to have experienced shifts in lithospheric plates to move them away from any possibility of future eruptions.

Volcanoes are both a hazard to people on earth, and help them. Short term hazards are balanced by the overall value of geologic forces that happen which protect the long-term stability of the planet.

Learn More!
General Resources about Volcanoes

Online Resources

• USGS Publication: Volcanoes
  Online Edition by the USGS. This online book about volcanoes is one of the most complete sources for learning about the geology of volcanoes. Extensive photographs and diagrams enhance the learning process.

• How Stuff Works: Volcanoes
  This seven-part article series offers simple but complete information about all aspects of volcanoes. A Web site not to be missed!

• Volcano World
  "The Web's Premier Source of Volcano Info", featuring "Ask a Volcanologist", Volcano Adventures, Teaching and Learning, Workshops and much more.

• Volcanoes
  An Annenberg/CPB exhibit that helps students to understand volcanoes - what causes them and why they are difficult to predict. The site also offers interactive activities to help students learn.

• Hawaiian Volcano Observatory
  Detailed information and history on all of Hawaii's volcanoes.

• Volcanoes of the United States
  An online publication by the USGS, with detailed information and history on all of the United States' volcanoes.

• How Hawaiian Volcanoes Work
  Part of the Hawaiian Volcano Observatory, this site explains how volcanoes work while using Hawaiian volcanoes as an example.

• How Volcanoes Work
  An AP-level look at the science behind how volcanoes work.

• USGS: Volcanoes
  This is the USGS's home page on volcanoes-- offering links to major Volcano Observatories and volcano publications.

• The Volcanoes of the Cascades
  Majestic and Perilous Natural Wonders Crown the Pacific Northwest Landscape

• Volcano Science
  This Explorezone Web site offers brief general information about volcanoes, and volcanoes in history.

• American Museum of Natural History - Earth Bulletin - Volcanoes
  This site is a well-designed collection of information on all recent volcano eruptions around the world.

• Arnold, Eric, Knutson, Doug (Illustrator), Volcanoes! (Step into Reading, Step 3, paper), Random House

• Van Rose, Susanna, Stevenson, James (Photographer), Eyewitness: Volcano & Earthquake, DK Publishing

• Ganeri, Anita, DK Readers: Eruption -- The Story of Volcanoes (Level 2: Beginning to Read Alone), DK Publishing

• Berger, Melvin, Why Do Volcanoes Blow Their Tops? : Questions and Answers About Volcanoes and Earthquakes, Scholastic Reference

• Haduch, Bill, Volcano! : An Explosive Tour of Earth's Hot Spots, Discovery Kids

• Wood, Lily, Volcanoes, Scholastic Reference

• Vancleave, Janice Pratt, Janice Vancleave's Volcanoes : Mind-Boggling Experiments You Can Turn into Science Fair Projects, John Wiley & Sons

• Adams, Simon, The Best Book of Volcanoes, Kingfisher Books

LESSON 1:
Volcano Lessons from the USGS

Concepts:
You will learn about earth science, earth systems and volcanoes.

Lesson:
The USGS (U. S. Geological Survey) offers the USGS Learning Web. Within this resource, they offer 6 valuable volcano lesson and activities. Many of the activities are demonstrations that will help students, particularly elementary-level students, visualize the physical, chemical, geologic and biologic processes being presented. Each lesson includes extensive activities, diagrams and worksheets.

Lesson 1: Windows into the Earth
The lithosphere is the Earth's hard, outermost shell that is divided into a mosaic of 16 major slabs, or plates. The first lesson introduces the nature of volcanoes and volcanic eruptions

Lesson 2: Creators and Destroyers
This lesson continues to explain how volcanoes are related to the Earth's lithosphere. Students focus on the May 18, 1980 eruption of Mount St. Helens.

Lesson 3: Up in the Air
The atmosphere is the mixture of gases that envelops the Earth. This lesson explains how volcanoes can affect the atmosphere.

Lesson 4: Fire, Water and Ice
This lesson explains how water from the hydrosphere and cryosphere can combine with volcanic materials from the lithosphere to produce mudflows and floods.

Lesson 5: Death and Recovery
The biosphere is the realm of all living things, including humans. This lesson addresses the effect volcanic eruptions have on the biosphere, the realm of all living things.

Lesson 6: Living with Volcanoes
The final lesson addresses the fact that volcanic eruptions can occur in populated areas.

LESSON 2:
Volcano Vocabulary

Concepts:
You will learn about vocabulary, earth science and volcanoes.

Lesson:
After learning about volcanoes, test the children's vocabulary. They can study vocabulary words by printing out the glossary on the USGS Teacher Guide. Then, use this worksheet and have children fill in the definitions. Use the glossary to check answers. As an extension activity, have students' practice spelling the words and later use the words as part of a test. You can use our test sheet or writing paper to test students. Bonus! Try this Volcano Crossword.

Additional Resources:

• Erupt-A-Word, A Volcano Crossword

• Volcano World's Games and Fun Stuff

LESSON 3:
Consider This: 2 "Situations" Presented by NASA

Concepts:
You will learn about research, scientific analysis and proposal writing.

Lesson:
The Exploring the Environment project by NASA has proposed 4 fictional problems for students:

Situation 1:
Business and community leaders in the city of Orting in Pierce County, Washington State, wish to build a new high school to accommodate and encourage the local population explosion. But given its proximity to Mount Rainer, there are problems…

Read the full description, and ask students to research Mount Rainer with the links provided. They will need to write a proposal for the county!

Situation 2:
Scientists at the Hawaii Volcano Observatory have notified newly elected county officials on the "Big Island" of Hawaii that they expect a new eruption of Kilauea. The Park is closed, but local businesses want to stay open, and residents of the area want to know if they should evacuate...

Read the full description and ask students to do calculations and make some estimations!

Situation 3:
A new eruptive cycle of Mount Hood in northern Oregon has been in progress for several months. The extended period of relative quiet (no eruptions) has prompted numerous requests of government officials to lift restrictions-but should they be lifted?

Read the full description and ask students to do calculations and make some estimations!

Situation 4:
The volcanic nature of the area around Yellowstone National Park is well known, but in the last year, a new cycle of volcanic activity has begun. The number and strength of earthquakes have increased; new hot springs have appeared and existing ones have grown...

Read the full description and ask students to make some estimations and recommendations! Learn more information about the volcanoes involved at the project's main page http://davem2.cotf.edu/ete/modules/volcanoes/volcano.html .

Additional Resources:

• Try another Situation! Will That Volcano Spoil Our Party?
  While this project is geared towards groups of class children of 3 or more, it offers an exciting analysis project for students 6-12.

LESSON 4:
Build Your Own Volcano!

Concepts:

Lesson:

3D Clay Models
Use the maps found at the Web sites above to build a clay model of 2 different types of volcanoes. Older children can research particular volcanoes and build more details about its form, height and structure, and even use different colors of clay to depict lava flows that occurred at different times. Use the salt dough recipe, or choose one of several different types of dough.

Exploding Volcanoes
Build your own exploding volcano!

http://volcano.und.nodak.edu/vwdocs/volc_models/explosive.html">Make Your Own Volcano from Volcaono World
• Homemade Volcano from ScienceBob.com.

LESSON 5:
Volcano Web Quest!

Concepts:

Lesson:
3rd-6th graders can explore FEMA and complete this Volcano WebQuest. .

7th-12th graders should go to Maggie Johnson's Kilauea WebQuest page. This site offers Web resource reference, and then asks:

• What is a volcano?
• What causes volcanoes to form?
• Are there different types of volcanoes?
• What is the relationship between earthquakes and volcanoes?
• What does plate tectonics have to do with volcanoes?
• What are the parts and structure of volcanoes?
• What are the risks to people and property from volcanic eruptions?
• Can we predict when a volcano will erupt?
• What role have volcanoes played in the evolution of life on the planet?

LESSON 6:
Another Volcano Webquest

Concepts:
You will learn about volcanology and Internet research.

Lesson:
In this Webquest, children are challenged to explore various specific Web sites to answer questions such as "What is a Volcano?" or "What Comes Out of a Volcano?. Use this worksheet to have students track their answers in written format.

Additional Resources:

• Volcano Webquest
  This additional Webquest offers nine tasks to complete in the learning process about volcanoes. Students visit sites to find answers.

LESSON 7:
Volcanoes in History: In Old Pompeii

Concepts:
Students will learn about the history of Pompeii and its destruction; they will gain insight into the past through archaeological interpretation; and they will synthesize historical information through imaginative writing.

Lesson:
Visit the In Old Pompeii Lesson Plan. In this lesson, students take a virtual field trip to the ruins of Pompeii to learn about everyday life in Roman times, then create a travelogue to attract visitors to the site and write an account of their field trip modeled on a description of Pompeii written by Mark Twain.

Additional Resources:

• Pompeii and Mount Vesuvius
• Pompeii Forum Project

LESSON 8:
Can We Predict Volcanic Eruptions

Concepts:
You will learn about ancient history, earth science and volcanoes.

Lesson:
Visit the exhibit Volcanoes: Can We Predict Volcanic Eruptions?. This is an Annenberg/CPB exhibit that helps students to understand volcanoes-what causes them and why they are difficult to predict. The site also offers interactive activities to help students learn.

Article by Patricia Carnabuci, HLN Curriculum Development
Article © Homeschool Learning Network, All Rights Reserved.