The following questions were answered by expert volcanologist Dr. Stanley Williams. Dr. Williams was online with Scholastic Network in February 1995.
How long does it take for a volcano to cool?
Volcanoes usually have a life of many thousands of years. Once a volcano has begun to erupt, it usually takes about ten years before that particular eruption comes to an end. Sometimes the eruption lasts for hundreds of years.
How does a volcano build up the pressure to erupt?
The magma (molten rock) which is erupted from a volcano comes from deep inside the earth — usually from about 150 kilometers deep. The pressure there is enormous. The pressure forces the magma to rise through the crust of solid rocks, creating a volcanic eruption.
Do volcanoes spew ash or lava first?
Volcanoes release ash at the beginning of an eruption because the amount of gas is very high and it drives the explosions. After that time, the lava may come out but it usually has very little energy, so it is not very dangerous.
How can you tell if a volcanic eruption might occur?
Volcanoes that are approaching an eruption will usually have unusual earthquakes and emit very different gases. Some of the volcanoes even change shape — like the "bulge" of Mount St. Helens that moved toward Seattle at about four meters per day. Forecasting volcanoes is still very hard because we don't usually have the right measurements before it happens. In Mexico in 1993, we measured a really high release of sulfur dioxide, one of the volcanic gases, and warned the Mexican government of the possibility of an eruption. It finally erupted just before Christmas. Forecasting an eruption is the main reason for our research and it is really very difficult. What we need, as scientists, is more eruptions! We need more chances to test our ideas or hypotheses.
How many volcanoes erupt every day?
The Smithsonian Institution has the Global Volcanism Network and a monthly bulletin about eruptions. About 50 to 60 eruptions happen each month. Some volcanoes are in constant activity — Stromboli, Kilauea, or Sakurajima, for example. There are many examples of volcanoes which show some sign of renewed danger and then erupt within an hour, though more commonly, within one day. Most eruptions last hours but some continue for weeks and months.
How many times does the average volcano erupt each century?
I would say that the average volcano erupts about one time every 100 years, but that varies from one volcano to the next. My favorite, Masaya, has been very active every 25 years, but has not had any important eruptions for about 200 years.
At what speed does a volcano erupt?
There are many different speeds that we try to measure or estimate with erupting volcanoes. When volcanoes erupt explosively, they throw rocks at velocities of 200-300 m/sec. After the initial eruption, the volcanoes may release a lava flow. The lava flow usually goes slowly — a few m/hour.
Can volcanoes blow up out the sides, rather than top?
Mount St. Helens is a good example of a volcano blowing out of the side. That is not an unusual thing.
What happens to the sea animals that live in areas around the volcanoes when they erupt?
I have not studied underwater volcanoes extensively, so I could not tell you exactly what happens to the sea animals during an eruption. I have heard that oceanic volcanoes can release strong acid water, which is harmful to sea life. This is happening at Fernandina volcano in the GalÃ¡pagos. However, I think that most animals in the sea would be able to move away from the eruption fast enough so that they are not seriously injured.
What was the largest volcanic eruption?
Approximately 75,000 years ago, the volcano Toba, in Indonesia, had the largest volcanic eruption ever known.
What was the worst explosion in modern times?
The worst eruption was that of Tambora, in Indonesia. In 1815, this eruption killed about 90,000 people.
Where and when did the first volcano erupt?
The first volcanic eruption happened before the first human existed. The earth has had erupting volcanoes since just about the first years that it existed — about four and a half billion years ago. In fact, some of the best places for finding the fossils of ancient humans are in east Africa because they are buried in ashes of ancient volcanoes that erupted around them. Of course, the other planets in our solar system have erupting volcanoes on them, as well.
Anyone who has witnessed a volcano erupting needs no further evidence to know that Earth is a dynamic planet. Volcanoes are one of the major mechanisms for creating new crust. They are powerful, breathtaking, and dangerous, and offer scientists an unparalleled glimpse at Earth's interior. Although the processes that form magma are not well understood, volcanoes — and the igneous rocks they produce — can be studied and explained in the context of plate tectonics. In this lesson, students investigate the processes that build volcanoes, the factors that influence different eruption types, and the threats volcanoes pose to their surrounding environments. After exploring these characteristics, students use what they have learned to identify physical features and eruption types in some real-life documented volcanic episodes.
- Understand what volcanoes are, how they form, and the rocks they create
- Create a notebook of volcano characteristics
- Use acquired knowledge to identify several types of modern volcanic eruptions around the world
Grade Levels: 6-8 , 9-12
Three to four 45-minute class periods, or two 90-minute class periods
Use these resources to create a simple assessment or video-based assignment with the Lesson Builder tool on PBS LearningMedia.
Before the Lesson
If possible, arrange Internet access for all students to work in pairs.
Students will learn about volcanoes and then apply their knowledge by 1) exploring the physical characteristics of various types of volcanoes and 2) identifying the types of volcanoes featured in several case studies. In order to complete the lesson's objectives, students should have a basic understanding of plate tectonics, including the different types of plate boundaries.
Part I: Understanding Volcanoes
1. Before beginning the media-based activities, divide the class into small groups (3-5 students each) and distribute a copy of the World Map Without Volcanoes PDF Image to each group. (If copies cannot be made, use a map in a textbook or one in the classroom and distribute removable dot stickers.) Mention that Hawai'i is one place that is well known for its volcanoes. Now ask the groups to list as many other states and countries as they can that have volcanoes. You may want to suggest that they think about major eruptions that have appeared in the news recently, or famous ones that have happened in history (e.g., Vesuvius and Krakatau). Next, have them mark the locations of the volcanoes on their maps. Before moving on, ask the students the following:
- Do you see any patterns?
- Can you think of any possible explanations for the patterns you see?
2. Now hand out copies of the World Map With Volcanoes PDF Image marked and have the groups look at both maps. Ask about the distribution of volcanoes, and have students hypothesize why they are where they are and why certain areas are more active than others. If there is time, have the groups share their lists and other findings with the class.
3. Ask students to explore the Volcanism HTML Interactive and record in their notebooks answers to the questions below. Students will use the recorded information in the case study activity that concludes the lesson plan. As an optional activity, have the students check out the Mountain Maker, Earth Shaker Flash Interactive to review the basics of plate tectonics.
- How do volcanoes form?
- What are the four primary types of volcanoes? Name and describe each type in detail. Encourage students to sketch the shape of each type and note its plate tectonic setting (i.e., over hot spots, spreading centers, or subduction zones).
- Where do volcanoes form?
- Rocks are classified by what they are made of and how they form. Igneous rocks always begin as magma. What are the two main types of igneous rocks, and what is the main difference between them? How does each type form into solid rock?
4. Next, ask students to check out the Volcanic Eruptions and Hazards HTML Interactive and record in their notebooks answers to the following questions:
- Will an effusive eruption have more gas and be more dense (viscous) than an explosive flow, or will it be less gaseous and less viscous? How does each type of eruption cause damage?
- Which type of eruption appears to be the more hazardous to humans? Explain your answer.
- Of the numerous hazards caused by volcanic eruptions, list and describe at least three that cause damage on a local level, and at least one that has global implications.
5. Now ask the students to look at the dynamic landforms and features in the Anatomy of a Volcano Flash Interactive and Volcanic Features HTML Interactive . Have them write down the following vocabulary list of features and describe each one: lava, tephra, lava lake, vent, fissure, dike, magma, caldera, crater, geyser, spring, `a`a flow, pahoehoe flow, and lava tubes. As an additional, optional activity, ask students to explore the Virtual Lava Tube Flash Interactive and address the following questions using the resource:
- How do lava tubes form, and where are they most likely to be found?
- What is the difference between how two common cave features -- stalactites and stalagmites -- form in limestone caves and how they form in lava tubes?
- Besides stalactites and stalagmites, choose three lava tube features that interest you, and explain how they form.
Part II: What Can We Learn from Magma and Lava?
6. Volcanoes vary greatly in terms of the composition and temperature of the magma they produce, and these characteristics affect how they will erupt. Scientists study lava, fresh from Earth's mantle, to learn more about the inner workings of volcanoes. The Lava Sampling on Kilauea Volcano, Hawaiʻi QuickTime Video demonstrates the simple, yet risky, technique one researcher uses to access lava just as it reaches Earth's surface. Show this video to the class, or have them watch it on their own computers, and ask them to answer the following questions in their notebooks:
- Why does scientist Michael Garcia refer to the basalt he is walking on as "the youngest real estate on Earth"?
- What does viscous mean?
- For what scientific reason does Dr. Garcia quickly quench the hot lava with water?
- What has careful study of the composition of the lavas from Kilauea and Mauna Loa revealed about their origins and relationship?
You can continue this line of volcanic study by showing the Dating Lava Flows on Mauna Loa Volcano, Hawaiʻi QuickTime Video , which provides further insight into the Hawaiian volcanoes and describes the effective method one scientist has found of dating prehistoric lava flows.
Part III: Case Studies — Applying Your Knowledge
7. Mount Pinatubo
Ask the students to view the Mount Pinatubo: Predicting a Volcanic Eruption QuickTime Video and the Mount Pinatubo: The Aftermath of a Volcanic Eruption QuickTime Video . Using the notes they have taken during the lesson, have them answer the following questions in their notebooks. Engage them in a class discussion before proceeding to the next case study.
- Was the Mount Pinatubo eruption an effusive or explosive eruption?
- Based on your observations, what type of volcano is Mount Pinatubo? On what evidence do you base your answer?
- Over what type of plate boundary is this volcano located? Is this tectonic setting consistent with your answer to the first question?
- Because vulcanologists were able to accurately predict the timing of this eruption, the lives of hundreds of people who evacuated the nearby area were probably saved. What evidence did the scientists observe that prompted them to call for an evacuation?
Ask the students to think about what might make predicting a volcanic eruption difficult and what problems might result from inaccurate (false-positive or false-negative) predictions. Have them record their ideas in their notebooks and then explore the Forecasting Volcanic Eruptions HTML Interactive . When they're finished, have them consider their previous notebook entries and ask them to record their answers to the following questions. Engage them in a class discussion before proceeding to the next case study.
- What problems did the inaccurate eruption forecast of the Tungurahua volcano cause for the people of Ecuador and what difficulties might this cause for community officials in the future?
- What three variables do scientists monitor when attempting to forecast volcanic eruptions?
- What are some of the hurdles that vulcanologists face when trying to make accurate eruption forecasts?
Next, have students view the Plate Tectonics: The Hawaiian Archipelago QuickTime Video and respond to the following questions. Again, engage them in a class discussion before proceeding to the next case study.
- Based on your observations of this video and previous videos you have seen, what type of volcanoes are Kilauea and the other Hawaiian volcanoes? On what evidence do you base your answer?
- Does Hawai'i experience effusive or explosive eruptions?
- Explain Hawai'i's setting in terms of plate boundaries. What makes it so unusual?
10. Mount St. Helens
Finally, have students view the Mount St. Helens: Before and After Flash Interactive and respond to the following questions. Discuss their responses.
- Describe what is happening throughout the eruption. What kind of material is being ejected by the volcano? Do you see lava? What happens to all of the ash?
- Based on your observations, what type of volcano produced this eruption? On what evidence do you base your answer?
- Based on the before and after images, identify ways in which both the volcano and surrounding area were changed by the 1980 eruption.
- Based on the satellite images, how has the affected area changed in the time since the eruption?
- What are some similarities and differences in the destruction caused by effusive and explosive eruptions? What, if anything, was surprising to you about the blowdown, lahar, and pyroclastic flow images?
- What factors play a part in the recovery of vegetation (and wildlife) in areas affected by volcanic eruptions?
Check for Understanding
Have students discuss the following:
- What are the differences between the four types of volcanoes? Is there one distinguishing characteristic, or more than one?
- Which types of volcanoes form on divergent plate boundaries? On convergent plate boundaries? What is a hot spot?
- Is it possible for scientists to predict when a volcano will erupt so they can call for the evacuation of the area around it? If so, what kind of evidence do the scientists need to make such a prediction?
- Describe the hazards that volcanoes present for humans who live near them.
The Digital Library for Earth System Education (www.dlese.org) offers access to additional resources on this topic.