Volcanologists (geologists who study volcanoes) classify volcanoes as either active, dormant, or extinct. An active volcano is a volcano that is currently erupting or has erupted recently, such as Mount St. Helens, which most recently erupted in 1980.
A dormant volcano is one that has not erupted recently but is expected to do so again. Prior to its 1980 eruption, Mount St. Helens had been classified as dormant.
An extinct volcano is a volcano that volcanologists do not think will ever erupt again, such as Mount Buninyong in Australia.
It is often difficult to determine which volcanoes are extinct and which are dormant. The reason for this is volcanoes can go decades, hundreds of years, or even hundreds of thousands of years before they erupt. Even the experts can't agree on the difference.
Some volcanologists have classified volcanoes as dormant that have not erupted in the last 10,000 years. The cutoff of 10,000 years is used because it marks the end of the last ice age and the beginning of the Holocene Epoch. While the 10,000-year mark gives an easy way to distinguish between active and dormant volcanoes, not all volcanologists are in agreement on this cutoff. Other volcanologists consider volcanoes that have erupted in historical times to be active. However, the term historical times is somewhat arbitrary and can vary, depending on what part of the world you are investigating.
All volcanoes are fed by and get their energy from magma, molten rock coming from the Earth's mantle. Dormant volcanoes still have access to magma, while most extinct volcanoes do not. This is due to shifting tectonic plates. As the plates move, the volcano moves off the hot spot, or magma source. When this happens, the volcano is cut off from the magma source. Typically, a new volcano can form over the hot spot.
Another way to look at this is to use a car as an example. If you have a tank full of gas but the car is parked in the driveway, it still has access to its energy source. This is evident when you start the car to drive away. However, if the car is empty and you never put gas in the car again, it will never run. The car, just like the volcano, must have access to its energy source.
Five Dormant Volcanoes
While there are numerous dormant volcanoes found all over the world, some of the more notable include the following:
- Lake Barrine is a freshwater lake that formed 17,000 years ago after a series of volcanic eruptions in Queensland, Australia. The crater eventually filled with rain, making what is now a freshwater system.
- Mount Kilimanjaro in Tanzania, Africa, is the tallest volcano in Africa and last erupted 360,000 years ago.
- Salina in Sicily, Italy, is the second largest island in the Aeolian Islands. Salina last erupted 13,000 years ago and its highest peak, at 3,156 feet, is the tallest in the archipelago.
- Diamond Peak in Oregon, U.S., part of the Cascades Mountain Range in the Western United States, is 8,744 feet tall. This glacier-carved shield volcano's last eruption is believed to have been more than 11,000 years ago.
- Bowie Seamount in the Northeast Pacific Ocean is completely submerged. Seamounts are not your typical volcanoes with tall peaks; these volcanoes have a flattened top. Bowie Seamount stands 10,000 feet above the ocean floor. Eruptions at Bowie started over 100,000 years ago and stopped between 10,000 and 15,000 years ago.
Volcanoes are classified as either active, dormant, or extinct. The difference in the classification is when the volcano last erupted. Most volcanologists agree active volcanoes are those that erupt regularly or have erupted in the last 10,000 years. Dormant volcanoes are volcanoes that have not erupted in the last 10,000 years but are expected to erupt again. Extinct volcanoes are volcanoes that are never expected to erupt again. Another difference between dormant and extinct volcanoes is dormant volcanoes still have access to their magma or energy source, while extinct volcanoes often do not.
Things to Know About Volcanoes
|Active volcano||a volcano that is currently erupting or has erupted recently|
|Dormant volcano||one that has not erupted recently but is expected to do so again|
|Extinct volcano||a volcano that volcanologists do not think will ever erupt again|
|Magma||molten rock that rises from the earth's mantle|
|Hot spot||a magma source|
|Famous dormant volcanoes||Lake Barrine, Mount Kilimanjaro, Salina, Diamond Peak and Bowie Seamount|
After concluding this lesson, you will be ready to:
- Contrast dormant and extinct volcanoes
- Discuss a volcano's energy source
- Name five present-day dormant volcanoes around the globe
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In this activity, students will conduct a case study of a specific dormant volcano.
- After reviewing the lesson, students should discuss:
- Why do some volcanoes go dormant?
- Is a dormant volcano safe?
- How can volcanologists know whether a dormant volcano will or won't erupt again?
- How can they know when a volcano last erupted?
- What dormant volcanoes do you know about (that aren't listed in the lesson)?
Dormant Volcano Case Study Assignment Instructions
- Instruct students to research other dormant volcanoes and choose one on which to focus. This should not be one of those mentioned in the lesson.
- Now, students should take time to research their chosen volcano and write a report answering these questions:
- Where is it?
- What is its name?
- What type of geological manifestation has it taken on (for example, it could be a full island or a lake)?
- Are there people living on or near it?
- When is it supposed to have erupted last?
- How do scientists know when it last erupted?
- Is it an important part of the culture in its region?
- (Speculation) What might be the consequences if it were to suddenly erupt again?
- To extend this assignment, instruct students to prepare a brief oral presentation based on the information they have learned.
- The presentation should include all of the previous information as well as at least one visual aid related to the chosen dormant volcano.
- If necessary, students may research one of the mentioned dormant volcanoes in the lesson. However, they must include more information than given in the lesson in their report and/or oral presentation.
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