Lesson Plan

Soda Bottle Volcano

A teacher holds a plastic bottle with white bubbles streaming from the top, demonstrating the Soda Bottle Volcano.
A teacher demonstrates the Soda Bottle Volcano.

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Grade Level:
Fifth Grade-Eighth Grade
Earth Science, Geology, Volcanoes
40 minutes
Group Size:
Up to 36
large field
conduit, magma, magma chamber, exsolution, fumaroles, pumice, scoria, throat, volcanic ash, demonstrating, inferring, observing, predicting, pressure, gases, volcano, crater, mount rainier, Mount Rainier National Park, Living with a Volcano in Your Backyard, Cascades Volcano Observatory


Examine how gases provide for explosive volcanic eruptions by making comparisons to gases in a soda bottle and by conducting a carefully controlled "eruption" of baking soda/vinegar or soda water. This lesson plan is part of the "Living with a Volcano in Your Backyard" curriculum, created through a partnership between Mount Rainier National Park and the US Geological Survey Cascades Volcano Observatory.


Students will:

  • Understand the important role of gases in providing energy for explosive volcanic eruptions
  • Understand how pressure affects gases
  • Learn how gases influence the texture and appearance of volcanic rocks


Water- the surprisingly essential ingredient in explosive volcanic eruptions

Hot magma and water vapor seem incompatible. Yet, water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), and lesser amounts of rarer gases take up as much as ten percent of the magma (by weight) that lies beneath some Cascade volcanoes. These gases are important because their expansion provides the energy that blasts magma to Earth's surface during an explosive volcanic eruption. About 80 kilometers (50 miles) below the Earth's surface, water sweats off the subducted oceanic plate and promotes the formation of magma, which then rises into the Earth's crust.  Water vapor and other gases, elements and minerals coexist as a mixture of molten or partially molten magma having a texture similar to hot oatmeal.

A magma chamber is like a pot of dessert pudding. Imagine magma as home-cooked pudding bubbling in a pot topped by a tight lid. Some of the ingredients in the pot combine as they cool; this is similar to the process of elements combining to form minerals. During this process, tiny bubbles of gas separate from their more solid surrounding neighbors. Since gases are lighter, they rise to the top of the pudding (or magma). As gases separate progressively from the pudding, bubbles rise, expand, and form a gas-rich layer at the top of the pot (or magma chamber).

The pot boils over
The pressure of rising gases eventually forces the pot lid to vibrate. Puffs of steam break out between the pot and lid in the same way that volcanic gases escape the top of a magma chamber through cracks and openings in surrounding rocks. The upward pressure of gases eventually exceeds the downward pressure exerted by the lid, and the pudding and gases pour over the side of the pot and onto the stovetop. This is the same concept as lava escaping across the slopes of an erupting volcano. Some of the pudding propels explosively out of the pot and splatters everywhere, similar to magma erupting from a volcano as rock fragments or ash.


Gas bubbles determine the texture of volcanic rock
During an explosive volcanic eruption, gases escape into the atmosphere; however, some become trapped in the quickly cooling magma. The erupted magma, in the form of ash and lava, may contain bubble holes from the former presence of gases. The resulting rocks appear similar to foam from a bottle of soda. These rocks are called pumice and scoria. Sometimes the gas-rich magma erupts so explosively that it breaks into tiny fragments known as volcanic ash.

Fumaroles at Mount Rainier
Hot gases often mix with groundwater before venting to the surface as fumaroles. Steam and gases that spew from the fumaroles make the air smell unpleasant and deposit colorful minerals on Earth's surface. Active fumaroles are found at most Cascade volcanoes. Fumaroles are evidence that Mount Rainier is an active volcano. Inside Mount Rainier's summit craters, heat from fumaroles has melted out a system of narrow ice caves and a sub-ice lake, possibly the highest lake in the United States. Temperatures at the hottest fumaroles range between 70-90°C (150°-200°F) and produce enough heat to keep some parts of the summit craters snow-free year round. Early climbers used the ice caves as shelter. They described huddling around the fumaroles and feeling scalded on one side and frozen on the other! Fumaroles exist also on the upper flanks of Mount Rainier at Disappointment Cleaver, Willis Wall, Sunset Amphitheater, the South Tahoma headwall and the Kautz headwall. These fumaroles have lower temperatures due to increased dilution by groundwater. Some gases rise to the surface through thermal springs near Winthrop and Paradise Glaciers, the Nisqually and Ohanapecosh Rivers, and Longmire Springs.


How the soda water experiment is like a volcano
The wide body and narrow neck of a soda bottle roughly resemble the shape of a magma chamber and the conduit or throat within a volcano. The pressurized soda water represents gas-rich magma that is under pressure from overlying rocks.


Carbonated beverages get their fizz from the gas carbon dioxide. When the bottle is capped, carbon dioxide dissolves within the soda from the pressure exerted on it. It also occupies the void between the surface of the liquid and the cap. Shaking the bottle adds energy and causes gas in the soda water to separate, forming tiny bubbles throughout the liquid. Formation of the bubbles increases pressure inside the bottle. Quickly removing the cap releases this pressure, and the bubbles immediately expand. Forced up the narrow neck, the fluid and bubbles burst from the high-pressure environment of the bottle to the lower pressure of the atmosphere. Bubbles of water vapor and other gases within magma undergo a similar progression. They are initially dissolved in magma, then depressurization of the magma chamber frees the bubbles from the magma in a process called exsolution. The bubbles rise to the top of the magma chamber. Pressure from the gas bubbles propels both the magma and gas up the conduit. The gas bubbles now rapidly expand to thousands of times their original volume when escaping up the conduit to the top of the erupting volcano.


How is the vinegar and baking soda eruption unlike a volcano?

Combining baking soda and vinegar causes a chemical reaction that quickly produces

carbon dioxide bubbles. This demonstration differs from the processes within real volcanoes, because the gases that cause explosive eruptions do not result from sudden chemical reactions. In the soda water and baking soda/vinegar experiments, carbon dioxide acts as the main gas driving the explosion. In most volcanic eruptions, water is the principal gas driving an explosive eruption and not carbon dioxide.


Why Volcanoes Stink

Two of the principal gases released from volcanoes, water and carbon dioxide, are odorless. Volcanoes also release sulfur dioxide and hydrogen sulfide into the atmosphere in lesser amounts. These gases have strong smells. Sulfur dioxide has an odor similar to struck matches. Hydrogen sulfide smells like rotten eggs or sewer gas and can be sensed even in low concentrations.



Teacher and graphics pages include teacher narrative and visuals for introducing and explaining the role of gases in an eruption.




Look for evidence of students' understanding of the following concepts: that magma contains gases under great pressure; that gases provide the energy for volcanic eruptions; that gases influence the texture and appearance of volcanic rocks. Look for students' recognition of the differences between the baking soda and vinegar eruption, which is based on chemical reactions, and an actual volcanic eruption, which is based solely upon pressure release.

Park Connections

Eruptions at Mount Rainier, an episodically active composite volcano, are driven by gases that build up in the magma chamber located 5 miles below the surface.


  • Ask students to use different shaped containers that represent the magma chamber and conduit of a volcano. How does shape affect the eruption results?
  • For younger students, direct them to draw lines on a piece of paper that divide it into six sections. Ask students to draw a before, during, and after experiment picture in squares 1, 2, and 3. Instruct students to draw pictures in squares 4, 5, and 6, of what a volcano would look like if it behaved like the experiment represented in squares 1, 2, and 3 respectively.
  • Instruct students to make a four-page book that illustrates gas bubbles increasing in size as the magma rises in the Earth and ends with a volcano erupting.
  • Search for the link between volcanic gases and acid lakes. Ask students to use the Internet to research this topic. Some examples of lakes containing volcanic gases include Lake Nyos, Cameroon, Kawa Ijen, Indonesia, and Santa Ana, El Salvador.
  • Direct students to explore Internet-based computer programs that simulate volcanic eruptions.

Additional Resources

Decker, R. and Decker, B., 1998. Volcanoes: W.H. Freeman and Company, New York, 321 p.

Francis, P., and Oppenheimer, C., 2003. Volcanoes: Oxford University Press, 536 p.


VanCleve, Janice, 1994. Volcanoes-mind-boggling experiments you can turn into science fair projects: John Wiley and Sons, New York, 89p


conduit, magma, magma chamber, exsolution, fumaroles, pumice, scoria, throat, volcanic ash

Last updated: February 28, 2015