Volcano Eruptions with Soda

All erupting volcanoes can be modeled using some pretty simple items.

For scientists, models can play an important part in their research. Models show parts, relationships, and sequences that may be too small or too big for a lab setting. Some simple activities using Alka-Seltzer® tablets or a bottle of soda pop (with or without Mentos candy) can model and help explain the out-of-sight, underground science of erupting volcanos.

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Experiment Materials

  • 16 or 20 oz (473 or 591 ml) Clear plastic bottles of soda
  • Safety glasses
  • Large, open lab space (outside!)
  • Paper towels and water (a hose?)
  • Meat thermometer (optional)
  • Adult supervision



No doubt you’ve seen and even done this before now. True, maybe it was an accident, but odds are you did it on purpose. This may be the first time, however, you’ve connected an erupting soda to an erupting volcano.

The Materials List shows using either 16 or 20 oz (473 or 591 ml) bottles of soda. Practice with a couple of them, but when it comes to the main event, you may want to have some 2-liter bottles ready for shaking. Let’s face it, it’s more volcanic bang for your buck! That said, keep in mind that each bottle you shake has a price tag on it. (Be sure to work within your science budget.)


Keep the soda you’re testing at room temperature and keep the lid sealed tightly. Move to your outside lab and shake the bottle of soda hard for fifteen or twenty seconds.


Without letting it rest, place the shaken bottle on a firm surface and quickly remove the lid. Don’t just loosen it – remove it! Yes, you’ll likely get soaked but it’s all  the name of science.


When you think about it, there’s no such thing as “room temperature” magma.

There are only two safe ways to warm a bottle of soda. The simplest (and safest) way is to let the unopened bottle sit in direct sunlight for several hours. – OR – You can place the unopened bottle of soda in a container of warm water, changing the water as needed. The target temperature is about 85 F (29 C). NEVER use a stove or microwave or some other device to heat a bottle of soda. Good science is safe science, no matter what.


Move to your outdoor lab and repeat Steps 2 and 3. It’s a good idea to have the results recorded in a video for careful review (and lots of laughs) later.

Four things to keep in mind:

  1. Wear your safety glasses!
  2. Be sure to test both regular and diet sodas this way. You may be surprised at the differences.
  3. Any remaining soda in the bottle is still OK to drink, so you don’t have to waste it. Sure, it’ll be flat but it tastes pretty good. No doubt you can explain why it’s flat, too.
  4. This is when the cleanup of your outdoor lab may require a hose. Do a good job!

How Does It Work

Let’s get back to why you were making a big mess. Volcanoes form when chambers or cavities in rocks below the Earth’s surface are full of magma (hot, liquid rock) that blasts to the surface. These “magma chambers” often remain sealed for thousands of years as the pressure builds to unbelievable levels. A huge amount of gas is mixed with the magma and it’s this gas that accounts for the pressure. At some point, the pressure is sufficient to break through a crack or weak spot in the rock or crust around it. The magma, the gas, the dust, and anything else with it can be blasted for miles into the atmosphere over days and days. FACTOID: When magma gets onto the surface by oozing or blasting, it’s called lava.

Think of the soda as the magma and the plastic bottle as the magma chamber. The spewing soda, then, becomes the magma leaving the magma chamber. The built up pressure (caused by your shaking the soda) in the magma chamber blasts through a crack or weak spot (the open lid). The pressure forces everything out of the chamber. The blast might form a crater around the opening where lava and ash spill out and are collected. It can form a cone, a shield, a ridge, or nothing at all depending on where it’s happening. On some large volcanoes, the magma chamber is miles and miles wide and sometimes its top portion collapses on itself after an eruption. A large a caldera, which is a huge, bowl-shaped crater, can form. The whole of Yellowstone National Park (Wyoming, USA) is inside a gigantic caldera.

Like gas trapped in magma, warm soda will fizz much more than room temperature soda because of the solubility of gases in liquids. The warmer a liquid, the less a gas will remain dissolved (scattered) among its molecules. As a liquid is heated, any gas within it is also heated causing the gas molecules to move faster and faster. They quickly diffuse (escape) from the liquid into bubbles so less gas remains dissolved in it. With no way to expand in the hot liquid, the pressure inside the bubbles goes way up. The magma is looking for a way out to ease the pressure. It finds a weak spot or a crack in the rock around it and… BOOM! You have an eruption!

Take It Further

In order to understand the build-up of pressure caused by gases trapped in a liquid, check out these additional activities:

Alka-Seltzer Rocket

A simple film canister becomes a magma chamber. You’ll discover that changes in the tablet size used and the water temperature around it will mean big changes in the “eruption” you create.

Mentos Geyser Eruption

This classic activity uses the same factors to produce an eruption of soda from a 2-liter bottle. Also, different nozzle shapes at the top of the “magma chamber”and warmer temperatures result in different “eruptions” as well.

Safety Information

Any time there are things being heated, erupting, and blasting in your lab, you must wear safety glasses and have adult supervision. Besides, it’s easier to clean up when you have some help.

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