Spud Launcher: What Happens when Magma Hardens Inside a Volcano?

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Author: Janice VanCleave


What happens when magma hardens inside a volcano?


  • Ruler
  • Potato
  • 2-liter plastic soda bottle
  • 1/2 cup (125 ml) white vinegar
  • Outdoor table
  • Dish towel
  • Rubber band
  • Scissors
  • Bathroom tissue
  • 1 teaspoon (5 ml) baking soda


NOTE: This is an outdoor activity.

Spud Launcher

Spud Launcher

  1. Ask an adult to prepare a potato cork by following these instructions:
    1. Cut a 1-inch (2.5-cm) cube from a potato.
    2. Press the mouth of the soda bottle into the center of the cube.
    3. Push down while twisting the bottle around to cut about halfway through the cube.
    4. Carefully separate the bottle from the newly formed potato cork.
  2. Pour the vinegar into the bottle.
  3. Lay the towel on the table.
  4. Place the bottle in an upright position in the center of the towel.
  5. Fold the towel up the sides of the bottle, leaving only the mouth of the bottle exposed.
  6. Secure the towel around the bottle with the rubber band.
  7. Cut a 3-inch (7.5 cm) strip of bathroom tissue.
  8. Spread the baking soda across the center of the tissue.
  9. Roll the paper around the baking soda. Secure the packet by twisting the ends of the tissue.
  10. Drop the packet of baking soda into the bottle and stop the bottle with the potato cork.
  11. Stand about 1 yard (1 m) away from the bottle and observe.


In a short period of time, the potato cork pops out of the bottle and is propelled upward.


The paper roll opens in the liquid, and the baking soda and vinegar mix together, producing carbon dioxide gas. As the amount of this gas increases inside the bottle, pressure increases in all directions, including on the bottom of the potato cork. With enough pressure, the cork is pushed out of the bottle with enough force to propel it through the air. This experiment can be related to the eruption of a volcano that has a hardened plug of magma in the top of its vent left over from an earlier eruption. The plug of magma prevents gas from bubbling to the surface and escaping. As in the bottle, the trapped gas builds up pressure until finally the magma plug is blown out. NOTE: The towel covering the bottle is a safety precaution in the event that the potato plug is not pushed out and the pressure breaks the bottle.

Spud Launcher


WARNING: When exploring ways to change the original experiment, DO NOT seal the bottle with a cap or a tight-fitting cork.

Does the amount of gas affect the results? The amount of reacting materials (baking soda and vinegar) regulates the production of carbon dioxide gas. Repeat the original experiment four times. First use 1/2 teaspoon (2.5 ml) of baking soda, and then increase the baking soda to 2 teaspoons (10 ml). Repeat again, keeping the amount of baking soda constant but changing the amount of vinegar. First use 1/4 cup (63 ml) of vinegar, and then increase the vinegar to 1 cup (250 ml).


Discover more about volcanic eruptions. Make drawings that can be displayed and a chart showing names and locations of the different volcano types.

  • Violent eruption with very thick magma and lots of gas. Magma often hardens before leaving the vent, resulting in an explosion with ash and rock fragments propelled upward.
  • Active eruption with thin magma containing large amounts of gas. Hot lava shoots out the top of the volcano.
  • Quiet eruption with thick magma containing small amounts of gas. Thick lava forms a huge dome.
  • Quiet eruption with thin magma containing small amounts of gas. Watery lava flows out in a steady stream.

Spud Launcher


Volcanoes with a magma plug have the most violent eruptions, but the other types of eruptions also cause great changes in the land and affect the lives of many people. Find out more about the effects caused by erupting volcanoes such as Krakatoa in 1883 on an Indonesian island, Mount St Helens in 1980 in the state of Washington, and Mount Pinatubo in 1991 in the Philippines.

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