Volcano in a Cup – Erupting Wax

Create a violent, bubbling storm of wax within the confines of a beaker

When you hear about a volcano erupting, what do you think is going on? If you're like us, you think of red hot chunks of rock being hurled thousands of feet in the air, flows of liquid magma, and plumes of smoke. That's not always the case. Some volcanoes erupt underwater and their smoking hot by-products are immediately cooled. With the Storm in a Cup, you can see what happens underwater on a smaller, safer scale.

Experiment Materials

  • Burner or hot plate
  • Sand
  • Wax
  • Heat-proof glass beaker(Pyrex)
  • Water


  1. Place a small piece (about 1″ x 1″) of wax in the bottom of a glass beaker. Try to get it as close to the center of the beaker as possible.
  2. Pour enough sand into the beaker to completely cover the cube of wax.
  3. Slowly pour water into the beaker until the cup is nearly full. Don't fill it up all the way or you might have some spillage.
  4. Place the beaker onto a burner or hot plate and turn the heat on to a medium-high temperature setting.
  5. Now the fun part… observe! As the wax heats beneath the sand, it melts and finds its way out of the sandy trap.

How Does It Work?

The core of the earth has liquid hot magma that, on occasion, erupts through the crust. The volcanic eruptions we generally think of occur on land and result in the sky-high smoke plumes and lava flows that we see on the news. Now think about how much of the earth's crust is exposed land compared to how much is underwater. Nearly 80% of all volcanic eruptions occur underwater, but until scientists got footage of an underwater eruption in 2009, we had no idea what they looked like.

With the Volcano in a Cup, you recreate liquid hot magma by heating wax that is covered by sand. The liquid hot wax bubbles through the sand and causes miniature eruptions in the surface of the sand as it does so. Think of each bubble in the sand's surface as an underwater volcano. When the wax bubbles through the surface of the sand, it is met by much colder water that cools the wax and causes it to harden.