Tutorial: Make an Underwater Volcano Erupt in a Test Tube

Happy Science Fair, everyone!

Our homeschool group's Science Fair was last week, and it's the first time that the girls have not shared a single project. This year, Sydney's project was on measuring birds--

--and Willow's project was on underwater volcanoes:

For Sydney's project, she and Matt researched a few birds of North America (primarily through The North American Bird Coloring Book ), then together they drew them to scale, colored them realistically, and aligned them up with an outline of Miss Syd, herself, to show their sizes in relation to her.

Will researched underwater volcanoes using library books, Primary Search articles (an EBSCO search engine for elementary children), and Netflix documentaries, took notes, wrote a report, colored a world map and drew in the Ring of Fire, and cut out pictures of underwater volcanoes to glue to her project board, which may not look very tidy, but does look as if she did it independently, which she did.

She also did a demonstration of an underwater volcano in a test tube:

To do this demonstration for yourself, you need a narrow test tube, a heat gun (we also use these for our melted crayon canvas art), sand, water, and crayon bits.

1. Drop a peeled bit of crayon into the bottom of a test tube, then cover it with a deep layer of sand, and then pour water on top. If you haven't covered the crayon deeply enough, the water will force the crayon up over the sand, since it's less dense--if this happens, gently pour in more sand on top. Will also had good luck pouring in water, then the crayon, and then the sand, to avoid the sudden force of the water.
2. As you work, explain to your audience that the sand is the ocean floor, the crayon is the solid rock in the lower crust of the earth, and the water is the ocean water.
3. Aim the heat gun close to the test tube (which is heat resistant--you ARE using a test tube, right?), approximately where you remember the crayon being, and turn it on high. You don't have to be too fussy about holding the test tube in a spot that's away from the heat gun--as long as you don't aim it at your fingers, you'll be fine.
4. Patiently hold the heat gun in the same spot for several seconds. You'll feel shocks and tremors in the tube as the heat gun (which represents an upwelling heat source from the earth's mantle) begins to melt the crayon, causing it to change shape underneath the sand.
5. The melted crayon is hot, and wants to rise above the cold water and the dense sand, so eventually it will erupt from underneath the sand. As it rises, the water will cool it and cause it to resolidify, and you can see how underwater volcano eruptions can form mountains, and then even islands.

With a lot of effort, you can clean the crayon wax off of the test tube, but frankly, I treat these test tubes as disposable once we've done this demonstration using them. Perhaps next we'll grow a little test tube demonstration garden in them!