Building a Better Volcano
Feb 28, 2017
Written by Mr. McConnell, Upper Team Instructor
Early in February, my Earth Science class learned about the forces that produce volcanic eruptions. This presented an opportunity for a classic high school science demonstration, the baking soda and vinegar volcano. Though, despite its popularity, I dislike this demonstration. Beyond superficial similarities it has nothing to do with volcanoes. A baking soda and vinegar volcano is powered by a chemical reaction evolving carbon dioxide, but a real volcano is a driven by convection. So I set to work on making a better volcano model and putting an end to the old flawed model.
The premise was simple, but the execution was much tougher than I expected. At its most basic, I needed a vessel filled with solid wax and a way to heat it. As the wax melted, it would expand. The liquid would then exceed the volume of the vessel and overflow the top.
My first experiment used a 1L Erlenmeyer flask of wax partially submerged in boiling water. The wax began to melt from the bottom up and before it could break its way through to the surface it sprung a leak in a hairline fracture. Not quite what I wanted, but very similar to a volcano’s side vent.
The second attempt used a 500mL flask which could be more completely submerged in the water. Again it began to melt, but the pressure grew too quickly. The side of the beaker blew off like a tiny Mount Saint Helens.
The classes last and most successful eruption, used a canning jar with a hole in the lid. I rose the temperature of the water very slowly. For three hours the wax soaked and melted. Finally, the eruption began. Tiny wax bubbles crackled on the lid as the last air was forced out by the pressure of the wax. The upper team students each came to the classroom as the liquid wax escaped the lid and pooled on the surface. Eventually though, the pressure distorted and lifted the entire lid off of the jar.
Demonstrating the slow and powerful forces that shape our earth are tough to present in a small and safe way. My miniature Kilauea has room for improvement, and I may revise it more in another year of Earth Science. However, I think that making a better volcano matters because flawed analogies lead to flawed understanding. For students to understand a process correctly, it needs to be presented as realistically as possible.