MAGMA, MOUNDS, AND MILKSHAKES: EXPLORING CONCEPTS IN VISCOSITY AND VOLCANIC ERUPTIONS

When covering any introductory topics on volcanoes and volcanic eruptions, it is extremely important for students to understand the relationship between viscosity, and the composition of a magma. This is because ultimately, the viscosity of the magma controls the type of eruption, the kind of volcanic products produced during an eruption, and the shape of the volcano. Many invoke the comparison of molasses, or some other sticky liquid that flows extremely slowly when compared to the low viscosity of water, when first introducing viscosity differences in magmas. This simple visualization clearly exemplifies the differences in the extremes of viscosity, but once concepts such as silica content, type of volcanic eruption, and volcano shape are introduced, the molasses and water analogy fails to provide the necessary components to continue this parallel. Here I introduce a different type of foodstuff to use in the magma viscosity analogy; the milkshake.

This lesson would start by introducing milk and a thick milkshake for our low and high viscosity liquids, respectively, to represent our magmas. Follow with an explanation and introduction to the mineral silica and that as the amount of silica in a magma increases, so does the viscosity. In this analogy, ice cream represents the silica, and the viscosity of the milk will increase as more ice cream is added. This can be taken one step further by starting with chocolate milk, to represent a mafic magma, to show how the rock type will lighten in color and produce felsic magmas as you add more silica. By experimenting and trying to create volcanic eruptions through a straw with the different liquids, students will be able to replicate effusive and explosive style eruptions while correlating this to the viscosity and silica content. And finally, by dumping these liquids onto a solid surface, the process of shield and stratovolcano formation can be discussed by observing the shapes of the subsequent puddles.

While this analogy might seem silly, experience has shown that it is often the most outrageous analogies or anecdotes that remain with the students long after the course has ended. Furthermore, by relating a concept as seemingly intangible as how volcanoes erupt to something as mundane as a milkshake, educators can help place a complex scientific topic on a level that is easier to understand.