Student Experiments for Investigations of Physical Controls on Viscosity and the Implications for Volcanic Hazards

Interactive laboratory investigations and demonstrations using analog materials can be used to introduce students to the rheologic properties of magmas and lavas. Using such an approach, students investigate the physical, compositional, and thermodynamic controls on viscosity through observations, experimental investigations, calculations, and computer simulations. During lab exercises, which are typically preceded by a reading assignment and brief introduction, students use analog materials (e.g. corn syrup) to experiment with parameters controlling viscosity. They prepare a set of syrup solutions at 3 (or more) temperatures, another set of syrup solutions with varying proportions of particles (e.g. sand), and a final set of syrup solutions mixed with water. A fourth experiment, which produces somewhat more complex results, can be prepared by using a hand mixer to make syrup with varying proportions of bubbles. Students make qualitative observations of the relative force required to blow bubbles into the syrup solutions with a straw as an analog for comparing the effects of viscosity on the formation and bursting behavior of gas bubbles in magma. During class, students observe syrup "lava flows" flowing on a slope. Measured flow characteristics are used to calculate viscosities for each "lava" using a dynamic visual equation (DVE) of the Jeffries equation. The DVE, which was created in Flash MX, allows students to explore interactively and visually how changing various parameters in the Jeffries equation affects fluid viscosity. Before each experiment, a critical set of questions lead students to make predictions and hone their observational skills. The questions also help students generate graphs and sketches and write brief reports to synthesize their observations. Additional activities incorporating volcanic hazards associated with low versus high viscosity flows and highly viscous explosive eruptions bring students back to very real applications of the principles investigated. In some cases, classroom activities have led students to independent research. One such project used analog flow materials to illustrate the effect of the shape and abundance of crystals on lava flow morphology. Students report having a clearer understanding of the viscous properties of lavas and magma, allowing more advanced discussions of volcanologic and petrologic principles such as conduit flow dynamics, crystallization of magmas, and volcanic hazards.