Academic journal article Journal of Geoscience Education

Active Learning Strategies for Constructing Knowledge of Viscosity Controls on Lava Flow Emplacement, Textures and Volcanic Hazards

Academic journal article Journal of Geoscience Education

Active Learning Strategies for Constructing Knowledge of Viscosity Controls on Lava Flow Emplacement, Textures and Volcanic Hazards

Article excerpt

ABSTRACT

We present instructions for a series of quantitative experiments designed to help students build their intuitive knowledge of the rheological properties of fluids. The results of the experiments are quantified by students and are used to calculate fluid viscosities using Jeffreys Equation. During the course of the experiments, students test hypotheses about the effects of temperature, dissolved H2O, and the addition of bubbles or solid particles on fluid viscosity. They extend their experimental results to assess the role of viscosity in understanding volcanic hazards due to explosive eruptions and lava flows. Students can use a Dynamic Visual Equation (DVE) for Jeffreys Equation as either a pre-lab introduction to use of the equation or as a tool to calculate viscosities during the lab in place of a spreadsheet or calculator. Informal assessments of student attitudes suggest the experiments heightened student interest and learning.

INTRODUCTION

Viscosity is one of the important rheological properties of magmas and lavas discussed in detail in undergraduate geology courses (e.g., Baker et al., 2004). A working knowledge of viscosity is important for understanding the time-scales of magma transport, the velocities of lava flows, the explosivity of volcanic eruptions, and the hazards associated with different types of volcanic activity. Many undergraduate college students already have an intuitive sense about the behaviors of fluids under changing conditions of temperature and of dissolved water content. However, students do not necessarily realize that they can apply these intuitions to situations outside of their normal life experiences, such as the studies of magma transport, lava emplacement and volcanic hazards. We have designed a series of demonstrations and laboratory experiments that allow students to explore ways in which temperature, dissolved water, and addition of solid particles or bubbles can affect the viscosity of readily available and safe fluids and, by analogy, of magma and lava. Based on the results of the experiments, students gain quantitative insight into the effects of viscosity on volcanic eruptions and hazards.

The experiments discussed herein have been used at a wide variety of educational levels as demonstrations and as more quantitative laboratory exercises. The demonstrations nave been used to help K-16 students visualize the effect of viscosity on lava emplacement processes and the role of crystallization in controlling viscosity. More quantitative, student-directed projects have been used in college-level introductory geology and petrology courses. In these courses groups of students performed the experiments independently and used the Jeffreys equation to calculate fluid viscosities. Several of the experiments were tested on geoscientists during the July 2003 NSF-sponsored workshop, Teaching Petrology in the 21st Century (http://serc. carleton.edu/NAGTWorkshops/petrology/index.html ). The feedback from these demonstrations improved several of the exercises. The experiments have also been used as an award winning secondary school science fair project (C. Stanley, pers. comm., 2005).

The objectives of this paper are to: i) outline methods for helping students to explore fundamental controls on viscosity through a series of laboratory experiments, ii) discuss methods for using viscosity experiments to teach about lava emplacement and understand volcanic hazards, iii) explain how the experiments can be quantified using the Jeffreys equation and a spreadsheet/calculator or a Dynamic Visual Equation (DVE), which can help students improve tneir a quantitative understanding of viscosity.

VISCOSITY: AN IMPORTANT RHEOLOGICAL PARAMETER

The viscosity of a substance is the property that determines how rapidly the substance will respond to shear stress; for liquids, this is most obviously reflected in how rapidly a liquid will flow down an inclined surface. …

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