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How Do We Estimate Magma Viscosity?

Module by Chuck Connor, University of South Florida, Tampa. This cover page by Ali Furmall, USF, now at U. Oregon.
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This activity was selected for the On the Cutting Edge Exemplary Teaching Collection

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This page first made public: Oct 25, 2007

This material was originally developed by Spreadsheets Across the Curriculum as part of its collaboration with the SERC Pedagogic Service.


In this Spreadsheets Across the Curriculum activity, students look at how magma viscosity is affected by temperature, fraction of crystals, and amount of water present. They will be introduced to Newtonian and non-Newtonian viscosity as well as the Arrhenian model for viscosity. This is a self-paced activity in which students follow a PowerPoint presentation to create spreadsheets and graphs using Excel.

Learning Goals

Students will:
  • Use the VFT model to calculate magma viscosity.
  • Make use of unit conversions involving acres.
  • Look at Newtonian and non-Newtonian viscosities.
  • Use an Arrhenian viscosity model.
  • Examine the effect of water on magma viscosity.
  • Examine the effect of crystal growth on magma viscosity.
  • Develop a spreadsheet to carry out a calculation.
In the process the students will:
  • Learn a relationship between melt viscosity and magma viscosity.
  • Increase their skill at unit conversions.
  • Use linear regression to determine the relationship between multiple variables.

Context for Use

Equipment: Each student or pair of students needs a computer with Excel and PowerPoint.

Classes: This module has been used in an Introductory Physical Volcanology course with upper level undergraduates.

In the class, the module was introduced during lab to be completed as homework due the following week. Students turned in hard-copies of the Excel spreadsheets and graphs, as well as their working Excel files. This worked well for junior and senior level students with excellent quantitative skills.

Description and Teaching Materials

PowerPoint SSAC-pv2007.QE522.CC2.7-Student (PowerPoint 1.4MB Dec19 07)

If the embedded spreadsheets are not visible, save the PowerPoint file to disk and open it from there.

This PowerPoint file is the student version of the module. An instructor version is available by request. The instructor version includes the completed spreadsheet. Send your request to Len Vacher ( by filling out and submitting the Instructor Module Request Form.

Teaching Notes and Tips

This module, like the others in this collection, works best if coordinated with lecture and lab material.

If students have difficulty in getting their equations to produce the correct numbers in the orange cells – especially if their results are off by orders of magnitude – tell them to check their unit conversions. You cannot ever emphasize unit conversions enough.

Some students jump ahead to the end-of-module assignments without working through the main part of the module carefully. Those students have trouble.


The end-of-module questions can be used for assessment.

The instructor version contains a pre-test

References and Resources

Shaw, H.R., 1972, Viscosities of magmatic silicate liquids: An empirical method of prediction. American Journal of Science, 272, 870-889. (one of the first people to discuss the relationships between thermodynamic properties of silicates and physical properties of magmas)

Hess, K-U., and D.B. Dingwell, 1996, Viscosities of hydrous leucogranitic melts: A non-Arrhenian model, American Mineralogist, 81, 1297-1300. (the VFT method used in this module)

Spera, F., 2000, Physical properties of magma, In: Sigurdsson et al., eds., Encyclopedia of Volcanoes, Academic Press, 171-190. (an accessible discussion)