How are Flow Conditions in Volcanic Conduits Estimated?

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

Summary

Title slide for Conduit Flow

In this Spreadsheets Across the Curriculum activity, students will examine flow conditions in volcanic conduits. Laws of conservation of mass and momentum are used to estimate variations in magma density and velocity. Students will use simplified equations of state to model steady-state Plinian eruptions. This is a self-paced activity in which students follow a PowerPoint presentation to create spreadsheets and graphs using Excel.

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Learning Goals

Students will:
  • Examine processes operating in volcano conduits during Plinian eruptions.
  • Use Henry's Law to make estimations regarding the mass fraction of volatiles dissolved in a magma.
  • Consider variations in volatile exsolution in equilibrium and disequilibrium conditions.
  • Develop a spreadsheet to carry out a calculation.
  • Examine homogeneous and heterogeneous bubble nucleation
  • Use conservation of mass and Henry's Law to estimate ascent velocity of a magma.
In the process the students will:
  • Begin to see the value of calculations based on approximate assumptions.
  • Recognize that estimating flow conditions in a volcanic conduit is a complex process that does not conform well to generalization.
  • Gain an understanding of how pressures and magma density vary as a function of depth.

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.CC2.2-Student (PowerPoint 1.7MB 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 (vacher@usf.edu) 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.


Assessment

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

The instructor version contains a pre-test

References and Resources

Jaupart, C., 2000, Magma ascent at shallow levels, In: Sigurdsson et al., eds., Encyclopedia of Volcanoes, Academic Press, 237-245. (an accessible discussion)

Woods, A.W., 1995, The dynamics of explosive volcanic eruptions., Reviews in Geophysics 33: 495-530. (detailed discussion of magma ascent)