Porosity and Permeability of Magmas

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 is replicated on a number of sites as part of the SERC Pedagogic Service Project

Summary

Magma Porosity

In this Spreadsheets Across the Curriculum activity, students will consider porosity and permeability of a magma and the means that gas may escape the magma. They will use iteration to calculate ideal values for porosity, pressure, and volume. 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:
  • Link porosity and permeability using empirical relationships.
  • Explore one mechanism by which gases may escape from a magma.
  • Use Excel's iteration function to calculate accurate values for porosity, pressure, and bubble volume.
In the process the students will:
  • Gain an understanding of the interdependence of porosity, bubble volume, and pressure on melt density.
  • Learn to use Excel's iteration function.
  • Calculate pressure using a sum of partial densities.

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.CC2.6-Student (PowerPoint 956kB Nov1 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

Cashman, K.V. and Mangan, M.T. ,1994, Physical aspects of magmatic degassing II. Constraints on vesiculation processes from textural studies of eruptive products. Reviews in Mineralogy, 30: 447-478. [a starting point for understanding bubbles in rocks]

Blower, J.D., 2001, Factors controlling permeability-porosity relationships in magma. Bulletin of Volcanology 63: 497-504. [accessible development of a best-fit statistical model of permeability based on analysis of pyroclasts].