Bubbles in Magmas

Module by Chuck Connor, University of South Florida, Tampa. This cover page by Ali Furmall, USF, now at U. Oregon.
This material is replicated on a number of sites as part of the SERC Pedagogic Service Project

Summary

Bubbles in magma

In this Spreadsheets Across the Curriculum activity, students are introduced to the process of bubble formation and rise within a magma. The ideal gas law is utilized to illustrate the change in volume of an individual bubble as it rises through the magma. Forces acting on the bubble (gravitational, viscous, and buoyant) determine the bubble's velocity. 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:
  • Use the Ideal Gas Law to make estimations regarding the growth and rise of bubbles in magmas.
  • Make use of unit conversions involving moles.
  • Calculate the net forces acting on an individual bubble.
  • Calculate the terminal velocity of the bubble.
  • Calculate the change in volume of the bubble as a function of depth.
  • Develop a spreadsheet to carry out a calculation.
In the process the students will:
  • Increase their skill at unit conversions.
  • Recognize the relationship between volume and pressure in an ideal gas.
  • Be introduced to (or be reminded of) the various forces acting an object as it rises or falls through a medium.
  • Identify the relationship between net force and terminal velocity.

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.CC2.1-student (PowerPoint 1.8MB Dec6 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

Hurwitz, S., and O. Navon, 1994, Bubble nucleation in rhyolitic melts: experiments at high pressure, temperature, and water content. Earth and Planetary Science Letters 122: 267-280. [a very comprehensive introduction to essential research about bubbles in magmas].

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]