How Fast Do Materials Weather?
This material was originally created for
Starting Point:Introductory Geology and is replicated here as part of the SERC Pedagogic Service.
Summary
In each activity described below, instructors giving a lecture on weathering ask students to calculate weathering rates from tombstone weathering data. Atmospheric (and precipitation) chemistry determines the rate of weathering for marble tombstones. Show the students data from a rural and an urban cemetery, ask them to estimate rates, and then have them speculate as to why the rates are so different.
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Learning Goals
This exercise provides:
- A real-world context for rock weathering
- An opportunity for students to exercise and develop their quantitative skills.
- A measure of human impact even on marble in the sharp contrast between effects on polluted and unpolluted areas
Context for Use
This in-class exercise should take only a few minutes and is appropriate for a lecture on acid rain and/or rock weathering.
Description and Teaching Materials
The data for this example of tombstone weathering from two Australian cemeteries are from Dragovitch, 1986 .
- Show the plot of weathering depth vs. age for limestones in an urban environment, either as a powerpoint slide or as a 1/4-page handout
- Animated PowerPoint slide (PowerPoint 42kB Oct22 03) - click once for trendline, again for rate. Based on example by G.S. Hancock, College of William and Mary.
- Graphic ( 7kB Oct22 03) for handout. Based on example by C.M. Bailey, College of William and Mary.
- Ask students to determine the relationship between weathering depth and age.
- Call on students to describe the relationship.
- For an animated Powerpoint slide, show an estimated "best-fit" line through the data by clicking on the image.
- Ask students to estimate the mean weathering rate (in mm/century) and check their answer with their neighbor.
- Have each student write their answers on the handout (or index card for a PowerPoint example) and turn it in or call on students to give answers and discuss.
- Repeat the process with data from another cemetery, such as Wollongong. Wollongong's data are strange; the tombstones don't decay over same time period as Sydney's, but they seem to start off badly degraded. Wollongong has been industrializing rapidly, with a copper refinery in 1907 and a steelworks in 1928. The concentrated acidic precipitation strips the finish off tombstones very rapidly!
Data for two Australian cemeteries, both from Dragovich (1986):
- Sydney ( 785bytes Oct22 03)
- Wollongong ( 477bytes Oct22 03)
Teaching Notes and Tips
Each activity could be used in large as well as small classes. One way to introduce such activities would be to show an image of a tombstone.
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Assessment
Informal for the in-class exercises. The instructor may wish to have the class estimate the weathering rate for one cemetery in class, and then have students estimate the rate for another on a test or a quiz.
References and Resources
- Cemetery Geology
Studying rock types, weathering processes and human history in a cemetery.
- Weathering rates of marble in urban environments, eastern Australia. Dragovitch, 1986 An excellent source of data for tombstone weathering in two different cities: the booming (and polluted) metropolis of Sydney, and Wollongong, where pollution rates haven't changed much. (citation and description)
- Scientist Uses Tombstones to Track Environmental Changes. Mayell, 2001 Geomorphologist Tom Meierding visited more than 700 cemeteries and measured 15,000 tombstones to see what kind of environmental changes they might reveal. (citation and description)
- Reinforcing quantitative skills with applied research on tombstone-weathering rates. Roberts, 2000 This Journal of Geoscience Education article describes a tombstone weathering exercise that reinforces quantitative skills with applied research. Shelia Roberts at Western Montana College incorporates a student driven research project as a major component of her surficial geology course to engage students in quantitative analysis. Her paper describes a framework for guiding student designed research projects to enable quantitative learning. (citation and description)
- Twenty-year weathering remeasurements at St. Paul's Cathedral, London. Tudgill et al., 2001 This article describes how weathering of building stones in London records acid rain deposition for a twenty-year period. (citation and description)
Robert Inkpen's Gravestone Weathering (more info) Resource Site includes:
- Detailed lecture material (including the math and definitions)
- Description of methods (for an associated field lab)
- Bibliography of papers of interest to students looking at gravestone weathering
- Data for tombstone weathering in several cemeteries in Great Britain, some of them more subject to acid precipitation than others (i.e. Swansea!), plus weathering rates for other sites