If you aren't moving at a snail's pace, you aren't moving at all. -Iris Murdoch
Tuesday, November 02, 2010
I was going to try and post this Sunday, but I ran out of time. I'm having one of my classes measure some tombstones for their lab activity. They'll collect data on the width of marble tombstones a measurement at the top, and one at the bottom. Then they'll plot the change in thickness versus the date on the grave.
This is a pretty easy and fun activity - it's got some good pedagogy, too. It forces the students to actively participate in the learning activity, students have an opportunity to collect, graph, and analyze data. It also has connections with interesting and current research in the weathering rates of various materials.
I'm having the students use rulers, rather than calipers - I feel like the risk of damaging the grave markers is too high with students using a couple dozen steel calipers. I may try to get some inexpensive plastic-jawed calipers in the future. As a test, I gathered a few measurements from a nearby cemetery to see if students would be able to get usable data. Most of the thickness variation was more than 1mm, so they should get precise enough measurements to see a general trend. At the end of the week, we'll collate all the measurements and then the students will analyze and plot the class data - turning in a lab report next week.
My quick data collection produced a weathering rate estimate of about 0.03 mm/yr, which is fairly slow, compared to some other locations. But my data set is pretty small - and I suspect a few of these gravestones were "resurfaced" in some way.
A few links:
I based my lab activity off of the SERC's weathering rate activity write up:
GSA is sponsoring a research/outreach program about gravestone weathering, too - some cool and time-appropriate citizen science:
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I should have my mom do this - she's the historian of her town in WNY... and always visiting cemeteries searching for answers to genealogic mysteries. She could build quite a database I'm sure... cool idea.ReplyDelete
Why does weathering create a width difference along a tombstone?ReplyDelete
I suppose it should be more accurately described as a change in thickness (across the shorter dimension). The underlying assumption being that the vertical marble slab will weather faster at the top compared to the base (since rain falls from above). Alternately, if the ground-level moisture is constantly high, the base will weather away faster than the top.ReplyDelete
There's a bit of detail I'm glossing over with the activity - the main thing is to get students thinking about rates of change.
Awesome idea. I'm going to post a link to this on my blog as well (I think it fits in well with my theme). One comment, do you think that the weathered limestone from the top of the tombstone would reprecipitate on the bottom, making the bottom larger than it originally was?ReplyDelete
@Jazinator: It's possible that there are some more complex carbonate reactions taking place. I don't know if re-ppt'n at the base would be measurable with calipers across the entire thickness of the stone, over these time frames. From looking at other stonework and masonry, I have seen calcium "stains" dripping down from the mortar and such.ReplyDelete
It could certainly could be a long, drawn-out process with lots of intermediate steps of re-precipitation occurring. I would suspect this kind of process to be more likely on large monuments, or stones that don't become completely wet. Arid places, or areas prone to light rains. If it's ground moisture, you might see more precipitation below the soil/air interface rather than the stone.