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Looking for paleotsunami evidence: an example from Cultus Bay, Washington

This activity was authored by Andrew Moore, Earlham College for a combined University of Washington/NOAA Pacific Marine Environmental Lab tsunami certificate program.
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This is a partially developed activity description. It is included in the collection because it contains ideas useful for teaching even though it is incomplete.

Summary

In this lab activity, students work in groups of 3-5 to develop a search strategy for paleotsunami deposits. Students take virtual cores in an area, in three rounds of 10 cores each. After each round, they determine if they think they have found a tsunami deposit, and plan the next round of sampling. At the end, each group presents what they believe the tsunami history of the area to be.

Learning Goals

Concepts and content: Originally, this was intended as part of the "geology" module of a short course for disaster professionals. We wanted to make the case that finding tsunami deposits wasn't as simple as looking for sand, and that multiple teams of searchers might come to vastly different conclusions looking at the same set of ground. For college students, the same basic goals hold. Multiple groups can query the same dataset, yet come to vastly different conclusions. What does this say about the nature of science? Do publications equal "truth"?

This exercise tends to stress higher-order thinking (especially data analysis and synthesis), and can be frustrating for students who want to know "what the answer is".

I've always used oral presentation as the means for each group to communicate their results at the end of the exercise, but it could easily take the form of a written report.

Context for Use

This exercise was originally designed for a group of disaster managers from nations affected by the 2004 Indian Ocean tsunami. It ran for about 2 hours, but could have used 3 more effectively. Students should already understand something about how a tsunami history is determined, and something about how salt marshes work. In the original, this was done with an approximately one hour introduction. It could easily be done with written material instead.

The exercise could be shortened by changing the sampling density, or by further limiting the search area. Workflow could be vastly improved by querying an SQL or HTML database of cores rather than using the instructor.

Description and Teaching Materials

Coming!

Teaching Notes and Tips

I think it's worth running this exercise without grading at least once before attempting it for a grade. Workflow can be problematic (it can often take time to get groups the cores they request), so a TA or assistant who understands the exercise to help is vital.

In the original, there was one map in the room, and groups were expected to report their results for others to see. This didn't tend to work well in practice, and I think the exercise works better if each group has a copy of their own map to work from. I've discouraged groups from talking to each other about their findings, but it does happen!

Assessment

References and Resources

On the actual deposit:

Atwater and Moore, 1992, A tsunami about 1000 years ago in Puget Sound, Washington, Science, v. 258, p. 1614-1617. [This contains a cross-section of the deposit that can be placed onto the core grid given here, and the authors' evidence for why they believe this to be a tsunami deposit.]

Weinmann, et al., 1984, Wetland plants of the Pacific Northwest, US ACE, Seattle. [This contains both descriptions of native wetland plants and how wetlands in the area are organized.]

Dawson and Shi, 2000, Tsunami deposits, Pure and Applied Geophysics, v. 157, p. 875-897. [This is a good reference for identifying tsunami deposits in marsh sequences, and could be used as introductory reading to the exercise.]

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