Tsunami and the Depth of the Ocean

Martin B. Farley, University of North Carolina at Pembroke

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This page first made public: May 30, 2013

Summary

An inquiry approach to using the celerity (=velocity) of a tsunami to measure the depth of the ocean along its path. Tsunami are shallow-water waves, because their wavelengths are so long relative to ocean depth. Shallow-water wave celerity depends on ocean depth. Students reason this out. They then determine the distance of the path of the tsunami from the epicenter of the 1964 Alaska Good Friday earthquake tsunami to various locations, use tsunami arrival times to calculate the velocity, and re-arrange the shallow-water celerity equation to calculate depth. Students evaluate the geographic distribution of water depths.

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Context

Audience

Introductory Oceanography course. The official audience up to last fall has been Science Education majors with an assortment of students from other majors, because until then we had no undergraduate major. For various reasons, most students taking the class are juniors/seniors.

Skills and concepts that students must have mastered

Basic algebra (re-arranging equations).
Characteristics of waves and how to estimate their celerity (shallow-water and deep-water)
Latitude and Longitude

How the activity is situated in the course

As a classroom lab in a sequence of instruction that includes lectures and labs on waves and their characteristics (including labs on shallow and deep water wave celerity and seiches)

Goals

Content/concepts goals for this activity

Investigation of shallow-water wave velocity and its uses
High velocity of tsunami

Higher order thinking skills goals for this activity

Evaluation of simple wave celerity concepts to apply to what appears to be a different phenomenon (tsunami)
Reasoning through hurdles (tsunami can't go overland) to reach an accurate conclusion
Analysis of water depths and explanations for geographic variance

Other skills goals for this activity

Practice in simple algebra and calculation
Use of WWW for calculation (great-circle distances in this case)

Description and Teaching Materials

Tsunami lab for ocean depth estimation student activity.doc (Microsoft Word 67kB May30 13) --Student handout
Tsunami lab solution set.doc (Microsoft Word 67kB May30 13)
Tsunami lab and Ocean Depths Instructor Notes.docx (Microsoft Word 2007 (.docx) 26kB May30 13)
Tsunami lab.xlsx (Excel 2007 (.xlsx) 40kB Jun11 13) – spreadsheet with raw data, calculations.
NOAA tsunami datasets (Excel 2007 (.xlsx) 69kB Jun11 13) - Data from NOAA database

Teaching Notes and Tips

See Instructor notes.

NOAA tsunami datasets.xlsx contains key data for all localities with arrival times in the NOAA tsunami database for the 1964 Alaska, 2010 Chile, and 2011 Japan tsunami. This gets around the glitch in extracting data from the Web described in my documents. These localities would allow you to add conveniently other locations to the activity.

Assessment

Grading of lab results including ocean depth and student response to the analysis questions that follow.

I have an exam question based on this lab that I use to see if students retain understanding of the approach. See instructor notes.

References and Resources

Most tsunami data are from National Geophysical Data Center / (NGDC/WDS) Global Historical Tsunami Database, Boulder, CO, USA. (Available at http://www.ngdc.noaa.gov/hazard/tsu_db.shtml)

See Warning in instructor notes for current (as of May 17, 2013) limitations of extracting data from this database.

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