# Tsunami and the Depth of the Ocean

#### 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.

Used this activity? Share your experiences and modifications

## 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)

## 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.