Constructing a 3D bathymetry model

Jessica Kleiss

Lewis & Clark College

I use this activity in my Introductory Oceanography course at the college level, offered to non-geoscience majors, yet who are likely to major in science.

1) Familiarity with common sea floor features such as seamounts, tablemounts, mid-ocean ridges, trenches, abyssal plains, coastal shelves, etc.
2) Familiarity with typical methods and instruments used to measure sea floor bathymetry, such as soundings, echo soundings, side-scanning sonar and multibeam sonar.

My course includes a weekly lab. This activity takes 2 lab periods to complete: one to build the box models, and one to take the ocean floor soundings. It would be feasible to complete in a 2-hour lab session. I include this lab early in the semester, usually as one of the first couple of labs.

1) Visualizing a bathymetric map as a 3D description of the sea floor.
2) Sea floor features (in coastal zones as well as deep-ocean basins)
3) Practices and challenges of observationally mapping the sea floor
4) The ocean is largely unexplored (ocean literacy concept #7)

1) Unit conversion and scale conversion between a topographic map and a scaled model
2) Experiment design, including sampling frequency and accuracy. The effect of the design on the outcome (in this case the contour map)
3) Quantitative reasoning

1) Dextrous manipulation of scissors, sharp edges, cardboard, and tape.
2) Project management, distribution and rotation of labor.
3) Manual graphing (eg. without a computer graphing program)

To prepare for this lab, students read a section of the textbook about observational techniques to measure the seafloor bathymetry as well as the occurrence of common sea floor features, such as seamounts, coastal shelves, mid-ocean ridges, and trenches. In the first lab, groups of students are provided with a bathymetric map, cutting board, sharp edges, and plenty of cardboard. They trace some contours from the map onto tracing paper, and then cut those out of the cardboard to construct a scale model of their given sea floor feature. They attach the sheets of cardboard with double-sided tape, and affix it to the bottom of a rigid box. The box lid has a grid of holes drilled into it. They determine the scale of the map (cm of the model to km in the ocean, for example), and affix the scale to the outside of the box. This concludes the first lab session.

In the second lab session, each team of students is provided with a box from an unknown team. The box is closed, and they do not know what ocean feature lay inside. They use bamboo skewers to take "soundings" at each of the drilled holes in the box lid, and mark their measurements on a piece of graph paper. Then they construct a contour map from the soundings, and try to identify the sea floor feature in the box from a global seafloor topography map that is hanging on a wall.

Students complete guided questions about the process of constructing their 3D scaled model and exploring the unknown ocean.

1) Groups of students hand in their constructed scale model to demonstrate their ability to do unit conversion and accurate scale conversion.
2) Groups of students hand in their soundings, contour map, and interpretation to demonstrate manual graphing proficiency
3) Students answer guided questions to help them interpret this activity as a metaphor for ocean exploration. (so they don't think they just did a lab about cutting cardboard!)

See uploaded documents for links to possible bathymetric maps