Mapping the Sea Floor

Engagement

30 Minutes

Ask the following questions, accepting all student ideas: How might scientists map the seamounts? What are some reasons that having a map of the seamounts and/or of the ocean floor might be helpful?

Show students the animated presentation “Who Cares about Seafloor Mapping?” This animation gives a brief history of sea floor mapping techniques, and explains multibeam and sidescan sonar.

During the presentation, pause for discussion at each of the “Did you know?” sections at the bottoms of the pages. Stop after you have read and discussed the page that describes LIDAR. Review sound waves, sonar, sidescan sonar, and multibeam sonar to be sure students have a basic understanding.

If students need more background on sound and how sound travels, see the Teacher Background section for resources.

Exploration​

2-3 Class Periods

Tell students they are going to create a model of a seamount or chain of seamounts and the surrounding ocean floor, then participate in a simulation of a sonar activity.

Remind students that canyons and seamounts are not the only structures found at the bottom of the ocean. Show them the Ocean Features diagram, noting the various features such as continental shelf, continental slope, abyssal plain, seamount, island, rift zone, mid-ocean ridge, and oceanic trench.

Part 1: Creating the Seafloor Model (60-70 minutes)

Divide students into groups of 2-3. Each group will build a sounding box, using the model seafloor instructions handout, Part 1. Have each team of students place rocks, sand, clay, and/or other materials in their box to create models of the ocean floor. They should include at least one seamount. Other ocean features mentioned above are optional. (To adapt this lesson for a range of learning styles and abilities, students can create their model seafloor using more familiar terms such as canyons, islands, or mountains.)

Each student should then draw a diagram of their model seafloor in their science notebook, labeling the features of the ocean floor.

If the box does not have a lid, secure aluminum foil or construction paper over the top.

Part 2: Sampling the Seafloor (30-40 min)

Be sure students have directions for Part 2.

Each team will tape a seafloor grid to the top of their box. The letters and numbers will form a system for referencing each square. For example the square in the upper left corner will be “A1,” etc. Each team needs several copies of the grid: one for the top of the box, and one for each team member to be used for data collection and making the map.

Distribute or have students select items to use as probes (skewers, knitting needles, pencils, straws, etc.). Use centimeter rulers and markers to create measuring instruments by placing marks in centimeter increments. As an alternate method, students can hold their finger at the box-top level of the probe when it has reached the bottom of the “ocean floor,” then lay the probe down along the edge of the ruler to measure the distance. Be sure that they record the distances on their second grid as negative numbers to indicate depth below the surface.

Remind students to began their data sampling in a systematic way. Suggest they start at one corner and continue along one line until all data are collected for that line, then start collecting data for the next line.

When they have taken readings for all the holes in the top of the box, they will have a grid with a number in each square.

Ask students to use the color chart on their handout, and color each square with the color that corresponds to the depth.
Next, ask them to draw lines that connect the squares that have the same colors to show what features are on their seafloor.
Then draw a line through the middle of each square to create the “contour lines”.
Finally, ask them to take the top off the box and see if their graph looks like the model!

Explanation

30 Minutes

Ask students if their sampling found all of the features on the bottom of their seafloor. Why or why not?

Display the models in a location where students can easily see them. Display the student maps and ask students to choose the model that it represents, explaining their choice.

Lead a discussion asking students to explain how this activity was similar to sonar in the “transect” method of sampling, and taking depth “soundings.” How would scientists use this information when planning for their dive? Discuss the advantages of various locations for diving missions or routes for a submarine to explore the bottom of the ocean. Hint: Areas likely to offer a variety of habitat types within a short distance will offer some of the best opportunities to get the most out of limited diving or submarine time. (Flat regions are more likely to have accumulations of sediment, and will provide different habitats than very steep areas. On the other hand, steep areas obviously have a greater range of depths within a short distance, so these are better sites to study how depth influences the distribution of various species.)

Elaboration

30 Minutes

Have students create a 3-D map showing the topography of the ocean floor using Excel and the instructions provided. It might be helpful to demonstrate with the sample data provided excel chart.

Ask students if they can come up with other ideas of gathering the same data they did with the sampling tool.

Evaluation

15 Minutes

Ask students to respond to the following questions in their science notebooks.

It has been said that sound is the “eyes” of the ocean. What might this mean?

You might also ask them to respond to one or more of the following:

1. Explain the difference between topographic and bathymetric maps.
2. Discuss how sonar can be used as a tool to map the ocean bottom.
3. Explain how hydrographic surveying has changed with the introduction of new technologies.
4. What type of old hydrographic surveying method is most like the sounding box activity?
5. How would you change your measurement method to find smaller objects, or to find more detail in the large objects on the bottom of your ocean?
6. In your opinion is sonar mapping an accurate way to measure the ocean floor? Explain why or why not.