Soundings: Mapping a Profile the Ocean Floor (page 2)
Try New Approaches
- Model measuring the depth of different parts of the ocean floor by taping a 4-foot (120-cm) piece of adding machine tape to a tile floor. Write 0 at one end and mark each foot (30 cm) from 1 foot to 4 feet (30 cm to 120 cm), as shown. Position a stool on the zero mark and a chair at the 1-foot (30-cm) mark, and stack five or six thick books at the 2-foot (60-cm) mark and two or three books at the 4-foot (120-cm) mark (see Figure 20.2). Now, using the stool, the chair, and the books as part of the ocean floor, repeat the original experiment, measuring the echo sound by bouncing the ball at each of the four marks. At zero, the stool that represents the shoreline, record the time as zero, then move to the 1-foot (30-cm) mark, drop the ball, and time the echo. Continue moving to each mark on the tape, dropping and timing the bouncing ball. Record the measurements in a data table like Table 20.1. Use the depth equation to calculate the depth at each distance from the shoreline, and record it in the data table.
- Use the calculated depths from the data table to plot a graph representing the profile of the ocean floor (see Figure 20.3).
- How does the distance between the echo soundings affect the accuracy of the profile? Repeat parts la and lb taking echo soundings every 6 inches from the model's shoreline. Compare the profiles made with l-foot (30-cm) soundings and 6-inch (l5-cm) soundings to determine which better represents a profile of the ocean model.
Design Your Own Experiment
- Design another ocean model representing a section of the ocean, and use sounding to map the ocean model's profile. One way is to place two identical chairs, with backs at least 30 inches (70 cm) tall, 4 feet (1.2 m) apart. Represent the surface of the ocean by tying a string horizontally between the highest points of the chairs. Use a black marking pen to mark off 3-inch (7.5-cm) intervals along the "surface" string. Place stacked books, a stool, and an upturned pot and bowl under the string. These objects represent features on the ocean floor.
- Use the data table to make a graph of your measurements. Title the graph "Ocean Model Profile." Display the graph and a photograph of the profile of the ocean model.
Cut a second string 12 inches (30 cm) longer than the height of the chairs. Tie a washer to one end. Use the pen to mark off a 1-inch (2.5-cm) scale along this second string. This string will be called the scale. Holding the free end of the scale, position it against the surface string, next to the back of one chair (this is the 0-inch, or 0-cm, mark) and slowly lower the scale until the washer touches an object or the floor. Use the marks on the scale to determine the depth of the ocean at that point. Round off the measurement to the nearest scale marking. Measure the depth of the ocean every 3 inches (7.5 cm) along the length of the surface string, and record the depth measurements and the distances from the shoreline (the zero mark) in a data table like Table 20.1.
Get the Facts
The profile of the ocean floor is divided into four areas: the continental shelf, the continental slope, the continental rise, and the abyss. Which areas make up the continental margin (water-covered area from the shoreline of the continents to the abyss)? What is the location and size of each area? For information about these four ocean areas, see Don Groves, The Oceans (New York: Wiley, 1989), pp. 96-97. Display a diagram of the ocean profile showing the four areas.
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