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# Topography: Highs and Lows of the Earth's Surface

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Author: Janice VanCleave

The Earth's surface has features with different elevations, such as mountains, valleys, and lakes, called topography. Three-dimensional (3-D) models, topographic maps, and profile diagrams can be used to show the elevation of surface features.

In this project, you will show how topographic maps use contour lines to indicate the elevation of a land area. You will determine the effect that changes in elevation have on the distance between the map's contour lines. You will use marks called hachures to indicate depressions and craters on your map. You will also measure the elevation of a gently sloping hill, draw a profile map of the hill, and make a 3-D model ofthe profile of the hill.

### Getting Started

Purpose: To produce a 3-D model of a mountain.

### Materials

• Apple-size ball of clay
• Sheet of typing paper
• Metric ruler
• Pen

### Procedure

1. Lay aside a grape-size piece of clay. Use the remaining clay to mold a mountain with an uneven landscape. Make depressions in the side and/or a crater (a hollowed-out area at the top of a volcano) in the top.
2. Set the clay mountain in the center of the paper.
3. Insert the zero end of the metric ruler into the grape-size piece of clay, and stand the ruler vertically next to the clay mountain.
4. On one side of the clay mountain, use a toothpick to draw a straight vertical line from the top of the mountain to its base.
5. Align the vertical line drawn on the clay, with the edge of the ruler, then mark heights 1 cm apart on the clay mountain: Holding the toothpick horizontally across the l-cm mark on the ruler, insert the end of the toothpick into the line on the clay. Repeat this procedure at each centimeter mark until you reach the top of the mountain (see Figure 2.1).
6. Turn the mountain one quarter turn and repeat steps 4 and 5. Repeat the procedure two more times so that heights are marked on four sides of the mountain.

### Results

A mountain model with different indicated heights is made.

### Why?

In this experiment, you made a 3-D model of a mountain. The toothpicks are placed at different heights to indicate elevation (height above sea level).

### Try New Approaches

Topography is the description of the size, shape, and elevation of a region of land. A topographic map is a flat map that shows the shapes and heights of a land area using contour lines (lines that connect points on a map that have the same elevation). The difference in elevation between one contour line and the next is called the contour interval. The contour interval on the map in this experiment is I cm.

How can a topographic map of the clay mountain be made? Make the map by removing the ruler and following these steps:

1. Use a pen to trace around the base of the mountain. Make a mark on the paper at each vertical line on the clay model.
2. Wrap an 18-inch (45-cm) piece of dental floss around the mountain at the I-cm height, letting the floss rest on the toothpicks. Cross the ends of the floss, then pull them in opposite directions to cut through the clay model.
3. Lift the top section of the clay straight up, remove the bottom slice without moving the paper, and lower the top section. The lines on the clay should match the marks on the paper. Trace around the base of the clay.
4. Repeat steps 2 and 3 for the remaining heights marked on the clay with toothpicks.
5. Remove the top, final section of the clay mountain from the paper and observe the tracings on the paper.
6. Label the contour lines with the appropriate elevations, as shown in Figure 2.2. Use hachures (short lines drawn inside a contour line) to indicate a depression or crater. The free ends of these lines always point downslope.

The closeness of the contour lines indicates the slope (the degree of steepness of an inclined surface) ofthe land. When the lines are far apart, the slope is gentle, but when they are close together, the slope is steep. Science Fair Hint: Stack the slices of each clay mountain and display the models along with their topographic maps.

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