3.5: Lab Exercise (Part B)
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Part B - Practice Questions
For Questions 5 through 9, refer to Figure 3.4 below, which shows a hill, an intermittent stream, and two index contours (darkened contour lines). Assume the contour interval for this map is 5ft, and the index contour that is crossing the stream has an elevation of 70ft.
5. Which way is the stream flowing, to the North to the South?
6. What is the elevation of the highest contour on this portion of the map?
7. Calculate the relief of this map (Hint: Review the “Contour Lines” section in this chapter for assistance calculating relief).
8. Calculate the gradient of the stream between the highest and lowest contour lines that you can see crossing the stream. These two contour lines are 2 miles apart.
9. The hill in the above diagram has a slightly steeper side on which side of the hill, the west or east side?
You have learned that the spacing between contour lines indicates the slope of the Earth’s surface and that the shape of the contour line as it crosses flowing water can indicate the slope direction. You have also learned that enclosed (circular) contour lines indicate a hill or mountain. However, sometimes there are circular depressions (for example, a sinkhole) found on the Earth’s surface and these depressions may appear as hilltops on a topographic map unless a new convention is used. Contour lines with small perpendicular lines (called hachure marks) are used for such depressions on a topographic map. The contour interval for the map is still obeyed when contouring a depression. The only difference is that the hachure marks on the contour lines indicate that you should count down in elevation, not up, as you move towards the center of the hachured contour circles. However, if there is a depression at the top of a hill or mountain (for example, a volcanic crater), then the first contour line that is hachured must be the same elevation of the closest contour line that is not hachured. The reason for the repeat is that a person climbing the hill will reach the highest contour line, walk a little higher still (before descending into the depression (crater)), and will, therefore, encounter the same elevation line while descending (see Figure 3.5).