The current concerns with global warming have prompted an awareness of secondary problems such as changes in water levels of major lakes and oceans. We can address this problem with an activity designed to increase student awareness of the effects of changing water levels. This activity, by teacher John Mascazine, is also helpful in teaching students how to interpret and use contour maps.

 Objectives
When students have completed this activity, they will be able to:

• create and interpret a contour map
• describe how contour maps can be used to study changes in water levels and land elevations

 Materials (for each group of four students)

• 2 liter soft drink bottle
• lump of clay, enough to fill the bottom of the 2 liter bottle
• clear overhead transparency or plastic sheet
• metric ruler
• overhead transparency marker
• container for holding water

1. Cut off the top of the 2 liter bottle about 15 to 20 cm from the top. We will use the bottom section without the colored bottom cup. Use a bottle that will stand without a bottom cup.
2. Use clay to form a hill and any other landscape features you chose in the bottom of the bottle. You may choose to leave one area depressed to simulate a pond or lake.
3. Make marks on the side of the container to indicate 1 cm increments from the bottom to the top.
4. Record the level of the land/clay in accordance with the marks on the side of the container. How many centimeters does your clay landscape rise from the bottom of the container?
5. Slowly pour water into the container and onto the clay landscape. Add water until it becomes level with the first centimeter mark above some of the clay. Describe how much of the clay landscape is now covered with water.
6. Put two or three small marks on the rim of the bottle. These will correspond to marks that will be make on the transparency sheet to help keep its position constant.
7. To construct a contour map, place a blank transparency on top of the container. Draw a circle on it to indicate where it touches the rim of the container, and mark your registry points from the rim as well.
8. Look straight down from above the bottle (not at an angle) and draw a line on the transparency where the water meets the clay (the shoreline).
9. Take off the transparency and add more water to the bottle until it is level with the second centimeter mark. Replace the transparency in exactly the same location (lining it up with the dots and rim circle). Draw another line on the transparency as in the above step to indicate the new water level.
10. Continue adding water a centimeter at a time and drawing new contour lines (where the water meets the clay) until the clay is completely submerged.
11. The finished transparency can be traced onto a sheet of paper for future reference.

1. How can contour maps be useful to geologists, farmers, marina owners, boaters and others whose work is directly related to the coastal landscape?
2. If the water level decreased 1 cm in elevation on your model, as it is likely to do in the Great Lakes with global warming, how much more land was exposed? Figure out how you could determine this mathematically and defend your answer. If the water level rose 1 cm, as the ocean is likely to do in response to global warming, how much land is flooded? Figure out how you could determine this mathematically and defend your answer.
3. If a contour map has an area in which the contour lines are very close together, what does that indicate?
4. How are flat areas shown on a contour map?
5. Describe how a lower water level, such as what the Great Lakes will likely have with global change, has different effects on steep versus flat areas. Describe how a rising sea level, has different effects on steep versus flat areas.

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Sample of a contour map created by this method.