We'll build a model to gain a better understanding of how the landforms can change over time. Plaster of Paris or clay is good for making models of land. We'll build ours in a large, very deep pan.

The model should depict various levels of landforms (hills, valleys, river beds, lakes, etc.), but the greatest height should not be higher than the side of the pan.

After the plaster has hardened, slowly pour water into the pan. Some of the hills will become islands, shorelines will change, and some areas will be flooded. (This is very similar to the changes in landforms that occur when a dam is
built and a reservoir is created by flooding a natural valley.)

What is seen is much like the trailing edge or submerging portion of a continent.

Use a drinking straw to dip out the water. What is seen now is similar to the leading or emerging edge of a continent.

As an extension of this activity, you can develop a contour map of the land model. To do this, hold a ruler vertically against the bottom of the pan and pour in water until it reaches the a depth of 1/2 inch.

Now, with a soft pencil, mark the water level in a continuous line wherever the water touches the land. When you are finished, add another half inch of water, and mark again. Repeat until the highest part of the model is submerged.

When the water has been poured off, look straight down on the model and draw a picture of the lines just as you see them. The water levels can be marked on the lines. From your picture, you will be able to tell the heights of each
hilltop, which way rivers flow, where level areas are, and which slopes are steepest.

If possible, compare your picture with geological survey maps. The "picture" you have made is actually a contour map, which geologists use for many purposes.