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Wash Out: How do Slow, Low-Energy Waves Affect a Beach?

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Author: Janice VanCleave

Problem

How do slow, low-energy waves affect a beach?

Materials

  • Paint-roller pan
  • 1 quart (lliter) sand
  • 2 quarts (2 liters) tap water
  • Pencil

Procedure

Wash Out

  1. Cover the bottom of the pan with the sand, building up a small "beach" at the shallow end.
  2. Pour the water into the deep end of the pan.
  3. Make a mental note of the appearance of the sandy beach in the pan.
  4. Make waves by laying the pencil in the deep end of the pan and slowly moving the pencil up and down with your fingertips. Push the pencil about 1 inch (2.5 cm) below the water each time.
  5. Observe the beach after the water waves have hit against it.

Results

The water washes some of the sand from the "beach" and moves it to the deeper part of the pan.

Why?

The area where the ocean and the land meet is called the shoreline. The shore is the land at the shoreline. If it is a smooth, sloping stretch of sand and pebbles, the shore is called a beach. Water waves are repeating disturbances on the surface of water. When ocean waves hit the beach, water moves forward for a short distance, then drains back toward the deeper part of the pan. As the water drains, some of the sand moves with the water. Along a real shoreline, the waves bring sand toward the beach in one area as they strip sand away from another area. This displacement (movement from one place to the other) of sand is an example of erosion. In this experiment, the slow, low-energy waves erode away a small part of the beach.

Let's Explore

Wash Out

  1. How would fast, high-energy waves affect the results? Repeat the experiment, quickly moving the pencil up and down, pushing the pencil at least 2 inches (5 cm) below the water each time. Science Fair Hint: Make a diagram similar to the one here showing the sea, the shoreline, and the beach.
  2. How does the material on the shore affect the results? Repeat the original experiment, using aquarium gravel instead of sand.

Show Time!

Wash Out

  1. Weathering is the process by which rocks are broken into small pieces. One type of weathering is called abrasion, which occurs when rocks rub against each other and wear each other down. Demonstrate abrasion. First, observe the surface of a large rock; then, rub a piece of coarse sandpaper against the rock's surface. Again observe the rock's surface.
  2. Currents (swift streams of water) in oceans flow parallel to the shoreline. This moving water transports sediments(weathered rock material). When the water is slowed, it deposits some of the sediment it is carrying. Demonstrate how the movement of water affects the amount of sediment it deposits. Fill a jar about half full with tap water. Add 1/4 cup (63 ml) of sand, and close the jar with its lid. Holding the ends of the jar, turn it sideways and hold it at eye level. Shake the jar vigorously ten or more times observing its contents. Notice any sand buildup on the lower side of the jar. Repeat, shaking the jar gently.

Check It Out!

Headlands are projections of land that extend from the shore into deep water. These projections slow incoming waves and deflect them away from the beach. Find out more about headlands. How do waves affect headlands? How are sea cliffs formed from headlands? How are sea caves, sea arches, and sea stacks formed? Diagrams of the progression of the erosion of headlands into other rock structures can be displayed. For information, see pages 87–94 in Janice VanCleave's Oceans for Every Kid (New York:Wiley, 1996).

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