Waves are born when wind blows across a body of water and roughens its surface.
Oceanographers
think that waves occur because wind exerts uneven force on the
roughened surface of the water, pressing down water in one place and lifting it in another.
When a wave forms, the wind sustains it by exerting high pressure over the
crest
(the highest point in a wave) and low pressure over the
trough
( the lowest point in a wave). This difference in air pressure pushes down the crest and lifts the trough.(see figure 6 in appendix) Once waves are created, how big they get is determined by wind speed,
wind duration
(how long it blows), and
fetch
(the distance of water over which wind blows). Once a wave starts moving, it continues until it dissipates or breaks. Waves can break in several ways. They can spill forward, with the crest sliding down the front of the wave, or the can topple, with the crest curling over and plunging ahead of the rest of the wave. Less often they surge, with the crest peaking as if to plunge, but the base surging up the beach face so the crest collapses and disappears.(see figure 7 in appendix) Since Long Island Sound is relatively small, nearly all waves continue until they strike the coast. This striking of the coast causes the erosion that continues to shape our coastline.
An activity you can do with your class to illustrate this information would be to set up a long aquarium. In this aquarium have a side built up with sand and rocks. Have the students take notice of the shape of the sand and rocks which form a “coastline”. With a washable marker, draw the outline of the “coastline” on the outside of the aquarium. Next, set up a fan to blow on the water in the aquarium an the opposite end of your “coastline”. The fan blowing at various speeds will simulate calm and stormy weather. Turn the fan on and the wind from the fan should form waves in the aquarium water. These waves will crash into the sand and rocks that are representing the “coastline”. The crashing waves will reshape the sand and rock of the “coastline”. Turn the fan off and observe the newly formed “coastline”. Also, observe the difference from the line that represented the old coastline to the new. This activity gives the students a visual representation of the process of erosion and how our coastline was formed.
*Make sure the students understand that this process takes many years.
Activity clearly explained in appendix.