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Roger Weller, geology instructor
by Nicolas Rodriguez
Rocks and Waves
In the realm of oceans and rivers, there are many types of waves and currents. Many of them are directly affected by, or directly affect landforms, beach shapes, earthquakes and volcanoes, even slopes within the body of water itself. The first question to e addressed, although seemingly simple, is what is a wave? This means that by merely stepping into water a person can create a wave. But, what about those huge waves? The ones that people actually ride on. What causes those?defines a wave as ďa disturbance on the surface of a liquid body, as the sea or a lake, in the form of a moving ridge or swell.Ē
Before that question is answered, first the different types of waves must be defined. There are many different classifications for waves, the most important ones to consider are breaking waves, which are defined by a wave when the wave collapses in on itself, there are two types of breaker waves. A plunging breaker is a wave that approaches a steeper beach and moves over a pocket of air at very high speeds. And a spilling breaker is the version of the wave that crashes on a sandier beach and has its energy spread out over a much larger area. There are also deep water, or swell waves. Swell waves are straight, long, powerful, and travel very long distances. There are plunging waves, that are characterized by breaking on a steep beach, and shallow water waves like tsunamis that exist in water much shallower than themselves. While these are not all the types and classifications of waves, these are the most important to this article.
The next question is, what causes a wave? Some of the most prevalent causes of waves are high winds, earthquakes or underwater volcanic eruptions, and gravity pulls from the ocean. Following the act that causes a wave, especially a wave with a point of origin deep within the ocean, the wave will travel through ocean in an oscillatory motion in deep deep waters. What causes a wave to break is when the wave approaches the shoreline and begins to slow down at the base of the wave causing the top of the wave will continue moving at a sustained speed and then will eventually speed past the base, breaking over the top of the wave. This especially true in waves like tsunamis. Starting deep in the ocean, a tsunami may only be three to six feet high in deep ocean, but as it approaches a shoreline become almost one-hundred feet tall.
The next subject to broach is how the ocean waves are affected by a shore line. In most beaches, a slow, and gradual shore line allows the wave to break in a controlled manner that isn't dangerous to a surfer. These waves break in deeper water, and lack solid danger to them. However, in some beaches, usually with a steep drop, or coral reef, the waves break in a much more violent fashion. Because the water did not shallow out in a gradual fashion and instead was sudden, the slowing of the wave is much more rapid as well, meaning that the energy of the wave is dispersed very quickly and can make the wave more dangerous. Also, because the wave breaks in much shallower water it becomes easier for a surfer to get hurt because the wave can crash him or her into the shallower shoreline.
Finally, how a wave breaks upon the shore affects how the beach is eroded and what type of material itís made up of. There are a few things to consider when looking at shoreline erosion. The first is what the beach is made up of. A shore that consists of softer sediments is more likely to be eroded than a shore characterized by larger chunks of rocks. The second is how much sediment is transported by a wave. Waves bring with them all kinds of soft sands and deposit them on the beach, and then as the wave recedes into the ocean it takes with it some sand back. If the waves are bringing in less sediment than they are taking, then the problem of beach erosion could be a very serious problem. Itís a bit of a cycle.
Ultimately the waves and beach erosion is a cycle. Lower energy waves deposit less sand than they take, and as such begin to erode away the beach that has the gradual sloping, transforming it into a beach that is extremely less gradual causing the wave to become much stronger and deposit more sediment turning the beach into a more gradual one. Surprisingly, waves and how they are formed are greatly interconnected with geology and its workings.