A large part of the earth's population likes to live close to the ocean for numerous reasons, may it be fishing, work or simply recreation. But unfortunately, the ocean shore is also a potentially dangerous place, as proven by recent natural disasters like the 2004 Tsunami in the Indian Ocean and the flooding of New Orleans. Uncontrollable masses of water contain huge amounts of energy and have an incredible potential to destroy, whenever they are pushed above river banks and ocean shores by storms or other natural forces. Coastal inhabitants know and often take advantage of the natural conditions and variability. Waves in a moderate form are fun to swim in and if you are a surfer, you probably even know that wave conditions are best for surfing after a storm or during full moon cycles when the tides are high. Boaters and fishermen also have to consider the tides. Of course, when there is no water it is hard to use the boat and fish also know when the tide is high, because that is when the fishing is best.
So what factors determine the height of a wave and the sea level variation due to tides?
Breaking waves on a beach are a result of a water parcel approaching shallow water. In most oceans there is almost always some kind of wave motion in the water, depending on currents, the local topography and mainly the winds. So, the bottom of a wave approaching shallow water is slowed down due to frictional forces with the sea floor and the top part all of a sudden moves faster than the bottom part, the wave rolls over, it breaks. The height of the breaking waves what we know as surf is strongly dependent on the geography and on the weather and places along the Pacific coast like California or Hawaii are known for the good surf in winter. Away from the beaches, the height of the wave is an important factor for navigation, ranging from recreational small boats limited to quiet waters to super tankers that can navigate under any condition. In the open ocean, tsunamis are not dangerous because the wave length is so long that ships do not feel them. Tsunamis only get dangerous when they build up in height through the interaction with the coastal topography. However, cases occur and every sailor has a story to tell you about ships disappear and even big ships being seriously damaged by giant waves, so called Rogue Waves. Rogue waves result from the interference of two or more waves. The open ocean is a mix of different waves with different characters generated in different areas from different storms. Chances are small but it happens that wave maxima from different waves meet and have constructive interference, a build up of the wave enormous heights reaching up to 100feet.
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