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If you have spent any amount of time along the shore you have noticed the daily rhythm of the water flowing in and out as if retreating to some far off place. This gentle cycle of the ocean is what we call a tide.
What Causes Tides?
The water on the planet's surface is affected by the gravitational forces of the earth and the moon that keep the planet on which we live in elegant balance as it spins on its axis. This push and pull movement on the planet exerted by the sun and the moon creates a movement in the water that covers the earth, creating the flow of tides. The rising and receding water of the tides can influence the shore as well as the areas along bays and estuaries. The land of these areas is exposed when the water recedes, a point known as low tide, and submerged under water once again during the time referred to as high tide. Certain tides can also be effected by wind and weather, such as the storm surge that often occurs during a hurricane.
This movement also affects the water off of the shore creating a moving stream in the water known as tidal currents. During this process of water flowing in and out of the tidal zones there is a moment of stillness just before the movement begins to reverse itself, this is known as a slack tide when the water is at a stand still, technically speaking.
These regular cycles of water result in a tidal community that lives in between the highs and lows of the rising sea, such as crabs that feed on the land after the waters have retreated.
In addition to the daily high and low tides, two other types of tide cycles occur resulting in the spring tide and the neap tide. A spring tide occurs when the moon and sun are lined up opposite from one another which reinforces the dual gravitational influences upon the tides, stretching the tidal range to its greatest point. When this occurs the resulting tides are referred to as Spring Tides. Similarly, when the gravitational forces of the sun and moon are operated against one another, this results in the tides having the shortest range creating what is known as a neap tide.
The following model represents this phenomenon: