Coastal systems and Tides
Tides are caused by the gravitational pull of both the moon and sun. Tides are long-period waves that move through the ocean because of the gravitational pull. Earlier in the semester I mentioned in my initial reflection how if you ever been to the beach at night the moon has a gravitational pull on the ocean which causes high tides where the water reaches to where you would normally be able to walk. Because these tides tend to move towards the coast, it creates a rise of the sea surface. When the tides rise to it's highest point it is then known as a "high tide" and when it is at its lowest it's known as a "low tide".
The distinction between high and low tides is called a "Tidal range". A tidal range is the difference in height between a high and low tide. Tides proceed toward the coastlines where they appear as the rise and fall of the sea surfaces. The horizontal movement of water where the main focus of the rising and falling of the tide is called a "Tidal current". The incoming tide along the coast and into the bays are called "Flood currents", while the outgoing tide is called an "Ebb current".
Tidal currents typically transport sediment, the same way long shore currents do. The speed necessary to transport sediment, "typically sand" is generated under certain conditions usually at the mouths of estuaries or in other places where there is a withdraw in the coast where tidal exchange must take place. Tidal currents on the open coast, meaning along a beach or on a rocky coast, are not quick enough to transport sand. As the tides come in and retreat along a beach or rocky coast , it causes the shoreline to move. The movement of the shoreline changes the zone where waves and long shore currents can do their work.
Coastal areas experience two high and two low tides every lunar day. A high tide will occur as gravity pulls the ocean towards the moon creating a high tide. When the gravitational pull is weaker, the areas at a 90 degree angle to the moon will experience low tides. The most widespread land forms of erosional coasts are sea cliffs. These cliffs range from only a few meters high to hundreds of meters above sea level. Many coastal locations have a thin narrow area of sediment forming. This sediment may consist of sand but is more commonly composed of coarse material. The coasts of California contain many places where this situation prevails. A narrow beach along a rocky coast provides the cliffs protection against direct wave attack and slows the rate of erosion.
Work cited
US Department of Commerce, National Oceanic and Atmospheric Administration. “Tides and Currents.” NOAA's National Ocean Service, 16 Nov. 2009, https://oceanservice.noaa.gov/navigation/tidesandcurrents/.