SAVANNAH, Ga. (WSAV) — This Thursday is day 4 of World Space Week. Today, we are going to talk about something that is directly affected by space. Ocean tides happen every day all across the world and have a huge effect on navigation and the natural environment.
High & Low Tide Causes
Tides are the regular rise and fall of water levels along the coast and are essentially very long-period waves that move though the ocean due to the gravitational pull of the moon and sun. This wave originates in the ocean and then move toward the shoreline and makes the level to go up and then go down.
Gravity is one of the major forces that work to create tides. The moon and the sun’s mass work to pull the surface of the ocean water. Since the moon is much closer to the earth than the sun, the gravitational force of it is much greater than the sun. The sun’s effects on generating tides is half of what the moon generates.
The pull of the moon and sun cause the high and low tide though the creation of a bulge of water toward the moon. The rotation of the earth creates another bulge of water away from the moon. The bulge if water is the high tide. In between is where you have the low tide.
The timing and position of the water bulges is dependent on the position of the moon as it orbits the earth.
Types Of Tides
Tides are not the same everywhere because the earth is not a perfect sphere and the continents block the flow of water that tends to be westward due to the rotation of the earth.
There are three main types of tides; Semidiurnal, diurnal, and mixed semidiurnal tides. Here in the Coastal Empire and Lowcountry, we have semidiurnal tides.
Semidiurnal tides are when there are two high tides and two low tides per day of relatively equal size every lunar day. In fact, most of the Atlantic coast of the U.S. experiences this type of tide.
Since the Earth rotates through two of the tidal bulges every lunar day, coastal areas experience two high and two low tides approximately every day. According to NOAA, high tides happen about 12 hours and 25 minutes apart and it takes six hours for the water along the shore to go from high tide to low tide or low tide to high tide.
In the Gulf of Mexico, they have diurnal tides meaning there is one high tide and one low tide per day. The reason for this is the time it takes for the water to flow in and out of the Gulf though the Florida Straights to the Atlantic or into the Caribbean Sea. The flow of the water is restricted by land.
Small-Scale Tidal Influences
Local topography and seafloor terrain in addition to the sun and moon influence the magnitude of tides. Even on a small scale the shape of the shoreline or a bay can help to magnify or lessen the effects of tides.
Narrow inlets help to amplify the rage between the high and low tides. On average around the world, the rage between high and low tide is about 3 ft. In northern latitudes, the many narrow bays can amplify that rage to greater than 50 feet.
The Bay of Fundy in Nova Scotia, Canada has the largest average tidal range in the world at 52 ft.
The shape and orientation of the Georgia and South Carolina coasts amplifies the range, though not as much as in Nova Scotia. Here we typically have a tidal range between 7 and 8 ft. from high and low tide.
Spring Tides & Neap Tides
There are times in the year where tides are much higher than what is considered normal or lower than normal for a location. Higher than normal tides from a full moon are called spring tides or “king tides.”
Spring tides have a greater range between high and low tide because the tidal bulge around the earth becomes bigger from the greater gravitational pull of the moon.
The term spring tide is a little misleading since they happen during the whole year, regardless of the season. They happen twice during a lunar cycle.
Seven days after the spring tide, you get a neap tide. These tides are what is considered normal for a particular location.
The main driving force of tides is the moon and suns gravitational pull along with the earth’s rotation. At times though, the weather can help to increase or decrease tides due to the wind.
At Ft. Pulaski, the record tide level is 12.6 ft. and that happened due to hurricane Matthew.