Tides are the consistent rise and fall of the sea's level caused by the Sun's and Moon's gravitational pull on Earth. Our oceans respond to this pull much more than the solid earth. The Moon has a stronger effect on our tides since it is four hundred times closer to the Earth than the Sun.

Tidal bulges are created as the moon revolves in its orbit around the Earth (www-class.unl.edu, 2001).

 

This image represents the Earth and oceans not affected by the Sun or Moon's gravitational pull. Notice the uniformity of oceans.

 

See how the gravitational pull between the Earth and the Moon cause the oceans to bulge; therefore creating high tide on the side closest to the Moon and low tide on the opposite.
oceanlink.island.net/oinfo/ tides/tides.html

When the Sun and Moon are aligned with each other and the Earth, the Sun's gravity will pull on our ocean in the same direction that the Moon is pulling it, creating the highest, high tide and the lowest, low tide of the month. These are called 'Spring Tides', not named for the season, but to illustrate a leaping motion instead.

oceanlink.island.net/oinfo/ tides/tides.html

When the Sun and Moon form a 90° angle in relation to the Earth, 'Neap Tides' are formed. Half of the tidal bulge faces the Moon and the other faces the Sun. Remember, since the moon is closer to Earth than the Sun, the bulge will be larger on the side closest to the Moon. These produce the highest low tides and the lowest high tides.

oceanlink.island.net/oinfo/ tides/tides.html

Between each high tide is a low tide and in South Carolina, we experience two high tides and two low tides everyday. This is called a 'semidiurnal tide', meaning; semi= half, diurnal = daily". The vertical difference in the height of the water between the high and low tides is called the tidal range.

Tidal ranges can be divided into three categories (Pinet, 2000):

  1. Microtidal - Tidal range is between 0 - 2 meters (or 0 - 6 feet). Local examples for this range include the regions between Cape Hatteras, NC and Bull Bay, NC.
  2. Mesotidal- Tidal range is between 2 - 4 meters (or 6 - 12 feet). Local examples for this range include the regions between Bull Bay, NC andSavanah, Ga.
  3. Macrotidal - Tidal range is greater than 4 meters (or greater than 12 feet). Portions of Georgia's southern coastline have a tidal range of approximately 3 meters

 

For additional information, download the following activities:

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NOTE: Each activity is correlated to the S.C. Science Curriculum Standards

 
1. Discover How Tides Are Formed - D. Frankenberg and L. Mauldin
2. Tidal Pattern Discovery - Leslie R. Sautter, COASTeam and the College of Charleston's Dept. of Geology

3. Making a Tide Chart (Teacher Sheet) - D. Frankenberg and L. Mauldin

Making a Tide Chart (Student Sheet) -D. Frankenberg and L. Mauldin

4. The Moon's Affect On the Water (Teacher Sheet) - D. Frankenberg and L. Mauldin

The Moon's Affect On the Water (Student Sheet) - D. Frankenberg and L. Mauldin