Low tides and high tides are among the most noticeable features of beaches. These tides impact the value of harbors and the necessity of high sea walls around cities. The difference between high tide and low tide is not one of just higher or lower water levels but of a range of factors spread throughout the year.
The most obvious difference between low tide and high tide is the water level at a given point. Generally, high tide and low tide occur twice a day each, meaning that there is a six-hour period between each. The water level can vary by as much as 3 feet in height, meaning that the ocean now encroaches farther along a beach. The change in water level is not a cause of low tides and high tides but is a consequence of other changes.
The Lunar Cycle
The lunar cycle is the primary determinant of tidal behavior. When the moon is over a given location, the surface of the Earth is closer to the moon than to the center of the planet, meaning that the moon exerts an effect on the tides. When the moon is overhead, it causes the tide to rise, and when it passes away, the tide returns to normal. The moon causes two high tides and two low tides each day as it circles the Earth.
The sun's gravity also impacts the high tides and low tides. When the moon is new and when it is full, the sun, the moon and Earth are all aligned, which causes the highest variation in tides. During a new moon, the high tide will be higher. When the moon is at first quarter or third quarter, the sun will cancel out the moon's gravity, which will cause a weaker tidal range.
The moon does not orbit at a constant height from the Earth, meaning that at points it is closer, and at points farther away. This naturally impacts the tides. During the time the moon is farthest from the Earth, the tidal range is diminished, and when it is closer, the tidal range is higher. The difference between low tide at one point of the cycle and high tide at another may be small.