Tides as a Natural Clock

By Jason Tentinger

Natural clocks are processes that can be used to gain an idea of how much time has passed since a certain starting point. There are many natural clocks that exist and are used frequently. One of these natural clocks is the tides. Every day, most beaches exhibit two high tides and two low tides. These tides are mostly due to the gravitational pull of the moon. The Sun's gravity also causes tides, but its effect is much weaker because it is much farther from Earth than the moon. When the Sun and moon are aligned, the Sun's added gravitational pull causes high tides to be higher and low tides to be lower, which is also known as a greater tidal range. When they are not aligned, tidal range is smaller. As long as the Earth continues to rotate under the moon it will continue to create tides.

Tides are not only reliable but can also prove rather useful. The tides are handy because they occur on beaches where there are many people who can use these natural clocks to keep time. Almost everyone who has spent time near the ocean has experienced the rise and fall of the tides. The rising water can force those nearest the shore to relocate their beach towels after a certain length of time. Whether or not one is consciously using the tide as a natural clock, the rise and fall of the water gives a noticeable indication of how long it has been since one first arrived at the beach.

One can easily use tides as a natural clock. If someone knows the length of the interval between high and low tides, he or she can figure out how long it has been since a designated starting point. The tide can also be used to time the few hours between successive tides. Because the tides come in and go out successively, either high or low tide can be used as an initial condition to begin timing.

The tides can be used as an excellent natural clock near every body of water where tides occur. However, one must first become accustomed to the tides in each particular area before this clock can be utilized. The tides are slightly different for every coast. Although tides will still go in and out, some coasts experience a 12 hour tide instead of a 24 hour tide. Also, the local geography can affect the tide. Scientists call this the local effect, and must take it into consideration when predicting the tides. In fact, there are so many variables affecting the tide that in order to predict them accurately, scientists measure the tide levels at a certain location for nineteen years before calculating the mean level. They then consider the impact of the positions of the Sun and Moon and the local effect.

The differences in tides can make it difficult for someone who is not familiar with a particular beach to judge how high or low the tide is, or approximately what time the tide should be low or high. It is also important to note that the tide will not always rise to exactly the same height. Storm surges and strong winds blowing towards land or out to sea can cause heightened or lowered tides.

tidal phasesThe tides create a useful natural clock for humans and animals alike. A fish called grunion times its spawning cycle around the tides. Grunion always spawn on land right after the peak of the highest tide in a series of steadily higher tides. If the fish were to spawn while the tide was still rising their eggs would be carried out to sea. Also, because each tide will steadily be lower day after day after the highest of the series has passed, the eggs have a smaller chance of being washed out to sea by increasing tides. It only takes the eggs about ten days to hatch, which is about the length of time it will take for the next series of rising tides to begin.