Storm surge flooding along the East Coast as Sandy moved ashore Monday was made worse by the higher tides caused by the full moon. This news confused many local viewers and readers who are unfamiliar with tidal forces.
Tides are actually caused by the difference in the gravitational forces on one side of Earth compared to the other. The ocean on the side of Earth closest to the moon is pulled moonward relative to the more rigid Earth, whereas the ocean on the side opposite the moon is pulled less than the rigid Earth. This causes the liquid oceans to bulge toward and away from the moon and also explains why there are two high tides and two low tides each day.
But at the time of the full moon, the moon and the sun are in a line so that their gravitational forces combine to cause the ocean to bulge even more. This is called the spring tide because the two high tides are very high and on the same day, the two low tides are very low.
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