Large bodies of water such as oceans are always in motion, due to the gravitational pull of the moon, and somewhat of the sun. Because the gravity is varied on the ocean, depending on how close a specific part of the ocean is to the moon, high tide bulges are formed on opposite sides of the planet, and in between, areas are experiencing low tides. The period between high tides is approximately 12.4 hours.
High and low tides are fairly easy to predict and are normally posted along coastlines. Not only are these events predicted, the tide elevation is also given, and for the most part, fairly accurate. Drastic changes in tide elevations are normally the direct result of weather such as wind velocity, and hurricanes, but they can also be increased dramatically due to earthquakes.
Semidiurnal tides are the high and low tides that occur every 24.8 hours. Some locations have two high tides per day at about the same elevation, however some have only one. Areas that have only one high tide and one low tide per day are called diurnal tides. Tidal range is also determined throughout the month in conjunction to the moon. When the moon is full, and the sun, moon and earth are in alignment, the tides are high and are called “spring tides.” When all of these factors are at their lowest during the month, tides are known as “neap tides.”
Variations in coastal regions and land masses also affect daily tides, so different locations experience different tidal ranges. In some areas, the difference between high and low tide can be as much as 30 feet or more, and in others, less than 2 fee during the day. Bays and shelves also contribute to this effect. In order to record and compute data related to tides, an entire “tidal epoch”, or cycle is studied. This epoch lasts around 18.6 years.
Storm surges are of course, the unusual tides that are produced by a particular weather condition, such as a hurricane. The tides that are generated from these events are determined and predicted by determining when the strongest part of the storm will make landfall, and if it will coincide with high tide. These are the most damaging, since they combine with higher sea levels to produce tides that normally impact large areas.
Tides are the very visible signs of gravity, and the effect of the moon on the earth’s surface. They can be responsible for creating new features in the ocean and on the shore, and they can be helpful and sometimes harmful.