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What Are Ocean Bulges Caused by?

Oceans are caught in an endless cosmic drama, constantly acted upon by gravity, geology, wind and life. Even something seemingly simple as ocean bulges are caused by a complex dance of the influences of the sun, the moon and the earth's rotation and geological processes that have directly impacted the way people have lived, fished and traveled throughout history.

Moon
- The most significant former of ocean bulges are moon tides. Though constantly pulling on Earth, the moon's gravity only has an effect on water, since it is moving. While most places on earth experience two peak-to-trough tide cycles a day, since the moon does not orbit the earth directly over the equator but is inclined between 5 and 23.5 degrees, some places experience one tidal cycle daily, and others--such as around the equator--experience little tide at all.
Inertial Force
- The moon does not revolve around Earth, rather both rotate around a central point of gravity, a point around 1,070 miles deep inside the earth. The inertia of this rotation causes oceans on Earth to bulge outward away from the gravitational center as the planet spins, called inertial force. Since the bodies share a central gravitational point, this bulge is always on the opposite side of the planet from the moon, causing the two daily tide cycles: one from the moon, one from inertial force.
Sun
- Though its pull on oceans is 46 percent that of the moon's, the sun's influence on tides is noticeable as the moon cycles through the month. During new and full moons, the alignment of sun and moon makes their gravities pull in the same direction, multiplying the tidal effect, resulting in higher high tides and lower low tides, called spring tide. During quarter moons, the sun and moon align perpendicular to Earth and their gravities pull in opposite directions, bringing higher low tides and lower high tides, called neap tides.
Tsunamis
- When an oceanic plate moves underneath a continental plate, causing an earthquake, a bulging column of water rises above the underwater fault as the plate goes under, while the subsequent subsiding of the continental plate causes the column to sink shortly afterward. As water then seeks to return to a common level, the water surface raises and lowers. As the water becomes shallower, the resulting tsunami waves grow bigger and gain speed. They approach shore as enormous, bulging walls of water.

Nature