Getijbulges

Getijbulges, or tidal bulges, are the raised areas of Earth's oceans created by the gravitational forces exerted by the Moon and the Sun on the planet's rotating ocean. As the Moon or Sun attracts Earth's oceans, the water on the side of Earth nearest the attracting body experiences a stronger pull than the center, producing a bulge. A second bulge forms on the opposite side due to inertia—the Earth is pulled toward the Moon while the far side lags, creating a second high water area. The rotation of the Earth under these bulges means that most coastlines experience regular high and low tides. The Sun's gravity also contributes, though its effect is weaker than that of the Moon except when aligned during full or new Moon phases.

The strength and timing of these bulges depend on geometry. When the Sun, Moon, and Earth align, tidal forces add up to produce higher high tides and lower low tides, known as spring tides. When the Sun and Moon are at right angles relative to the Earth, tides are milder, known as neap tides. Local factors, such as coastline shape, seafloor depth, and basin width, modulate the amplitude and timing of the bulges.

On most coastlines, tides are semidiurnal, with two roughly equal high tides per lunar day. Some regions experience diurnal or mixed tides depending on latitude and basin geometry. Amplitudes range from a few decimeters to several meters, with large basins like the Bay of Fundy reaching double-digit tides.

Getijbulges influence navigation, coastal planning, and ecology, and they are harnessed for tidal power in suitable locations. Measurements by tide gauges, buoys, and satellite altimetry track the bulges and feed predictive models used in weather, shipping, and coastal management.