sjávarföll

sjávarföll, or tides, are the regular rise and fall of sea level along coastlines caused by the gravitational forces of the Moon and the Sun acting on the Earth's oceans. The resulting cycle produces alternating high tides and low tides and repeats roughly every 12 hours and 25 minutes at mid-latitudes, though the exact timing and height vary by location.

Tidal patterns vary by region. Most places experience semidiurnal tides, with two high tides and two low tides each day, but some areas have diurnal tides (one high and one low per day) or mixed tides. The tidal range—the difference between high and low water—depends on coastline geometry, bathymetry, and the alignment of the Moon and Sun. Spring tides occur when the Sun and Moon are aligned, increasing the range, while neap tides occur when they are at right angles, reducing it.

Prediction and measurement: Tides are predictable using celestial mechanics, and are monitored by tide gauges around the world. Tide tables and forecasts are essential for navigation, harbor operations, coastal planning, and recreational activities. Tidal currents can be strong in narrows and estuaries, influencing safety and shipping, while intertidal zones created by tides support diverse ecosystems.

Context: In Iceland and similar northern coastal regions, varying coastal geometry, fjords, and offshore shelves produce a range of tidal regimes. Local tide ranges and currents are monitored for maritime safety, fisheries, and coastal management, and long-term changes in sea level may affect future tidal behavior and coastal infrastructure.