Tides are the regular rise and fall of the ocean’s surface, a phenomenon governed by the gravitational forces exerted by the Moon and the Sun on Earth’s waters. The tidal range is defined as the vertical difference in height between a high tide and the subsequent low tide at a given location. While the average tidal range across the open ocean is modest, typically around one meter, certain coastlines experience dramatic fluctuations. This article explores the physical mechanisms that amplify these oscillations and identifies the locations globally where the largest tidal ranges are found.
Understanding Tidal Range
The primary mechanism driving all tides is the gravitational pull of the Moon and the Sun, combined with the Earth’s rotation. As the Earth spins, different parts of the planet pass through areas of high gravitational influence, causing the oceans to bulge toward the Moon and away from it simultaneously. This creates two high tides and two low tides, known as semidiurnal tides, over roughly a 24-hour and 50-minute period.
The magnitude of this daily fluctuation varies cyclically throughout the lunar month. When the Sun, Earth, and Moon align in a straight line, their gravitational forces combine to produce the greatest vertical differences, known as spring tides. Conversely, when the Sun and Moon form a right angle relative to Earth, their pulls partially cancel each other out, resulting in the smallest tidal variations, called neap tides. These astronomical forces establish the baseline for tidal movement everywhere, but local geography transforms a standard tide into an extreme one.
The Location with the World’s Highest Tide
The undisputed record holder for the largest tidal range in the world is the Bay of Fundy, located between the Canadian provinces of New Brunswick and Nova Scotia. At its inland reaches, particularly in the Minas Basin, the maximum tidal range can surpass 16 meters (over 50 feet). This means that the water level can rise and fall the height of a four- or five-story building twice daily, exposing vast expanses of ocean floor at low tide.
The sheer volume of water involved is staggering; in a single half-day tidal cycle, around 100 to 160 billion tonnes of water flows in and out of the Bay of Fundy. This flow is greater than the combined total flow of all the world’s freshwater rivers during the same period. While the Bay of Fundy holds the record, other locations also experience exceptional ranges due to similar geographic conditions.
Other notable sites with extremely high ranges include Ungava Bay in northern Quebec, Canada, which has reported mean ranges close to those of Fundy. The Severn Estuary and Bristol Channel in the United Kingdom also regularly experience high ranges, with maximums approaching 15 meters (49 feet). These locations demonstrate that the extreme tidal phenomenon requires a specific set of physical conditions.
Oceanographic Factors that Create Extreme Ranges
The dramatic amplification of tides in these locations results from the interaction of three primary oceanographic factors: basin shape, bathymetry, and tidal resonance.
Basin Shape
The geometric shape of the water body is a significant factor, often involving a wide mouth that opens to the ocean and gradually narrows toward the head of the inlet, creating a funneling effect. As the incoming tidal wave moves into this constricting space, the water is physically squeezed into a smaller volume, forcing the water level to stack vertically and increase the range.
Bathymetry
The bathymetry, or underwater topography, also plays a role, as the bay generally becomes shallower toward the coast. This shallowing causes the tidal wave to slow down, which subsequently forces the wave to grow taller as the energy is conserved, further contributing to the vertical range. This effect is particularly pronounced where a continental shelf is relatively wide and shallow.
Tidal Resonance
The most profound amplifier is tidal resonance, a phenomenon where the natural oscillation period of the basin matches the timing of the incoming oceanic tide. Water naturally sloshes back and forth in a confined basin, similar to water in a bathtub, at a specific period determined by the basin’s length and depth. In the Bay of Fundy, the time it takes for a tidal wave to travel from the mouth to the head of the bay and return is very close to the 12-hour and 25-minute interval between successive high tides in the Atlantic Ocean. This near-perfect synchronization means that each new incoming tide pushes the water just as the previous wave is returning, reinforcing the movement and dramatically amplifying the resulting tidal range.