The Bay of Fundy, nestled between the Canadian provinces of New Brunswick and Nova Scotia, is renowned worldwide for possessing the highest tidal range on the planet. Water levels fluctuate by an average of 16 meters (about 52 feet), a scale unmatched by the global average tidal range of roughly one meter. Approximately 100 billion tonnes of seawater flow in and out twice a day, exceeding the combined flow of all the world’s freshwater rivers. This extraordinary spectacle results from a specific combination of geographical and physical factors that amplify the ocean’s normal tidal forces.
The Funnel Effect: Tapering Geometry
The physical shape of the Bay of Fundy is the first factor in this amplification, creating a hydraulic squeezing effect likened to a funnel. The bay is broad at its mouth, opening widely to the Gulf of Maine, but it progressively narrows and shallows toward its inland extremities, such as the Minas Basin and Chignecto Bay. This tapering geometry forces the immense volume of incoming water into an ever-decreasing cross-sectional area.
As the tidal wave enters, the water mass is constrained by the narrowing shoreline and the rising seafloor. This reduction in space forces the water to pile up, increasing its vertical height. This geometric effect provides the initial mechanical lift, ensuring the tide height at the head of the bay is far greater than at the entrance.
Tidal Resonance: The Key Amplification
The primary reason for the extreme tides is the phenomenon of tidal resonance, a form of synchronized oscillation. Every body of water in a partially enclosed basin, like the Bay of Fundy, has a natural period of oscillation, or seiche, which is the time it takes for a standing wave to slosh from one end to the other and back again. This period depends on the basin’s length and depth.
The Bay of Fundy’s natural oscillation period aligns almost perfectly with the dominant semi-diurnal lunar tide (M2). This M2 tidal cycle, driven by the moon’s gravity, has a period of approximately 12 hours and 25 minutes between successive high tides. The near-perfect timing means the new incoming tidal crest arrives just as the reflected wave from the previous tide returns to the bay’s mouth.
This synchronized timing causes each successive tidal pulse to reinforce the previous one, similar to pushing a child on a swing at the right moment. This continuous, rhythmic synchronization, known as resonance, causes the tidal wave to grow dramatically as it progresses up the bay. The basin’s length and depth configuration, which creates this near-perfect timing, is the most powerful mechanism responsible for the massive amplification.
The Role of the Continental Shelf
The tidal wave entering the Bay of Fundy is already amplified due to the surrounding oceanic geography, particularly the Scotian Shelf and the Gulf of Maine. Tidal energy originating in the deep Atlantic Ocean must first traverse the relatively shallow continental shelf system of the Gulf of Maine. This expansive area acts as a pre-amplification stage.
As the tidal wave moves onto the shallowing shelf, the process of shoaling causes the wave to slow down and consequently increase its height. This initial boost means the wave entering the bay is already significantly larger than a typical deep-ocean tide. The bathymetry of the Gulf of Maine focuses this energetic wave toward the narrow opening of the bay, providing the resonant system with an amplified input.
Local Impacts of Extreme Tides
The massive exchange of water caused by these extreme tides impacts the local environment and human activity. The volume and velocity of the water create unique phenomena, such as the tidal bore—a wave front that rushes upstream against the normal flow of rivers like the Shubenacadie. The powerful currents also maintain extensive, nutrient-rich mudflats exposed at low tide.
These intertidal zones are among the most fertile ecosystems on Earth, supporting invertebrates that sustain millions of migrating shorebirds during their annual journeys. Beyond ecology, the predictable, high-velocity currents flowing through the Minas Passage present a promising site for tidal power generation. Projects like the Fundy Ocean Research Centre for Energy (FORCE) seek to harness this reliable energy source using in-stream turbines.