About the Tidal Bore

With the world’s highest recorded tides the Bay of Fundy is witness daily to one of nature’s unique shows not found anywhere else.

Tides and Tidal Bores

One hundred billion tonnes of seawater flows in and out of the Bay of Fundy twice a day bringing with it an amazing array of currents, waves, swells, rip-currents, whirlpools and up to class four whitewater rapids. Unlike the open Atlantic Ocean side of Nova Scotia where the tides occur twice every 24 hours and at a more or less constant range or height (4 to 8 feet), the unique configuration of the Bay of Fundy (funnel shaped and great depth) results in the tidal waters moving in and out of the bay in a rocking motion (think of a wave in a bathtub) producing a significantly higher tidal height particularly when it reaches the head of the Bay.

Tides are often said to be the pulse of the planet. They originate because the force of gravity decreases with distance from a massive body which in our case is the Moon. The Moon exerts a force on the Earth and the Earth responds by accelerating toward the Moon. The waters on the side of Earth facing the Moon, since they are closer to the Moon, accelerate more and move ahead of the Earth while the waters on the side of Earth furthest from the Moon fall behind the Earth as it continues to rotate, resulting in two water bulges on Earth . As the Earth rotates under these two bulges (one bulge facing the Moon, the other facing away from the Moon) the rise and fall of Earth’s oceans results. Since the Earth is rigid, the ocean floors do not flex; therefore, we have the rise and fall of the oceans. Although the Sun exerts a much larger gravitational force on Earth, because the Moon is much closer it can produce a variation in force on Earth which is much stronger than the Sun’s. It is this variation which produces tides and when the Moon is in its new and full phases and closest to Earth it becomes in sync with the two tidal bulges and the result is ‘spring’ tides (not related to the season but to the springing up effect of the water). When the Moon is further away from Earth and out of step with Earth’s water bulges (first and last quarters) it produces the lowest tides which are called ‘neap’ tides.

What is a bore?

The tidal drama in the Bay of Fundy unfolds every 12 hours when the tidal bore (‘bore’ comes from the Old Norse word ‘bara’ meaning a wave or swell) forms as the tide enters the Bay and moves toward the rivers which enter it. The largest of these rivers is the Shubenacadie and the immense force of the incoming tide will reverse the outgoing river and send it almost 40 km backwards. The bore or first tidal wave will gather height and strength as it nears the head of the Bay and enters the Shubenacadie River at Maitland. It will rise and fall as it pushes upriver depending on the width and depth of the river at any particular point. The bore can be as little as a small rolling wave or 11 feet in height depending on the size of the tide and the river location. Its speed can reach up to 12 km an hour and can be heard well before it is seen.