Why do tides happen?
The answer to “why do tides happen” is GRAVITY … a natural phenomenon which attracts all things with mass like planets and stars to one another.
Our nearby moon has the greatest influence. As the moon orbits our planet, it pulls earth and water towards it. A bulge or “high tide” forms on the side of the planet facing the moon … and on the opposite side too as water at Earth’s center straightens out. Tidal strength varies. It’s greatest when Sun, Earth and Moon are aligned … causing a “spring tide”. Canada’s Bay of Fundy … a funnel-shaped arm of the North Atlantic has the highest tides in the world !
It happens here for two main reasons:
First the shape of the bay. The entrance is wide and deep. By contrast, the east end is narrow and shallow with no outlet. As the tidal waters flow in (an amount equal to the flow of all the world’s rivers) the water is squeezed upward … creating giant tides. Tides at the east end of the bay can reach 53 feet !
Secondly the bottom topography and timing of the tides work with the shape of the bay to create a natural resonance … a rocking effect that exaggerates the tides. As the tide retreats, the high waters at the east end collapse and rock back toward the entrance of the bay … intensifying the low tide.
Here at the Reversing Falls Rapids, there are three distinct tidal conditions:
LOW TIDE. As the water rushes out to the Bay of Fundy, dramatic whirlpools form.
SLACK or NEUTRAL tide is the time between low and high tides. Opposing forces are in balance, and waters are calm for about 20 minutes. This is the time vessels can safely sail through the gorge.
HIGH TIDE. A force strong enough to reverse the direction of the Saint John River and raise water levels as far away as Fredericton …. 90 kilometers to the north !
Only a strong spring snowmelt in the watershed can temporarily stop this phenomenon !