Red's Round-the-World Extravaganza

 

Fundy National Park, New Brunswick, Canada

Bay of Fundy and Tides

At Fundy National Park, the difference between high and low tide can be as much as 12 metres. At the head of the bay, the tide can rise 16 metres, the height of a four-story building.

Guided walk on Alma Beach
© Parks Canada / Jacques Pleau, August 2002

Walking on the bottom of the bay is a favourite pastime of visitors. This is, of course, best done at low tide in the intertidal zone! At Alma Beach at the time of low tide, you can walk more than a kilometre from the high tide line across the tidal flats to the water's edge. Fundy's interpreters welcome you to guided walks along the coast.

What are Tides?

Tides are the periodic rise and fall of the sea caused by the gravitational pull of the moon and sun on the earth's oceans.

Time of High and Low tide

In the Bay of Fundy you can see two high and two low tides each day. The time between a high and low tide, on average, is six hours and 13 minutes.
If you come back to the same place two or three days in a row, you will notice that the water is at its highest and lowest about an hour later each day. This is because the tides work on a "lunar" or moon day which is 24 hours and 52 minutes long. While the earth is turning on its axis the moon is orbiting in the same direction around the earth and it takes one day and 52 minutes for a point on the earth to reappear directly beneath the moon.

The shoreline changes dramatically in just 6 1/4 hours---from low tide to high.
© Parks Canada / Jamie Steeves

The shoreline changes dramatically in just 6 1/4 hours---from low tide to high.
© Parks Canada / Jamie Steeves

Spring Tides and Neap Tides

The height of the tide varies from day to day but the fluctuations are predictable. They are mainly caused by: 1) the degree to which the sun and moon's influences are acting in the same direction; and 2) the varying distance between the moon and the earth.
Twice each month, at the time of the new moon and the full moon, the gravitational influences of the moon and sun reinforce one another and cause the tides to rise to greater heights and fall lower than average tides. These are called spring tides from the Old English word "springan" which means to well up. At the time of the quarter moon, when the sun, earth, and moon form a right angle, the difference between high and low tide is less than average. These are neap tides, from the Old English "nep", as in nipped in the bud. Every 27 and a half days, when the moon reaches a point in its orbit closest to the earth (called perigee) the tidal range is increased. When perigean tides coincide with spring tides, extreme tides can be expected. In the Bay of Fundy, these conditions may create tides as large as 16 metres (53 feet). Conversely, when the moon is at apogee, its farthest point from the earth, even spring tides are diminished.

The Bay of Fundy's Giant Tides

Fundy's tides are the highest in the world because of an unusual combination of resonance (or seiche) and the shape of the bay.
Like water in any basin, the water in the Bay of Fundy has a natural rocking motion called a seiche. You could compare this to the movement of water in a bathtub. Although the water in a bathtub sloshes from one end to the other and back again in a few seconds, it takes about 13 hours for the water in the bay to rock from the mouth of the bay to the head of the bay and back again. The Atlantic Ocean tide rising and flooding into the bay every 12 hours and 25 minutes reinforces the rocking motion. To imagine this, picture an adult giving a gentle push to a child on a swing. Just a very small push, at the right time, is enough to make it go higher and higher. A pulse from the ocean tides sustains the seiche in the bay.
The Bay of Fundy's length is important. That's what makes the seiche frequency match the pulse from the Atlantic Ocean tides.
The bay's shape is of secondary importance although still significant. The bay becomes narrower and shallower towards its head, forcing the water higher up the shores.

Other Large Tides

Other places in the world have large tides: the Port of Bristol in England; the Sea of Okhotsk, northeast of Japan; Turnagain Arm in Alaska; the Bay of St. Malo in France; the Feuilles River in Ungava Bay, Quebec. All have tidal ranges of about 10 metres. However, not as much water is moved at these locations as in the Bay of Fundy where the tidal contribution equals the total daily discharge of all the world's rivers -about 100 cubic kilometres of water.

All information taken directly from the following site - http://www.pc.gc.ca/eng/pn-np/nb/fundy/visit/marees-tides.aspx#a05


Red asked me to add this link to some Australian tide information, (it was suggested by her friend) have a look!!

http://www.abc.net.au/science/articles/2002/05/01/2683462.htm

Monica