The tides around the Mont-Saint-Michel

In the Bay of the Mont-Saint-Michel, it has been said that the incoming tide races in at the speed of a galloping horse! Not quite – unless you call 4mph a gallop!

What causes the tides?

Gravity. The tidal phenomenon is essentially the effects of the Moon and the Sun on the seas and oceans on the Earth, where their gravitational pull causes a bulge towards them.

So why are there two tides per day?

As the Moon orbits the Earth, the two pull on each other. This creates the first tide. But as the Earth and Moon orbit the Sun, locked together their centrifugal force creates the second tide. Try rocking round a bowl of milk – the centrifugal force will create a wave on the surface. That’s just what happens when the Sun and the Moon act upon the earth.

Why do we talk about flood and neap tides ?

When the Sun and the Moon align, the combined gravitational pull flexes the oceans more, creating a flood tide. However, when the Sun is at right angles relative to the line of the Moon and the Earth, the gravitational forces are to a degree cancelled out, creating smaller tides called neap tides. Tides are measured by coefficients; the higher the number, the higher the tide. Above a coefficient of 110, the Mont-Saint-Michel becomes an island.

Why do the tides at the equinox have the highest coefficient?

Twice a year the sun is aligned to the equator and its gravitational pull upon the Earth is at its greatest. If on top of that, the Moon is aligned with the Earth and the Sun, then the tides will be even stronger.

What is a tidal bore?

No, it’s not me going on and on about tides! It’s when the incoming tide from the English Channel buts up in the Bay of the Mont-Saint-Michel against tidal waters in the opposite direction from that of the three rivers, the Couesnon, the Sélune and the Sée. This is quite a rare natural phenomenon, but is much appreciated by experienced kayakers, who come to surf the crest of the wave! In French we call it le mascaret (‘tidal bore’ in English).

Where are the best spots to see the tidal bore?

There’s no shortage of lookout points to see the tidal bore. One of the best has to be from the ramparts of the Abbey of the Mont-Saint-Michel. If you want to get really close, then you can observe it from the raised roadway joining the Mont-Saint-Michel to the mainland or you could observe the huge forces of nature by positioning yourself in a safe place close to one of the river mouths.