In the bay of Mont-Saint-Michel, the tide is said to rise at the speed of a galloping horse. It's a bit of a stretch, but still, the water is moving at a speed of about 6 km / h. ! When the Moon and Sun are aligned, their forces of attraction add up to each other and create high tides. The sea can then retreat up to 10 km. These tides are defined by coefficients: the higher the coefficient, the higher the sea level will be. From the coefficient of 110, Mont-Saint-Michel becomes an island again.