In the bay of Mont-Saint-Michel, the tide rises very quickly, at the speed of a galloping horse goes the saying. This is probably a bit of an exaggeration, but its advance is still at about 8-10 km/h. When the Moon and Sun are aligned with the Earth, their forces of attraction add up and generate the high tides. The tides are determined by coefficients: the higher the coefficient, the higher the sea level. Above a coefficient of 100, Mont-Saint-Michel becomes an island again.