Mont Saint-Michel is transformed into an island by spring tides

At certain times throughout the year, Mont Saint-Michel in Normandy becomes completely cut off from the mainland as the spring tide rushes in to flood the surrounding bay. 

'Spring tides' are those which occur around the times of new and full moons meaning high tides are higher, and low tides lower, than their usual levels.

The scene at Mont Saint-Michel only lasts a few hours but the views can be spectacular, particularly at dusk or dawn.

It is best to be on the lookout 30 minutes or more before the tide peaks to make sure you experience the whole event. Roche Torin, Grouin du Sud and Pontaubault bridge are recommended places to watch the sea gradually turn the mount back into an island.

If you are close to the Couesnon River then you may also see the tidal bore that comes up the river and into the bay with a spring tide. 

Tidal coefficient is a number used to represent the size of tidal variation. During a spring tide, the moon and sun are in alignment and gravitational forces on the oceans are at their greatest. 

This causes an extreme difference between high and low tides and the tidal coefficient is at its highest at this point. 

The Channel is home to the biggest tides in Europe and to be considered a spring tide, the coefficient must be at 90 or higher. 

In order for Mont Saint-Michel to become an island once more there has to be a significantly high spring tide with a coefficient of 110 or more.

Major conservation works saw the removal of an existing concrete causeway leading across to Mont Saint-Michel to be replaced with a bridge on stilts that allows the tide to flow beneath it. 

Due to the level where the bridge connects back to the ground, spring tides can now flow in and the base of the outer ramparts becomes submerged, cutting off Mont Saint-Michel from the mainland.

The next time you will be able to see Mont Saint-Michel as an island is Sunday March 30 and Monday March 31 when the tidal coefficient is expected to reach 114. 

Spring tides should again be large enough later in the year on Wednesday October 8 with the coefficient reaching 110.

You can visit Mont Saint-Michel by walking across the bridge which takes around 45 minutes or you might prefer to walk across the bay at low tide with a guide. 

Depending on the season, free shuttle buses also run throughout the day that will set you down a quarter of a mile from the site.

More information is available from Mont Saint-Michel Tourist Office.