It is well known that waves are the source of increased sea level during storms, but how high can the water reach? This question has been studied in details for gently sloping beaches or coral reefs. New measurements for a steep cliff off the French west coast are providing clues to the formation of mysterious piles of rock at the same. The observed water motions could explain some anomalous high water levels reported on top of cliffs around the world. In the study to be published soon in Geophysical Research Letter, the measurements show that oscillations with periods of a few minutes, also known as 'surf beat' or 'infragravity waves' can add 3-meters to the water level, allowing waves to attack the top of the cliff and go over the top. This strong oscillation of the sea level is clearly driven by the normal waves, with an amplitude that increases with both wave height and period. The oscillations are also confined very close to the cliff itself.