Why does this shoreline change this way?

Question

There are different reasons why a shoreline can change, including tides. But I've found a phenomenon that I can't explain.

It happens in a Mediterranean beach called L'Esparrelló/La Caleta (link to Google Maps). The central part on this beach (maked in blue in the image below) is closed by two rock promontories (marked in red). The thing is, sometimes you can access to the beach without get into the water from point A but not from point B, and sometimes it's the opposite.

Sometimes one promontory closes the beach and sometimes it is closed by the other. Last summer, for instance, the Google Maps image was accurate: You could access the beach from point B, but not from point A. This summer, it's the opposite: It's not possible to access the beach from point B without getting wet, but it is possible from point A.

I have not observed any change in the amount of sand.

What explains this?

Answer 1

Short version; the beach moves because the waves change.

Long version; Beaches, and in fact entire bays, conform in shape and alignment to the prevailing wave patterns in the area. The exact magnitude and alignment of wave trains varies due to chaotically complex interactions between surface winds, subsurface currents, local seabed features, tide, larger basin geomorphology, season, surface temperature, humidity, other wave trains, etc... Different magnitude waves can preferentially pile sand up on the beach or pull it out into deeper water while wave trains on different alignments will push sand along the coast until the beach is parallel to the oncoming waves. On some coasts certain factors like strong prevailing winds and/or currents are so dominant that the wave alignment never varies noticeably during or between years. In more sheltered settings, like the Mediterranean, small changes in the dominant wind direction or the strength/direction of currents can make a noticeable difference to the alignment of the main wave patterns and the beaches that they form. Sand doesn't usually move very quickly, except during large storm events, so the change to the beach won't be noticeable over night but for those who don't visit a particular beach often the changes can be quite drastic and feel very sudden.