Answer:
It is because the waves that are generated during the winter are very huge and of increasing wavelength, that frequently erodes the beach and exposes the hard rocks and cobbles on the surface. The sand particles are carried to offshore along with the waves, thereby making it a rocky beach.
Whereas during winter, the waves generated are very calm and moderate and carries the offshore sands to the beach area.
This is the reason why the beaches are more rocky in winter compared to the summer.
