Constructive waves help to build beaches by gentle waves carrying material up the beach and depositing it; therefore, creating a beach, the wave energy is absorbed by the beach and causes little erosion to cliff faces. There is a strong swash but a very limited backwash.
Destructive waves erode cliffs rapidly and remove beach material by short steep waves that plunge onto the beach with force. There is a fairly strong swash, but a much stronger backwash. The beach sediment is sucked back down the beach by a strong backwash, leaving the beach to absorb less wave energy. The cliff is harmed with erosion by breaking waves, the eroded material is then removed by waves. The upper part of the cliff is weakened by salt spray.
Marine erosion is the wearing away of rocks by the action of the sea.
Weathering is the breaking down of rocks by the action of the weather, plants or chemical action.