algae chalk cliff coast England erode erosion face Great Britain green kent landscape low natural nature rock sea seaweed shore sky stone tide white background bladderwrack brown littoral olive Pembrokeshire plant rocks slimy texture united kingdom wales welsh beach coastal coastline Cornish cornwall english grass meadow ocean sand surf water waves blue low tide Molluscs mussels Mytilus seascape shellfish view forceful powerful rough slap smack spray violent boulder cloud foam fun holiday horizon leisure rocky shoreline Spain summer vacation wave breakwater cliffs crashing groyne railing Seaford stack stormy Sussex clean Lofoten Islands mountains norway norwegian smooth wet block cracked eroded fissure fractured Gower