blue coastline Cornish cornwall danger England english Great Britain natural nature ocean rocks sea seethe seething shore surf tide treacherous water waves Armeria cliff flowers hillside thrift wild coast current engulf fierce overwhelm Pembrokeshire pour smash spume swirl united kingdom violent wales welsh field green meadow atlantic coastal crash crashing energetic energy foam furious fury lava laval madeira rock rocky surge surging tidal vigorous vigour wave engulfing force power roaring turbulent white