A beach is a sloping stretch of sand, shingle, gravel, and other material along the shore
of a lake, river, or sea. Caused by erosion and deposition of sediment by
waves, a beach usually extends from the furthest point reached by the waves
out to a water depth of around 10 meters. Waves breaking on the beach move
the sediment back and forth so the heavier pebbles remain on the upper beach
and the sand moves downward toward low water.
AND PLANETARY SCIENCE