Why Are Beach Pebbles Round?
The pebbles that are to
be found on a beach are invariably round and smooth owing to the constant
battering they have received from the sea. Originally pebbles were part of much
larger rocks, but various natural phenomena, such as earthquakes and volcanoes,
have gradually broken them down.
When caught in the movement of sea, and constantly rubbed against other hard materials, the pebbles finally lose their irregularities and present a smooth round surface. Many of the rocks of today will be pebbles in thousands of years’ time, and many of today’s pebbles will eventually be turned into sand by the constant, wearing action of the sea.
A beach composed chiefly of surface pebbles is commonly termed a shingle beach. This type of beach has armoring characteristics with respect to wave erosion, as well as ecological niches that provide habitat for animals and plants. Inshore banks of shingle (large quantities of pebbles) exist in some locations, such as the entrance to the River Ore, where the moving banks of shingle give notable navigational challenges.
Pebbles come in various colors and textures and can have streaks, known as veins, of quartz or other minerals. Pebbles are mostly smooth but, dependent on how frequently they come in contact with the sea, they can have marks of contact with other rocks or other pebbles. Pebbles left above the high water mark may have growths of organisms such as lichen on them, signifying the lack of contact with seawater.
The typical size range is from 2 mm to 50 mm. The colors range from translucent white to black, and include shades of yellow, brown, red and green. Some of the more plentiful pebble beaches are found along the coast of the Pacific Ocean, beginning in the United States and extending down to the tip of South America in Argentina.
Other pebble beaches are found in northern Europe (particularly on the beaches of the Norwegian Sea), along the coast of the U.K. and Ireland, on the shores of Australia, and around the islands of Indonesia and Japan.