Why are some beaches sandy and others either shingle or pebbles

Question

Why are some beaches sandy and others either shingle or pebbles

Answer 1

Sand is broken down rock.  It depends on how much erosion there has been.

Answer 2

The nature of an individual beach will depend on both the source of the sediment and the effect of local topography. Even on sandy beaches you will often see pebbles and shingle at the top of the beach. This is often a "Storm Beach" http://en.wikipedia.org/wiki/Storm_beach laid down when high energy waves in a storm are able to move larger stones and deposit them at the strandline. For sand to form then there must be a source that is easily erodable into sand grains and a lot of beach sand is reworked, eroded sandstone. This seems a circular argument but sandstone is often deposited by rivers - tecnically, in fluvial environments. Of course modern rivers also carry sand grade sediment into the sea to be deposited along the shoreline. Other good sources of sand are eroded volcanic rocks, (often relatively soft) and coral. Bad sources are very resistant igneous or metamorphic rocks like granites, which tend to result in rocky coasts, and limestones which break down and go into supension or  even solution.

If the coast has very high energy waves, the sand can be stripped from the beach, while the larger pebbles and rocks are not able to be removed (as it takes more energy to move them the larger they are).

Answer 3

sandy beach- kill devil hills, OBX