Why do some beaches have sand and others have pebbles?

Asked by Joe Saint

There are many factors that determine what kind of beach occurs on any part of the coast. The shape of the coastline, the local geology and the prevailing weather conditions are all significant factors. The size of particles that make up a beach are often a reflection of the energy of the waves that hit the shore. In low-energy environments, such as shallow bays or estuaries, we often see very fine particles such as silt or mud deposited. Higher-energy beaches are often characterised by larger particles, such as pebbles or even boulders.

The famous pebble beaches along the south coast of England are often composed of flint derived from the chalk cliffs that are found locally. The chalk is dissolved in the sea water, leaving the flint behind, and this combined with the steeply sloping shoreline gives us the pebbly beaches.

Peter Davidson, Curator of Mineralogy, Nation Museums Scotland