Sand accumulates on the beach from longshore drift or onshore currents. At low tide, the sand dries out allowing the prevailing winds to move the loose sand up the beach. Most moves by saltation in a series of short hops but strong winds may be powerful enough to carry the finer sand grains for longer distances. At Morfa Harlech and Aberffraw, there is a large tidal range which exposes wide expanses of sand at low tide. Much of the fine material is glacial in origin and probably accumulated offshore at the end of the last ice age.