By wind, Wales

Wind picks up and transports grains of sand by saltation, where sand grains bounce along the ground. If you stand on a windy beach, you can feel them stinging your ankles!

When the wind speed drops a little, sand stops being moved and is deposited, often building up dunes like the ones shown below.

Sometimes, sand dunes gradually move down-wind as sand is blown up the dune and over the crest It is then deposited where there is shelter from the wind - shown in the diagram.