A landform (hill, mound, or ridge) of sand or other loose material that is formed by wind action. Dunes exist due to the ability of wind to transport unconsolidated material and are mainly associated with desert regions where windblown sand occupies extensive areas. In the recent geological past, desert areas may have been even larger during dry periods in the Pleistocene glaciation. At that time great areas of loess (windblown silt) were deposited across North America, Europe, and Asia. Dunes also form in coastal areas. Migration of active dunes can bury archaeological deposits.