The coastal plain consists mainly of sand dunes and polders. Creepers, grasses and sedges stabilise sand dunes and uncompacted sediments. The park contains the tallest sand dunes in North America. Smaller dunes form and migrate along the flanks of the larger dunes and sand ridges. It is long and covered in sand dunes and grasses. Tottori is home to the Tottori Sand Dunes, Japan's only large dune system. Algeria also has ergs, or sand dunes, between mountains. Extensive crescent-shaped sand dunes are present. The magnificent sand dunes at Greenwich are of particular significance. Another concern was the rebuilding of the sand dunes along waterfronts. This is especially important in areas such as sand dunes. This process results in the formation of ripples and sand dunes. White Sands contains various forms of dunes. It also acts as a windbreak and helps in stabilizing shifting sand dunes. It is situated about west of Amsterdam and near the coastal dunes.