Harbor seals of Düne
Until the 17th century, Düne was connected to Heligoland. On New Year's Eve 1721 a big storm surge separated the dunes from Heligoland. Therefore the island that arose was called Düne (English: Dune). In 1935 the size of the island was 10 hectares (25 acres). In 1940 the Nazi government increased the size of the island to 40 hectares (99 acres). This increase was for military use. An airfield was built that is still used today. The Heligoland Airport has two runways, of which the longest is 500 meters (0.31 mile). The actual artificial island is still 40 hectares.