Glacial periods, meltwater, tidal waves and, eventually, humans have shaped the area that we know today as the Wadden Sea. It's a unique landscape.

The Wadden Sea is the area between the 23 Wadden Sea islands and the mainland. It stretches 500 kilometres from Blåvands Huk in Denmark to Den Helder in the Netherlands, and is the longest unbroken stretch of sand and mudflats in the world. The area was formed through a combination of glacial deposits, tidal waters, waves, mud, plants and an incredibly large amount of animal excreta. Only late in the history of the Wadden Sea did humans begin to interfere with the landscape in their quest for new land and protection from the sea.

First there was the ice

The early history of the Wadden Sea was characterised by the two last glacial periods, when huge ice sheets covered large parts of Northern Europe and altered the landscape around and beneath the ice. The earlier of these two glacial periods (Saale) peaked at around 140,000 years ago and covered large parts of Northern Europe. When the ice melted, it revealed the area that is now the Wadden Sea as a hilly landscape much akin to the type of landscape that is characteristic of Eastern Denmark today. The remainder of the hills from that time can be seen today as the elevated sections of land along the Wadden Sea; they are known locally as geest. The last glacial period (Weichsel) ended at around 11,500 years ago. However, during this glaciation the ice only reached up to around 80 kilometres east of the Wadden Sea area. Rivers of meltwater flowed from the ice sheet and made their way around the 'hill islands' 

bringing with them sand and gravel on their journey to the sea. The large amounts of sand and gravel settled as thick, smooth, westward-sloping blankets between the 'hill islands', turning the landscape into a flat plain.

The islands emerge

The ice retreated again and the sea started to rise. Around 8,000 years ago, the water had risen so much that the sea had become what we know today as the North Sea. Since this time, the tidal waters, the wind and the waves have formed the landscape. The North Sea moved the sand from the large meltwater rivers back towards the coast, where it settled as sand flats. However, over time the sand flats reached a height at which they were only flooded occasionally and, thus, the characteristic Wadden Sea landscape - the highsands - were formed. The islands were invaded by plants that could trap the drifting sand between their stems and, thus, the first sand hills were born, and thereby the Wadden Sea islands.

Animals and plants

During high tide, around 2 km³ of water washes through the Danish Wadden Sea. The water brings large amounts of sand and clay into the lagoons between the islands and the mainland where a small amount is deposited in the calm environment.

The mudflats are home to a myriad of bottom-living animals such as mussels and snails, which filter the water and clay particles in their search for food. The fine particles pass through the animals and come out the other end as larger particles. The coarse particles are not as easily moved around by waves and currents, so the animals are instrumental in supplying material to the mudflats.

The human factor

The lush marshland areas attracted humans early on, and they settled on higher-lying geests, where they were protected from flooding. For additional protection against the sea, the first dykes were established in the Tøndermarsken salt marsh in the Middle Ages. Today, the only marshland area that has not been protected with dykes is the marshland around Ho Bugt and in the Varde Å river valley. AS a result, most of the marshland areas are no longer subject to the natural mashland developments with regular flooding and supply of new material to the land. In step with technological development, humans began in earnest to change the landscape. The Grådyb channel near Esbjerg was made deeper and dams were established at Rømø and Sild. These infrastructure projects are examples of how humans have displaced the natural balance of erosion and deposition in the Wadden Sea. 

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