Moraines at the right angle to the ice flow direction

End moraines belong to this category and they may either be large or small, short or long. The end moraines were formed along the ice margin and have a symmetrical shape with a gentle stoss-side (proximal) and steeper lee-side.

A closely related type of moraine, the De Geer moraine, occurs in clusters in lowland areas. De Geer moraines, also called washboard moraines, are till ridges up to 5 m high, 10-50 m wide, and in some cases 1000 m or more in length. The moraines occur in large groups at 40-300 m intervals, mostly in low-lying landscape areas. The Kvarken Archipelago has the highest number of De Geer moraines and they occur in compact clusters. In the northern and eastern parts of the area, the moraines seem to be related to, or deposited on the top of, drumlins and other moraine formations.

De Geer moraines

Picture 1: De Geer moraines in Svedjehamn, Björköby

According to the current moraine genesis theory, the moraine ridges were formed beneath the ice in crevasses running parallel to the ice margin. In the Kvarken Archipelago, the water depth during deglaciation was 250-280 m. Huge icebergs were released from the ice front and the De Geer moraines reflect the probable position of the retreating ice margin.

Picture 2: The formation of De Geer-moraines. Source: Världsarv i samverkan 63°N, Botnia-Atlantica