Dassen Island is a South African island in the Atlantic Ocean. It is situated about 10km west of Yzerfontein and 55km north of Cape Town. The flat and low-lying island measures about 3.1 km long northwest-southeast, and 1 km wide, with an area of 2.73 km² [1]. It is a proclaimed nature reserve.
The geological structure of the island is composed of a fine-grained tourmaline granite (with a few areas of biotite granite) outcrop covered with sand. Some of the granite features along the shore - to just above the high-water mark - consists of large, rounded boulders which stick out above the sand. Although temporary pans form during the winter in the interior, there is generally little fresh water on the island.
Except on its eastern side, Dassen Island is surrounded by reefs and consequently many ships have run aground here.