Sand is continuously moving around at the top of the beach and it needs an obstruction to break the force of the wind, so that sand begins to accumulate. Seaweed, dead seabirds, driftwood and other detritus may all serve this purpose. These embryo dunes may disappear as quickly as they form but some may eventually be colonised by plants and the sand stabilised. Conditions here are very extreme, with high pH values (over 8), rapid drainage, no humus, high wind speed and lots of salt spray. These young dunes may reach no more than 1 metre in height.