wave erosion of Sandy Hirst at spring tide

wash-over channel on the spit at spring tide

wash-over sediment after spring tide

Significance: a small spit and backing salt marsh at Tyne Mouth, near Dunbar                            

Tyne Mouth estuary, East Lothian with the wooded head of Sandy Hirst Spit in the centre

Sandy Hirst spit at Tyninghame was perhaps first recorded by the Ordnance Survey in 1853 and showed a form similar to that of today. This longevity is consistent with the apparent maturity of the vegetation on the spit, with marram and sea buckthorn growing with other shrubs and small trees, including sycamore. The opposing spit across Belhaven Bay is a more recent feature, emerging from a sand bank since 1946.

The spit is unusual as it rests partly on an inter-tidal shore platform littered with stranded glacial erratics. As waves sweep into Tyne Mouth, a powerful circulation can develop on the north shore which carries material towards and along the spit. Material is lost from the tip of the spit to the tidal flows in the channel of the River Tyne. Undermined trees at the spit head and the steepened eastern neck of the spit indicate significant contemporary erosion.

At spring tides the neck of the spit is washed over, with water draining to the backing salt marsh. It is possible that the neck is periodically breached by storms as shell layers are seen in hand borings in the salt marsh that indicate significant transport of debris from the spit during these events. With sea levels projected to rise by up to 30 cm this century it is likely that the spit will continue to shift westwards on to the areas currently occupied by salt marsh.

The salt marsh shows a well-developed pattern of creeks and salt pans. There is no known investigation of its stratigraphy, an absence that hinders understanding of the age and origin of Sandy Hirst. Hand augering, plus the presence of large glacial erratic boulders within the mud, indicate that the inner part of the salt marsh is only ~1 m thick and rests on an extension of the shore platform. One possibility is that the sea is presently reoccupying an earlier but post-glacial shore platform.

salt marsh at high water