Topography

Firth of Forth

Significance: a valley carved below sea level by the Forth ice stream and drowned by post-glacial sea level rise

The firths of the east coast of Scotland are fjörds - the valleys have been over-deepened by glacial erosion and subsequently invaded by the sea.  During the cold stages of the Pleistocene ice advanced from the south-west Highlands and was channelled through the existing Forth valley at Stirling. Erosion was most intense beneath the zone of most rapid flow of the ice stream, particularly where the ice was funnelled between the Ochils and the high ground south of Cambusbarron.

The Firth of Forth is a broad funnel-shaped fjörd. Beneath the estuary and its sediments lies a rock floor that locally extends well below sea level. Careful collation of borehole records by Brian Sissons has revealed the complex form of the rock head profile of the Forth Valley.  West of Stirling rock basins have been gouged from the soft Carboniferous sedimentary rocks to a depth of 200 m below present sea level.  The resistant sill on which Stirling Castle sits has been lowered, dissected and streamlined. Deep tunnel valleys, probably cut by glacial meltwater moving under pressure, run along the foot of the Ochils and down the axis of the Firth of Forth.  The deepest part of the Forth valley is off Grangemouth.  Other basins occur upstream of the Forth Bridge and sea bed east of the bridge has high relief, with the islands of Inchcolm, Inchcape, Cramond and others rising abruptly from a sea floor at -20 m. East of Edinburgh the floor of the Firth of Forth generally lies around -40 m, only deepening to -60 m off St Abbs. Rockhead generally lies only 10-15 m beneath the sea bed. The deepest part of Firth swings around the headland at North Berwick.

The shores of the Firth of Forth show a sequence of raised beaches which provide a detailed record of the pattern and timing of sea level change during and after ice retreat. On the floor of the Forth the muddy sediments of the St Abbs and Forth Formations record the change from glacimarine to marine sedimentation over the past 15,000 years (Gatliff, et al., 1994).

The Forth's Natural Environment ( by Chris Smout - Forth Estuary Forum)

From earliest times, man and nature have interacted in the Firth of Forth, in recent centuries with largely catastrophic consequences for the natural world. Settlement began on the shore some 10,500 years ago. The first Mesolithic people were hunter gatherers who lived entirely from what they could find in the wild: Neolithic people who followed them introduced herding, and eventually cultivation, but still depended to a large extent on what they could find, as demonstrated by 6,000 year old middens containing millions of oyster shells, often well inland from the modern shore line of the upper estuary. Early people, however, lacked the technology to make much of an impact on the biodiversity of the Forth. Probably the first notable modification of nature occurred on the islands in the Middle Ages, when the introduction of sheep and rabbits wiped out the original scrub cover, and the culling of seabirds and their eggs made gulls and puffins a rarity. However, there was still plenty of fish and shellfish to provide a living for the coastal burghs and to feed the towns. The first bad effects of over-exploitation of these resources were felt in Victorian times, when the immense oyster beds around Edinburgh were wiped out and the Lammas Drave herring fishery, which had supported the East Neuk and East Lothian towns for centuries, was also destroyed by over-fishing. At the same time there was severe pollution from sewage and industrial waste, which was not brought under control until the late twentieth century. Developments in trawling for haddock and cod, and the coming of steam drifters and echo location of the herring shoals off the May, wiped out the remaining fisheries in the Firth of Forth in the twentieth century. Today nothing is caught commercially except for prawns, a few scallops, crabs and lobsters. On the other hand, the rise of wildlife protection has led to a surge in the numbers of seabirds like puffins and gannets, and grey seals, assisted by the growing quantities of small fish that multiplied when the large ones were fished out. Today the Forth is cleaner than it has been for centuries, but the vast natural resources of the past are unlikely ever to return.

Kinghorn

Kinghorn Loch and Spillway