Coastal geography

The waves of different strengths that constantly hit against the shoreline are the primary movers and shapers of the coastline.

Due to gravity, the water then falls back perpendicular to the beach, dropping its sediment as it loses energy (this is called backwash).

LSD helps create many landforms including barrier islands, bay beaches and spits.

The lack of sediment on headlands removes the protection of waves from them and makes them more vulnerable to weathering while the gathering of sediment in bays (where longshore drift is unable to remove it) protects the bays from further erosion and makes them pleasant recreational beaches.

The shells and skeletons of many organisms are of calcium carbonate and when this is broken down it forms sediment, limestone and clay.

Sea levels are currently quite high, while just 18,000 years ago during the Pleistocene ice age they were quite low.

As tectonic plates move about the Earth they can rise and fall due to changing pressures and the presence of glaciers.

The weight of the ice caused northeast Scotland to sink, displacing the southeast and forcing it to rise.

At current estimates the southeast is sinking at a rate of about 2 mm per year, with northeast Scotland rising by the same amount.

Slowly over time sediment simply builds on this area, extending the spit outwards, forming a barrier of sand.

Eventually the spit will not be able to grow any further because it is no longer sufficiently sheltered from erosion by waves, or because the estuary current prevents sediment resting.

Occasionally, if there is no estuary then it is possible for the spit to grow across to the other side of the bay and form what is called a bar, or barrier.