Geology
Ten thousand years ago a band of relatively resistant Chalk rock, part of the Southern England Chalk Formation ran from the Isle of Purbeck area of south Dorset to the eastern end of Isle of Wight, parallel to the South Downs. Inland behind the Chalk were less resistant sands, clays and gravels. Through these weak soils and rocks ran many rivers, from the Dorset Frome in the west and including the Stour, Beaulieu River, Test, Itchen and Hamble, which created a large estuary flowing west to east and into the English Channel at the eastern end of the present Solent. This great estuary ran through a wooded valley and is now referred to as the Solent River.
When glaciers covering the north of Britain melted at the end of the last ice age, two things happened to create the Solent. Firstly, a great amount of flood water ran into the Solent River and its tributaries, carving the estuary deeper. Secondly, post-glacial rebound after the removal of the weight of ice over Scotland caused the island of Great Britain to tilt about an east-west axis, because isostatic rebound in Scotland and Scandinavia is pulling mantle rock out from under the Netherlands and south England: this is forebulge sinking. Over thousands of years, the land sank in the south (a process still continuing) to submerge many valleys creating today's characteristic rias, such as Southampton Water and Poole Harbour, as well as submerging the Solent. The estuary of the Solent River was gradually flooded, and eventually the Isle of Wight became separated from the mainland as the chalk ridge between The Needles on the island and Old Harry Rocks on the mainland was eroded. This is thought to have happened about 7,000 years ago.
The process of coastal change is still continuing, with the soft cliffs on some parts of the Solent, such as Fort Victoria, constantly eroding, whilst other parts, such as Ryde Sands, accreting.
The Solent is a comparatively shallow stretch of tidal water. It has an unusual double tide that is both favourable to maritime activities as well as a hazard with its strong tidal movements and quickly changing sea states.
Coupled with the above, the Solent is renowned for its large volume of vessel usage, thus resulting in one of the highest density of declared lifeboat stations in the world. This includes six RNLI (e.g. Calshot and Cowes) and five independently run stations (e.g. Hamble Lifeboat and Gosport and Fareham Inshore Rescue Service).
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