Horsea Island - Geology

Geology

The solid geology of the site is Upper Chalk, covered by post-glacial drift deposits comprising mostly brickearth, a loess from the west of England eroded and deposited downstream by the river system which once occupied the area now known as the Solent and its margins before inundation by the sea. Much of these deposits were covered by the chalk fill imported from Ports Down to create the torpedo lake. Where still exposed, beyond the lake at the eastern end of the site, the brickearth comprises fairly equal proportions of sand, silt, and clay, with occasional flints. Owing to the high clay content, the rock is of low permeability, occasioning flooding after prolonged rainfall during winter. In the extreme south east corner of the site, brick and concrete rubble has been used to construct the bunding to enhance protection from the rising sea.