A Changing Landscape
The Undercliff is a belt of fallen land 12Km long, running from Bonchurch in the East to Blackgang in the West. It was formed as a result of both aggressive coastal erosion and the unusual geological conditions following a rise in sea levels after the last Ice Age between 8000 - 4000 years ago.
Over this timescale, the ground became detached from the Southern Downs in a series of back-tilted terraces and slides, to form a landscape more closely resembling what we see today. Parts of the Undercliff are affected by slip planes, some of which are still moving today. Ground movement is encouraged by a layer of Gault clay (locally called 'blue slipper') under the chalk and Greensand rocks, which causes sliding, particularly after periods of prolonged rainfall. This is aggravated by coastal erosion at the base of the cliffs. Fortunately, most of Ventnor is relatively stable, the landslide complex being most active at its eastern and western most ends which are much less developed.
The Southern side of the Island, due to its exposed location is particularly affected by coastal erosion. Marine erosion can result in parts of the ancient landslide complex becoming 'unlocked' and sliding forward. Therefore coast protection schemes for these areas have to take account of the dual problems of erosion by the sea and landsliding. Although much of the developed Ventnor frontage is protected it is recognized that it is not possible, or even desirable to protect all areas of coast for environmental reasons.
Gore Cliff (above right) was the site of a major landslide in 1928 that cut off the coastal road that ran around to Blackgang. The road had to be located inland. In 1995 a large slide at Bonchurch saw 750 000 tonnes of land slip into the sea over a few days.
This complex geology combined with the sheltered position of the area has given rise to the unique and rugged Undercliff environment and also goes some way towards explaining the character of the town that has grown up from it.
"If you want to find out more, the Isle of Wight Coastal Visitors Centre is the first port of call for those interested in the geology , environment and natural history of the Undercliff. At the Centre you will find displays, models, an aquarium, library and giftshop."
Gore Cliff, site of a major landslide in 1928 which cut off the
coastal road to Blackgang.