ABSTRACT
Beachy Head and the Seven Sisters cliffs to the west are made of a hard chalk and stand up to 160 m above sea level along the southern coast of England. On 10 and 11 January 1999, the upper part of Beachy Head collapsed. The fallen portion was about 70 m long and 17 m deep with a mass of 50,000-100,000 tonnes, which buried the cliff base and is seen as 5-10 m of accumulated chalk rubble with blocks up to 4 m in diameter. The failure occurred along one of the vertical joints or minor fault planes that are common in the chalk. To the east of the main slip, a fracture some 2 m deep and 1 m wide and extending up to 10 m from the cliff edge has appeared. It runs down most of the cliff face. The toe of the chalk rubble erodes at high tide, when it produces a sediment
plume that runs from just east of Beachy Head Cave to the unmanned Beachy Head Lighthouse. The cause of the rockfall is not certain, but 1998 was a wetter year than normal, and during the fortnight before the fall heavy rain fell on most days. The wet conditions may have increased the pore pressures in the chalk and triggered the rockfall. Events such as the Beachy Head rockfall have been occurring for thousands of years along southern and eastern English coastlines and have led to cliff retreat.
